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2014 Tri River Area
Pest Management Workshop
101 Ag Insects
1
Responding to Rootworm
Trait Failures
Frank B. Peairs
Colorado State University
(970) 491-5945
WESTERN CORN ROOTWORM
ROOTWORM FIELD BIOLOGY
EGGS: In soil from August to May
LARVAE: Feed on corn roots during June
and early July
PUPAE: In soil during July
ADULTS: Emerge in July and August. Feed
on corn and other plants. Lay eggs in corn
until frost.
WESTERN CORN ROOTWORM DAMAGE
AVERAGE GRAIN YIELD LOSS*
TO WESTERN CORN ROOTWORM
• Loss of 1 node = 18% yield loss
• Affected by location, weather,
year
*Excludes lodging losses
TOXIN EVENT TRADENAME
Cry34Ab1/Cry35Ab1 DAS 59122-7 Herculex RW
Cry3Bb1 MON 863 YieldGard Corn Rootworm
Cry3Bb1 MON88017 YieldGard VT
mCry3Aa MIR 604 Agrisure RW
eCry3.1Ab 5907 Agrisure Duracade
Bt Toxins - Rootworm
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
2
Multiple Toxins:
Agrisure 3122, AcreMax XTreme,
SmartStax
• 2-3 lep toxins
• 2 rootworm toxins
• LibertyLink
• glyphosate tolerant
• RIB and 5% refuges
RIB
Structured Refuge
Modified from Zhao et al. Nature Biotechnology 21: 1493.
RIB Strategy
♂(S) -> ♀(S) -> ♂(R) -> ♀(R)
A D U L T R O O T W O R M E M E R G E N C E , A K R O N , C O : 1 9 9 7
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
1 6 2 2 2 8 2 8 1 4 1 9 2 5 1
AD
ULT
S P
ER
TR
AP
RIB Strategy
• Uniform rootworm mating (exposed vs not
exposed) achieved more quickly
• Ear protection may be reduced due to
refuge pollen
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
3
• All single-toxin events have had
performance problems, which may or
may not be due to resistance
(environmental, rootworm abundance,
seed source)
• Two-toxin events seem to have fewer
problems
• Some evidence for Cry3 cross-
resistance
Rootworm Efficacy Issues
• Lab resistance is documented for all
events
• Level of expression
• Not high dose
• Not as effective as corn borer
events
Rootworm Efficacy Issues (cont.)
Documented Field Resistance
• Failures of cry3Bb1 events in NE Iowa
• Associated with continuous corn
(same event) and low refuge
compliance
• Many other reports, especially in NE
and CO
mCry3Aa root from Mesa County
• Take an IPM approach!
•Rotate
•Untraited hybrid + larval control
based on thresholds
•Adult control
•2-toxin events
•Spider mites
Confirmed Failures
• New events are in continual
development
•New Bt toxins and combinations
•RNA interference
•New non-Bt toxins
Rootworm Efficacy Issues (cont.)
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
4
• Double stranded RNA
applied to plant
• broken into small
interference RNA
• binds to messenger
RNA preventing
formation of key DNA
Crop rotation is an highly effective
nonchemical control if economics permit
• Larvae have narrow host range
• Newly hatched larvae have limited mobility
• Eggs are laid in current crop
• If following crop is not corn -- larvae starve
CHEMICAL CONTROL STRATEGIES FOR
WESTERN CORN ROOTWORM
EGG LARVA PUPA ADULT
SEPTEMBER – JUNE
JUNE -JULY
JULY -AUGUST
JULY -SEPTEMBER
SOIL TREATMENTS
SEED TREATMENTS
TRANSGENIC HYBRID
GRANULES OR
LIQUIDS BY
GROUND OR
SPRINKLER
LIQUIDS BY AIR,
GROUND OR
SPRINKLER
PRE-EMERGE
TREATMENT DECISION
• One scouting report in prior season with
more than 18,000 beetles per acre
• Unscouted continuous corn
PRE-EMERGENCE PERFORMANCE: 1987 – 2006 POSTEMERGE
TREATMENT DECISION
• One scouting report in prior season with more than 18,000 beetles per acre
• Unscouted continuous corn
• 1 – 2 larvae per root system• >8 on a single-trait is indication of failure
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
5
POST-EMERGENCE PERFORMANCE: 1987 – 2005 POSTEMERGE -- CHEMIGATION
Lorsban 4E*, 1 lb (ai)/acre
1.2 root rating, 182 bu/acre
Untreated
3.8 root rating, 132 bu/acre
*Bifenthrin also reported to work well
ADULT TREATMENT DECISION
• 3 Beetles per 10 ear zones*
(2 for retreat)
• 6 Beetles per 10 plants*
(4 for retreat)
• 6 Beetles per trap per day
(4 for retreat)
*(30,000 plants/acre)
ADULT TREATMENT TIMING
• At or above the decision level
• 10% gravid females
• 2 – 3 weeks after first beetle
ADULT TREATMENT EFFICACY(1992, 1 - 6 ROOT RATING)
Adult control (1991) 2.2
Larval control (1992) 3.8
Untreated (1991, 1992) 5.1
Properly timed western corn
rootworm adult treatments
can occur during pollen shed:
POLLINATOR PROTECTION
IS REQUIRED!
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
6
TSM BGM
CORN SPIDER MITES
TSM BGM
TYPICAL CORN SPIDER MITE SOURCESCORN SPIDER MITES:
RESPONSE TO DIMETHOATE
0
2
4
6
8
10
12
14
16
18
Texas Colorado
Mea
n LD
50
TSMBGM
• BGM is native
• Pest of various grass crops
• Key pest of Colorado corn
CORN SPIDER MITES:
PEST STATUS
• Egg, 3 immature stages, adult
• Egg to adult in 10 – 20 days
• In lab, 70x increase per generation
CORN SPIDER MITES:
LIFE CYCLE (BGM)
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
7
• Overwinter as orange-yellow
fertilized females on alternate grass
hosts
• Walk or “balloon” back to corn in
spring
CORN SPIDER MITES:
LIFE CYCLE (BGM)
• Infestations start on undersides
of lower leaves
• Gradually move into upper part
of plant
• Most damage occurs between
pollen shed and denting
CORN SPIDER MITES:
LIFE CYCLE (BGM)
Severe BGM injury results first in death
of leaf edges, then the entire leaf
Grain yield loss over 25 years at Rocky Ford – 22%
Dry matter loss in 3 silage studies – 25%
• Drought stress
• Post-reproductive growth stages
• No TSM
• Insecticides
• Low rainfall
• Few natural enemies
• >95F temperatures
CORN SPIDER MITES:
FACTORS FAVORING BGM
INFLUENCE OF IRRIGATION
ON CORN SPIDER MITES
Iliff – 2007
0
50
100
150
200
250
300
Linear Wiper
Mit
es
pe
r P
lan
t
Limited Full
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
8
CORN SPIDER MITES:
Response to insecticide treatment
0
10
20
30
40
50
60
Penncap M, 1 pt. Untreated
Sq.
In. L
eaf A
rea
Dam
aged
Biological control is often the
only control needed for spider
mites in corn
Spider Mite Management Options
• Preserve biological control
• Preventive miticides
• Reactive miticides
• Preventive vs. reactive depends on
local resistance problems, other pests
• Crop near tasseling?
• Most plants infested?
• Parts of crop drought stressed?
• Mite predators scarce?
CORN SPIDER MITES:
PREVENTIVE MITICIDE QUESTIONS
• Max temps ≥ 95°F for next 2 weeks?
• Field history of mite problems?
• TSM problems expected?
≥3 “Yes” answers indicates reasonable
need for preventive treatment
CORN SPIDER MITES:
PREVENTIVE MITICIDE QUESTIONS
PREVENTIVE MITICIDES Rank in trial
*Total treatments in trial in ()
2006 2007 2010 2011 2013
(26*) (20) (20) (20 & 16) (20 & 20)
Onager 1E, 10 oz 1 1 1 9 & 4 9
Oberon 4SC + dimethoate,
4 + 16 oz 2 4 2 8 --
Oberon 4SC, 4 oz 4 12 9 17 & 13 8
Comite II + dimethoate,
36 + 16 oz 5 8 10 6 --
Comite II, 36 oz 24 20 19 13 --
Zeal 72W, 2 oz** 18 -- -- 10 6
Portal, 32 oz -- -- -- 6 11
*Total treatments in trial
**Not registered
2014 Tri River Area
Pest Management Workshop
101 Ag Insects
9
• Damage in lower 1/3 of plant and
colonies in middle 1/3
• Texas A&M dynamic threshold
CORN SPIDER MITES:
ACTION THRESHOLDS
Reactive Treatments
REACTIVE MITICIDES
Rank in trial
*Total treatments in trial
** Not registered until 2014
2000 2001 2004 2005 2006 2007 2011 2013
(12*) (14) (18) (15) (26) (20) (20 & 16) (20 & 20)
bifenthrin 3 6 8 9 23 14 20 & 8 --
bifenthrin +
dimethoate1 3 1 8 6 5 2 1 & 4
dimethoate 10 11 15 14 19 6 16 11 & 5
Agri-Mek** 6 1 2 1 7 -- 1 3
Portal -- -- -- -- -- -- 11 2
• 3 GPA minimum
• Control improves up to 5 GPA,
perhaps higher
• Buffer dimethoate
• Surfactants?