Monitoring and decision making strategies for soybean aphid management. Jordan Bannerman Department of Entomology University of Manitoba

Transcription

1 Monitoring and decision making strategies for soybean aphid management Jordan Bannerman Department of Entomology University of Manitoba

2 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

3 SBA in Manitoba An occasional economic pest Probability of death during winter McCornack et al. (2005) Environmental Entomology

4 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

5 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 Journal of Economic Entomology

6 SBA scouting Plant staging Koch & Potter UMN extension

7 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)

8 SBA speed scouting Speed scouting method Sequential sampling method, but based on same threshold already discussed Worksheet available (goo.gl/uc9vus) itunes app available ( Hodgson et al Journal of Economic Entomology

9 SBA speed scouting Begins (and potentially ends) with sampling 11 plants, each at least 30 paces apart Hodgson et al Journal of Economic Entomology

10 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 Pest Management Science)

11 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 Pest Management Science

12 Natural enemies of SBA Ladybird beetles Predatory bugs Lacewings Predatory flies Parasitoid wasps

13 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 Journal of Economic Entomology

14 NE scouting Sweep-netting Plant counts Walking observation Bannerman et al Journal of Economic Entomology

15 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 Pest Management Science

16 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 DAT Make decision based on DAT scout later, control, or no longer a concern

17 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 Pest Management Science

18 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

19 Acknowledgements Alejandro Costamagna Brian McCornack Dave Ragsdale

20 Useful resources Soybean aphid scouting guide ( Soybean aphid economic threshold paper ( Manitoba Insect & Disease Updates (

21 References Koch, R., Potter, B. Scouting for Soybean Aphid. July University of Minnesota Extension Hallett et al Incorporating natural enemy units into a dynamic action threshold for the soybean aphid, Aphis glycines (Homoptera: Aphididae). Pest Management Science, 70: Bannerman et al Comparison of Relative Bias, Precision, and Efficiency of Sampling Methods for Natural Enemies of Soybean Aphid (Hemiptera: Aphididae). Journal of Economic Entomology, 108: Ragsdale et al Economic Threshold for Soybean Aphid (Hemiptera: Aphididae). Journal of Economic Entomology, 100: Hodgson et al Enumerative and Binomial Sequential Sampling Plans for Soybean Aphid (Homoptera: Aphididae) in Soybean. Journal of Economic Entomology 97(6): ).