Soybean aphid management: New challenges posed by insecticide resistance Robert Koch Department of Entomology
Soybean aphid
Foliar insecticides for soybean aphid in MN Group 1 AChE inhibitors Group 3 Na channel modulators Group 4 nachr agonists 1A methomyl 3A alpha-cypermethrin 4A acetamiprid beta-cyflufthrin chlothianadin 1B acephate bifenthrin imidacloprid chlorpyrifos cyfluthrin thiamethoxam dimethoate deltamethrin esfenvalerate 4D flupyradifurone gamma-cyhalothrin lambda-cyhalothrin Group 9 Chordotonal organ permethrin modulator zeta-cypermethrin 9D afidopyropen
Foliar insecticides for soybean aphid in MB Group 1 AChE inhibitors Group 3 Na channel modulators Group 4 nachr agonists 1A methomyl 3A alpha-cypermethrin 4A acetamiprid beta-cyflufthrin chlothianadin 1B acephate bifenthrin imidacloprid Concept chlorpyrifos cyfluthrin thiamethoxam dimethoate deltamethrin Cygon, etc. Concept esfenvalerate 4D flupyradifurone Group 23 gamma-cyhalothrin Inhibitors of lambda-cyhalothrin Group 9 acetyl CoA Matador & Voliam Chordotonal organ carboxylase permethrin modulator 23 spirotetramat zeta-cypermethrin 9D afidopyropen Movento
Problem: Insecticide-resistant soybean aphids
Pyrethroid-resistant soybean aphid 1 st report in North America 2015-2016 widespread reports of pyrethroid failures Laboratory bioassays confirmed resistance MN & IA Bifenthrin or λ-cyhalothrin ~40-fold resistance Hanson et al. 2017
Counties with pyrethroid performance issues Koch et al. 2018; Koch & Potter unpublished
Resistance monitoring (2017, 2018) Field-collected & laboratory aphids Glass-vial assays Diagnostic concentration (LC99) 10 adults per vial Mortality assessed after 4 h Biased-reduced GLM on controladjusted mortality, and one-sided Dunnett s test
Koch, unpublished χ 2 = 436.99, df = 18, P < 0.0001
Koch, unpublished χ 2 = 444.9, df = 23, P < 0.0001
Koch, unpublished χ 2 = 509.35, df = 20, P < 0.0001
Koch, unpublished χ 2 = 347.3, df = 20, P < 0.0001
Pyrethroid resistance General mechanisms Metabolic monooxygenases (cytochrome P450) esterases glutathione S-transferases Target site insensitivity knock down resistance (kdr; super-kdr) Reduced cuticular penetration Liu 2012
How did we get here? Reliance on few insecticide groups for aphid management Persistent infestations in/near MN Treating more than needed Treating fields below threshold Adding insecticide when targeting weeds or pathogens ( just in case ) Using low rates of insecticide
Insecticide resistance management
1. Don t spray when not needed
1. Don t spray when not needed 250 aphids/ plant Graph by Losey & DiTomasso
1. Don t spray when not needed Data from Ragsdale et al. 2007. JEE 100(4): 1258-1267 graphs from K. Tilmon
1. Don t spray when not needed 5,500 CAD Damage boundary 4,500 CAD 250 aphids/ plant Ragsdale et al. 2007; Koch et al. 2016
2. If you spray, do it right
2. If you spray, do it right Rates Use only labeled rates of insecticides High labeled rates may be preferred
2. If you spray, do it right Rates Nozzles, volume & pressure Small droplets Ground: >15 gal/ac at >30 psi Air: 3-5 gal/ac
2. If you spray, do it right Rates Nozzles, volume & pressure Environmental conditions Avoid spraying under conditions that promote droplet or vapor drift Windy, temperature inversion, etc.
3. Post-application scouting
3. Post-application scouting Scout field 3-5 days after spraying to check effectiveness No longer assume insecticides will provide effective control
4. If you have a failure
4. If you have a failure Alternate insecticide group for next spray Group numbers are on labels Mixtures are generally less effective for resistance management
5. Integrate other management tactics Host plant resistance Biological control
Host plant resistance
Hanson et al. 2016 Host plant resistance
Biological control: Predatory bugs Parasitic wasps Lady beetles
Biological control: Selective insecticides Koch, unpublished
Biological control: Selective insecticides Koch, unpublished
Conclusions 4 years of pyrethroid failures & confirmed resistance Few tools available to manage soybean aphid Products Groups Matador 3A X Voliam Xpress 3A+28 X Concept 4A+3A X Cygon, etc. 1B Movento 23
Conclusions 4 years of pyrethroid failures & confirmed resistance Few tools available to manage soybean aphid What to do? Don t spray when not needed If you spray, do it right If you have a failure, alternate insecticide groups
https://doi.org/10.1093/jipm/pmy014
Thank you Questions??? Robert Koch: koch0125@umn.edu All products listed in this presentation were examples and do not constitute endorsements