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Western Bean Cutworm Egg Masses, Larvae Found in Ohio

Agriculture.com Staff 07/25/2010 @ 11:00pm

For the first time since the trapping of Western bean cutworm moths in corn began in 2006, Ohio State University research entomologists have identified egg masses and larvae. The find reveals that populations continue to increase and that growers will need to monitor the pest in the future.

“The infestation of egg masses and larvae was light, but this just verifies that we won’t see this pest decreasing in the coming years, and growers will really have to start scouting for it each season,” Andy Michel, an OSU entomologist with the Ohio Agricultural Research and Development Center, says in a university report.

Western bean cutworm is a common pest of Western corn-producing states that is rapidly expanding eastward and finding a niche throughout the Midwest. The number of adult moths trapped in Ohio each year has been steadily increasing.

In 2006, entomologists caught three moths in the traps. In 2007, six were caught. That number jumped to 150 in 2008 and to 550 in 2009. This year, that number has skyrocketed to 1,834 through July 20.

“We’ve more than tripled what we caught last year and the season is not over yet,” Michel says. “We still have a least a month to go for adult moth flights.”

The data suggests that Western bean cutworm will continue to spread across Ohio and increased feeding damage is likely. The larvae mainly feed on the corn ears, nibbling on the tips and boring into the middle of the ear, impacting kernel quality and affecting yields. Feeding damage can also create opportunities for disease development.

“Indiana saw damage in 2007 with economic damage following shortly thereafter. In Michigan, the first damage was found in 2007 and economic damage occurred in 2009. In Ontario, Canada, the first moth was caught in 2008, and the first damage was found last year,” says Michel. “Significant damage hasn’t been found yet in Ohio, but we know it’s coming. All the data suggest we’ll see some level of damage soon and it will most likely first occur in northwest Ohio.”

Western bean cutworm moths emerge in Ohio as early as June with peak flight around mid-July. The adult moths lay eggs on corn plants with the larvae hatching out in mid-August and developing through September. They mainly feed on the corn ears, drop from the plant in the fall, overwinter in the soil and emerge as adult moths again the following spring.

Entomologists have established a scouting protocol for identifying egg masses, as well as a threshold for treatment.

“The best time to scout for egg masses is before the corn has tasseled. The females prefer pre-tasseled corn and once that corn tassels, they tend to just fly around looking for a suitable host,” says Michel.

When scouting for egg masses, inspect 20 plants at five different locations in the field. The economic threshold for treatment is 5 percent of plants that have egg masses or larvae.

“Timing of egg scouting is critical,” says Michel. “If you are over the threshold and need to apply chemicals, you really need to time it when the larvae are hatched but before they enter the ear. Once they enter the ear, they are protected.”

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