Saturday, October 16, 2021

Mid-July insect update for Georgia

lesser cornstalk border
the most damaging pest of peanut in Georgia is lesser cornstalk borer.

Continued rainfall in Georgia is mostly good news for peanut growers from an insect management point of view (disease management is a different story, but Dr. Bob Kemerait can tell that one).

The most damaging pest of peanut in Georgia is the lesser cornstalk borer (LCB). While it does not disappear when rainfall is plentiful, outbreak populations will not occur over a large area. That doesn’t mean thresholds can’t be exceeded in individual fields, and it is wise to scout. This is especially true of later planted fields with sandy soils where the vines have not lapped the row middles.

I am continuing to see low numbers of tobacco budworm (TBW) caterpillars in my research plots, and I am still getting reports of some fields being sprayed for this pest. At this point in the season, it is important to use thresholds for making caterpillar treatment decisions.

The threshold is an average of 4 to 8 caterpillars per row-foot across 10 randomly selected locations in a field (sample 3 feet of row at each location). Use the lower end of the threshold when plants are small or stressed and the higher end of the threshold when the vines are rank and/or rapidly growing.

Spraying caterpillars when populations are below threshold provides no value to the grower. Every peanut field in Georgia needs to be scouted, but every field does NOT need to be sprayed.

Velvet bean caterpillars and soybean loopers

It is about time for velvet bean caterpillars and soybean loopers to show up across larger portions of our growing area. In what seems to be a favorable year for caterpillars, I have already heard reports of fall armyworm exceeding thresholds in peanut.

The caterpillar thresholds given above are the same for all the foliage feeding species we encounter in peanut. We have good insecticide options for caterpillar management.

Knowing the identity and relative abundance of the species present in a field can help determine which active ingredient to choose. University of Georgia county Extension agents can help with insecticide decisions.

Three cornered alfalfa hoppers

Three cornered alfalfa hoppers (TCAH) are present in peanut fields, and their numbers generally increase from mid to late summer. Though this insect is often present in very high numbers, it is not considered a major pest of peanut.

Can TCAH cause yield loss? Yes, but the losses are typically minor, and managing the insect presents some challenges. First, the insect is highly mobile. Killing the adults in a field today will not matter much if more fly in at the end of the week.

Second, the insecticides available to kill TCAH do not have long residual activity, and efficacy is not always that great. Add to all that the fact that these insecticides can flare spider mites in non-irrigated fields, and you can make a pretty good argument for leaving TCAH alone.

There are situations where I think treatment for TCAH will pay, but I am generally not worried about this insect.

If you have questions about insect management in peanut, please contact your local University of Georgia County Extension agent.

University of Georgia Cooperative Extension contributed this article.

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