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Armyworm on the march in parts of southwest Ohio
Ohio Farm News
By Steve Bartels

Armyworm is a common pest in Ohio, but it usually is not a severe problem because numbers are not commonly great. That is unless you have an outbreak, which has happened in a couple of fields in the county this spring.

The worms were first found on June 3 in a grass hay field in unbelievable numbers. As they crossed the lane to move into another section of the field, they actually made the tires of the tractor slimy when it drove over them.

These large numbers are usually limited to fields of rye or an old grassy alfalfa field. Wheat is not one of their preferred crops. They can be found occasionally in wheat in large numbers however, as they were on June 7. The feeding of the larvae is on the margins of the leaf.

They feed until there is nothing left but the stems. As the leaves disappear, they begin to feed on the stem, cutting heads of wheat. The treatment threshold on wheat is six larvae per foot of row, or 18 per two square feet. Even if there are less than 18 larvae per two square feet, rescue treatment should be undertaken if heads are being clipped. It is not common for the larvae to clip heads because, just as they did in our local field, they would eat most of the leaves off before they clipped the head.

As the wheat begins to turn color, the leaves are less succulent and less attractive to the larva to eat. The insects start to move to look for better pasture. If there is a nice green early whorl stage or younger corn crop next to the wheat, they can do substantial damage in a very short period of time.

During the heat of the day, the armyworm will be hiding in the ground residue or in the central whorl of the corn. You may first notice the ragged marginal feeding on the leaves instead of the larvae themselves. A full-grown larva will reach 1.5 inches. That size worm can eat a lot of leaf surface in a day.

Check your wheat fields to make sure they are not damaging that crop. As the wheat begins to dry down, you will want to check nearby cornfields closely. If you can catch them just as they are entering a field, it is usually not necessary to spray the whole field.

You spray the edge of the field, setting up a chemical barrier. If an area of the field is showing 50 percent of the plants damaged and the larvae are an inch or less long, rescue treatment should be applied immediately.

There are a number of products labeled for use on corn or on small grain. Be sure to watch the harvest interval if you need to spray your wheat. You don’t want to use a product that is going to delay your harvest.

If you have not encountered any problems with the insect by late June, you are probably out of the woods.

This farm news was published in the June 21, 2006 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee.