Monitoring and decision making strategies for soybean aphid management Jordan Bannerman Department of Entomology University of Manitoba
Overview Soybean aphid (SBA) incidence and timing SBA economic threshold and EIL SBA scouting Role of natural enemies in SBA suppression Natural enemy (NE) scouting Dynamic action thresholds
SBA in Manitoba An occasional economic pest Probability of death during winter McCornack et al. (2005) Environmental Entomology
SBA damage symptoms Leaf distortion Stunted, yellowing plants Sooty mold on leaves Virus transmission Yield reductions of 40 percent or greater can occur in heavily infested fields if left untreated
Economic (action) threshold 250 aphids per plant on average and.. More than 80% of the plants have aphids Plants are not yet at R6 growth stage Aphid populations are increasing Provides a 7 day lead time to take control action before the economic injury level of 675 aphids/plant is reached Ragsdale et al. 2007. Journal of Economic Entomology
SBA scouting Plant staging Koch & Potter. 2014. UMN extension
SBA scouting Plant counts 20 whole-plant counts, each 20+ paces from one another Weekly basis once plants are in vulnerable reproductive stage (R1 to R5)
SBA speed scouting Speed scouting method Sequential sampling method, but based on same threshold already discussed Worksheet available (goo.gl/uc9vus) itunes app available (http://bit.ly/21eejst) Hodgson et al. 2004. Journal of Economic Entomology
SBA speed scouting Begins (and potentially ends) with sampling 11 plants, each at least 30 paces apart Hodgson et al. 2004. Journal of Economic Entomology
Can we improve decision making? We have a good simple action threshold in place But we also know that natural enemies can exert significant control on soybean aphids in North America (including Manitoba) Could a dynamic action threshold that integrates both aphid and natural enemy counts improve upon the threshold currently used? (Hallett et al. 2012. Pest Management Science)
Incorporating natural enemy counts into action thresholds One needs to determine: The natural enemy assemblage in a region The impact (voracity) of various species of natural enemies on aphid populations How best to scout natural enemies in soybean Hallett et al. 2012. Pest Management Science
Natural enemies of SBA Ladybird beetles Predatory bugs Lacewings Predatory flies Parasitoid wasps
NE scouting What method or methods are most appropriate? To accurately and efficiently count both large and small natural enemies while also scouting for soybean aphid Bannerman et al. 2012. Journal of Economic Entomology
NE scouting Sweep-netting Plant counts Walking observation Bannerman et al. 2012. Journal of Economic Entomology
Dynamic action thresholds An ET that changes depending on the abundance (and identity) of natural enemies counted while scouting Research suggests conversion of natural enemy counts into standardized units may work best E.g. 1 NEU = Number of NEs required to consume 100 aphids in 24 hours Determining the best method to sample/count NEs requires further research Hallett et al. 2012. Pest Management Science
Plant counts (normal method) to count SBA and NEs Determine the number of natural enemy units per plant (with help of disc counter) Determine dynamic action threshold NE units per plant 0 0.5 1 1.5 DAT 250 367 483 600 Make decision based on DAT scout later, control, or no longer a concern
Trial use in Ontario Initial trial use of DAT by growers: Resulted in all 4 growers choosing not to spray All 4 would have sprayed based on the conventional ET of 250 aphids per plant None of the fields actually reached the EIL Hallett et al. 2012. Pest Management Science
Summary There are several options when scouting soybean aphid There is a good simple threshold, that is useful for economic decision making, but quite conservative Incorporation of natural enemy data appears to improve economic decision making in soybean Further work is needed to test/refine DATs and determine the best natural enemy sampling methods to employ
Acknowledgements Alejandro Costamagna Brian McCornack Dave Ragsdale
Useful resources Soybean aphid scouting guide (http://bit.ly/1tw7hnj) Soybean aphid economic threshold paper (http://bit.ly/1lovnn4) Manitoba Insect & Disease Updates (http://bit.ly/1n4ads9)
References Koch, R., Potter, B. Scouting for Soybean Aphid. July 2014. University of Minnesota Extension Hallett et al. 2012. Incorporating natural enemy units into a dynamic action threshold for the soybean aphid, Aphis glycines (Homoptera: Aphididae). Pest Management Science, 70: 879-888 Bannerman et al. 2015. Comparison of Relative Bias, Precision, and Efficiency of Sampling Methods for Natural Enemies of Soybean Aphid (Hemiptera: Aphididae). Journal of Economic Entomology, 108:1381-1397 Ragsdale et al. 2007. Economic Threshold for Soybean Aphid (Hemiptera: Aphididae). Journal of Economic Entomology, 100:1258-1267 Hodgson et al. 2004. Enumerative and Binomial Sequential Sampling Plans for Soybean Aphid (Homoptera: Aphididae) in Soybean. Journal of Economic Entomology 97(6): 2127-2136).