Lesser cornstalk borer (LCB) is the most destructive insect pest of peanut in the Southeast, and it thrives in hot, dry conditions. It doesn’t get a whole lot hotter or drier in South Georgia than it has been the last couple weeks, and reports of LCB infestations in peanuts have predictably started to arrive.
What should growers do about LCB? The most important thing a grower can do is monitor fields regularly and take appropriate action if/when infestations are discovered. Three insecticide active ingredients are recommended by the University of Georgia for LCB management in peanut: chlorpyrifos, chlorantraniliprole, and novaluron. Chlorpyrifos (Chlorpyrifos 15G) can only be applied as a granular product banded over the row. It requires rainfall or irrigation for activation, and applications are often followed by outbreaks of caterpillars and/or mites. Chlorantraniliprole (Prevathon) and novaluron (Diamond) are applied as broadcast foliar sprays. Rainfall or irrigation after application may improve efficacy, but I have no data to support this, and both products have provided good control in UGA trials without additional water.
Severe LCB infestations are not common in irrigated peanut after the vines have lapped the row middles IF adequate irrigation is applied. However, LCB is often found in irrigated fields (especially those with sandy soils) prior to row closure when environmental conditions are favorable. LCB caterpillar feeding in the crown of seedling plants can reduce yield even if adequate water is available later in the growing season. It is important to remember that while LCB does not survive well in moist conditions, one or two rainfall events will not eliminate an established population, and we will probably not be able to “irrigate LCB away” prior to row closure.
The two mistakes that are most likely to be made when LCB infestations are on the rise are:
1. Treating fields with an insecticide when no insects are present. No matter how bad LCB gets in 2019, it will not be in every field.
2. Failing to treat or treating too late when thresholds are reached.
Scouting is the best way to avoid these mistakes. It is hot and dry and there are lesser cornstalk borers in some of our peanut fields, and we cannot do anything about any of that. What we can do is stay calm and make wise decisions that will protect our peanuts and maximize our return on investment.
If you have questions about managing lesser cornstalk borer or other insect pests in peanut, contact your local UGA County Extension Agent.