IMPACT OF SPODOPTERA EXIGUA, BEET ARMYWORM ON TOMATO JAMES EDWIN

IMPACT OF SPODOPTERA EXIGUA, BEET ARMYWORM ON TOMATO

by

JAMES EDWIN TAYLOR

(Under the Direction of David Riley)

ABSTRACT

Spodoptera exigua, beet armyworm is a major agricultural pest in the USA and in

tropical and subtropical areas of the world. It has recently become a problem pest in vegetable

production in South Georgia especially in tomato. In 2004 and 2005, an insecticide efficacy trial

was conducted to determine proper insecticides and rates to control beet armyworm. In 2005 and

2006, an artificial infestation trial was conducted to determine the effect of beet armyworm on

tomato yield. A minimum economic injury level of one beet armyworm larva per 20 tomato

plants was determined to prevent economic yield loss in tomato.

INDEX WORDS: Spodoptera exigua, beet armyworm, tomato, action threshold, economic

injury level


by

JAMES EDWIN TAYLOR

Bachelor of Science and Agriculture, University of Georgia, 2004

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment

of the Requirements for the Degree

MASTER

OF SCIENCE

ATHENS, GEORGIA

2006

© 2006

James Edwin Taylor

All Rights Reserved


by

JAMES EDWIN TAYLOR

Major Professor: David Riley

Committee: John Ruberson Alton Sparks

Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia August 2006

ACKNOWLEDGEMENTS

I would like to thank my family for their support and willingness to help throughout my

academic career. I would like to make a special thanks to Mom and Amy for one hot day of

harvesting tomatoes. I would like to thank everyone at the Vegetable Entomology Lab for there

hard work and persistence. This includes Jackie Davis, Donnie Cook, Kim Wilson, Sophie

Tison, Rue Chitwood, Brooke Myers, and Sheena Griffin.

I would like to thank my committee members Dr. John Ruberson and Dr. Alton Sparks

for the valuable insight throughout my research. I would like to especially thank Dr. David Riley

in his mentorship and time that was spent helping me to obtain this degree. He always seemed to

point me in the right direction to keep me on track and his willingness to help me with areas that

I was struggling was greatly appreciated.

I thank Carol Ireland, Jenny Granberry, Marianne Stephens, Kayla Conway, and Haley

Carmichael for their administrative help. I would like to extend a special thanks to Detsy

Bridges because she was always willing to go that extra mile to lend a helping hand.

I would also like to thank BASF Chemical Company for providing the monetary support

for my research.

iv

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS........................................................................................................... iv

LIST OF TABLES........................................................................................................................ vii

LIST OF FIGURES ..................................................................................................................... viii

LIST OF PICTURES .......................................................................................................................x

CHAPTER

1 Introduction....................................................................................................................1

Background ...............................................................................................................1

Purpose of Study .......................................................................................................3

References Cited........................................................................................................4

2 Review of Literature ......................................................................................................8

Beet Armyworm Biology ..........................................................................................8

Beet Armyworm Management Strategies ...............................................................10

IPM Strategies .........................................................................................................12

References Cited......................................................................................................17

3 Efficacy of Metaflumizone against Spodoptera exigua in Relation to Tomato Yield.23

Introduction .............................................................................................................23

Methods and Materials ............................................................................................25

Results .....................................................................................................................26

Discussion ...............................................................................................................29

v


4 Artificial Infestation of Beet Armyworm, Spodoptera exigua in Tomato...................40

Introduction .............................................................................................................40


Results .....................................................................................................................44

Discussion ..............................................................................................................48


5 Economic Injury Levels for Beet Armyworm in Tomato............................................71

Introduction .............................................................................................................71


Results ....................................................................................................................74

Discussion ..............................................................................................................79

Reference Cited .......................................................................................................81

6 Summary ......................................................................................................................87

Reference Cited ...................................................................................................................89

Biography ............................................................................................................................98

vi

LIST OF TABLES

Page

Table 3.1: 2004 Summer Spray Trial Treatment List ....................................................................34

Table 3.2: 2005 Summer Spray Trial Treatment List ....................................................................35

Table 3.3: 2004 Summer Tomato scouting and yield data ............................................................36

Table 3.4: 2005 Summer Tomato scouting and yield data ............................................................37

Table 4.1: 2006 Seasonal Artificial Infestation Harvest................................................................58

Table 4.2: 2006 Early Artificial Infestation Harvest .....................................................................59

Table 4.3: 2006 Late Artificial Infestation Harvest .......................................................................60

vii

LIST OF FIGURES

Page

Figure 2.1: Relationship of Economic Injury Levels (EIL) and Economic Thresholds (ET)........15

Figure 3.1: 2004 Beet Armyworm Means by Scouting Date.........................................................38

Figure 3.2: 2005 Beet Armyworm Means by Scouting Date.........................................................39

Figure 4.1: 2005 Seasonal Scouting Numbers of Beet Armyworm...............................................61

Figure 4.2: 2005 Early Infestation Seasonal Beet Armyworm Counts..........................................62

Figure 4.3: 2005 Late Infestation Seasonal Beet Armyworm Counts ...........................................63

Figure 4.4: 2005 Late Infestation of Beet Armyworm Numbers per Scouting Date.....................64

Figure 4.5: 2006 Spring Infestation (early and late combined) Seasonal Means of Beet

Armyworm ....................................................................................................................65

Figure 4.6: 2006 Early Infestation Beet Armyworm Counts.........................................................66

Figure 4.7: 2006 Late Infestation Beet Armyworm Counts ..........................................................67

Figure 4.8: 2006 Spring Infestation Beet Armyworm by Scouting Date ......................................68

Figure 4.9: 2006 Early Season Infestation Marketable Fruit Weights...........................................69

Figure 4.10: 2006 Spring Infestation Fruit Holes per Treatment...................................................70

Figure 5.1: 2004 Regression of Beet Armyworm to Marketable Fruit Numbers .........................82

Figure 5.2: 2006 Spring Early Season Infestation of Beet Armyworm Counts to Marketable Fruit

Weight ...........................................................................................................................83

Figure 5.3: 2006 Spring Early Season Infestation of Beet Armyworm Counts to Marketable

Fruit Numbers................................................................................................................84

viii

Figure 5.4: 2006 Spring Infestation (early and late combined) of Beet Armyworm Larvae

Counts to Marketable Fruit Weight...............................................................................85

Figure 5.5: 2006 Spring Infestation (early and late combined) of Beet Armyworm Larvae

Counts to Marketable Fruit numbers.............................................................................86

ix

LIST OF PICTURES

Page

Picture 4.1: Beet armyworm fruit feeding in Tomato....................................................................52

Picture 4.2: Beet armyworm feeding on foliage ............................................................................53

Picture 4.3: Beet armyworm feeding directly on developing fruit ................................................54

Picture 4.4: Top of leaf surface of artificial infestation .................................................................55

Picture 4.5: Egg mass position.......................................................................................................56

Picture 4.6: Beet armyworm larvae hatching and feeding on foliage............................................57

x

CHAPTER 1

Introduction

Background

Tomato production in the United States is valued at 1.3 billion dollars for fresh market

tomatoes, with Florida, California, and Georgia leading the commercial fresh market production

(Tomatoes National Statistics 2006). Georgia’s 2004 farm gate value of tomato was over 100

million dollars (Boatwright and McKissick 2004). The main insect pests of tomatoes in Georgia

are thrips, aphids, whiteflies, stink bugs, and Lepidopterans. Lepidopterans are major pests of

tomato in the Southeastern United States and it has been shown that there is a major economic

loss associated with their damage (Liburd et al. 2000). Due to the importance of many

Lepidopteran species, including Spodoptera exigua (beet armyworm), it is important to

understand the relationship between the insect and the crop. I focused on beet armyworm

because of its recent importance in Georgia tomato production.

The beet armyworm, Spodoptera exigua, is a major agricultural pest in the USA and in

tropical and subtropical areas of the world (Liburd et al. 2000). The beet armyworm is a tropical

insect and its native host range is Southeast Asia. It is especially important for vegetable

production as it is able to cause economic damage(Zalom et al. 1986, Mitchell and Tumlinson

1994, Yee and Toscano 1998). It was first discovered in the United States in Oregon in

approximately 1876 and has since spread throughout the continental United States, Mexico, and

the Caribbean (Mitchell 1973). In some areas of tomato production, it has become a major pest

of both fresh-market and processed tomatoes (Lange and Bronson 1981, Brewer et al. 1990).

2

The beet armyworm is capable of feeding on the foliage, but most insecticide spray

programs target the protection of fruit.

Many tactics have been used to control the beet armyworm, with chemical control being

the most used. Using insecticides on a wide scale has introduced resistance in some populations

so other management methods have been evaluated. Specific documentation of resistance in beet

armyworm field populations to chemical insecticides include (Meinke and Ware 1978, Brewer

and Trumble 1989, Van Laecke and Degheele 1991, Brewer and Trumble 1994, Aldosari et al.

1996, Mascarenhas et al. 1998, Moulton et al. 2000, Moulton et al. 2002, Wolfenbarger 2002).

Other control tactics such as biological control (Moar and Trumble 1987, Liburd et al. 2000,

Bianchi et al. 2002), pheromone disruption (Mitchell et al. 1997, Wakamura and Takai 1997,

Kerns 2000), and plant defense compounds (Farrar and Kennedy 1991, Eigenbrode et al. 1994)

have been studied and evaluated for control of the beet armyworm.

With insecticide resistance being a potential problem in field populations of beet

armyworm, strict adherence to an integrated pest management (IPM) strategy is warranted. IPM

uses multiple tactics to reduce selection pressure for a single control tactic i.e. insecticides. Also,

IPM dictates that insecticide control be used when economically justified, i.e. economic

threshold. In tern economic thresholds are based on an economic injury level, which is simply a

point in which cost of control is equatl to loss from a given pest. The development of reliable

economic injury levels and treatment thresholds for beet armyworm will be critical for an IPM

program in tomato. Current control methods for beet armyworm in tomato are based on

Lepidopteran thresholds so there is a lack of knowledge that directly pertains to the beet

armyworm. It is important to understand beet armyworm biology on tomato and understand the

damage that this insect is able to produce at different growth stages of the tomato plant.

3

Purpose of the Study

The goal of this research was to better understand the effect of beet armyworm,

Spodoptera exigua (Hübner), on tomato production throughout the tomato growing season. The

approach was to first use data from insecticide efficacy trials in staked tomatoes to estimate a

relationship of beet armyworm to tomato yields. Artificial infestations were used to look more

precisely at the relationship of the beet armyworm and tomato in terms of damage. Also, new

action thresholds for beet armyworm control were tested against currently used calendar sprays.

The specific objectives for my research were:

1) To investigate the efficacy of currently used insecticides labeled for Spodoptera exigua

control on tomato and relate beet armyworm numbers to yield loss in these trials.

2) To investigate the effectiveness of artificial infestation of Spodoptera exigua on tomato in

the field and relate beet armyworm larval densities to harvestable yields.

3) To estimate an economic injury level (EIL) for BAW and test action thresholds for

control of Spodoptera exigua in tomato based on this EIL.

The overall hypothesis for this research was that beet armyworm infestations can cause

significant yield loss in tomato at population levels that can occur in the field in Georgia.

4

References Cited: Aldosari, S. A., T. F. Watson, S. Sivasupramaniam, and A. A. Osman. 1996. Susceptibility of

field populations of beet armyworm (Lepidoptera: Noctuidae) to cyfluthrin, methomyl,

and profenofos, and selection for resistance to cyfluthrin. Journal of Economic

Entomology. 89: 1359-1363.

Bianchi, F., J. M. Vlak, R. Rabbinge, and W. Van der Werf. 2002. Biological control of beet

armyworm, Spodoptera exigua, with baculoviruses in greenhouses: Development of a

comprehensive process-based model. Biological Control. 23: 35-46.

Boatwright, S. R., and J. C. McKissick. 2004. 2004 Georgia Farm Gate Value Report. In G. C. E.

S. C. Agents [ed.]. The University of Georgia.

Brewer, M. J., and J. T. Trumble. 1989. Field monitoring for insecticide resistance in beet

armyworm (Lepidoptera: Noctuidae). Journal of Economic Entomology. 82: 1520-1526.

Brewer, M. J., and J. T. Trumble. 1994. Beet armyworm resistance to fenvalerate and methomyl-

resistance variation and insecticide synergism. Journal of Agricultural Entomology. 11:

291-300.

Brewer, M. J., J. T. Trumble, B. Alvarado-Rodriguez, and W. E. Chaney. 1990. Beet armyworm

(Lepidoptera, Noctuidae) adult and larval susceptibility to 3 insecticides in managed

habitats and relationship to laboratory selection for resistance. Journal Of Economic

Entomology. 83: 2136-2146.

Eigenbrode, S. D., J. T. Trumble, J. G. Millar, and K. K. White. 1994. Topical toxicity of tomato

sesquiterpenes to the beet armyworm and the role of these compounds in resistance

derived from an accession of Lycopersicon hirsutum f. typicum. Journal of Agricultural

and Food Chemistry. 42: 807-810.

5

Farrar, R. R., Jr., and G. G. Kennedy. 1991. Relationship of leaf lamellar-based resistance to

Leptinotarsa decemlineata and Heliothis zea in a wild tomato, Lycopersicon hirsutum f

glabratum. Entomologia experimentalis et applicata. 58: 61-67.

Kerns, D.-L. 2000. Mating disruption of beet armyworm (Lepidoptera: Noctuidae) in vegetables

by a synthetic pheromone. Crop Protection. 19: 327-334.

Lange, W. H., and L. Bronson. 1981. Insect Pests of Tomatoes. Annual Review Of Entomology.

26: 345-371.

Liburd, O. E., J. E. Funderburk, and S. M. Olson. 2000. Effect of biological and chemical

insecticides on Spodoptera species (Lep., Noctuidae) and marketable yields of tomatoes.

Journal of Applied Entomology-Zeitschrift Fur Angewandte Entomologie. 124: 19-25.

Mascarenhas, V. J., J. B. Graves, B. R. Leonard, and E. Burris. 1998. Susceptibility of field

populations of beet armyworm (Lepidoptera: Noctuidae) to commercial and experimental

insecticides. Journal of Economic Entomology. 91: 827-833.

Meinke, L. J., and G. W. Ware. 1978. Tolerance of three beet armyworm strains in Arizona to

methomyl. Journal of Economic Entomology. 71: 645-646.

Mitchell, E.-R., M. Kehat, F.-C. Tingle, and J.-R. McLaughlin. 1997. Suppression of mating by

beet armyworm (Noctuidae: Lepidoptera) in cotton with pheromone. Journal of

Agricultural Entomology.

Mitchell, E. R. 1973. Migration by Spodoptera exigua and S. frugiperda, North American style,

pp. 386-393. In L. R. Rabb and G. G. Kennedy [eds.], Movement of Highly Mobile

Insects: Concepts and Methodology in Research. North Carolina State University,

Raleigh, North Carolina.

6

Mitchell, E. R., and J. H. Tumlinson. 1994. Response of Spodoptera exigua and S. eridania

(Lepidoptera, Noctuidae) males to synthetic pheromone and S. exigua females. Florida

Entomologist. 77: 237-247.

Moar, W. J., and J. T. Trumble. 1987. Biologically derived insecticides for use against beet

armyworm. California Agriculture. 41: 13-15.

Moulton, J. K., D. A. Pepper, and T. J. Dennehy. 2000. Beet armyworm (Spodoptera exigua)

resistance to spinosad. Pest Management Science. 56: 842-848.

Moulton, J. K., D. A. Pepper, R. K. Jansson, and T. J. Dennehy. 2002. Pro-active management of

beet armyworm (Lepidoptera: Noctuidae) resistance to tebufenozide and

methoxyfenozide: Baseline monitoring, risk assessment, and isolation of resistance.

Journal Of Economic Entomology. 95: 414-424.

Tomatoes National Statistics. 2006. In U. S. D. o. Agriculture [ed.]. National Agriculture

Statistic Service, http://www.nass.usda.gov:8080/QuickStats/index2.jsp#top.

Van Laecke, K., and D. Degheele. 1991. Synergism of diflubenzuron and tebflubenzuron in

larvae of beet armyworm (Lepidoptera: Noctuidae). Journal of Economic Entomology.

84: 785-789.

Wakamura, S., and M. Takai. 1997. Communication disruption for control of the beet

armyworm, Spodoptera exigua (Hubner), with synthetic sex pheromone. Japanese

Agriculture Research Quarterly. 29: 125-130.

Wolfenbarger, D. A. 2002. Inheritance of resistance by a strain of beet armyworm to fenvalerate,

methomyl, methyl parathion, and permethrin. Resistant Pest Management Newsletter. 12:

25-27.

http://www.nass.usda.gov:8080/QuickStats/index2.jsp#top

7

Yee, W. L., and N. C. Toscano. 1998. Laboratory evaluations of synthetic and natural

insecticides on beet armyworm (Lepidoptera: Noctuidae) damage and survival on lettuce.


Zalom, F. G., L. T. Wilson, and M. P. Hoffmann. 1986. Impact of feeding by tomato fruitworm

Heliothis zea (Lepidoptera Noctuidae) and beet armyworm Spodoptera exigua

(Lepidoptera Noctuidae) on processing tomato fruit quality. Journal of Economic

Entomology.

CHAPTER 2

Review of Literature

Beet Armyworm Biology

The beet armyworm, Spodoptera exigua, is a major agricultural pest in the USA and in

tropical and subtropical areas of the world (Liburd et al. 2000). The beet armyworm is a tropical

insect and its native host range is Southeast Asia. It is especially important for vegetable

production because it is able to cause serious economic damage in multiple crops (Zalom et al.

1986, Mitchell and Tumlinson 1994, Yee and Toscano 1998). It was first reported in the United

States in Oregon in 1876 and has since spread throughout the continental United States, Mexico,

and the Caribbean (Mitchell 1973). In some areas of tomato production, it has become a major

pest of both fresh-market and processed tomatoes (Lange and Bronson 1981, Brewer et al. 1990).

The beet armyworm is capable of feeding on the foliage, but most insecticide spray programs in

tomato are driven by insect pressure after fruit set and typically consist of weekly sprays once

presence has been established (Webb et al. 2001).

Beet armyworm, Spodoptera exigua, biology was reviewed by Capinera (2001). It is a

polyphagous pest on many crops and has a world wide distribution in tropical and subtropical

regions. It lacks a diapause mechanism and daytime temperatures of below 10ºC are detrimental

to the life cycle of the insect. This lack of diapause mechanism leads to a tropical distribution

but it is able to overwinter in Arizona, Florida, and Texas, however abundance greatly decreases

in the winter months (Liburd et al. 2000). It is found in the southern half of the United States

during the warmer months (Capinera 2001). The life cycle can be as short as 24 days, and over

9

six generations have been reared during one growing season in Florida (Wilson 1934).

Generation time can be as long as 126 days depending on climate (Campbell and Duran 1929).

Eggs are laid on leaves in clusters of approximately 50-150 per mass and an adult female can lay

as many as 1200 eggs during her lifetime, but egg production is usually limited to 300-600 per

adult female. They are usually laid on the underside of the leaves and the egg mass is covered

with white/grey scales placed on the egg mass. The eggs will hatch within 2-3 days and the

newly hatched larvae feed gregariously in their early stages. The larvae are only 1.0 mm long at

hatching but grow to 2.5, 5.8, 8.9, 13.8, and 22.3 mm during instars 1-5, respectively (Wilson

1934). During maturity, larvae become solitary and very mobile (Capinera 2001). Also,

cannibalism can occur at high densities or in areas of poor nutrition including foods that contain

low nitrogen (Al-Zubaidi and Capinera 1983).

The larvae are dull or pale green, but sometimes they can be very dark. They can have a

pattern of dark spots or dashes, which is present dorsally and dorsolaterally. Fifth instar larvae

vary the most in coloration and sometimes have a pink or yellow color ventrally and a white

stripe laterally. The body of all larval instars is usually absent of hairs or spines. Pupation

occurs in the soil usually within one cm of the soil surface. The pupa is light brown and

measures 15-20 mm long and is enclosed within a chamber constructed from sand and soil held

together by oral secretions. The duration of pupal stages is from 6-7 days during optimal

weather conditions as found in tropical and subtropical climates.

The adults have a wingspan of 25-30 mm. Their front wings are gray and brown with a

pale spot near the center of each wing and the rear wings are white or grey with a dark line at the

outside margin. Mating occurs soon after adult emergence and oviposition begins within 2-3

10

days. Adult moths usually live for 9-10 days with oviposition taking place over a 3-7 day

interval (Capinera 2001).

Beet armyworm attacks both foliage and fruit and is a very important late season pest of

tomatoes. As young larvae feed gregariously they are able to skeletonize foliage, but as they

mature they become solitary and eat large holes in the foliage. After fruit set, the armyworm can

feed directly on the fruit. This is especially important in fresh market tomato as the presence of

holes cause fruit to be unmarketable. In processing tomatoes the demand for perfect fruit is

lower, but the larvae that feed into the fruit can appear as contaminates (Zalom and Jones 1994).

Beet Armyworm Management Strategies

Many control tactics have been used to manage the beet armyworm, with chemical

insecticides being the most commonly used tactic. However, intensive use of insecticides on a

regional scale can lead to resistance in beet armyworm populations so other control tactics are

critical for management. Meinke and Ware (1978) first reported reduced efficacy of methomyl

on a natural population of beet armyworm due to insecticide resistance. Yoshida and Parrella

(1987) detected resistance to methomyl in floricultural crops in Florida. Other carbamate class

resistance has been shown in vegetable crops (Brewer and Trumble 1989, Brewer et al. 1990,

Aldosari et al. 1996, Kerns et al. 1998, Mascarenhas et al. 1998). The organophosphate class of

insecticide was shown by Robb and Parrella (1984) to have reduced effects on a resistant strain

of beet armyworm. Resistance to pyrethroid insecticides has also been documented (Chaufaux

and Ferron 1986, Brewer et al. 1990, Shimada et al. 2005). The beet armyworm has also been

shown to develop resistance to chitin synthesis inhibitors (Van Laecke and Degheele 1991, Van

Laecke et al. 1995). Spinosad has been considered a new IPM-compatible insecticide due to its

11

reduced risk status by the US Environmental Protection Agency, but due to its widespread use in

vegetable pest management, resistance has already been recorded (Moulton et al. 2000). Along

with chemical insecticide control, several biological insecticides have been evaluated to control

beet armyworm. Bacillus thuringiensis and nuclear polyhedrosis viruses (NPVs) have shown

variable levels of efficacy (Moar et al. 1986, Smits et al. 1987, Kolodny-Hirsch et al. 1993,

Liburd et al. 2000, Bianchi et al. 2002).

Pheromones have been used in management strategies for some insect pests, whether

used for mating disruption or monitoring of adult flight. The beet armyworm and its pheromone

components have been identified by researchers and are viewed as potential means for mass

trapping, disruption of mating communication, monitoring and surveying (Mitchell 1986).

Tingle and Mitchell (1975) used female adult beet armyworms to collect adult males for

evaluation of pheromone traps. Since the publication of Tingle and Mitchell (1975), there has

been some debate on the exact components of beet armyworm sex pheromone. The beet

armyworm sex pheromone compounds collected from live female moths were analyzed and

evaluated in the field by Tumlinson et al. (1990). Five components were found in the pheromone

and further research has led to blends that allow pheromones to be used in disruption of

pheromone communication of beet armyworm in field settings (Shorey et al. 1994).

Mating disruption has been used as a control tactic for beet armyworms in several crops

such as cotton, onions, head lettuce, and broccoli (Mitchell et al. 1997, Wakamura and Takai

1997, Kerns 2000). Synthetic pheromone blends have been produced and used for disruption of

mating communication of beet armyworm. Wakamura et al. (1989) used synthetic pheromone to

control beet armyworm in Welsh onion. Similar studies have shown that pheromones can also

be used to control beet armyworm in tomato. Shorey and Gerber (1996) used puffers

12

(commercially purchased machines to emit pheromone) to release pheromone and were able to

control beet armyworm to some degree. They proposed that pheromone disruption could be used

to control beet armyworm in a large field with complete elimination of ability of the males to

locate female moths. Unfortunately, in their small field evaluations female moths that mated

outside of the test area were able to fly in and oviposit, showing the limitations of this method of

controlling beet armyworm (Shorey and Gerber 1996).

Varietal resistance to pests has also been used in many agricultural crops for control of

beet armyworm. Unfortunately, there are no resistant cultivars of tomato for the control of beet

armyworm due to the little variation for pest resistance within the germplasm (Farrar and

Kennedy 1991, Eigenbrode et al. 1994). Producing resistant cultivars has been hindered by

multigenic inheritance, epistatic gene effects and unfavorable linkages (Fery and Kennedy 1987,

Eigenbrode et al. 1994, Mutschler et al. 1996).

IPM strategies

The relationship between the damage caused by an insect and its plant or animal host can

be related to an economic value and is a fundamental concept of integrated pest management

(IPM) (Stern et al. 1959). The main focus of IPM is using multiple control tactics to reduce

injury or damage to the commodity to an economically justifiable level. Injury and damage are

generally used interchangeably, but it is important to note the difference. Injury is physical

damage or harm to a valued commodity caused by the activity or presence of an insect. Damage

is the monetary value lost to the commodity due to injury by the insect pest. Pest infestations

cause injury, but not all injuries can be labeled as damage. Some injury is usually tolerated by

the plant because it doesn’t result in monetary crop loss.

13

There is a point in the growth of the pest population where an economic damage level is

reached where control practices are economically warranted (Meyer 2003). Stern et al. (1959)

defines economic damage as “the amount of injury which will justify the cost of artificial control

measures”. Economic damage can be very different in different commodities and can very

greatly with commodities depending on the growth stage of the crop. Consequently, economic

damage begins at a point when the cost of damage equals the cost of suppression. Pedigo et. al

(1986) uses the term damage boundary or the damage threshold to describe another damage

level. The damage boundary is the lowest level of injury that can be measured in terms of yield

loss and occurs before economic loss to production. It is considered by Pedigo et al (1986), to be

a basic IPM principle which involves the damage boundary/economic damage relationship. No

amount of injury below the damage boundary warrants suppression, but injury predicted to result

in economic damage does warrant pest control action.

To control a pest insect and keep the population below a damaging level it is important to

know the point at which cost of control equals the amount of damage the pest causes. This is the

economic injury level and is defined by Stern et al. (1959) as the lowest population density that

will cause economic damage. Below the economic injury level, control would not be cost

effective because the cost of treatment outweighs the amount of damage that the pest population

is able to inflict. Above the economic injury level, control is warranted because the pest

population is able to cause more monetary damage than the cost of control. The economic injury

level is a very basic decision rule, but it is a theoretical value. It is a measure which researchers

and growers use to evaluate the destructive status and potential of a pest population. The

economic injury level is usually expressed as a pest density, but it is actually a level of crop

damage estimated from pest numbers.

14

A simplistic view of economic injury levels can be seen in the equation:

In this equation, C = the unit cost of controlling the pest, N = the number of pest injuring the

commodity unit, V = the unit value of the commodity, and I = the percentage of the commodity

unit injured. Another formula by Pedigo et al (1986) uses injury equivalents due to the fact that

economic injury levels are directly related to damage and only indirectly related to pest numbers.

Pedigo et al (1986) defines an injury equivalent as the total injury produced by a single pest over

an average lifetime. When using injury equivalents the economic threshold is below the

economic injury level as defined by Stern et al. (1959). Pedigo et al (1986), states that the

economic injury level is controlled by five primary variables,

EIL = C/VIDK

where C = cost of the management tactic per production unit, V = market value per production

unit, I = injury units per pest, D = damage per injury unit, and K = the proportional reduction in

pest attack. The economic injury level is the basis on which pest control decisions are made.

Because of the dependence on cost and value, the economic injury level can only be calculated

after the determination of the value of the damaged product or commodity.

Since the economic injury level is a theoretical level there was a need for a practical

working level where some type of pest control action should be taken. This is called the

economic threshold and is defined by Stern et al. (1959), as “the population density at which

control action should be determined to prevent an increasing pest population (injury) from

reaching the economic injury level”. It is measured in insect density and the economic threshold

15

is actually a point in time to take action, as numbers of insect pests are an index of time. The

term action threshold is commonly referred to in place of economic threshold. It is usually

expressed in pest density or in terms of an injury measurement of the commodity. The economic

threshold is always lower than the economic injury level because control tactics must take place

before the economic injury level is reached. This threshold is complex and depends on the

estimation of other values associated with its value: the economic injury level, the pest and host

phenology, pest population growth and injury rates, and time delays associated with IPM tactics

used.

Figure 2.1: Relationship of economic injury levels (EIL) and economic thresholds (ET) (Pedigo

1996)

As shown in Figure 2.1, as an insect population increases, a control method must be used before

16

the population reaches the economic injury level. The economic threshold or action threshold is

lower than the economic injury level, due to the lag in application time and the time it takes the

control method to take effect. The economic threshold is greatly dependant on the type of

control method used as there may be significant lag times in some control methods. Both the

economic injury level and the economic threshold can be based on a single seasonal value, or be

based on critical periods throughout the season such as seedling, vegetative, or fruit formation.

Also, some thresholds use the distinction of early vs. late season and have individual thresholds

assigned to pest insects based on the location and amount of damage within the season (Riley

2004).

17

References Cited:

Al-Zubaidi, F. S., and J. L. Capinera. 1983. Application of different nitrogen levels to the host

plant and cannibalistic behavior of beet armyworm, Spodoptera exigua (Hubner)

(Lepidoptera: Noctuidae). Environmental Entomology. 13: 1687-1689.

Aldosari, S. A., T. F. Watson, S. Sivasupramaniam, and A. A. Osman. 1996. Susceptibility of



Entomology. 89: 1359-1363.

Bianchi, F., J. M. Vlak, R. Rabbinge, and W. Van der Werf. 2002. Biological control of beet

armyworm, Spodoptera exigua, with baculoviruses in greenhouses: Development of a

comprehensive process-based model. Biological Control. 23: 35-46.





habitats and relationship to laboratory selection for resistance. Journal of Economic

Entomology. 83: 2136-2146.

Campbell, R. E., and V. Duran. 1929. Notes on the sugar-beet army worm in California, pp. 267-

275. California Department of Agriculture.

Capinera, J. L. 2001. Handbook of Vegetable Pests. Academic Press, San Diego, California.

Chaufaux, J., and P. Ferron. 1986. Sensibilite differente de deux populations de Spodoptera

exigua Hub. (Lepid., Nocutidae) aux baculorvirus et aux pyrethrinoides de synthese.

Agronomie. 6: 99-104.

18

Eigenbrode, S. D., J. T. Trumble, J. G. Millar, and K. K. White. 1994. Topical toxicity of tomato

sesquiterpenes to the beet armyworm and the role of these compounds in resistance

derived from an accession of Lycopersicon hirsutum f. typicum. Journal of Agricultural

and Food Chemistry. 42: 807-810.

Farrar, R. R., Jr., and G. G. Kennedy. 1991. Relationship of leaf lamellar-based resistance to

Leptinotarsa decemlineata and Heliothis zea in a wild tomato, Lycopersicon hirsutum f

glabratum. Entomologia experimentalis et applicata. 58: 61-67.

Fery, R. L., and G. G. Kennedy. 1987. Genetic analysis of 2-tridecanone concentration, leaf

trichome characteristics, and tobacco hornworm resistance in tomato. Journal of

American Society of Horticutural Science. 112: 886-891.

Kerns, D.-L. 2000. Mating disruption of beet armyworm (Lepidoptera: Noctuidae) in vegetables

by a synthetic pheromone. Crop Protection. 19: 327-334.

Kerns, D. L., J. C. Palumbo, and T. Tellez. 1998. Resistance of field strains of beet armyworm

(Lepidoptera: Noctuidae) from Arizona and California to carbamate insecticides. Journal

of Economic Entomology. 91: 1038-1043.

Kolodny-Hirsch, D. M., D. L. Warkentin, B. Alvarado-Rodriguez, and R. Kirkland. 1993.

Spodoptera exigua nuclear polyhedrosis virus as a candidate viral insecticide for the beet


Lange, W. H., and L. Bronson. 1981. Insect Pests of Tomatoes. Annual Review of Entomology.

26: 345-371.




19






Meyer, J. R. 2003. Economic Injury Level. NC State University.

http://www.cals.ncsu.edu/course/ent425/tutorial/economics.html

Mitchell, E.-R., M. Kehat, F.-C. Tingle, and J.-R. McLaughlin. 1997. Suppression of mating by

beet armyworm (Noctuidae: Lepidoptera) in cotton with pheromone. Journal of

Agricultural Entomology.





Mitchell, E. R. 1986. Pheromones: as the glamour and glitter fade the real work begins. Florida





Moar, W. J., W. L. A. Osbrink, and J. T. Trumble. 1986. Potentiation of Bacillus thuringiensis

var. kurstaki with thuringiensis on beet armyworm (Lepidoptera: Noctuidae). Journal of

Economic Entomology. 79: 1443-1446.


20



Mutschler, M. A., r. W. Doerge, S. C. Lui, J. P. Kuai, B. E. Liedl, and J. A. Shapiro. 1996. QTL

analysis of pest resistance in the wild tomato Lycopersicon pennellii: QTLs controlling

acylsugar level and composition. Theoretical and Applied Genetics. 92: 709-718.

Pedigo, L. P. 1996. Economic Thresholds and Economic Injury Levels. Iowa State University.

http://ipmworld.umn.edu/chapters/pedigo.htm

Pedigo, L. P., S. H. Hutchins, and L. G. Higley. 1986. Economic injury levels in theory and

practice. Annual Review Of Entomology. 31: 341-368.

Riley, D. G. 2004. Economic Injury Level (EIL) and Economic Threshold (ET) Concepts in Pest

Management, pp. 744-748. In J. L. Capinera [ed.], Encyclopedia of Entomology. Kluwer

Academic Publishers, Dordrecht.

Robb, K. L., and M. P. Parrella. 1984. Controlling the beet armyworm. Florida Review. 22: 22-

25.

Shimada, K., K. A. Natsuhara, Y. Oomori, and T. Miyata. 2005. Permethrin resistance

mechanisms in the beet armyworm (Spodoptera exigua (Hubner)). Journal of Pesticide

Science. 30: 214-219.

Shorey, H. H., and R. G. Gerber. 1996. Disruption of pheromone communication through the use

of puffers for control of beet armyworm (Lepidoptera: Noctuidae) in tomatoes.

Environmental Entomology. 25: 1401-1405.

Shorey, H. H., C. G. Summers, C. B. Sisk, and R. G. Gerber. 1994. Disruption of pheromone

communication in Spodoptera exigua (Lepidoptera: Noctuidae) in tomatoes, alfalfa, and

cotton. Environmental entomology. 23: 1529.


21

Smits, P. H., M. Van De Vrie, and J. M. Vlak. 1987. Nuclear polyhedosis virus for control

Spodoptera exigua larvae on glasshouse crops. Entomologia Experimentalis et Applicata.

43: 73-80.

Stern, V. M., R. F. Smith, R. v. d. Bosch, and K. S. Hagen. 1959. The integrated control concept.

Hilgardia. 29: 81-101.

Tingle, F. C., and E. R. Mitchell. 1975. Capture of Spodoptera frugiperda and S. exigua in

pheromone traps. Journal of Economic Entomology. 68: 613-615.

Tumlinson, J. H. M., E. R., and H. S. Yu. 1990. Analysis and field evaluation of volatile blend

emitted by calling virgin females of beet armyworm moth, Spodoptera exigua (Hubner).

Journal of Chemical Ecology. 16: 3411-3423.

Van Laecke, K., and D. Degheele. 1991. Synergism of diflubenzuron and tebflubenzuron in

larvae of beet armyworm (Lepidoptera: Noctuidae). Journal of Economic Entomology.

84: 785-789.

Van Laecke, K., G. Smagghe, and D. Degheele. 1995. Detoxifying enzymes in greenhouse and

laboratory strain of beet armyworm (Lepidoptera: Noctuidae). Journal of Economic

Entomology. 88: 777-781.




Wakamura, S., M. Takai, S. Kozai, H. Inoue, I. Yamashita, S. Kawahara, and M. Kawamura.

1989. Control of the beet armyworm Spodoptera exigua Hubner (Lepidoptera Noctuidae)

using synthetic sex pheromone I. effect of communication disruption in welsh onion

fields UK. Applied Entomology and Zoology. 24: 387-397.

22

Webb, S. E., P. A. Stansly, D. J. Schuster, and J. E. Funderburk. 2001. Insect Management for

Tomatoes, Peppers, and Eggplant. University of Florida. http://edis.ifas.ufl.edu/IN169

Wilson, J. W. 1934. The asparagus caterpillar: its life history and control, pp. 1-26. Florida

Agriculture Experiment Station Bulletin.




Yoshida, H. A., and M. P. Parrella. 1987. The beet armyworm in floricultural crops. California

Agriculture. 41: 13-15.

Zalom, F. G., and A. Jones. 1994. Insect fragments in processed tomatoes. Journal of Economic

Entomology. 87: 181.





http://edis.ifas.ufl.edu/IN169

CHAPTER 3

Efficacy of Metaflumizone against Spodoptera exigua

in Relation to Tomato Yield

Introduction

The beet armyworm (BAW), Spodoptera exigua (Hübner), is a major agricultural pest in

the USA and in tropical and subtropical areas of the world (Liburd et al. 2000). The beet

armyworm is a tropical insect and its native host range is Southeast Asia. It is especially

important for vegetable production because it is able to cause serious economic damage in

multiple crops (Zalom et al. 1986, Mitchell and Tumlinson 1994, Yee and Toscano 1998). It was

first reported in the United States in Oregon in 1876 and has since spread throughout the

continental United States, Mexico, and the Caribbean (Mitchell 1973). In some areas of tomato

production, it has become a major pest of both fresh-market and processed tomatoes (Lange and

Bronson 1981, Brewer et al. 1990). The beet armyworm is capable of feeding on the foliage, but

most insecticide spray programs in tomato are driven by insect pressure after fruit set and

typically consist of weekly calendar sprays once presence has been established.

The most common control tactic used to manage the beet armyworm is the use of

chemical insecticides. However, intensive use of insecticides on a regional scale can lead to

resistance in beet armyworm populations so other control tactics are critical for management.

Beet armyworm has become resistant to many different chemistries of insecticide

24

(Meinke and Ware 1978, Robb and Parrella 1984, Chaufaux and Ferron 1986, Yoshida and

Parrella 1987, Brewer and Trumble 1989, Brewer et al. 1990, Van Laecke et al. 1995, Aldosari et

al. 1996, Kerns et al. 1998, Mascarenhas et al. 1998, Shimada et al. 2005). Spinosad has been

considered a new IPM-compatible insecticide due to its reduced risk status granted by the US

Environmental Protection Agency, but due to its widespread use in vegetable pest management,

resistance has already been recorded (Moulton et al. 2000).

It is important to avoid resistance in field populations of insects and as new chemistries

are designed, the task becomes easier as growers are able to use different classes of insecticides

during the growing season to control pests. One new insecticide produced by BASF chemical

company is BAS 320 I (metaflumizone) a member of the semicarbazone class of insecticides. It

is a new chemistry with a novel mode of action. It has shown efficacy against beet armyworm

and other Lepidopteran pests and is scheduled to be registered for several different commodities,

including tomato. It has also been designated by the US EPA as a reduced risk candidate due to

its favorable toxicological and environmental profiles, in particular low toxicity to beneficial

insects (Project 2006). With these qualities BAS 320 I is a prime candidate for use in IPM and

IRM programs. The objectives of these tests were to (1) determine the field efficacy of

metaflumizone against BAW, (2) evaluate the effect of various adjuvants on efficacy, and (3)

investigate the timing of sprays effect on efficacy. To determine the efficacy of BAS 320 I, it

was compared to local commercial insecticides in an insecticide efficacy trial. The hypothesis

that metaflumizone was equal in efficacy to commercially available treatments was accepted if

BAS 320 I performed as well as commercial standards. Additionally, the relationship of beet

armyworm to tomato yield was investigated in these studies. The hypothesis was that beet

armyworm abundance is negatively correlated with marketable tomato yield.

25

Materials and Methods

Insecticide efficacy field trials were conducted in tomato at the University of Georgia

Coastal Plain Experiment Station in Tifton, Ga. in the summers of 2004 and 2005 on a Tift

pebbly clay loam soil or sandy loam types. All field tests used methyl-bromide fumigated beds

@ 200 lbs/acre (98:2) (Hendrix and Dail, Tifton GA). Fertilizer rates for tomato were 825

lbs/acre of 6-6-18 and tomatoes were maintained with standard plasti-cultural practices.

2004 Summer. In 2004, tomato, (Lycopersicon miller hyb. Solar Set), were transplanted

with 2-ft in-row spacing into 1 row (6-ft wide) methyl-bromide fumigated white plastic mulched

beds in 35-ft long plots on June 16th. Seven weekly insecticide applications were made from

July 2nd to August 26th. Nineteen treatments were evaluated in this insecticide efficacy trial

(Table 3.1). Scouting was initiated on June 30th and continued weekly until first harvest.

Scouting included whole plant inspections of 6 plants per plot. Tomatoes were harvested from

10-ft of row (5 plants) on September 2nd and 11th and fruit were categorized as marketable or

unmarketable according to USDA standards (USDA 1991). Worm damaged fruit was the

number of fruit per plot that had larval Lepidopteran feeding damage on the outside (surface) or

inside (holes). Lepidopteran damage was the only criterion used to determine marketability, and

the average fruit weight and number of fruit per plot were measured.

2005 Summer. In 2005, (Lycopersicon miller hyb. Bella Rose), was transplanted with

1.5-ft in-row spacing into 1 row (6-ft wide) methyl-bromide fumigated white plastic mulched

beds in 45-ft long plots on June 30th and July 1st. Seven insecticide applications were made

beginning August 2nd until September 13th (Table 3.2). Scouting was initiated on August 1st and

continued weekly until harvest. Scouting included whole plant inspections of 6 plants per plot.

Tomatoes were harvested from 7.5 ft-of row (5 plants) and 50 fruit samples on the 20th of

26

September and fruit were categorized as marketable or unmarketable according to USDA

standards. Lepidopteran damage was the only criterion used to determine marketability and the

average weight per plot was determined. Worm damaged fruit was the number of fruit per plot

that had larval Lepidopteran feeding damage on the outside (surface) or inside (holes) and

included all medium, large and extra large fruit. Marketable fruit included all clean medium,

large, and extra large fruit. Data were analyzed using PROC GLM and LSD tests for analysis of

variance and separation of means, respectively. PROC CORR (Pearson’s correlations and

contrast analysis) was used to compare specific treatments (SAS Institute 2003).

Results

2004 Summer. There was a significant treatment effect in terms of efficacy, with some

treatments showing good control of beet armyworm (F= 3.11; df= 18, 54; P < 0.0001) and

Lepidopteran pests (F= 3.89; df= 18, 54; P < 0.001) over all dates (Table 3.3). Metaflumizone

showed excellent control of Lepidopteran larvae, but the number and timing of sprays did alter

the efficacy of the product. As compared to current commercial products, BAS 320 UHI

performed numerically as well or better than these standards; spinosad and indoxacarb. At the

highest rate BAS 320 UHI 22.3 FL OZ/A + Laytron B1956 5 FL OZ/A was the best at reducing

beet armyworm worm larvae throughout the season (0.06 BAW per scouting date), though it

wasn’t statistically significant from the Avaunt 3.34 OZ WT/A + Penetrator Plus 16 FL OZ/A

(0.31 BAW per scouting date) or the Spintor 2SC 6 FL OZ/A + Penetrator Plus 16 FL OZ/A

treatments (0.69 BAW per scouting date) (Table 3.3). BAS 320 UHI 22.3 FL OZ/A without an

adjuvant performed well against beet armyworm (0.63 BAW per scouting date) and had the

highest marketable fruit weight (16.09 lb) of all treatments. Contrast analysis suggests that the

27

addition of Penetrator Plus didn’t significantly change the efficacy of BAS 320 UHI (F = 1.22; df

= 1, 54; P = 0.27). BAS 320 UHI with Penetrator plus was significantly more effective than

BAS 320 UHI with Laytron we see a significant reduction in efficacy in the Penetrator Plus

adjuvant (F = 4.42; df = 1, 54; P < 0.05). The high rate of BAS 320 UHI was not significantly

better in controlling beet armyworm than the low rate (F = 0.44; df = 1, 54; P = 0.51). The best

BAS 320 adjuvant treatments in terms of BAW were BAS 320 UHI 22.3 FL OZ/A and Ag oil

(1%) and BAS 320 UHI 22.3 FL OZ/A Laytron B1956 (Table 3.3).

Some correlations among seasonal larval means indicated significant beet armyworm –

tomato plant interactions. Over the 2004, beet armyworm larvae were significantly correlated to

total Lepidopteran larvae (R = 0.97; n = 76; P < 0.001). Also, beet armyworm larval counts

were negatively correlated with marketable fruit numbers (R = -0. 41; n = 76; P <0.001) and

marketable fruit weight (R = -0.41; n = 76; P < 0.001). However, beet armyworm larvae counts

were not correlated to unmarketable fruit numbers (R = -0.11; n=76; P = 0.35), but were

negatively correlated with unmarketable fruit weight (R = -0.24; n= 76; P < 0.05) indicating that

other variables were affecting the yield and number of damaged fruit or that the sampling means

were not adequate for seeing a relationship.

There were some minor negative correlations between beet armyworm larvae numbers

before July 14th and marketable fruit weight (R = -0.25; n = 76; P < 0.05) and numbers of

marketable fruit (R = -0.26; n = 76; P < 0.05). Unmarketable fruit counts and unmarketable fruit

weight were not correlated with beet armyworm count (R =0.04; n = 76; P = 0.71) (R = -0.05; n

= 76; P = 0.63), respectively.

Correlation data of beet armyworm numbers after July 14, 2004 (approximately first

fruit) show that beet armyworm larvae after fruit set was significantly correlated to total

28

Lepidopteran larvae numbers (R = 0.97; n = 80; P < 0.0001). Beet armyworm scouting numbers

were negatively correlated to harvestable tomato numbers which included all undamaged

medium, large, and extra large fruit (R = -0.39; n = 80; P < 0.001), and with undamaged tomato

weight (R = -0.39; n = 80; P < 0.0005). Worm damaged fruit numbers and weight were

negatively correlated to beet armyworm and total Lepidopteran larvae counts.

2005 Summer. The 2005 summer trial used similar treatments as 2004, to look at insecticide

efficacy of the BASF product in new formulation, BAS 320I 240 SC. In 2005, there was a

significant treatment effect in terms of efficacy with some treatments showing good control of

beet armyworm (F= 4.48; df= 9, 27; P < 0.001) and other Lepidopteran pests (F= 7.81 df= 9, 27;

P < 0.001). Unlike the previous season, the 2005 summer trial had relatively low pest pressure,

which made it more difficult to discern effects of adjuvants on BAS 320. Also, threshold sprays

were used to compare current calendar spray insecticide applications to a Lepidopteran larvae

threshold insecticide application. Treatments based on thresholds provided similar beet

armyworm control as weekly sprays (Table 3.4). The threshold of 1 larva per 40 plants was

sprayed on week one, week four, and week five while the threshold of 1 larva per 20 plants was

sprayed on week one, week four, and week six (Table 3.2). Along with low Lepidopteran

pressure, a whitefly – transmitted gemnivirus (>90% infection) introduced variability into the

yield data unrelated to the insecticide treatments (Riley, unpublished data).

The commercially used treatments performed as expected in this test with all weekly

treatments being statistically different from the check in beet armyworm larvae counts and worm

damaged fruit numbers (Table 3.4). The untreated check plot had less than 3% worm damaged

fruit so incidence of fruit feeding by Lepidopteran larvae was low, unmarketable fruit numbers

and unmarketable fruit weight were not good measures of treatment effect. The 1 BAW larva/40

29

plants reduced BAW numbers and damage as compared to the check, whereas 1 BAW larva/20

did not (Table 3.4). Using contrast analysis, there was no statistical difference in beet armyworm

counts in the threshold sprays, 1 larva/40 plants (F = 2.42; df = 1, 27; P = 0.13) and 1 larva per

/20 plants (F = 3.48; df = 1, 27; P = 0.07). There was not a significant reduction in total

Lepidopteran larvae in the weekly treatment of BAS 320I as contrasted to the 1 larva/20 plants

threshold (F = 5.53; df = 1, 27; P = 0.09).

The other treatments which included the BAS 320I 240SC @ 11.4 FL OZ PROD/A with

various adjuvants had no detectable Lepidopteran larvae and no unmarketable fruit.

Interestingly, Avaunt 30WG @ 3.43 OZ/A, beet armyworm numbers during the season were

comparable to the threshold treatments, but the Avaunt treatment had no unmarketable fruit.

Discussion

Many control tactics have been used to manage beet armyworm, but chemical

insecticides continue to be the most commonly used. Various insecticides were used in these

trials and BAS 320 showed good efficacy towards beet armyworm and other Lepidopteran pests

including tomato fruitworm, tobacco hornworm, southern armyworm, and cabbage looper. In

2004, weekly applications of BAS 320 UHI was able to maintain Lepidopteran pests below

thresholds, but adjuvants appeared to change the efficacy. Correlation data between beet

armyworm early season counts and yield data suggested that BAW larvae were important during

the early season near fruit set. There were negative correlations of early season BAW densities

with tomato yield, but late season populations of BAW didn’t result in greater unmarketable

fruit. So, beet armyworm is associated with unmarketable yield.

30

In 2005, BAS 320I 240SC was used to evaluate thresholds that were developed from the

2004 season data. Unlike the 2004 season, 2005 had relatively low Lepidopteran pest pressure.

BAS 320I 240SC did show similar efficacy to Avaunt. The threshold treatments of 1 larva per

40 plants and 1 larva per 20 plants were shown to have similar efficacy in terms of BAW in

scouting numbers compared to weekly sprays of Avaunt. The threshold of 1 beet armyworm per

40 plants was able to keep fruit damage under acceptable levels. From 2004, 2005 Insecticide

Efficacy trials beet armyworm does negatively impact marketable tomato yields.

31

References Cited:

Aldosari, S. A., T. F. Watson, S. Sivasupramaniam, and A. A. Osman. 1996. Susceptibility of



Entomology. 89: 1359-1363.






Entomology. 83: 2136-2146.

Chaufaux, J., and P. Ferron. 1986. Sensibilite differente de deux populations de Spodoptera

exigua Hub. (Lepid., Nocutidae) aux baculorvirus et aux pyrethrinoides de synthese.

Agronomie. 6: 99-104.

Kerns, D. L., J. C. Palumbo, and T. Tellez. 1998. Resistance of field strains of beet armyworm

(Lepidoptera: Noctuidae) from Arizona and California to carbamate insecticides. Journal

of Economic Entomology. 91: 1038-1043.


26: 345-371.




32















Project, F. A. N. P. 2006. Metaflumizone.

http://www.fluoridealert.org/pesticides/metaflumizone.page.htm

Robb, K. L., and M. P. Parrella. 1984. Controlling the beet armyworm. Florida Review. 22: 22-

25.

SAS Institute 2003. SAS/STAT user's guide, version 9.1 SAS Institute., Cary, NC.


mechanisms in the beet armyworm (Spodoptera exigua (Hubner). Journal of Pesticide

Science. 30: 214-219.


33

USDA. 1991. United States Standards for Grades of Fresh Tomatoes. USDA.

http://www.ams.usda.gov/standards/tomatfrh.pdf

Van Laecke, K., G. Smagghe, and D. Degheele. 1995. Detoxifying enzymes in greenhouse and

laboratory strain of beet armyworm (Lepidoptera: Noctuidae). Journal of Economic





Yoshida, H. A., and M. P. Parrella. 1987. The beet armyworm in floricultural crops. California

Agriculture. 41: 13-15.






34

Table 3.1. 2004 Summer Spray Trial Treatment List

Treatment Application Rate Adjuvant Spray Schedule1

1. Check

2. BAS 320 UHI 27.4 FL OZ/A Penetrator Plus @ 16 FL OZ/A ABCD 3. BAS 320 UHI 27.4 FL OZ/A Penetrator Plus @ 16 FL OZ/A AC 4. BAS 320 UHI 27.4 FL OZ/A Penetrator Plus @ 16 FL OZ/A BCDEFG 5. BAS 320 UHI 27.4 FL OZ/A Penetrator Plus @ 16 FL OZ/A BD 6. Avaunt 3.34 OZ WT/A Penetrator Plus @ 16 FL OZ/A ABCDEFG 7. BAS 320 UHI 18.3 FL OZ/A ABCDEFG 8. BAS 320 UHI 22.3 FL OZ/A ABCDEFG 9. BAS 320 UHI 18.3 FL OZ/A Penetrator Plus @ 16 FL OZ/A ABCDEFG 10. BAS 320 UHI 22.3 FL OZ/A Penetrator Plus @ 16 FL OZ/A ABCDEFG 11. BAS 320 UHI 18.3 FL OZ/A Silwet @ 5 FL OZ/A ABCDEFG 12. BAS 320 UHI 22.3 FL OZ/A Silwet @ 5 FL OZ/A ABCDEFG 13. BAS 320 UHI 18.3 FL OZ/A Ag oil (1%) @ 96 FL OZ/A ABCDEFG 14. BAS 320 UHI 22.3 FL OZ/A Ag oil (1%) @ 96 FL OZ/A ABCDEFG 15. BAS 320 UHI 18.3 FL OZ/A Laytron B1956 @ 5 FL OZ/A ABCDEFG 16. BAS 320 UHI 22.3 FL OZ/A Laytron B1956 @ 5 FL OZ/A ABCDEFG 17. F1785 50 DF 0.054 LB AI/A ABCDEFG 18. F1785 50 DF 0.071 LB AI/A ABCDEFG 19. Spintor 2SC 6 FL OZ/A Penetrator Plus @ 16 FL OZ/A ABCDEFG 1 The spray schedule corresponds to A= 1st Spray, B= 2nd Spray, etc.

35

Table 3.2. 2005 Summer Spray Trial Treatment List

Treatment Application Rate Adjuvant Spray Schedule2

1. Check 2. BAS 320I 240SC 11.4 FL OZ prod/a ABCDE 3. BAS 320I 240SC 16.0 FL OZ prod/a ABCDE 4. BAS 320I 240SC 11.4 FL OZ prod/a Penetrator Plus @ 16

FL OZ/A ABCDE

5. BAS 320I 240SC 11.4 FL OZ prod/a Ag oil (1%) @ 96 FL OZ/A

ABCDE

6. BAS 320I 240SC 11.4 FL OZ prod/a Silwet @ 5 FL OZ/A ABCDE 7. BAS 320I 240SC 11.4 FL OZ prod/a Laytron B1956 @ 5

OZ/A ABCDE

8. Avaunt 30 WG 3.43 OZ/A ABCDE 9. BAS 320I 240SC 16.0 FL OZ prod/a Lep. Larvae

threshold 1/40 plants ADE

10. BAS 320I 240SC 16.0 FL OZ prod/a Lep. Larvae threshold 1/20 plants

ADF

2 The spray schedule corresponds to A= 1st Spray, B= 2nd Spray, etc

36

Table 3.3. Tomato scouting and yield data from Tifton, Ga. Summer 2004, seasonal means of Lepidopteran larvae were based on scouting of 6 plants. Worm damaged fruit and marketable tomato weight was based on 5 plants.

st spray, B=2nd spray, etc. * The rate is given in product per acre and the spray schedules corresponds to A=1

Treatment (rate and spray schedule*) Beet Armyworm

Hornworm WormDamaged Fruit

Marketable Tomato wt (lb)

Check 1.56ab** 0.41a 1.13abcde 2.38d F1785 50 DF 0.071 LB AI/A (ABCDE) 1.72a 0.34abc

0.78def 3.76cdBAS 320 UHI 27.4 FL OZ/A (AC) + Penetrator Plus 16 FL OZ/A

1.50abc 0.22abcd 1.06abcdef 4.08cd

F1785 50 DF 0.054 LB AI/A (ABCDE) 1.25abcd 1.00abcdef0.38ab 3.49cdBAS 320 UHI 27.4 FL OZ/A (BD) + Penetrator Plus 16 FL OZ/A 1.00abcde 0.13cd 0.63f 6.46bcd BAS 320 UHI 22.3 FL OZ/A (ABCDE) + Penetrator Plus 16 FL OZ/A 0.94abcde 0.16bcd 1.00abcdef 10.16abcd BAS 320 UHI 18.3 FL OZ/A (ABCDE) + Penetrator Plus 16 FL OZ/A 0.78bcdef 0.13cd 1.09abcdef 10.42abcd BAS 320 UHI 18.3 FL OZ/A (ABCDE) + Laytron B1956 5 FL OZ/A 0.75bcdef 0.16bcd 1.31abc 10.96abc Spintor 2SC 6 FL OZ/A (ABCDE) + Penetrator Plus 16 FL OZ/A 0.69cdef 0.13cd 0.84cdef 13.00abBAS 320 UHI 22.3 FL OZ/A (ABCDE) 0.63def 0.13cd 1.09abcdef 16.09a BAS 320 UHI 27.4 FL OZ/A (ABCD) + Penetrator Plus 16 FL OZ/A 0.56def 0.16bcd 1.34ab 8.00abcd BAS 320 UHI 18.3 FL OZ/A (ABCDE) + Silwet 5 FL OZ/A 0.53def 0.19abcd 0.75def 10.68abcd BAS 320 UHI 22.3 FL OZ/A (ABCDE) + Silwet 5 FL OZ/A 0.50def 0.13cd 0.72ef 8.97abcd BAS 320 UHI 18.3 FL OZ/A (ABCDE) + Ag oil (1%) 96 FL OZ/A 0.41ef 0.06d 0.97abcdef 13.22ab BAS 320 UHI 27.4 FL OZ/A (BCDE) + Penetrator Plus 16 FL OZ/A

0.38ef 0.13cd 0.91bcdef 15.48a

BAS 320 UHI 18.3 FL OZ/A (ABCDE) 0.34ef 0.19abcd 1.41a 15.72aAvaunt 3.34 OZ WT/A (ABCDE) + Penetrator Plus 16 FL OZ/A 0.31ef 0.09dc 0.97abcdef 13.32ab BAS 320 UHI 22.3 FL OZ/A (ABCDE) + Ag oil (1%) 96 FL OZ/A 0.25ef 0.25abcd 1.22abcd 15.27a BAS 320 UHI 22.3 FL OZ/A (ABCDE) + Laytron B1956 5 FL OZ/A 0.06f 0.13cd 0.81edf 15.64a

** Means within columns followed by the same letter are not significantly different (P > 0.05, LSD test)

37

Table 3.4. Tomato scouting and yield data from Tifton, Ga. Summer 2005, seasonal means of Lepidopteran larvae were based on scouting of 6 plants. Worm damaged fruit and marketable tomato weight was based on 5 plants.

Treatment (rate and spray schedule)

Cabbage Looper

Hornworm Beet Armyworm

Worm Damage Fruit

Marketable Tomato wt (lb)

Check 0.84a* 0.56a 0.69a 0.75a 3.028a BAS 320I 240SC 16.0 FL OZ/A threshold 1/40 plants

0.36ab 0.27b 0.23b 0.12b 7.425a

BAS 320I 240SC 16.0 FL OZ/A threshold 1/20 plants

0.28ab 0.09bc 0.28b 0.25ab 8.413a

Avaunt 30WG 3.43 OZ/A 0.06b 0.00c 0.25b 0.00b 7.738a BAS 320I 240SC 16.0 FL OZ/A 0.06b 0.03c 0.00b 0.00b 5.725a BAS 320I 240SC 11.4 FL OZ/A + Silwet 5 FL OZ/A

0.03b 0.00c 0.00b 0.00b 1.237a

BAS 320I 240SC 11.4 FL OZ/A + Laytron B1956 5 FL OZ/A

0.03b 0.00c 0.00b 0.00b 5.188a

BAS 320I 240SC 11.4 FL OZ/A + Penetrator Plus 16 FL OZ/A

0.00b 0.00c 0.00b 0.00b 4.500a

BAS 320I 240SC 11.4 FL OZ/A + Ag oil (1%) 96 FL OZ/A

0.00b 0.00c 0.00b 0.00b 4.013a

BAS 320I 240SC 11.4 FL OZ/A 0.00b 0.00c 0.00b 0.00b 2.888a

* Means within columns followed by the same letter are not significantly different (P > 0.05, LSD Test)

38

0

0.51

1.5

22.5

3

3.54

4.5

6/30/2

004

7/7/20

04

7/14/2

004

7/21/2

004

7/28/2

004

8/4/20

04

8/11/2

004

8/18/2

004

Scouting Date

BA

W N

umbe

rs p

er 6

/pla

nts

Check Avaunt BAS 320 UHI Spintor 2SC All

Weekly Insecticide Applications

Figure 3.1. 2004 Beet Armyworm means by scouting date. Arrows indicate weekly spray events.

39

Weekly Insecticide Applications4.5

4 3.5

3 BAW Means by 6 plants

2.5 2

1.5 1

0.5 0

8/1/2005 8/8/2005 9/16/2005 8/12/2005 8/19/2005 8/26/2005 9/2/2005 9/9/2005-0.5

Scouting Date

Check Threshold 1 larvae/40 plants BAS 320 I Weekly Sprays Avaunt

Figure 3.2. 2005 Beet Armyworm means by scouting date. Arrows indicate weekly spray events.

CHAPTER 4

Artificial Infestations of Beet Armyworm, Spodoptera exigua

In Tomato

Introduction

Lepidopteran insects are major pests of tomato in the Southeastern US and there is a

major economic loss associated with their damage (Liburd et al. 2000). In recent years, one

particular Lepidopteran species, the beet armyworm Spodoptera exigua (Hübner), has increased

in importance in the summer-fall growing season (D. Riley, personal communication). Thus, it

has become important to understand the relationship between beet armyworm and tomato. The

relationship between the damage caused by an insect and its plant or animal host can be related

to an economic value. This relationship is a fundamental concept of integrated pest management

(IPM). The first step in determining this relationship is to determine yield loss per pest. Within

this experiment, the goal was to create a beet armyworm population in tomatoes through

artificial infestation and relate larval numbers to yield.

The beet armyworm (BAW), a tropical insect native to Southeast Asia, is considered a

major pest in many agricultural areas of the world in vegetable, field, and flower crops. It was

first discovered in the United States in Oregon in approximately 1876 and has since spread

throughout the continental United States and has spread to Mexico and the Caribbean (Mitchell

1973). In some areas of tomato production it has become a major insect pest of both fresh-

market and processed tomatoes (Lange and Bronson 1981, Brewer et al. 1990). The beet

41

armyworm is capable of feeding on the foliage but most insecticide spray programs in tomato are

based on insect pressure after fruit set because of direct feeding by this pest on fruit. After fruit

set is the most critical time in tomato production because any damage to the fruit is directly

related to economic loss as these fruit are unmarketable (Picture 4.1).

Beet armyworm attacks both foliage and fruit and is thought to be a very important late

season pest of tomatoes. As young larvae feed gregariously they are able to skeletonize foliage,

but as they grow they become solitary and eat large holes in the foliage (Picture 4.2). After fruit

set the armyworm can feed directly on the fruit (Picture 4.3). This is especially important in

fresh market tomatoes as the presence of holes can lead to unmarketable fruit. In processing

tomatoes the demand is lower for perfect fruit, but the larvae that feed into the fruit can appear as

contaminates (Zalom and Jones 1994).

Based on data collected during the summer of 2004 it was proposed that a working action

threshold of 1 larva per 20 plants to be used as a target infestation level for evaluation in this

experiment. The objectives of these tests were to: (1) develop an effective method of artificial

infestation of beet armyworm in tomato, (2) use artificial infestation in a field trial to create a

BAW population within the range of 1 – 40 larva(e) per plot (30-35 plants), and (3) investigate

the relationship of beet armyworm larvae to tomato yield at different crop stages. The

hypothesis was that artificial beet armyworm infestations using egg masses could establish a

range of BAW levels in the field sufficient to cause significant yield loss in tomato.

Methods and Materials

The experiments were conducted at the Coastal Plains Experiment Station in Tifton, Ga.

at the Tifton Vegetable Park in the spring of 2005 and 2006 on a Tift pebbly clay loam soil or

42

sandy loam types. All field tests used methyl-bromide fumigated beds applied at 200 lbs/acre

(98:2) (Hendrix and Dail, Tifton, GA). Fertilizer rates for tomato were 825 lbs/acre of 6-6-18

and plants were maintained with standard plasti-cultural practices.

Spring Infestation 2005. In spring 2005, tomato, (Lycopersicon esculentum Miller hyb.

Marglobe), was transplanted with 2-ft in-row spacing into 1 row (6-ft wide) black plastic

mulched beds in 55-ft long plots on April 11th, 2005. There were 30 plants per plots. Scouting

was conducted weekly from May 16th until harvest. Scouting included whole plant inspections

of 6 plants per plot. The trial was conducted as a split plot, randomized complete block design

with infestation date (early and late) as the main plot, and infestation levels were randomized

within each infestation date with 4 replicates total. The test was conducted during the spring to

avoid natural populations of beet armyworm and other Lepidopteran pests (D. Riley, personal

communication). There were no insecticide applications during the test.

We conducted two individual infestations, early infestation was initiated on April 15th

and late infestation was initiated on May 12th. Beet armyworm larvae were obtained from a

laboratory colony that had been in culture for 9 months. The first attempt at infestation was to

apply 2nd instar larvae to individual plants. There were four treatments which were: control (no

larvae), 2 larvae, 5 larvae, and 25 larvae per plot. Scouting the following week indicated there

were no beet armyworm larvae present in the field. Since larval infestations appeared to fail we

decided to infest using beet armyworm egg masses. We then re-infested the early season plots at

the same time as the late season infestation. Egg masses were collected from cages and cut into

individual ¼ egg masses. We attempted to keep the numbers of eggs to approximately 15-30 per

egg mass. The egg masses were then pinned to the underside of the leaf surface in the middle of

the canopy (Picture 4.4, 4.5, 4.6). Sheets holding egg masses were pinned with the egg masses

43

facing the leaves so that the neonates would hatch directly onto foliage and increase likelihood of

establishment (J. Ruberson, personal communication).

Each individual treatment included ¼ egg mass (app. 15-30 eggs) placed on each plant.

The four treatments were: control (no egg masses), 2 egg masses, 5 egg masses, and 25 egg

masses per plot. The early infestation was on May 12th, 2005 and the late infestation was on

May 12th, 2005. Plots were harvested by removing 50 mature fruit per plot on 6/14/05, 6/21/05,

and 6/30/05. Fruit was then evaluated based on size and worm damage with Lepidopteran

damage as the only criteria used to determine marketability (USDA 1991). Worm damaged fruit

was the number of fruit per plot that had Lepidopteran larvae feeding damage on the outside

(surface) or inside (holes). Lepidopteran damage was the only criteria used to determine

marketability. Data was analyzed using GLM and LSD tests (SAS 2003) for analysis of variance

and separation of means, respectively.

Spring Infestation 2006. In spring 2006, tomato, (Lycopersicon esculentum hyb.

Amelia), was transplanted with 1.5-ft in-row spacing into 1 row (6-ft wide) black plastic

mulched beds in 55-ft long plots on March 16th, 2006. Unlike the previous year a tomato spotted

wilt-resistant variety was used. Scouting was conducted weekly from April 6th until the 2nd

harvest. Scouting included whole plant inspections of 6 plants per plot. The trial was conducted

as a split plot, randomized complete block design with infestation date (early and late) as the

main plot, and infestation levels were randomized within each infestation date with 4 replicates

total. The test was conducted during the spring to avoid natural populations of beet armyworm

and other Lepidopteran pests (D. Riley, personal communication). There were no insecticide

applications to the test plots during the test. One replicate was accidentally sprayed with Spintor

on the 3rd of May.

44

One early season (April 4th) and one late season (May 1st) infestation was made in each

main plot respectively. The four treatments were; control (no egg masses), 5 egg masses, 15 egg

masses, and 50 egg masses per plot. Beet armyworm larvae were obtained from a laboratory

colony that had been in culture for 9 months. The egg masses were taken from cages (cylindrical

bowls with paper inside) and cut out into individual egg masses. The egg masses were prepared

in lab and were cut to keep the numbers of eggs approximately 50-100 or one entire egg mass

each. The egg masses were then pinned to the underside of the leaf surface in the middle of the

tomato plant canopy (Picture 4.4, 4.5, 4.6). Sheets holding egg masses were pinned with the egg

masses facing the leaves so that the neonates would hatch directly onto foliage and increase

likelihood of establishment (J. Ruberson, personal communication).

Since the plots had an average of 30 plants, the 50 egg mass treatment had the 25 central

plants receive 2 egg masses each. Harvest was conducted on 24 May, 31 May, and the 7 June

2006. Fruit was then evaluated based on size and worm damage with Lepidopteran damage as

the only criteria used to determine marketability (USDA 1991). Worm damaged fruit was the

number of fruit per plot that had Lepidopteran larvae feeding damage on the outside (surface) or

inside (holes). Lepidopteran damage was the only criteria used to determine marketability. Data

was analyzed using GLM and LSD tests (SAS 2003) for analysis of variance and separation of

means, respectively. PROC CORR (Pearson’s correlations and contrast analysis) was used to

compare specific treatments (SAS Institute 2003).

Results

Spring 2005. A range in beet armyworm population levels was established in the field

from an artificial BAW infestation in tomato in early and late infestations (Figure 4.1). The

45

highest infestation levels had significantly more larvae than the two lowest infestation level

seasonal means (Figure 4.1). The early season infestation treatment effect on beet armyworm

was not significant in terms of BAW numbers (F = 1.00; df = 3, 9; P = 0.44) (Figure 4.2). There

was a significant treatment effect in terms of beet armyworm numbers (F = 9.09; df = 3, 9; P <

0.01) (Figure 4.3). The two highest infestation levels in the late infestation resulted in ≈ 1 beet

armyworm per 6 plants for a seasonal average (Figure 4.3) while the lowest density treatment

was 0.188 beet armyworm larva (Figure 4.3). The late infestation check received no beet

armyworm pressure throughout the season (Figure 4.3). Figure 4.4 shows numbers of beet

armyworm after the second infestation on each scouting date per 6 plants. The infestations did

produce damaged fruit, but there were no significant treatment differences in either the early (F =

1.33; df = 3, 9; P = 0.32) or the late infestations (F = 0.15; df = 3, 9; P = 0.93). There was

tremendous yield variation due to the presence of tomato spotted wilt, which infected >90% of

the plants in the field (Riley, unpublished).

Spring 2006. Beet armyworm population densities were similar to those observed in

2005 as we were able to see a treatment effect on beet armyworm counts in the field. Seasonal

means of beet armyworm were significantly affected by treatments (F = 38.62; df = 3, 9; P <

0.001) (Figure 4.5). The highest treatment, 50 egg masses per plot, had a seasonal average of

3.38 beet armyworm larvae per scouting date and was statistically different than the other

treatments (Figure 4.5). The 15 egg mass treatment was statistically different than the others

treatments, with 1.57 beet armyworm larvae per scouting date and the lowest infestation

treatments were statistically different from the highest two but did not individually separate

(Figure 4.5). The early infestation was significantly higher in terms of beet armyworm larvae

than the late infestation date (F = 24.89; df = 1, 9; P < 0.001). As mentioned earlier, there was

46

an accidental insecticide application in the 4th rep during the experiment, but there was not a

significant replicate (block) effect in beet armyworm counts in overall seasonal means (F = 2.18;

df = 3, 9; P = 0.16). There were only two other Lepidopteran insects present in scouting. Both

were detected in low numbers and neither showed a significant treatment effect, tomato

fruitworm (F = 0.2, df = 3, 9; P = 0.70) and hornworm (F = 0.20; df = 3, 9; P = 0.89).

Timing of egg infestations, significantly affected beet armyworm numbers scouted in the

field. Figure 4.8 shows the numbers of beet armyworm per scouting date over the entire season

in relation to infestation dates. There was a significant timing of infestation by infestation level

treatment interaction (F = 8.53; df = 3, 9; P < 0.01). Early season infestation showed beet

armyworm larvae counts as having a significant treatment effect (F = 41.01; df = 3, 9; P < 0.001)

(Figure 4.6). The highest treatment of 50 egg masses per plot yielded an average 4.94 beet

armyworm larvae per 6 plants per scouting date, which was statistically different from the

treatment with 15 egg masses per plot, which yielded 2.03 beet armyworm larvae per 6 plants

(Figure 4.6). The two lowest infestation levels were significantly different than the highest

infestation levels and were 0.91 for the 5 egg masses per plot and 0.09 for the check or 0 egg

masses per plot (Figure 4.6).

The late season infestation showed a significant infestation effect in terms of beet

armyworm seasonal means (F = 6.19, df = 3, 9; P < 0.05) (Figure 4.7). The highest infestation

level was statistically different from the lowest two infestation levels, with 1.82 beet armyworms

per 6 plants per scouting date (Figure 4.7). The 15 egg mass treatment had 1.11 BAW per

scouting date and was not statistically different than any late infestation treatments (Figure 4.7).

The 5 egg mass treatment had 0.29 BAW and the 0 egg mass treatment had 0.11 BAW per

47

scouting date indicating that even little or no egg masses were placed, some beet armyworm did

develop.

After combining early and late infestation treatments there were no significant treatment

effects in terms of marketable fruit weight (F = 2.04; df = 3, 9; P = 0.18) or unmarketable fruit

weight (F = 0.78; df = 3, 9; P = 0.53) (Table 4.1). There was a significant replication effect in

unmarketable fruit weight (F = 9.01; df = 3, 9; P < 0.01). Also, there was a significant effect

when early and late season treatments were combined in terms of unmarketable fruit weights (F

= 6.88; df = 1, 9; P < 0.05).

There was no significant interaction between timing of infestation and infestation levels

in terms of marketable fruit weight (F = 1.74; df = 3, 9; P = 0.23), but there was a significant

early infestation effect on marketable fruit weight (F = 4.28, df = 3, 9; P < 0.05) (Table 4.2)

relative to BAW egg masses (Figure 4.9). There was no significant infestation interaction

between time (early vs. late) and infestation levels (F = 1.54; df = 3, 9; P = 0.27). There was a

significant early infestation replicate effect on marketable fruit weight (F = 4.44; df = 3, 9; P <

0.05). There was no significant interaction between infestation time (early vs. late) and

treatment interaction in terms of unmarketable fruit weight (F = 0.84; df = 3, 9; P = 0.51). Early

season infestations had no effect on unmarketable fruit weight (F = 0.01; df = 3, 9; P > 0.05) or

unmarketable fruit numbers (F = 0.18; df = 3, 9; P > 0.05). The late season infestation did not

exert a treatment effect on either marketable (F = 1.34; df = 3, 9; P = 0.32) or unmarketable fruit

weight (F = 1.21; df = 3, 9; P = 0.36) (Table 4.3), but there was a significant replication effect in

unmarketable fruit weight (F = 10.79; df = 3, 9; P < 0.01) and unmarketable fruit numbers (F =

8.22; df = 3, 9; P < 0.01).

48

Even though there was not a strong treatment effect on tomato yield, there were

correlations of the early season infestation beet armyworm densities and yield. Beet armyworm

larval densities were negatively correlated with marketable fruit weight (R = -0.594; n = 16; P <

0.05) and marketable fruit numbers (R = -0.549; n = 16; P < 0.05). Extra large clean fruit

numbers were negatively correlated with BAW densities (R = -0.480; n = 16; P < 0.1). Beet

armyworm numbers were positively correlated with extra large damaged fruit numbers (R =

0.607; n = 16; P < 0.05) and extra large damaged fruit weight (R = 0.602; n = 16; P < 0.05).

Large clean fruit numbers and large clean fruit weight were negatively correlated with beet

armyworm numbers (R = -0.455; n = 16; P < 0.1) (R = -0.426; n = 16; P < 0.1), respectively.

Interestingly, the late season beet armyworm infestation showed no significant

correlations with any marketable (R = 0.120; n = 16; P = 0.66) or unmarketable fruit weight (R =

0.067; n = 16; P = 0.80). Another variable that was recorded during the last three scouting dates

was number of worm holes in damaged fruit on 6 plants per plot. Fruit hole numbers did have a

significant infestation treatment effect with the 50 egg mass treatment being significantly higher

than the other treatments (F = 4.37; df = 3, 9; P < 0.01) (Figure 4.10).

Discussion

From the 2005 experiment, it was concluded that an artificial beet armyworm population

could be created in a tomato field, but it was difficult to duplicate a population as large as the

naturally occurring population in the field as seen in 2004 Insecticide Efficacy trial (Chapter 3).

We decided that with a larger infestation, whether by increasing the number/size of egg masses

or using more than one infestation date, it could be possible to reach naturally occurring

population numbers. In 2005, the 25 egg masses per plot was the only treatment that would have

49

warranted an insecticide application in a commercial field, and in this test the yield wasn’t

reduced significantly in terms of marketable/unmarketable fruit weight or numbers. Also, in

2005 Tomato Spotted Wilt Virus (TSWV) played a major role in reducing the yield even though

steps were taken to count only damage caused by Lepidopteran larvae. The TSWV affected

approximately 90% of the crop by harvest and it is easy to conclude that it played a major role in

confounding any effect of Lepidopteran larvae pressure on yield.

In 2006, a TSWV resistant variety of tomato was used to reduce the impact of TSWV on

tomato yield. The treatment of 5 egg masses per plot was similar across years with 2005 being

0.531 BAW season long means and 2006 being 0.596 BAW season long means even though the

2005 treatment was ¼ the size the treatment in 2006. Also in 2006, BAW scouting indicated that

early season larval densities were higher than late season population densities (Figure 4.8). This

could be due to an increase of natural enemies or the increasing difficulty of finding a beet

armyworm in the canopy of a mature tomato plant. The smaller immature beet armyworms were

more often found in the canopy feeding on leaves or stems and were harder to see in larger

plants. As the larvae got into the 4th and 5th instar they appeared more likely to be found feeding

on the fruit and were easier to see. Thus, plant size likely introduced variability in the BAW

scouting data.

There was a significant reduction in yield due to the early infestation, but not the late

infestation. This is contrary to existing recommendations to tolerate more larvae early than late

(Webb et al. 2001). In the early infestation, marketable fruit weight was reduced in the highest

density treatment by 28% compared to the treatment that received no BAW egg masses. This

could mean that early infestations could significantly lower yield below levels that would be

50

acceptable in commercial fields. Future research will have to be conducted to look at the direct

interaction of BAW and tomato relative to plant age or fruit size.

Correlation results were interesting because they may give us insight into what size of

fruit is preferred for feeding by the beet armyworm. Only in the early infestation did we actually

see a correlation between BAW and yield, because it is generally accepted that late season

feeding would have a greater impact on yield. It is possible that early season infestations might

be more problematic for commercial growers due to the fact that insects can be out in the field

during times of first fruit formation and would be able to attack small fruit. Early damaged fruit

can make it to maturity, but unfortunately it will be unmarketable due to feeding damage. Late

season infestations lacked the same correlations, which leads to the conclusions that either late

season feeding is more variable in older tomato plants or that beet armyworm doesn’t necessarily

target older mature fruit. We observed late instar larvae feeding on fruit in some cases, but it

seemed that the majority of fruit feeding by beet armyworm in the late infestation was

attributable to 2nd to 3rd instar larvae (due to size of holes and surface damage of fruit near the

calyx).

The purpose of these experiments was to attempt to establish a known population of beet

armyworm in tomato in a field trial. This was shown to be feasible in multiple years in the

spring in Georgia when natural populations of beet armyworm are typically low. A range of 1-

40 beet armyworm larva(e) was produced in a field using artificial infestations. Early season

beet armyworm infestations had a greater impact on tomato yield than did late season

infestations. Future research could use this methodology as a model for infesting tomato with

beet armyworm and to create a population that could impact tomato yield. Also, a review of the

sampling method could help to improve correlations of beet armyworm densities to yield.

51

References Cited:




Entomology. 83: 2136-2146.


26: 345-371.













Zalom, F. G., and A. Jones. 1994. Insect fragments in processed tomatoes. Journal of Economic

Entomology. 87: 181.



52

Picture 4.1: Beet armyworm fruit feeding in Tomato

53

Picture 4.2: Beet armyworm feeding on foliage.

54

Picture 4.3: Beet armyworm feeding directly on developing fruit.

55

Picture 4.4: Top of leaf surface of artificial infestation.

56

Picture 4.5: Egg mass position. Egg masses were placed on the underside of the leave with the

egg masses facing the leaf surface.

57

Picture 4.6: Beet armyworm larvae hatching and feeding on foliage.

58

Table 4.1. 2006 Artificial infestation harvest (early and late treatments combined)

Treatment Marketable Fruit Wt (lbs)

Marketable Fruit Num

Unmarketable Fruit Wt (lbs)

Unmarketable Fruit Num

0 egg masses

48.591a

109.75a

9.088a

22.500a

5 egg masses 45.763a 101.25a 10.644a 27.750a 15 egg masses 52.150a 116.13a 10.544a 21.375a 50 egg masses 40.575a 92.38a 8.475a 25.625a

ª Means in a column followed by the same letter are not statistically different (LSD test, P < 0.05).

59

Table 4.2. 2006 Early artificial infestation harvest (early infestation treatments).ª





0 egg masses

47.975a

107.00a

8.300a

22.500a

5 egg masses 47.675a 102.50a 8.150a 21.250a 15 egg masses 44.713a 101.75a 7.988a 19.000a 50 egg masses 34.225b 79.50a 7.925a 18.500a


60

Table 4.3. 2006 Late artificial infestation harvest (late infestation treatments)





0 egg masses

49.088a

112.50a

9.875a

22.500a

5 egg masses 43.850a 100.75a 13.138a 34.250a 15 egg masses 59.588a 129.75a 8.963a 23.750a 50 egg masses 46.925a 105.25a 13.163a 32.750a


61

0.563a

0.25b

0.531a

0.031b

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 5 25

Number of 1/4 Egg Masses

Ave

rage

Num

ber o

f Bee

t Arm

ywor

mla

rvae

per

6 p

lant

per

plo

t

Figure 4.1. 2005 Seasonal scouting numbers of beet armyworm per six plants (early and late infestations combined).ª ª Means in a column followed by the same letter are not statistically different (LSD test, P < 0.05).

62

0.3125a

0.0625a0.0625a

0.3125a

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 5 25

Number of Egg Masses per Plot

Num

ber o

f Bee

t Arm

ywor

m la

rvae

per

6

plan

ts p

er p

lot

Figure 4.2. 2005 Early infestation seasonal beet armyworm counts.ª


63

0b

1.000a 0.935a

0.188b

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 2 5 25

Number of Egg Masses Per Plot

Ave

rage

Num

ber o

f Bee

t Arm

ywor

m la

rvae

pe

r 6 p

lant

/plo

t

Figure 4.3. 2005 Late infestation seasonal beet armyworm counts.ª


64

2nd Infestation

Treatments

00.5

11.5

22.5

33.5

44.5

5

5/16/2005 5/24/2005 5/31/2005 6/9/2005

Scouting Dates

Beet

Arm

ywor

m p

er 6

pla

nts

0 2 5 25

2nd Infestation

Number of ¼ Egg masses per plot

Figure 4.4. 2005 Late infestation of beet armyworm numbers per scouting date.

65

0.1c0.596c

1.569b

3.379a

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 15 50

Egg Masses per Treatment

Num

ber o

f Bee

t Arm

ywor

m L

arva

e pe

r 6

plan

ts p

er p

lot

Figure 4.5: 2006 Spring infestation (early and late combined) seasonal means of beet armyworm.ª ª Means in a column followed by the same letter are not statistically different (LSD test, P < 0.05).

66

4.938a

2.031b

0.906c

0.094c0

1

2

3

4

5

6

0 5 15 50

Egg Masses

Num

ber o

f Bee

t Arm

ywor

m L

arva

e pe

r 6

plan

ts p

er p

lot

Figure 4.6. 2006 Early infestation beet armyworm counts.ª


67

1.107ab

1.821a

0.286b

0.107b

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 5 15 50

Egg Masses

Num

ber o

f Bee

t Arm

ywor

m L

arva

e pe

r 6

plan

ts p

er p

lot

Figure 4.7. 2006 Late infestation beet armyworm countsª


68

0

5

10

15

20

25

4/6/20

06

4/18/2

006

4/25/2

006

5/2/20

06

5/9/20

06

5/16/2

006

5/23/2

006

5/30/2

006

Scouting Date

Bee

t Arm

ywor

m C

ount

s 6

plan

ts p

er p

lot

E1 E2 E3 E4 L1 L2 L3 L4Treatments

1st Infestation 2nd Infestation

Figure 4.8. 2006 Spring infestation beet armyworm by scouting date. E1=early infestation 0 egg masses, E2=early infestation 5 egg masses, E3=early infestation 15 egg masses, E4=early infestation 50 egg masses, L1=late infestation 0 egg masses, L2=late infestation 5 egg masses, L3=late infestation 15 egg masses, L4=late infestation 50 egg masses

69

34.225b

44.712a47.975a 47.675a

0

10

20

30

40

50

60

0 5 15 50

Number of Egg Masses

Mar

keta

ble

Frui

t Wei

ghts

(lbs

) per

10

plan

ts

Figure 4.9: 2006 Early season infestation marketable fruit weightsª ª Means in a column followed by the same letter are not statistically different (LSD test, P < 0.05).

70

0.35ab

0.617a

0.717a

0.2b

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 15 50

Number of Egg Masses

Ave

rage

Num

ber o

f Fru

ithol

es p

er 6

pla

nts

Figure 4.10. 2006 Spring infestation fruit holes per treatmentª ª Means in a column followed by the same letter are not statistically different (LSD test, P < 0.05).

CHAPTER 5

Economic Injury Levels for Beet Armyworm in Tomato

Introduction


tomatoes, with Florida, California, and South Carolina leading the commercial fresh market

production (Tomatoes National Statistics 2006). Georgia’s 2004 farm gate value of tomatoes

was over 100 million dollars (Boatwright and McKissick 2004). The main insect pests of

tomatoes in Georgia are thrips, aphids, whiteflies, stink bugs, and Lepidopteran insects.

Lepidopteran insects are major economic pests of tomato in the southeastern US (Liburd et al.

2000). Due to the importance of many Lepidopteran species, including the beet armyworm

Spodoptera exigua (Hübner), it is important to understand the economic impact of the

Lepidopteran larvae on tomato. Current action thresholds for beet armyworm in fresh market

tomatoes in Florida are 1 larva per 6 plants pre bloom and presence of larva(e) per field post

bloom and in California are 1 larva or egg mass in 5 minutes of sampling after fruit set (Webb et

al. 2001, Zalom et al. 2003).

Understanding the relationship between an insect and the damage it causes to host plant is

fundamental to integrated pest management (IPM) (Stern et al. 1959). To manage a pest insect

and keep the population below an economically damaging level it is important to first define the

point at which cost of control equals the amount of damage the pest can cause. This is the

economic injury level and is defined by Stern et al. (1959) as the lowest population density that

72

will cause economic damage. Pedigo et al (1986) stated that the economic injury level (EIL) is

affected by five primary variables. Pedigo et al (1986) defined an EIL = C/VIDK, where C =

cost of the management tactic per production unit, V = market value per production unit, I =

injury units per pest, D = damage per injury unit, and K = the proportional reduction in pest

attack. The economic injury level is the basis on which pest control decisions are made.

Because of the dependence on cost and value, the economic injury level can only be calculated

from specific determinations of the value of the damaged product or commodity for a specific

pest.

The specific objectives of this study were to: (1) relate beet armyworm population levels

to tomato yield loss using regression analysis from the 2004 insecticide efficacy trial (Chapter 3),

(2) relate beet armyworm population levels to tomato yield loss using artificial infestation data

from 2006 field experiments, (3) estimate economic injury levels based on early and late season

artificial infestations of BAW and (4) test action thresholds at or below the established EIL

levels from this study. The hypothesis was that action thresholds at or below the EIL for beet

armyworm would prevent significant yield loss as compared to a weekly spray program.

Methods and Materials

2004 Test. The experimental design for the 2004 Summer trial was described in Chapter

3. Regression analysis of tomato yield parameters to beet armyworm densities was determined

by the PROC REG function of SAS (SAS Institute 2003). Beet armyworm associated with 5%

yield loss from the regression analysis was used as a crude estimate for beet armyworm action

thresholds. The assumption was that BAW population densities associated with a 5% margin of

error around maximum yield, would be sufficient to prevent significant yield loss. In addition %

73

yield loss in the absence of insecticide control was estimated from this test along with the cost of

season-long insecticide control.

2006 Test. The experimental design for the 2005 Spring Artificial infestation was

described in Chapter 4. Regression analysis of tomato yield to beet armyworm densities was

determined by the PROC REG function of SAS (SAS Institute 2003). Regression analysis was

used to relate season-long, early, and late infestations to yield. The amount of yield loss per beet

armyworm was estimated from this test for EIL calculation.

Economic Injury Level (EIL). Economic injury level was defined by Stern et al. (1959)

as the lowest population density that will cause economic damage. I used Pedigo et al’s (1986),

definition of the economic injury level, which is controlled by five primary variables,

EIL = C/VIDK or EIL= C/VD’K

where C = cost of the beet armyworm insecticide treatment per production unit, V = market

value of tomato in Georgia in 2005 per production unit, I = injury units per beet armyworm

larvae, D = damage per injury unit, and K = the proportional reduction in beet armyworm attack.

The variables D and I can be combined into D’ which is defined as the percent yield loss per pest

individual. We used 2004 insecticide efficacy data (Chapter 3) to determine the constants C, and

K. Variables V and D’ were determined from data taken from the 2006 artificial infestation trial

(Chapter 4).

2005 Summer Threshold Evaluation. The experimental design for the 2005 summer

threshold test was described in Chapter 3. Two thresholds were tested against calendar sprays.

Thresholds tested were 1 BAW larva per 20 plants and 1 BAW larva per 40 plants. When

thresholds were reached BAS 320I 240SC was applied over the entire treatment and were

compared to weekly applications of BAS 320I 240SC.

74

Results

2004 Test. A regression analysis of the marketable fruit number relative to beet

armyworm larval numbers collected from the insecticide efficacy trial 2004 (Figure 5.1),

indicated that the 5% level of yield loss was associated with 0.15 beet armyworm larva per 6

plants or 1 BAW larva per 40 plants. One BAW per 40 plants was determined by solving for x

using a best fit line in a x-y scatter plot involving seasonal beet armyworm scouting by

marketable fruit numbers (Figure 5.1). Using the equation given by the best fit line y = -12.744x

+ 38.026 (r² = 0.16), we multiplied 5% to the y-intercept of 38.026. That gave us 1.9013, which

was then subtracted from 38.026 to produce a value of 36.125. So, the equation read 36.125 = -

12.744x + 38.026 and when solved for x = 0.149 or ≈ 0.15. So, a seasonal scouting average of

0.15 beet armyworm per 6 plants, would result in 5% yield loss based on this regression in terms

of marketable fruit numbers.

For the calculation of EIL total yield from the best treatment to the untreated control was

84%. Seven calendar sprays were used to prevent damage and the cost was estimated at $210

($30/spray). Since BAW populations were high during this test (Chapter 3) this was considered

a spray program for a worse case scenario. Both of these calculations were figured into the

economic injury level (EIL).

2006 Test. The 2006 spring infestation data (Chapter 4) was used to look at multiple

regression analysis for early, late, and season-long beet armyworm means to

marketable/unmarketable fruit weight and numbers. The regression analysis showed a marginal

negative effect (slope = -2.3541x + 50.067; r² = 0.13; P < 0.05) in season-long BAW means

compared to marketable harvest weight (Figure 5.4), but a greater negative effect in early

75

infestation densities to marketable fruit weight (slope = -2.7112x + 49.047; r² = 0.31) (Figure

5.2). Regression analysis of the relationship of early infestation BAW densities to marketable

fruit numbers also yielded a negative relationship (slope = -5.2388x + 108.12; r² = 0.29; P <

0.05) (Figure 5.3). The late season infestation showed no correlation between BAW means and

marketable harvest weight (slope = 1.5011x + 48.628; r² = 0.02; P = 0.66) or numbers (slope =

1.8556 + 110.6; r² = 0.01; P = 0.80).

Early infestation regression analysis of beet armyworm densities relative to marketable

fruit weight and marketable fruit numbers both showed negative slopes. Figure 5.2 is the

regression analysis and best fit line from early infested plots showing the relationship of season-

long means of beet armyworm larvae per 6 plants to marketable fruit weight. The relationship

equation was y = -2.7112x + 49.047, r² = 0.3149. When solved for 5% loss, x = 0.90. This

indicated that 1 beet armyworm per 6 plants could reduce yield to a 5% damage level. Figure 5.3

is the regression analysis and best fit line from the early treatment plots with seasonal means of

beet armyworm larvae per 6 plants to marketable fruit numbers. The slope equation is y = -

5.2388x + 108.12, r² = 0.2863. When solved for 5% loss x = 1.03. This would equate to ≈ 1

beet armyworm per 6 plants to reduce yield below a 5% damage level. No individual date gave

significant difference in regression of beet armyworm to marketable fruit weight or marketable

fruit numbers.

Late season beet armyworm densities did not correlate significantly with marketable fruit

weight and fruit numbers (slope = 1.5011x + 48.628; r² = 0.02; P = 0.66, and slope = 1.8556 +

110.6; r² = 0.01; P = 0.80 respectively). No individual date gave significant difference in

regression of beet armyworm to marketable fruit weight or marketable fruit numbers.

76

Regression analysis of season-long means of beet armyworm to marketable fruit weight

and marketable fruit numbers both showed a marginal negative effect (Figure 5.2 and Figure

5.3). Figure 5.4 is the regression analysis and best fit line from the seasonal means of beet

armyworm larvae per 6 plants from all 32 plots (early and late infestations combined) and

marketable fruit weight. The slope equation is y = -2.3541x + 50.067, r² = 0.1282. When solved

for 5% loss, x = 1.06. This would equate to 1 beet armyworm per 6 plants to reduce yield below

a 5% damage level. Figure 5.5 is the regression analysis and best fit line from the seasonal

means of beet armyworm larvae from all 32 plots (early and late infestations combined) per 6

plants to marketable fruit numbers. The slope equation is y = -4.9944x + 111.93, r² = 0.1421.

When solved for 5% loss x = 1.12. This would equate to ≈ 1 beet armyworm per 6 plants to

reduce yield below a 5% damage level set by growers.

Economic Injury Level (EIL). 2004 insecticide efficacy (Chapter 3) data was used to

determine the constants C, and K. C = the cost of BAW control per acre and from 2004 the cost

was approximately $30.00 per insecticide application per acre. $30.00 per acre was calculated

by averaging the cost of 4 commercially used insecticides in tomato for Lepidopteran control:

Spinosad, Indoxacarb, Emamectin, and Methomyl. Spinosad is $262.50 per pound of active

ingredient (ai), and maximum labeled application (0.156 lb ai/A) is $40.96 per acre. Emamectin

is $2,462 per pound of active ingredient and maximum labeled application (0.015 lb ai/A) is

$37.25 per acre. Indoxacarb is $262 per pound of active ingredient, and maximum labeled

application (0.065 lb ai/A) is $17.03 per acre. Methomyl is $25.12 per pound of active

ingredient and maximum labeled application (0.9 lb ai/A) is $22.61 per acre. The average per

acre for product of the 4 before mentioned insecticides was $29.46 or approximately $30.00. In

2004 there were seven insecticide applications for a total of $210.00 for season beet armyworm

77

control. K = proportional reduction in injury with control and was calculated to be an 84%

reduction in marketable fruit weight over seven insecticide sprays. This percentage was

calculated from the marketable fruit weight in the check (no insecticide treatment) divided by the

highest yielding treatment in 2004 insecticide efficacy trial.

Both V and D’ were determined by the data collected from the 2006 artificial infestation

(Chapter 4). V = market value of tomato per acre and was based on the marketable weight of 10

plants per plot. The fresh market value of tomatoes in Georgia in 2004 was $31 per cwt or per

100 lbs (Fonsah 2004). This $31 per cwt value was applied to the highest yielding treatment

(uninfested check plot) of the early and late infestation experiment and harvest yields were based

on 9,680 plants per acre (based on plants spacing and plot length) to determine V. D’ = percent

yield loss per pest and was determined individually for 3 different times (early, late, and season

long).

To determine the early season EIL the following values were used: D’ = the 50 egg mass

treatment’s marketable fruit weight (3.4225) / the 0 egg mass treatment’s marketable fruit weight

(4.7975) and the quotient subtracted from 1 to find the % yield loss or 28.7%. The 50 egg mass

treatment BAW seasonal means per plant was multiplied by 9,680 (plants/acre) to get number of

BAW larvae per acre or 7,966 BAW per acre. The yield loss % was divided by BAW per acre to

estimate D’ = 3.60 ℮ -5. Thus the equation EIL = C / VD’K would read EIL = $210 insecticide

applications per acre / $14,396 marketable fruit per acre * 84% reduction in injury with seasonal

insecticide control * 3.60 ℮ -5 percent yield loss per pest. The early season EIL = 0.051 or 1

BAW larva per 20 plants.

To determine the late season EIL the following values were used: D’ = the 50 egg mass

treatment’s marketable fruit weight (4.6925) / the 0 egg mass treatment’s marketable fruit weight

78

(4.9088) and the quotient subtracted from 1 to find the % yield loss or 4.40%. The 50 egg mass

treatment BAW seasonal means per plant was multiplied by 9,680 (plants/acre) to obtain number

of BAW larvae per acre or 2,937.9 BAW per acre. Then the yield loss % was divided by BAW

per acre to estimate D’ = 1.50 ℮ -5. Thus the equation EIL = C / VD’K would read EIL = $210

insecticide applications per acre / $14730 marketable fruit per acre * 84% reduction in injury

with seasonal insecticide control * 1.50 ℮ -5 percent yield loss per pest. The late season EIL =

0.11 or 1 BAW larva per 9 plants.

For season-long EIL, D’ = the 50 egg mass treatment’s marketable fruit weight (4.0575) /

the 0 egg mass treatment’s marketable fruit weight (4.8591) and the quotient subtracted from 1 to

find the % yield loss or 16.5%. The 50 egg mass treatment BAW seasonal means per plant was

multiplied by 9,680 to get number of BAW larvae per acre or 5,451.5 BAW per acre. The yield

loss % was divided by BAW per acre to estimate D’ = 3.03 ℮ -5. Thus the equation, EIL = C /

VD’K would read EIL = $210 insecticide applications per acre / $14,581 marketable fruit per

acre * 84% proportional reduction in injury with seasonal insecticide control * 3.03 ℮ -5 percent

yield loss per pest. The seasonal EIL = 0.059 or 1 BAW larva per 17 plants.

2005 Summer Threshold Evaluation. In 2005 the untreated check plot had less than

3% worm damaged fruit so incidence of fruit feeding by Lepidopteran larvae was low, so

unfortunately number of worm damaged fruit and weight of worm damaged fruit were not good

indicators of treatment effect in this test. Only one threshold spray significantly reduced

damaged fruit compared to the check (Table 3.4). The 1 larva/40 plants had 0.23 BAW larva per

scouting date and had 0.13 damaged fruit compared to the check which had 0.69 BAW per

scouting date and 0.75 damaged fruit. The 1 larva/20 plants had 0.28 BAW larva per scouting

date and had 0.25 damaged fruit (Table 3.4). There was no significant treatment effect in

79

marketable fruit weight (F = 0.67; df = 9, 27; P = 0.84) or unmarketable fruit weight (F = 1.52;

df = 9, 27; P = 0.19). Using contrast analysis there was no statistical difference in beet

armyworm counts in the two threshold sprays (1 larva/40 plants: F = 2.42; df = 1, 27; P = 0.13,

and 1 larva/20 plants: F = 3.48; df = 1, 27; P = 0.07) as compared to weekly sprays. There was a

significant reduction in total Lepidopteran larvae of the weekly BAS 320I as contrasted to the 1

larva/40 plants (F = 5.53; df = 1, 27; P < 0.05).

Discussion

From 2004 regression analysis we arrived at a threshold of 1 BAW larva per 40 plants

and used it as base for future artificial infestations and thresholds. Even though 1 BAW per 40

plants was the initial estimate, marketable fruit numbers were affected by other Lepidopteran

larvae. Regression analysis from 2006 artificial infestation data showed that season-long and

early season analysis that indicated beet armyworm had a negative impact on marketable yield.

Both season-long treatments and early infestation showed that 1 BAW larva per 17 and 20

plants, respectively, could cause economic damage at a 5% yield loss. The late season

infestation was not correlated with yield loss which was surprising as the current thresholds

(Webb et al. 2001) state that the late season is more important for beet armyworm control.

EIL estimates also indicate that late season beet armyworm infestations may not be as

important as previously thought. The late season EIL was 1 BAW per 9 plants where as the

early infestation that resulted in significant yield loss was 1 BAW per 20 plants, so a season-long

recommendation of 1 BAW per 20 plants would be a more realistic EIL for beet armyworm on

tomato. The impact of beet armyworm on tomato is dynamic throughout the season, but unlike

previous recommendations thresholds would actually go down during the season.

80

The 1 BAW larva per 40 plants was the only threshold to be statistically different in

terms of beet armyworm than the check, but in terms of marketable or unmarketable fruit weight

there was no difference in all of the treatments including weekly insecticide treatments of

commercially used products. In fact, marketable yields were as high in the threshold treatments

as any of the treatments in the trial. Based on review of the data presented, an EIL of 1 beet

armyworm per 20 plants in tomato would be recommended to keep beet armyworm below crop

damaging levels.

81

References Cited:

Boatwright, S. R., and J. C. McKissick. 2004. 2004 Georgia Farm Gate Value Report. In G. C. E.

S. C. Agents [ed.]. The University of Georgia.

Fonsah, E. G. 2004. Commercial Tomato Production Marketing and Management. The

University of Georgia.

http://www.ces.uga.edu/Agriculture/agecon/pubs/marketpubs/pdfpubs/Commercial%20T

omato.pdf




Pedigo, L. P., S. H. Hutchins, and L. G. Higley. 1986. Economic injury levels in theory and

practice. Annual Review Of Entomology. 31: 341-368.


Stern, V. M., R. F. Smith, R. v. d. Bosch, and K. S. Hagen. 1959. The integrated control concept.

Hilgardia. 29: 81-101.





Zalom, F. G., J. T. Trumble, C. F. Fouche, and C. G. Summers. 2003. Tomato Beet Armyworm.

University of California. http://www.ipm.ucdavis.edu/PMG/r783300311.html

http://www.ces.uga.edu/Agriculture/agecon/pubs/marketpubs/pdfpubs/Commercial%20Tomato.pdf



http://www.ipm.ucdavis.edu/PMG/r783300311.html

82

y = -12.744x + 38.026R2 = 0.1626

-20

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5 4

Beet armyworms per 6 plants

Mar

keta

ble

frui

t per

5 p

lant

s

Figure 5.1. 2004 Regression of beet armyworm larvae counts to marketable fruit numbers (an average of 0.15 larva per 6 plants resulted in 5% tomato yield loss)

83

y = -2.7112x + 49.047R2 = 0.3149

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6 7

Beet Armyworm Seasonal Means

Mar

keta

ble

Wei

ght (

lbs)

per

10

plan

ts

Figure 5.2. 2006 Spring early season infestation of beet armyworm larvae counts to marketable fruit weight

84

y = -5.2388x + 108.12R2 = 0.2863

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6 7


Mar

keta

ble

num

ber o

f Fru

it pe

r 10

plan

ts

Figure 5.3. 2006 Spring early season infestation of beet armyworm larvae counts to marketable

fruit numbers

85

y = -2.3541x + 50.067R2 = 0.1282

0

10

20

30

40

50

60

70

80

0 1 2 3 4 5 6 7


Mar

keta

ble

Wei

ght (

lbs)

per

10

plan

ts

Figure 5.4. 2006 Spring infestations (early and late combined) of beet armyworm larvae counts to marketable fruit weight

86

y = -4.9944x + 111.93R2 = 0.1421

0

20

40

60

80

100

120

140

160

180

0 1 2 3 4 5 6 7


Mar

keta

ble

num

ber

of F

ruit

per 1

0 pl

ants

Figure 5.5. 2006 Spring infestation (early and late combined) of beet armyworm larvae counts to marketable fruit numbers

CHAPTER 6

Summary


tomatoes, with Florida, California, and South Carolina leading the commercial fresh market

production (Tomatoes National Statistics 2006). Georgia’s 2004 farm gate value of tomato was

over 100 million dollars (Boatwright and McKissick 2004). Lepidopteran insects are major

economic pests of tomato in the southeastern US and it has been shown that there is a major

economic loss associated with their damage (Liburd et al. 2000). Due to the importance of many

Lepidopteran species, including beet armyworm, Spodoptera exigua, it is important to

understand the relationship between the insect and the crop. I focused on beet armyworm

because of its recent importance in Georgia tomato production.

Many control tactics have been used to manage beet armyworm and chemical insecticides

continue to be the most commonly used. Various insecticides were used in these trials and a new

BASF insecticide, BAS 320 (metaflumizone) showed good efficacy towards beet armyworm and

other Lepidopteran pests. In 2004, BAS 320 UHI was able to control Lepidopteran pests below

thresholds, but adjuvants appeared to affect the efficacy. BAS 320 UHI alone though was able to

keep beet armyworm numbers below crop damaging levels. In 2005, BAS 320I 240SC was used

to evaluate thresholds that were developed from the 2004 season data. Unlike the 2004 season,

2005 had relatively low Lepidopteran pest pressure so data concerning adjuvants was not

88

obtainable, but the product did show similar efficacy to the standard insecticide, Avaunt

(indoxacarb), for Lepidopteran larvae.

An artificial infestation method was used to establish population levels of beet armyworm

in tomato in a field trial. This was shown to be feasible in multiple years in the spring in Georgia

when natural populations of beet armyworm are typically low. From the 2005 experiment it was

concluded that an artificial beet armyworm population could be created in a tomato field, but a

level as large as a natural occurring population in the field in the summer of 2004 was not

attained. In 2006, we were able to increase population levels by adjusting egg mass numbers and

found that it was possible to create an artificial population of beet armyworm that could cause

significant yield loss. Future research could use this methodology as a model for infesting

tomato with beet armyworm and to create a population that could impact tomato yield. Also,

sampling studies could help to improve correlations of beet armyworm counts to yield.

From 2004 regression analysis we arrived at a threshold of 1 BAW larva per 40 plants

and used it as a base for future artificial infestations and thresholds. In 2006 artificial infestation,

both season long and early infestations showed that 1 BAW larva per 17 and 20 plants,

respectively, could cause economic damage at a 5% yield loss. The late season EIL was 1 BAW

per 9 plants where the early infestation that resulted in significant yield loss was 1 BAW per 20

plants. A conservative season-long recommendation of 1 BAW per 20 plants would be a more

acceptable EIL for beet armyworm on tomato.

Thresholds of both 1 BAW larva per 20 plants and 1 BAW larva per 40 plants were

applied in a field study in 2005, marketable yields were comparable to commercially used

treatments based on weekly calendar sprays. Based on review of the data presented, an EIL of 1

89

beet armyworm larva per 20 plants in tomato would be recommended to keep beet armyworm

below crop damaging levels.

90

References

Al-Zubaidi, F. S., and J. L. Capinera. 1983. Application of different nitrogen levels to the

host plant and cannibalistic behavior of beet armyworm, Spodoptera exigua

(Hubner) (Lepidoptera: Noctuidae). Environmental Entomology. 13: 1687-1689.

Aldosari, S. A., T. F. Watson, S. Sivasupramaniam, and A. A. Osman. 1996.

Susceptibility of field populations of beet armyworm (Lepidoptera: Noctuidae) to

cyfluthrin, methomyl, and profenofos, and selection for resistance to cyfluthrin.

Journal of Economic Entomology. 89: 1359-1363.

Bianchi, F., J. M. Vlak, R. Rabbinge, and W. Van der Werf. 2002. Biological control of

beet armyworm, Spodoptera exigua, with baculoviruses in greenhouses:

Development of a comprehensive process-based model. Biological Control. 23:

35-46.

Boatwright, S. R., and J. C. McKissick. 2004. 2004 Georgia Farm Gate Value Report. In

G. C. E. S. C. Agents [ed.]. The University of Georgia.


armyworm (Lepidoptera: Noctuidae). Journal of Economic Entomology. 82:

1520-1526.

Brewer, M. J., and J. T. Trumble. 1994. Beet armyworm resistance to fenvalerate and

methomyl-resistance variation and insecticide synergism. Journal of Agricultural


Brewer, M. J., J. T. Trumble, B. Alvarado-Rodriguez, and W. E. Chaney. 1990. Beet

armyworm (Lepidoptera, Noctuidae) adult and larval susceptibility to 3

91

insecticides in managed habitats and relationship to laboratory selection for

resistance. Journal of Economic Entomology. 83: 2136-2146.

Campbell, R. E., and V. Duran. 1929. Notes on the sugar-beet army worm in California,

pp. 267-275. California Department of Agriculture.

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Biography

I was born in Tifton Ga, on Nov. 19th, 1981. I graduated from Tift Co. High School in 2000. I

graduated from the University of Georgia with a B. S. in Biological Sciences in the College of

Agriculture and Environmental Sciences. I have worked in entomology for 8 years in various

disciplines including row crop, medical, veterinary, and fruit entomology. I will continue my

study of entomology by pursuing a PhD starting in the fall of 2006, at the University of Florida.

Documents

IMPACT OF SPODOPTERA EXIGUA, BEET ARMYWORM ON TOMATO JAMES EDWIN