True armyworms making annual migration through Missouri

Thursday, May 22, 2014 | 11:47 a.m. CDT

COLUMBIA — True armyworms have begun their seasonal march through southern Missouri and are expected to move northward as the year progresses, said Wayne Bailey, an MU Extension associate professor of entomology. This could potentially be bad news for local farmers who are growing corn, wheat or fescue, a type of grass crop.

True armyworms migrate with the assistance of strong winds and storm systems, which carry them from southwestern portions of the country into more northeastern regions. They usually arrive in Missouri during the first week of April and supplement the resident population, Bailey said.


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First generation larvae cause the most crop damage in May and June. They primarily target wheat and fescue, but also might feed on corn and grain sorghum. True armyworms can defoliate and destroy entire fields, Bailey said.

"If there are enough of them, they can eat all the foliage," he said.

These unwanted pests operate in cyclical patterns, with major outbreaks occurring once every four to five years. The larger outbreaks are known as economic infestations; the last one took place in 2009. That year, true armyworms swarmed fields, ravaged crops and even caused the cancellation of a Royals game, Bailey said.

True armyworms have already been confirmed in both Ozark and Douglas counties in southern Missouri, said Jill Scheidt, an MU Extension agronomy specialist. A crop consultant also reported an infestation in Golden City.

Bailey recommends scouting crops for infestation during early morning or late evening hours. Typically, true armyworm larvae are inactive during the day and tend to feed at night. Bailey also urges farmers to check their crops several times a week, from top to bottom.

Infestations reach threshold levels when at least four true armyworms are found per square foot or when at least 2 percent of crop heads have been clipped by farmers, Scheidt said. When threshold levels are reached, there are two suggested courses of action: spraying insecticides or harvesting early, Bailey said.

True armyworms can wreak havoc on farming operations. About 2006 or 2007, an infestation hit north-central Missouri and ate all the fescue in 12 counties, Bailey said.

This year, however, might not bring such a major outbreak.

"It's not near as bad as what we've seen in the past," said Stacy Hambelton, MU Extension agriculture business specialist.

Hambelton farms in Ozark County and once found true armyworms in his fescue. They ranged in size from a quarter-of-an-inch to an inch, he said.

"You could tell they had eaten a bit," he said. But, fortunately for Hambelton, infestation threshold levels were not reached.

Hambelton only knows of one farmer who has been forced to spray insecticides so far this year. The problem, he said, is that true armyworms are unpredictable and their distribution has no set pattern from year to year. You may have one person with severe damage and another person half-a-mile away with none, he said.

Bailey remained cautious about this year, however. We're about due for a major outbreak, he said.

Supervising editor is Mary Ryan.

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