PestWatch Report: August 17, 2022

Corn earworm numbers caught in traps reporting data this week were increasing at many sites this week. Sites in Blair, Bucks, Franklin, Lancaster, Lehigh, Montgomery, and York Counties experienced an average catch per night of 11–30 moths, which means a spray interval of 3–4 days would be suggested for corn that’s tasseling or silking. Bedford County experienced an average catch per night of 10 moths, meaning a spray interval of 4–5 days would be suggested. Sites in Indiana, Juniata, Mifflin, and Northampton Counties experienced an average catch per night of 2–4 moths, meaning a spray interval of 5-6 days. As a reminder, corn that is tasseling or silking is very attractive to corn earworm, as eggs are laid on silks, and control must be achieved while larvae are recently hatched before they’ve entered the ear.

Once the spray threshold is reached, you can consider products from the pyrethroid, diamide, or spinosyn class for effective control. We tend to see the best efficacy from non-pyrethroid products such as Coragen, Verimark, Blackhawk, and Radiant, as pyrethroid resistance has increased in migrating corn earworm populations. Particularly, we tend to see more resistance later in the season, as moths migrate from further south in the United States up to our region. Diamides and spinosyns do not provide effective control of other pests such as sap beetles, stink bugs, Japanese beetles, or adult corn rootworms. If you’re seeing these pests as you scout your corn, consider adding a pyrethroid or the premix Besiege to control those.

Fall armyworm catch remains low this week, with 12 or fewer moths in Bedford, Blair, Juniata, Lycoming, and Mifflin Counties and zero in all other counties reporting this week. By managing corn earworm, fall armyworm should also be adequately controlled. Fall armyworm damage can occur on the ear, as well as on the foliage. Foliage feeding will leave ragged edges and waste that resembles sawdust.  

Figure 2. Fall armyworm feeding damage on corn. Photo: Karly Regan, Penn State

Average weekly catch – 7-day moving average. The average catch per night (total catch, divided by the number of nights trapping), divided by the number of nights where data exist, multiplied by 7. If no data exist for that week, null is reported.

Thresholds: Reproductive (tassel/silk) and late vegetative corn attract moths. Shorten spray schedules when populations increase.