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Indiana Black Cutworm Beginning to Cut the Plants

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Black cutworms are descending upon the Indiana corn crop and their cutting activity appears to have begun in the south. Purdue Extension says record numbers invaded the state from southern states about the third week of March.

Now with warmer weather, plus rainfall and corn in the ground, entomologist John Obermeyer says the pests are likely doing what they’re known for.

“We start tracking their development with heat unit accumulations, and we’ve seen that all of southern Indiana now is at the point where cutworms are large enough that they can actually be cutting, their namesake, the plants. And we’re now following that through into central Indiana counties as we see with the warmth, not only is the crop now taking off, but so are the cutworm larvae.”

Scouting fields is now an imperative to locate the presence of black cutworm and take appropriate action. Which fields are most likely to be infested?

“Well there’s no question that the female moth is going to be attracted to fields that formerly had some type of weedy annual growth in them to lay her eggs. Those are definitely the high risk situations that we would encourage producers to get out and look in, even if those weeds have been dead for some time now. The eggs took some time to not only hatch but for the larvae to develop, and by that time the crop may be emerging, and that’s when the problems occur. The larvae have to feed on something and they certainly will on corn and even soybeans in many cases.”

Obermeyer says to control the insect scout early and often and apply insecticides when larvae are small. Large larvae are difficult to control. He added that producers may have a false sense of security with seed-applied insecticides or Bt-corn but, as was seen last year, those technologies don’t stand up to the severe infestations that are possible this year.

“Scout by inspecting 20 consecutive plants in each of five areas of a field for cutworms and feeding activity,” he said. “Be sure to check areas that had an accumulation of weedy growth before or at the time of planting.”

Obermeyer also said growers need to collect black cutworm larvae to determine the average instar, or development stage.

“A foliar, rescue insecticide may be necessary if 3 percent or more of the plants are damaged and black cutworm’s average larval instar is 4-6,” he said.

A larval instar guide is available inside the front cover of the Purdue Extension Corn and Soybean Field Guide, available for $7 through Purdue Extension: The Education Store.

Pheromone trap reports and updated heat accumulation graphics are available in Purdue Extension’s Pest and Crop Newsletter.

(Purdue Entomology photo/John Obermeyer)[audio:http://www.hoosieragtoday.com//wp-content/uploads//2012/05/2012-black-cutworm-update.mp3|titles=2012 black cutworm update]