Time to Scout Peanuts for Lesser Cornstalk Borer

Dr. Mark Abney, UGA Peanut Entomologist. If interested in signing up to receive updates from his blog, subscribe here.

Regardless of whatever else has to be done on the farm in South Georgia over the next fourteen days, one thing that needs to happen is scouting peanut fields for lesser cornstalk borer (LCB). This insect is the most damaging pest of peanut in Georgia; it feeds on stems, pegs, and pods, and it will reduce yield and increase the risk of aflatoxin contamination.

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Lesser cornstalk borer thrives when it is hot and dry. Conditions have been favorable for LCB since early May, and infestations have been detected in fields across much of South Georgia. The current extended weather forecast calls for very hot and dry conditions. This is likely to result in a rapid increase in LCB populations.

There are two big mistakes that we want to try to avoid, and both of them can be prevented with scouting.

First, not every field will need to be treated with an insecticide. Spraying every field because lessers “might” be present is a bad idea. We do not need to use insecticides to prevent LCB infestations. When the pest reaches threshold we can treat it, kill it, and move on.

Second, missing an LCB infestation will result in significant losses. Whether a grower usually scouts or not, every peanut field in Georgia needs to be scouted over the next two weeks (at least).

The two insecticides recommended for lesser cornstalk borer management in peanut are chlorantraniliprole (Vantacor/Prevathon) and novaluron (Diamond). If you are thinking about using any other product, please call your local county Extension agent so that he or she can talk you out of it. Using a less expensive product that doesn’t work will not save you any money. Using a product that contains a pyrethroid will put you at increased risk for spider mites in a year where the risk for spider mites is already very high.

Rain does not kill lesser cornstalk borers. The fact that we all got a good shower on Tuesday means nothing for the LCB population. The rain did wash away silk tubes and make scouting more difficult for a few days, but the insects are still here. If we experience lower temperatures and regular rainfall over the next three weeks, we will see lesser numbers dwindle. We can pray for that.

We cannot irrigate LCB away prior to canopy closure. Once peanut vines lap the row middles, irrigated fields that are watered adequately will rarely experience LCB populations above threshold.

A lesser cornstalk borer outbreak is most likely coming. There is no need to panic. Now is the time to be calm, scout, make wise management decisions, and get on with the business of growing the world’s best peanuts.

If you have questions about lesser cornstalk borer management or any other insect management issue in peanut, please contact your local extension agent.