Southern Corn Rootworm Comments at NC Peanut Meetings Peanut Notes No. 20 2023

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I discussed managing southern corn rootworm at the production meetings this winter. The slides from my presentation are linked below. Rick covers this topic in detail in 2023 Peanut Information, and as he develops more information on ways to manage this pest he will keep us posted. Here are some of the talking points from the meetings.

First, we don’t have any insecticides that are proven to be as effective as Lorsban. In absence of a suitable product, we need to look at the SCRW index to avoid risk when possible. Any conditions in the field that promote survival of the worm will increase risk. That is why soil texture and drainage as well as irrigation influence risk. Finer-textured, poorly drained soils have the greatest risk. Abundant rainfall or irrigation can also increase risk. The worms that feed on the pods are more likely to survive when soil moisture is higher.

Based on the current SCRW index, the most probable way you can minimize damage is to plant early. The reason this can be somewhat effective is because pods tend to me more developed when this insect becomes an issue (July and August) which results in less puncturing. If you do plant early, in part to avoid SCRW, make sure you have an effective thrips control program in place. We often need more than one insecticide treatment for thrips, especially when we plant early. This will be the case if you are using imidacloprid – it is less effective now in controlling thrips. Peanuts are also slower growing when planted early, and we often experience higher populations of this insect in early May. Keep in mind that we are also at greater risk for TSWV when we plant early. Thrips are the vector for this virus. If planting early, in addition to effective insecticide treatments for thrips, make sure you establish 4-5 plants/foot across the entire field. This is a buffer against TSWV. Consider using Phorate/Thimet if you plant early.

One of my slides shows SCRW damage after 3 foliar applications of Steward and Brigade. Rick also has other trials that went into more detail than the ones we report in the table. We show very little damage from SCRW with three bi-weekly sprays beginning in late June (targeting adults) and no yield response. When you run the economics, there is a loss with Steward. While it is an insecticide that is less likely to flare spider mites, it is expensive.

Does that data set prove that Steward is not effective in controlling SCRW? No. The reason is we did not have appreciable damage in the non-treated control. Although the areas of fields where these trials were conducted were considered moderate to high risk, we did not see very much damage. Not seeing excessive damage is a good thing (9 trials) in that the results suggest that SCRW risk, in general can be low. From a research standpoint, however, it would have been better if there was more damage. This would allow us to make a better comparison of treatments. With that said, Ethan Foote had trials at Rocky Mount and Lewiston with and without cereal rye. He applied Steward 3 times and saw no reduction in SCRW damage. Damage was greater in the rye areas and peanuts were noticeably less drought stress throughout the later part of the season. This points to the important role of moisture status on SCRW in soil and subsequent damage.

I spoke to a consultant a few weeks ago who was convinced Steward provided control. I enjoyed the conversation. But I never could get a clear answer on whether or not there was a non-treated area in the field. Both positive and negative controls strengthen research. While we can live without a positive control (in this discussion, Lorsban would be considered the positive control,) we absolutely need a negative control (non-treated areas) to draw meaningful conclusions.

2023 SCRW Comments