NDSU Extension - Williams County


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Cutworms May 5th, 2016

Cutworms May 5th, 2016

North Dakota State University Extension Service puts out weekly reports called the Crop & Pest report. These reports start in May and go through early fall, which highlights all of the times where pests, diseases and stress factors can occur for plants. One article in this report is about Cutworms, more exactly the Army and pale western cutworms which have been reported feeding on winter wheat and weedy cultivated fields in northwest North Dakota.  The army cutworms larvae are gray to brown with the top darker than the bottom with a pale mid-dorsal line.  The army cutworm is a climbing cutwork that consumes the leaves of its host plant, the plant can recover from army cutworm feedings.  These cutworms are currently at the end of the development and feeding period, so no control is recommended. Army cutwork moths will emerge in June and fly to the Rocky Mountains for a time of inactivity, late August to October they will fly back to the plains to lay eggs in the soil.  The report states that army cutworms are primarily an early season pest of cereal crop, especially winter wheat. The pale western cutworm overwinters in North Dakota as eggs which hatch soon into larvae early in the spring, when temperatures warm up to 50 degrees F. These cutworms are about 1 1/2 inches long when mature, and pale yellow with a white mid-dorsal line and two black inverted "V;'s on head.  They feed on the plant stems below the ground, if the growing point is destroyed from the larva feeding, the plant will not survive.  Field scouting for cutworms is critical and should begin as soon as the crop emerges, then the fields should be checked twice a week until past the early growth stages.  Cutworm damage symptoms are foliar defoliation or cut/wilted plants which lead to open patches in a field.  Examining 100 plants per five sampling sites by walking a 'W' or 'V" patters for a total of 500 plants in a field is recommended. The economic threshold for cutworms varies by crop.  Here's some of the thresholds for North Dakota field crops: alfalfa- 3 to 4 larvae per square foot (new stands only 2 per square foot), canola- 1 larvae per 3 feet of row, chickpeas/Field peas/ Lentils- 2 to 3 larvae per square meter, Corn- 3-6% of the plants cut, Small grains- 4 to 5 larvae per square foot, soybean- 1 larvae per 3 feet of row, sugar beets- 3 to 5 larvae per square foot and sunflowers- 1 larva per square foot. There are several different insecticides that registered for cutworm control, consult the 2016 North Dakota Field Crop Insect Management Guide for more details on insecticides.

Danielle Steinhoff

County Agent Update


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