PestWatch Report: September 7, 2022

Corn earworm numbers caught in traps reporting data this week were variable but exceeded 350 moths for the first time this season, pushing that location into the tightest recommended spray interval. Franklin County experienced an average catch per night of 50 moths, which would mean a spray interval of every 2–3 days would be suggested for corn that’s tasseling or silking. Sites in Lancaster, Luzerne, and Washington Counties experienced an average catch per night of 20–30 moths, which means a spray interval of 3–4 days would be suggested. Centre, Clinton, and York Counties experienced an average catch per night of 6–9 moths, suggesting a spray interval of 4–5 days. Butler and Lycoming Counties experienced an average catch per night of 3–5 moths, meaning a spray interval of 5–6 days is recommended. 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, as pyrethroid resistance has increased in migrating corn earworm populations. Notably, we tend to see more resistance later in the season, as moths migrate from further south in the United States up to our region. Consider consulting the Mid-Atlantic Commercial Vegetable Recommendations Guide for products to use. 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 see these pests as you scout your corn, consider adding a pyrethroid or the premix Besiege to control those.

Fall armyworm catch remains very low this week, with three or fewer moths caught in Bedford, Centre, and Franklin Counties and zero caught in all other counties reporting this week. 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. By managing corn earworm, fall armyworm should also be adequately controlled.

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.