Insecticide management of corn earworm and resistance monitoring

Researchers at the Virginia Tech Tidewater AREC have tracked corn earworm insecticide resistance using adult vial tests since 2003 and more recently with larval diet bioassays. This pest has been trending towards pyrethroid resistance in the last ten years in Virginia. At times, pyrethroid spray failures have occurred. Information gathered from these National Peanut Board supported projects allow us to make better pest management recommendations to growers. 
Pressure from corn earworm in southeast Virginia in 2018 was moderate. The Principal Investigator received reports of some local peanut fields that were treated for this pest; post­treatment field checks found that bifenthrin ( a pyrethroid insecticide) provided about 50-70% control. In the adult vial tests, 26% of moths survived a 24-hour exposure to the pyrethroid insecticide cypermethrin at 5 micrograms per vial. This is somewhat less than seasonal averages from recent years. In larval diet bioassays, where the surface of the insect diet was treated with insecticide, application of 8 parts per million of bifenthrin killed 50% of the population. Only about 2 parts per million were needed to kill 50% of a susceptible population. 
This research shows that corn earworm management recommendations need to consider potential resistance issues; this knowledge will help growers make better choices when insecticides are needed.