Lesser cornstalk borers (LCB) are soil pests that like dry weather, making them a classic indicator of drought. LCBs prefer various legumes, including peanuts and soybeans. In peanuts, LCB damage can cause crop contamination from webbing and direct yield loss if unchecked.
Four to five generations of LCBs may occur each year, with the worse cases being in areas with sandy soils. Moth numbers can often be high in central and southeast and Alabama. Currently, moth numbers exceed 3,000 from statewide traps (doubled activity since June), suggesting the scattered showers the state has received are not enough.
Problems from LCBs reduce with irrigation and rainfall. Chemical control with insect growth regulators (IGRs) (ones that are specific to immature stages of several major pests such as Dimilin or Diamond ) is only good when the caterpillar comes out of the webbing to molt or when they crawl on the ground, moving between plants. Some growers decided to spray when they saw larvae crawling, which is good for timing.
If the drought worsens, then growers should refrain from using too many repeated applications of synthetic pyrethroid to avoid spider mite issues. Insect growth regulators are excellent choices, but remember it is important to thoroughly spraying inside and under dense peanut canopies to properly control LCBs. Based on past research, substituting pyrethroids with IGRs can protect beneficial insects and mites that are needed, resulting in a more sustainable peanut production system.
Additional details about pest monitoring and scouting can be found on the Integrated Pest Management page of the Alabama Extension website. For further information, contact your county Extension commercial horticulture agent. To receive timely pest alerts, subscribe to the Alabama IPM Communicator Newsletter.