I mentioned last week that we were getting some reports of lesser cornstalk borer (LCB) in peanut, and that hot, dry conditions could result in more pressure. Over the last three days I have received a number of calls and emails from agents, growers, and consultants indicating that LCB is becoming more prevalent in peanut fields. You will usually see lessers in the driest spots in the field first; look for plants that are wilted and/or have skips beside them and plants at the ends of rows. Checking these areas first can save a lot of scouting time…if the larvae are not here they are not very likely to be in other parts of the field.
LCB larvae are not always easy to find. Studies conducted in Alabama in the 1980’s showed that the number of LCB moths in a field was a good predictor of future larval abundance. I am not sure we should go so far as to treat fields just because there are moths present, but we should be diligent about scouting for larvae in fields where we see moth activity.
Some things to know about LCB: eggs take about 4 days to hatch, from hatch to pupa takes about 19 days, pupation lasts 9 days, and the adult female will live about a week and a half under hot conditions. A single female moth can lay up to 110 eggs.
Rainfall will help slow population growth, and we do not usually see LCB problems under pivots when adequate water is being applied. It is important to scout young peanuts under pivots as these fields will probably not be getting irrigated enough to keep the pest at bay. We do not want to see crown damage occurring in young irrigated peanuts. Once the water needs of the peanuts ramp up, vines lap the row middles, and pivots are running full steam, LCB should become rare in adequately irrigated fields.
For growers who plan to use a foliar insecticide for LCB control there are a couple things to keep in mind. Insecticides will not be effective if they do not reach the target. I would not bother spraying for LCB with less than 15 gallons of water per acre; 20 gallons would be better. I am not aware of any studies that have been done, but spraying at night would almost certainly increase the likelihood of killing LCB with foliar insecticide applications. I am fully aware that suggesting night sprays and increasing spray volumes will give most growers a case of indigestion, but these could be the difference between getting control and wasting time and money.
If you have questions about lesser cornstalk borers or other insect pests of peanut, please contact your local county Extension agent.