Armyworms in Wheat

Armyworms in Wheat

Armyworms in wheat reports and observations have started to come in this week, mainly from the northern and eastern parts of Grant and Garfield counties. I have seen at least three fields in eastern Grant that had a significant enough population to warrant an insecticide application.

Armyworms feed at night and hang out under residue on the ground, in the shade during the day. Most years we usually find them under lodged or downed wheat. If the populations are high enough or the day is cloudy you can find them on the wheat heads. Another indication of their presence is a significant amount of “frass” or worm poop under the plant.

They start working on the lower leaves and move upward, but at this time of year they have made it to the head, clipping the awns (beards) of the heads, sometimes clipping the heads off of the plant, and finally digging into the grains themselves. It is at the head clipping, or grain digging, phase that significant yield loss can occur. The economic threshold is usually reported at 3 to 5 per row foot.

Generally speaking they will be in fields where the moth deposited her eggs and not necessarily in every field, just where you were unlucky.

Armyworms are susceptible to many natural enemies and are often controlled by them. Mainly here that beneficial would be the parasitic wasp.

This wheat crop is almost to the end of this torturous season and is quickly reaching the point where it will not seem as appetizing to these worms. A producer should also consider the time between asking for an application and the time an application can be made. In past armyworm years when the applicators have been swamped by requests, by the time the application was made the worms had cycled out.

As always it comes down to economics and it can be a tough call. If the insecticide with application costs around $10.00/acre that is about 1.33 to 1.5 bushel. If heads are on the ground or the grain is missing from standing heads it might be worth an insecticide.

Producers should keep in mind the pre harvest interval that any insecticide applied might have.


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