Crop & Pest Report

Accessibility


| Share

Scout for Grasshoppers and Armyworms in Wheat (07/12/18)

Isolated hot spots of grasshoppers and armyworms were reported in wheat from southeastern ND. Some fields needed to be treated with insecticides.

Scout for Grasshoppers and Armyworms in Wheat

Isolated hot spots of grasshoppers and armyworms were reported in wheat from southeastern ND. Some fields needed to be treated with insecticides.

With the recent thunderstorms, it is not surprising that armyworms were blown into ND, since this insect pest does not overwinter in ND. The University of Minnesota Extension also has reported armyworms in wheat in southwest Minnesota (Source: Bruce Potter, Extension IPM Specialist).

Full-grown larvae are green-brown, longitudinal stripes on sides and head is brown. They grow to a length of 1½ to 2 inches. Field scouting for armyworms should be done in field margins, low areas with vigorous plant growth, and areas where plants have lodged. Indications of armyworm feeding include leaf defoliation, worm frass (droppings) around the base of plants, and defoliated leaves in lodged areas of wheat fields. Larvae complete feeding in 3 to 4 weeks, staying in the area where they hatched until they run out of food. If all food is consumed, larvae often move in hordes or “armies,” eating and destroying vegetation as they move.

For proper pest management, it is important to scout and control armyworms while they are small larvae and before extensive feeding damage has resulted. Mature larvae that have completed their feeding are more difficult in terms of both control and economic return. Late spraying for armyworms is often referred to as “revenge” spraying, since the crop damage has already been done and no economic benefit is realized.

Look for larvae beneath plant debris around the base of plants and on heads of wheat or barley. Since armyworms feed at night, spray in early evening and use adequate water volume to get the insecticide into the crop canopy (3-5 gallons per acre by air). The current economic threshold is 4-5 armyworms per square foot in wheat or barley.

Grasshopper hot spots were reported earlier in the June 14th issue and June 28th issue of the Crop & Pest Report.  For grasshopper action thresholds, use the following:

  • In adjacent non-crop areas:  50 - 75 small nymphs per square yard (or 6 - 8 nymphs per square foot), or
  • Within the field:  30 - 45 nymphs per square yard (or 3 - 5 nymphs per square foot).

 jan 3

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

USDA logo

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.