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Scout Peanuts for Lesser Cornstalk Boers

It’s hot and dry, which means lesser cornstalk borers (LCB) will most likely be an issue in peanuts in 2022. Lesser cornstalk borers thrive in hot, dry conditions, and they generally do very poorly in fields that receive adequate moisture, but irrigated fields are not immune from attack. We do sometimes see LCB at damaging levels in irrigated fields, but that is not the norm. Lesser cornstalk borer is one of the most damaging and difficult to control pests in peanut. It feeds on stems, pegs, and pods, and it will reduce yield and increase the risk of aflatoxin contamination.

Dr. Mark Abney, UGA Peanut Entomologist has a few reminders for us when it comes to LCB:

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.

FMC and the University of Georgia have LCB traps across the peanut growing area.

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

Silk tubes from LCB
Lesser cornstalk borer moth. Moths are slender and will flush from the foliage as you walk through the field. The presence of moths is a good indicator of LCB infestation.

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 do not. 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 some may have received decent rain within the past week 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. However, once peanut vines lap the row middles, irrigated fields that are watered adequately will rarely experience LCB populations above threshold.

The threshold for LCB and how to scout is to measure three feet of row length and check all plants within those three feet. Repeat that process in ten different areas across a field. If you find LCB, LCB damage, or silk tubes in three (30%) of the ten spots checked, then its time to spray.

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.

A video on scouting for LCB can be found below: