By SHELLY STRAUTZ-SPRINGBORN
Michigan Correspondent

EAST LANSING, Mich. — A spray advisory to safeguard against western bean cutworm (WBC) in dry edible beans was issued last week for six Michigan counties, because of high trap counts and the known potential risk of the pest to the bean crop.

“I urge growers to treat fields with pods as soon as practical,” said Chris DiFonzo, Michigan State University field crops entomologist. “This spray will control western bean cutworm caterpillars before they chew into pods.”

The advisory was issued for Gratiot, Isabella, Kent, Mecosta, Midland and Montcalm counties.

“Corn is now mostly unattractive for egg laying” because it is done pollinating, DiFonzo said. “Moth numbers remain high in traps near dry bean fields in central Michigan, and I believe that moth catch peaked last week in the state. Flight started earlier and has peaked earlier by two weeks, perhaps related to the warmer season and earlier spring.”

WBC is a severe pest that feeds on ears of corn and the pods of dry beans, causing yield and quality losses. A trapping network has been set up throughout the state to determine flight patterns of the moth. Average trap counts are up this year, in several areas 50-100 percent more than last year.

By monitoring the trapping network data, DiFonzo and her team can pinpoint when there is moth flight in an area and when it is time to scout fields for the pest. “There is no need to panic,” she said.

“Experience from 2009 showed that in podded fields treated within one to two weeks after peak flight, bean damage was low or none.”

DiFonzo did not recommend a specific product, but said that pyrethroids have good efficacy against WBC, plus they provide residual activity to control larvae hatching a week or more after application.

“The treatment will also control cloverworm, Japanese beetle and potato leafhopper, all of which are increasing,” she said.

DiFonzo said farmers should delay treatment in fields that are only flowering until pods are present.

“As a good entomologist, I urge growers to check fields for pod feeding before spraying to confirm the presence of western bean cutworm,” she said.

“But the difficulty of scouting dry beans, the potential time needed to arrange for a spray and the threat to bean quality at harvest dictates that this more general recommendation is made to deal with the reality of the situation.”

WBC has been in Michigan the last few years. During the 2007 growing season, the northwestern quadrant of the state from Oceana County to Montcalm County and north was infested. In 2008, there was significant damage to dry bean crop in a few locations. Most beans in Montcalm County were sprayed in 2009, but those left untreated had significant damage.

Historically, WBC was a pest in the western Corn Belt. It has steadily spread from west to east, and has rapidly moved across the Corn Belt in the last 10 years. Unlike other cutworms, WBC is a late-season pest. It feeds primarily on corn ears, chewing and scarring kernels, and predisposing the ear to fungus and mold infections.

One generation of WBC occurs each year. Moth emergence usually begins in early July. Detection is generally more difficult in dry beans than in corn. In corn, the pest is usually eye level, but in beans, scouts basically have to crawl around on the ground to detect it because eggs are laid in area of dense bean foliage on the lower surface of leaves.

Typically, the pest is attracted to fields in which corn is tasseling or near tasseling and fields that have hybrids with upright leaf characteristics.

Dry beans are particularly attractive to WBC if neighboring cornfields have already tasseled. Larvae chew holes in pod walls and developing seeds. Most feeding occurs on cloudy days or at night.

If WBC development is not complete, as beans are pulled larvae may congregate under the windrow, feeding on pods and seeds until harvest. After hatching, larvae feed on host plants for about 31 days. When a larva finishes feeding and complete development, it drops to the ground and burrows into the soil where it overwinters, to begin the cycle again the next year.