Implications of Cover Crops for Soybean and Insect Management the good, the bad, and the ugly SCOTT D. STEWART THE UNIVERSITY OF TENNESSEE

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1 Implications of Cover Crops for Soybean and Insect Management the good, the bad, and the ugly SCOTT D. STEWART THE UNIVERSITY OF TENNESSEE

2 Cover Crops can have positive attributes that you are all well aware of including Erosion control Prevention of water / nutrient / pesticide runoff Soil health (organic matter, fertility) Weed control and/or a reduction in herbicide use Resources for pollinators A nursery for natural enemies Payments to growers The type of cover crop and when it is controlled (killed) relative to the planting date can have a huge impacts on the risks and benefits

3 Integrating Cover Crops and Herbicides for Weed Management Drake Copeland and Dr. Larry Steckel (University of Tennessee)

4 Plants/Acre Horseweed Control Horseweed in Vetch Cover Prior to Cotton C B A Cover No Herbicide A Cover Rup/Val 14 DBP No Cover No Herbicide No Cover Paraquat 14 DBP *No burndown applied at cover planting

5 Wheat/Vetch Cover No herbicide Cover crops offer weed SUPRESSION of Palmer Amaranth Level depends upon the weed G. Montgomery and L. Steckel

6 Planting Green

7 Cover Terminated 14 DAP (Roundup Xtend Soybeans) Steckel 2015

8 Plants/Acre Bushels/Acre Soybean Response to Termination Bushels/Acre Plants/Acre Termination Days +/- Planting 0 Wheat/vetch cover

9 Days until 4-inch tall Palmer Main effects of Termination Timing and Herbicide on Days until 4 Palmer Pigweed A A b a C C BC BC B DAP 14 DAP No Residual Dual Magnum Prefix Warrant Warrant Ultra Zidua Zidua + Flexstar Termination Timing XtendiMax + Roundup +...

10 Xtendimax + Roundup + No Residual No Residual: Terminated at Planting No Residual: Terminated at 14 DAP 83 Days After Planting

11 Xtendimax + Roundup + Residual Zidua TT 14 DAP Warrant TT 14 DAP Dual Magnum TT 14 DAP 83 Days After Planting

12 Weed Control Costs: Conventional vs. Planting Green Timing Conventional Cover Crop Planting Green Cove Type ---- Cereal Rye Cereal Rye + Vetch Wheat Wheat + Clover** Cover Crop Planting Prior to Planting At Planting EPOST MPOST ---- $26.40 $74.40 $8.00 $15.75 $17.00 (RPM + Sterling Blue + Verdict + MSO) $28.00 (Gramoxone + Boundary + NIS) $32.00 (RPM + Xtendimax + Warrant Ultra) $20.00 (Select+ COC + First Rate) $32.00 (RPM + Xtendimax + Warrant Ultra) $20.00 (Select + COC + First Rate) $32.00 (RPM + Xtendimax + Warrant Ultra) $20.00 (Select + COC + First Rate) $32.00 (RPM + Xtendimax + Warrant Ultra) $20.00 (Select + COC + First Rate) $32.00 (RPM + Xtendimax + Warrant Ultra) $20.00 (Select + COC + First Rate) LPOST $16.00 (RPM + Xtendimax) Total Costs $ $78.40 $ $60.00 $67.75 **Based on 30 inch Row Spacing

13 Reduced Tillage and Cover Crops Generally increases diversity of the arthropod community

14 It s not all peaches and cream (diversity is not always a good thing) There are potential problems with cover crops, particularly in the South, where they may serve as a nursery for insect pests Reduced tillage and cover crops provide a great environment for insects they just love hiding in there and also some non-insect pests like spider mites, slugs and voles Inherent challenges with establishing stands The Circle of Life

15 Cover crops can be a green bridge we have problems in no-till that we don t have in tilled soil

16 The Examples I am Going to Show are Worst Case Scenarios Long-standing IPM recommendation - destruction of cover crops or winter vegetation should be accomplished at least 3-4 weeks prior to planting crop to reduce the potential insect problems Cover Green Bridge Crop If it ain t brown don t put seed in the ground

17 Observations on Pea Leaf Weevil in Soybean Often abundant in fields behind winter field pea cover crops In some cases, it s been a BIG PROBLEM We ve also observed them in Tennessee behind cover crops containing vetch Larvae feed on nodules, and adults feed on foliage Can be controlled with labeled insecticides but continue to come out of cover crop residue for extended period, resulting in multiple applications Cover crop residue and extended period of adult emergence can be problematic

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19 Seed Treatments Help (e.g., Don Cook, MSU) Acceleron Cruiser NipsIt Inside Acceleron Poncho Acceleron Not Treated (- 32 B/A)

20 Tennessee, 2016 and 2017 Pea weevil behind vetch or vetch/grass cover Imidacloprid seed treatment

21 Insect populations following herbicide application to wheat and vetch cover crop in soybean Samples taken the day of planting (13 days after burndown application) 1 Average Relative Population Level Based on Sweep-net Samples No Burndown Burndown Tarnished plant bug Pea aphid Threecornered AH Lady Beetles

22 Tennessee, 2015 TCAH behind legume or legume/grass cover Threecornered alfalfa hopper

23 Cover crops Threecornered alfalfa hopper in soybean following vetch or Austrian winter peas Slugs, slugs, slugs in no-till fields with high residue and where cover crops were used Etc.

24 Brown stink bug Corn Behind Austrian Winter Field Peas Cover Crop, Arkansas, 2013 Planted Green Gus Lorenz (University of Arkansas)

25 The Midwest Increased incidence and injury from true armyworm following rye

26 Things You Should Consider if Using a Cover Crop Avoid the green bridge as much as feasible Otherwise: Consider the type of cover crop (avoid matching the crop if possible) Use an Insecticide Seed Treatment (the higher rates in corn) Consider a near-planting foliar insecticide treatment Scout fields early and often have a game plan with your consultant/crop scout Follow good IPM practices for other pests

27 Yield Increase from an Neonic IST Compared with non-treated plots (Mid-South) Crop Average Increase Number of Trials Gross Value Cotton 101 Lbs. Lint/Acre 67 $70 Corn 11.8 Bushels/Acre 91 $47 Soybean 2.0 Bushels/Acre 170 $20 Meta-analysis of replicated insecticide trials done from (AR, LA, MS, TN) North et al., Mississippi State University

28 Soybean Response to Insecticide Seed Treatment Bushels/Acre ( , N = 170) AR TN LA MS +2.48

29 No Worries Using an insecticide in a crop (like neonicotinoid seed treatments) will not result in toxic levels of insecticides in the nectar or pollen of a subsequent cover crop Despite words of caution in NRCS and other literature, this is a non-issue for pollinators visiting the flowers of cover crops (really a non-issue for the treated crop) Bee-attractive cover crops are a benefit to pollinators let s do our best not to spray insecticides when cover crops are flowering o Clovers, Austrian winter peas, rape/mustard, and vetch are very attractive to bees

30 Some Prognostication About Cover Crops Latitude is inversely related to insect diversity (including pests), and there are more and varied kinds of fun as you get closer to the equator Expect increased pest problems in the South associated with cover crops They will increases the value of at-planting insecticides and good IPM practices Also a threat of introducing weeds to production fields What about plant pathogens (seedling diseases in particular)?

31 What About Slugs in Cover Crops? Residue and a food source is the problem Will be worse behind high residue crops Cover crops often keep the soil cool and moist Scout intensely the first 2 weeks after planting Baits are effective Metaldehyde (Deadline MP), Iron phosphate Insecticides don t work Baits are not cheap and require some planning Can you use row cleaners?

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33 You can scout for them

34 We ve Just Talked About a Few Pests There s a lot of potential for weird stuff this is called job security for entomologists! We don t really know enough about how cover crops will change IPM

35 Again There are Positives for Cover Crops Cereal Rye/Cotton Thrips suppression + Water conservation + Weed suppression

36 Pesticide contamination of water is a hotbutton issue

37 and for Water Quality Regardless of any increase in insecticide use, I would expect cover crops to be a net benefit in terms of pesticide run-off Less movement of water and soil to peripheral, non-crop areas We are already managing seedling pests with seed treatments and foliar pesticide applications in many field crops

38 Soybean There are other fish to fry Insecticide resistance Soybean looper / diamides? Corn earworm / pyrethroids Invasive insects Kudzu bug Brown marmorated stink bug Redbanded stink bug Pest Guides (app)

39 UTcrops News UTCrops.com UT Pest Guides UT Variety Trials Soy Search

40 Questions?