The Armyworm Attack of 2008
What’s up with all the armyworms?

By Mike Stanyard

This year will definitely go down as the year of the armyworm in western New York. I received the first report of armyworm in wheat from Niagara County on June 11, and I was still finding them in corn in Wayne County on July 10.

Those first common armyworm (CAW) infestations arrived on early storms that hit Niagara and Orleans counties. This was evident by the advanced development and damage that wasn’t found in counties east of there.

Over the next two weeks, reports began to come in from adjacent counties all the way down to Seneca and Yates. New York wasn’t the only stop for armyworms this year. Along its journey northward, armyworms in high numbers infested grass and wheat fields in Kentucky, Illinois, Indiana, Ohio and Michigan.

Why now?
The most common question I get is “Why was it so bad this year?” To answer that, we need to go back to where the moths originated. CAW doesn’t overwinter in New York. Like its cousin the black cutworm, it overwinters in the south and migrates north each spring on storm fronts.

The vast wheat and hay fields in western New York are excellent homes for the moths, which like to lay their eggs in thick green vegetation. We can find small populations of CAW every year in New York, but outbreaks like this are uncommon. The last one occurred in 2001.

Armyworms are usually kept in check by a number of natural controls, such as a large predaceous tachinid fly. But not this year! For some reason the fly didn’t arrive in time to take out the armyworm. The large CAW population was allowed to feed unchecked by natural enemies, and severe damage occurred mainly in winter wheat. In some fields I counted as high as 20 CAW per square foot; we’re using five per square foot as a threshold.

This fly lays a small white egg just behind the head of the armyworm – I’ve seen as many as six eggs on one caterpillar. The egg hatches and the maggot burrows into the armyworm and feeds from the inside out. Not a pretty death but justifiable to those who had to spend $20 per acre to prevent CAW from decimating their wheat.

Consequence of CAW feeding

CAW feeds on the leaves of grasses, wheat and corn. The leaf feeding in wheat was substantial in some fields, and many sections were left with no leaves and still in the milk stage. Those plants will probably have lower test weights and, thus, be lower yielding. Wheat can continue to fill the grain with the green tissue left on the glume and stem. Therefore, wheat damaged in the early dough stage should have been able to complete filling.

Many thousands of acres of wheat and some corn and hay acres in our region were sprayed by ground and by air. With much of our wheat booked at historically high prices, spraying was justified. I think most of the wheat fields were sprayed in time to protect the yield potential. The majority of these fields still had at least the flag leaf to continue grain development.

Wheat harvest began over the July 4 weekend. And many of us are anxious to see how this year’s wheat crop survived the Armyworm Attack of 2008.
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