Thirty-one sites reporting this week. European corn borer (ECB)-E was caught at eight sites and ECB-Z was caught at only one site. Thirteen sites reported corn earworm (CEW), with ten sites high enough to be on a 4, 5, or 6 day spray schedule (see table below). Fall armyworm (FAW) was caught at fourteen sites and Western bean cutworm (WBC) were caught at twenty-five sites this week.

WBC continues to increase this week. Below is this week’s estimated WBC flight completion map created by Dan Olmstead, NEWA coordinator, and based on Hanson et al. See last week’s post for a summary.

Western bean cutworm estimated flight completion on 7.29.19.

Michigan State University recommends scouting for WBC egg masses when cumulative trap catch numbers reach 100 moth/trap for field corn, though I have found egg masses with cumulative trap catch of just one. Therefore it is recommended that all fields that are in the whorl or early tassel stage be scouted for egg masses with a 4% threshold for processing sweet corn and a 1% threshold for fresh market sweet corn. WBC will usually lay eggs on the upper side of the top 1-3 leaves of pre-tassel corn, close to the leaf base. After tasseling has finished WBC seek out younger corn or dry beans. To scout for egg masses check the top 3 leaves of ten corn plants in ten locations throughout the field. The eggs are easy to observe if you view the leaf while holding it towards the sun. The egg mass will appear as a distinct shadow (see photo).

It takes between 5-7 days for eggs to hatch. It is critical that sprays are timed before the larvae have a chance to enter the ear. The egg mass will become purple in color approximately 24 hours before egg hatch (see photo).

Dry Bean Western Bean Cutworm Alert
7.30.19
Marion Zuefle, NYS IPM Program
(Alert modified from Carol McNeil)
(Information and photos from T. Baute, OMAFRA)

This year we are monitoring eight WBC traps placed next to dry bean fields. The location of the traps are given in the image below. Dry bean growers should scout adjacent corn for WBC eggs and larvae when cumulative trap catch reaches 50 moths. This week the Riga site reached >50 cumulative moths. Peak WBC flight historically occurs the first week of August. All dry bean growers should begin scouting pods for WBC feeding about 10 days after peak flight regardless of cumulative trap catch, and should continue to scout for three weeks, especially if damage has been seen in recent years.

Check 10 random spots in a field, 5 plants per spot. Inspect all the pods on the plants looking for holes. Surface feeding can be caused by other insects. WBC will mine directly into the pod and will often feed on the seed inside. European corn borer will also feed inside the pod and would most likely still be present. If there is damage going directly into the pod and seed but no larva present, it is quite possibly WBC. During the day WBC larva are not actively feeding in the pod, instead they drop to the soil and will remain there until night. Fresh damage will be green, not brown.

If you have questions contact Marion Zuefle at mez4@cornell.edu or 315-787-2379.

This project is funded by the NYS Dry Bean Industry.

Location of WBC traps near Dry Beans in 2019.