Thinking About Insect Pests During Planting Season

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Black cutworm and cut cotton plant

There are some basic management practices that can affect, sometimes worsen, and other times be used to reduce risks of insect pest injury. Below, I’ve included some observations and suggestions for your consideration.

As a general rule of thumb (but not universally true), no-till production increases the risk of some problems including pests like cutworm, threecornered alfalfa hopper, slugs, and several below ground pests (e.g., wireworms and white grubs). Of course, tillage is not an option in most areas of Tennessee. Thus, most entomologists suggest applying a ‘burndown’ application of herbicides to kill any green vegetation at least 3-4 weeks in advance of planting. The goal is to avoid having “green bridge” where pests move from weedy or cover crop vegetation to the cash crop.

Making a burndown application well in advance of planting isn’t always possible, nor is it always compatible with the goals of those using cover crops. My recommendation in these situations is to make an application of a pyrethroid insecticide either with the burndown herbicide application or within a week of planting (before or after).

  • If you are applying herbicides to cover crops that have blooming and bee-attractive components like clovers, Austrian winter pea, vetch, and/or brassica species, then DO NOT include a pyrethroid insecticide.

Use an insecticide seed treatment in situations where the cover crop might host insect pests that also feed on the cash crop. As an example, we’ve seen significant issues where soybean are damaged by insects attracted to a cover crop having vetch or Austrian winter pea. This is primarily needed for soybean because virtually all cotton and corn seeds will already have an insecticide seed treatment. Of course, the risk of insect problems drops substantially if the cover crop is terminated 3-4 weeks in advance of planting.

  • Some of the common insect problems we’ve seen problems with in soybean following a cover crop include pea leaf weevil, southern corn rootworm, and threecornered alfalfa hopper following vetch or Austrian winter pest. We’ve also see occasional injury when true armyworm are present on barley, wheat, oat or rye grasses in the cover crop and then feed on seedlings. Following the above recommendations will greatly reduce the risk from these pests.

Cutworms in corn and cotton are a fairly uncommon but sometimes serious pest. An application of a pyrethroid insecticide as mentioned above within ±7 days of planting can substantially reduce the risks for a minimal cost. Even though the Bt traits in Bt cotton and corn have activity on small cutworms (some better than others), larger larvae that may be present in the field at planting are less susceptible and may still cause economic loss. Insecticide seed treatments normally don’t provide enough protection. Having said all that, I’ve recently had a tests where a high rate of a Poncho seed treatment in corn in combination with Bt corn did well at reducing cutworm damage.

Now for some dry weather!

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