Current status of and recommendations for RAB-LW suppression management in commercial avocado groves in Miami-Dade County

Jonathan H. Crane, Tropical Fruit Crop Specialist University of Florida, IFAS Tropical Research and Education Center 18905 S.W. 280 St. Homestead, FL 33031 http://trec.ifas.ufl.edu

5-24-12

Acknowledgments University of Florida, IFAS • Dr. Jorge E. Peña, Tropical

Fruits Entomologist • Dr. Randy C. Ploetz, Plant

Pathologist – Tropical Fruits • Dr. Edward A. Evans,

Agricultural Economist • Dr. Aaron J. Palmateer, Plant

Pathologist – Diagnostic Clinic

• Dr. Jason A. Smith, Forest Pathologist

• Dr. Lukasz L. Stelinski, Citrus Entomologist

USDA-ARS • Dr. Paul E. Kendra, Research

Entomologist • Dr. Nancy D. Epsky, Research

Entomologist • Dr. Robert R. Heath, Research

Chemist FDACS-Division of Plant Industry • Richard Gaskalla, Dir. • Denise Feiber, Media Specialist

Florida Avocado Administrative Committee • Alan Flinn

Miami-Dade Co. • Charles LaPradd, Agricultural

Manager

Current situation • 1 avocado tree in 1

commercial grove in the northeastern quadrant of the industry was confirmed positive for laurel wilt (LW) at the beginning of May 2012.

• To date, 11 trees have been diagnosed with LW in 5 commercial avocado groves.

LW, location of commercial groves with 1 or more LW positive trees.

Perspective • 11 LW positive trees/500,000 commercial avocado

trees = 0.00002% (a very, very small percentage) • The avocado industry, DPI, and UF/IFAS Research

and Extension faculty have been aware of and planning for the arrival of the redbay ambrosia beetle (RAB) and the pathogen laurel wilt (LW) since 2006. Hence this is not a surprise.

• Avocado plantings in Brevard Co. have not been quickly devastated by LW; avocado tree losses have occurred slowly over the last 6 years.

• This is not to say that quick and decisive action is not needed.

• Quite the contrary. • Due to what we now know about the beetle and disease, implementing an early detection and suppression program is a key factor in suppressing the spread of the beetle and the disease.

Laurel wilt key points • Early detection – scouting is key to

reducing the beetle population and limiting the spread of the disease.

RAB-LW control Industry-wide early detection and suppression of laurel wilt

Strategy – Industry-wide early detection and control of RAB and thus the spread of LW • Constantly control (suppress) the RAB population in

the commercial agricultural area. • The commercial avocado production area is

concentrated to the southeastern area of Miami-Dade County.

The concept • Over time the number of urban host avocado and

urban and natural area native trees will decline – so may the RAB population – providing a buffer adjacent to the agricultural area.

• In the production area – keep the RAB population to a minimum by scouting and control (suppression).

• Once the urban avocado and native tree populations are decimated the RAB population and LW may be more manageable in the production area.

Kendall Dr. (SW 88 St) and Krome Av. (SW 177 Ave)

Commercial avocado production area

Over time (2-3 years) potentially • Native hosts eliminated • Dooryard avocado trees eliminated • Expanding non-host zone • Continued decreased potential for increased RAB-LW

Expanding non-host zone over time

RAB-LW control strategy • Detecting infestations as quickly as possible

• Provides an opportunity for RAB-LW suppression • Monthly to periodic aerial survey of agricultural area

(grid) • Locate, ground truth, sample, control

• Ground scouting groves as frequently as possible • Sampling suspicious trees for LW • Waiting for verification of cause of decline –

• Lightning?; Flooding/root disease?; Severe drought?; Mechanical damage?; Other ambrosia beetles and their fungi?; Laurel wilt?

• Control action if warranted

Avocado production area and RAB-LW aerial survey area quadrants

1 2

3 4

The process • Aerial helicopter survey with GPS unit • Send Google Earth aerial maps and GPS

coordinates of suspect groves (trees) to Alan Flinn, Avocado Administrator • Sends out maps and GPS coordinates to industry

• Industry ground truths grove sites • Sample if warranted • Control action if warranted

Northwest quadrant example

Northwest quadrant example showing street location

Northwest quadrant example showing street location

Avocado – general view from air

Avocado LW suspect - note the distance

Avocado LW suspect

Avocado LW suspect

Avocado LW suspect

Avocado LW suspect

Broken branches not suspects

Avocado suspects

Avocado suspect

Scouting and identification • Frequent scouting is the key

• Early detection • Opportunity for suppression of RAB-LW

• Identification of LW • Proper sampling • Submission of samples • Decision and action

Scouting Symptoms to look for on avocado • Commonly sections of the tree

show symptoms and other sections do not

• Part of the canopy is dead

Scouting – look for • Leaf and young stem

wilting • Leaf color change from

green to dark green, bluish-green to greenish-brown.

• Dead leaves hanging on the tree

• Stem and limb dieback • Commonly sections of the

tree show symptoms and other sections do not

Scouting and inspection • Inspection of the trunk

and limbs • Dried sap • Sawdust (toothpicks) • Beetle entrance holes

Sampling equipment for LW • Tag the tree and note

the location • Sampling equipment

• Hand saw or hatchet • Disinfectant • Plastic bags • Magic markers • Leather gloves • Latex or oil-based

paint • Flagging tape

Sampling for LW Procedure

• Look for areas of the major limbs or trunk with holes in the bark.

• Take the sapwood chip samples from symptomatic major limbs and/or affected trunks.

• The stained (streaked) sapwood below the bark on major limbs or the trunk are the ideal sample. Small limbs and leaves are not good samples.

Tree

trun

k an

d lim

bs

Inspection and sampling • Remove the bark down to the

sapwood and look for dark streaking.

• The bark layer will be gray on the outside and pinkish colored, bark will not work as a sample. Cut into the sapwood.

• Dark streaks in the sapwood beneath the bark may indicate fungal infection – this is what to sample. Non-infected wood is usually white to yellowish with no dark staining or streaking.

• Paint the sampling wound with oil or latex-based paint to prevent beetle boring.

Label bag • Label the bag with

• Your name • Avocado cultivar • Avocado grove

location • Contact information • Date collected • Print on the bag

“Laurel wilt sample”

Name A

Your wood sample should look like this Symptomatic wood chips Take enough sample

1 gallon zip-lock bag

Note the dark streaks

Take your samples to: Plant Diagnostic Clinic

TREC 18905 S.W. 280 St.

Homestead, FL 33031 Tel: 305-246-7001

x.273 Open: 8AM-5PM

Mon.-Fri.

• Fill-in the diagnostic form

• Please note on the form that it is a laurel wilt sample

• Arrange payment ($40.00/sample)

• Testing should be complete within 10 business days.

Recommendations

Tree health Healthy trees - • Reduce the potential for ambrosia beetle attack. • Are more resistant to root diseases that attract

ambrosia beetles and • Have a greater potential to recover from insect and

disease attack. • Highly recommend proper fertilizer, irrigation, and

pest management be continued to maintain or improve tree health in grove.

RAB-LW control options Positive severely declining trees • Cut, chip, and tarp LW positive trees. • Cut, chip, and burn LW positive trees.

• Apply for burn permits ahead of time • Cut, chip, and bury wood of LW positive trees. • Cut, chip, and compost wood-chips of LW positive trees. • Spray wood chips with insecticide and/or tarp. • Large wood that cannot be easily chipped should be

destroyed or buried or sprayed with insecticide. • Stumps should be either ground out, pulled, or burned. Any

cut-ends of a remaining stump should be painted with pruning paint or oil- or latex-based paint or tar to prevent beetle boring.

• Stumps should be completely covered with insecticide.

RAB-LW control options Early symptomatic trees (wilting, section of tree showing

symptoms) • Options include cut, chip, and tarp, burn, or bury the

wood from the section of tree affected. Remove all wood with sapwood staining.

• Wood that cannot be chipped should be burned or buried or covered with a residual insecticide.

• Paint with pruning tar or oil-based or latex-based paint the cut limb(s) of the remaining tree to reduce RAB attractiveness and prevent beetle attack of the wound.

• Aerosol paint is not recommended as it does not prevent ambrosia beetle attack through the paint.

RAB-LW control options • Early symptomatic trees (wilting, section of

tree showing symptoms) continued... • To reduce beetle infestation of the cut limb

apply either Danitol®2.4EC, Permethrin®3.2AG, or Malathion 5EC to all surfaces of the stump of the tree along with a sticker (e.g., NuFilm®, Vapor Gard®). It will be necessary to reapply in 15 days or so.

In the immediate area of the grove where a positive LW tree was detected

• Make a late afternoon foliar insecticide application in the immediate area of the LW positive tree of either • Danitol®2.4EC or • Permethrin®3.2AG or • Malathion 5EC to kill flying RAB and to cover bark

surfaces of the trees within the grove. • Continue to monitor the grove for LW.

Insecticides registered for avocado Name Rate/A #

appl/yr Spray interval (days)

PHI

Danitol 2.4 EC (fenpropathrin)

21.3 oz 2 14 1

Malathion 5EC (malathion)

4.5 pt Open Not identified

7

Permethrin 3.2AG (permethrin)

8 oz 6 7-10 7

RAB-LW control options If it is suspected LW is moving to adjacent avocado trees by root grafting • Isolate affected and adjacent trees

by mechanically (i.e., ditch digger, back hoe, etc.) cutting the roots. The trench should create a barrier between affected/infected and healthy trees (at a right angle to the row orientation, cut across the entire row).

LW positive tree

RAB-LW control options to consider Avocado trees with “thin” bark, i.e., <7 years old • An emergency exemption for the use of Tilt®

(propiconazole) has been granted. Research has shown that a bark directed Tilt® plus 2% Pentra-Bark trunk and limb spray application appears to provide some protection against LW. However, the efficacy, frequency and cost of repeat applications is not known at this time and is under study.

RAB-LW control options to consider Mature avocado trees, i.e., >7 years old • No known effective treatment at this time?? • An emergency exemption for the use of Tilt®

(propiconazole) has been granted but research to determine efficacy, rates and economics are on-going.

• The fungicide is macro-infused into the tree’s flare-roots.

• Preliminary observations of macro-infused mature trees in Homestead resulted in no phytotoxicity.

Other cultural practices Pruning practices • The research of the entomologists suggests that

recently cut surfaces of avocado are more attractive to RAB than non-cut surfaces.

• RAB does bore into the bark and through the cut ends of pruned limbs.

• It is assumed that cutting increases the release of attractive volatiles naturally produced by the trees.

Strategy for pruning practices

• Where and when possible prune during the late fall and winter when RAB activity may be depressed. This may be mostly appropriate for mid- and late season avocado cultivars.

• Prune groves in the early morning and apply a contact insecticide with residual activity to cover cut surfaces during the late afternoon/early evening (4PM on). • Malathion

• Danitol®

• Permethrin®

FDACS/DPI Helpline 888-397-1517

DPI links: www.fl-dpi.com

http://www.freshfromflorida.com/pi/enpp/pathology/laurel_wilt_disease.html s a v e t h e g u a c . c o m

UF/IFAS Extension offices:

http://solutionsforyourlife.ufl.edu/map/index.html

UF/IFAS publications: http://edis.ifas.ufl.edu

UF/IFAS Tropical Research and Education Center: http://trec.ifas.ufl.edu