NDSU Extension - Mercer County


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Scout for Grasshoppers and Armyworms in Wheat

grasshoppers in wheat, armyworms in wheat, pest management

 Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

The current wet and humid weather along with increased temperatures has provided the perfect environment for insects to breed and develop. Producers are strongly encouraged to scout fields. The moisture greatly improved our potential to reach above normal yields this year so do not let insect pressure limit the potential.

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.

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).

Source: Janet Knodel – NDSU Entomologist – janet.knodel@ndsu.edu



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