Many hemp growers are beginning to harvest or are gearing up to harvest. Growers are spending more time in the field observing plants and collecting samples for testing to measure THC (tetrahydrocannabinol), CBD (cannabidiol) and CBG (cannabigerol). Growers should also continue to scout for pests.
Corn earworm is one of the most concerning pests of hemp this time of year. Last year we observed corn earworm (CEW) from late August to October, feeding on seed heads (grain production) or female flowers (cannabinoid production). The damage results in browning and die back of flowers and seed heads. I am now getting a few reports of CEW damage. Unlike last year though, there are insecticides available for use on CEW in hemp.
Corn earworm has caused yield loss in hemp across the country and in Indiana. Purdue and OISC worked to develop 24(c) Special Local Needs labels for Venerate XC, Gemstar LC, and Agree WG insecticides. Refer to the 24(c) labels for rates and timing of application for the various products, which can be found at the OISC pesticide site.
EPA also approved Spear-Lep, which is used for many different caterpillars, including CEW. These biopesticides are most effective when larvae are very young, instars 1-3. Using the corn earworm trapping network as a guide, you can look at moth flights across the state to see when flights are high in your area.
However, we do not have action thresholds for hemp yet. Smaller hemp farms may opt to hand pick CEW larvae off of their plants, but this can be very time consuming. With several insecticide options available, we hope to see better control of CEW this year.