Alternative Chemistries for Managing Corn Earworm in Sweet Corn
Figure 1: Consider rotating insecticides with different modes of action to prevent insecticide resistance. Photo by Thomas Ford, Penn State
The threat of synthetic pyrethroid resistance by corn earworm is a growing concern in the Mid-Atlantic region. Entomologists have encouraged growers to rotate insecticides with different modes of action and to limit synthetic pyrethroid insecticide usage to early in the growing season when pest pressure is light and when pyrethroid resistance has not had the opportunity to build up in the corn earworm population.
Insecticides that lie outside of the synthetic pyrethroid group, which are labeled for corn earworm management in sweet corn, include:
- spinosad (Blackhawk 36WG, Entrust SC) (Group 5)
- spinetoram (Radiant SC) (Group 5)
- methomyl (Lannate LV) (Group 1A)
- methoxyfenozide + spinetoram (Intrepid Edge) (Group 18 & 5)
- chlorantraniliprole (Vantacor) (Group 28)
- Polyhedral occlusion bodies (OBs) of the nuclear polyhedrosis virus of Helicoverpazea (Gemstar LC)
Most of the insecticides labeled against corn earworm are relatively familiar to most sweet corn growers. The insecticide Gemstar LC, however, may be the lone exception since this biologically based insecticide has been primarily used by organic sweet corn growers for managing corn earworms. Research conducted in 2015 by Dr. Shelby Fleischer, Dana Roberts, and Jeff Stoltzfus demonstrated that Gemstar LC was effective in managing corn earworm when generalist predatory insect populations were to be conserved in sweet corn plantings. The efficacy of Gemstar LC varied somewhat in their Penn State trials, but this bio-based insecticide seemed to be more effective when it was tank-mixed with Entrust SC (spinosad).
If ingested, Gemstar LC is an insecticidal virus that kills young corn earworm and tomato fruitworm larvae. Gemstar LC should be sprayed on sweet corn to target newly hatched larvae before they enter the ear. After ingesting this virus, larvae will stop feeding and become lethargic before perishing in a few days. Gemstar LC can be tank-mixed with an array of agricultural chemistries (unless otherwise specified on the pesticide label). In Colorado, some growers routinely tank-mix Gemstar LC with other labeled insecticides in their battle against both corn earworm and insecticide resistance.
