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Scout for Cutworms (06/07/18)

Cutworm damage is starting to show up in the emerging field crops. Cutworm larvae are difficult to scout for since they feed at night-and hide underneath clumps of soil during the day.

Scout for Cutworms

Cutworm damage is starting to show up in the emerging field crops. Cutworm larvae are difficult to scout for since they feed at night-and hide underneath clumps of soil during the day. With the warm temperatures, cutworms are feeding more. Scouting for cutworms is good insurance to prevent plant stand loss and maybe yield loss. This week, dingy cutworms were found reducing soybean plant stands to the point of needing to reseed the entire 40-acre field located in southeastern Cass County.

Cutworms generally have one generation a year. Dingy cutworms overwinter as partially mature larvae (or caterpillars) and then larva develop into a pupa (or resting non-feeding stage) in mid- to late June. The adult moth emerges from the puparium in July and moths lay eggs in late August into the fall. Eggs hatch into larvae that feed in the fall before burrowing deeper into the soil to overwinter. Most of the dingy cutworms observed in the 40-acre soybean field were quite large, >¾ inch, and the size of a pencil in width. The next life stage, pupa, were also being found in the soil. So, it may be too late for effective insecticide control when the majority of the larvae are mature (1½ inch for dingy cutworm) and/or pupating.

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                For damage, cutworms will cut young plants and defoliate leaves (climbing cutworms). Cut plants can be found drying up and lying on the soil surface. As damage continues, fields will have bare areas where plants have disappeared, often in the same plant row as the cutworm moves down the row feeding on consecutive plants. In a severe infestation, the entire field can be destroyed.

                Scout fields regularly by looking for freshly damaged (cut off) plants, dig two or more inches down around the cut off plant, and search for cutworms (larvae). When disturbed, cutworms curl up into a ‘C-shape.’ Row crops, such as soybean, canola, lentils and sunflowers, are more susceptible to cutworm damage than small grains, because cut plants do not grow back (grains compensate by tillering). If a foliar insecticide treatment is warranted, an evening application is best since cutworms actively feed at night.

Action thresholds for cutworms in different field crops are:

  • Alfalfa – 4 to 5 or more per square foot (new stands – only 2/sq ft)
  • Canola – 1 per square foot
  • Corn – 3-6% of the plants are cut and small larvae (<3/4 inch) present
  • Peas / Lentils – 2 to 3 cutworms per square meter
  • Small grain – 4 to 5 cutworms per square foot
  • Soybean – 1 cutworm per 3 feet of row or 20% of plants are cut
  • Sugarbeet – 4-5% cutting of seedlings or 3-5 larvae per square foot
  • Sunflower – 1 per square foot or 25-30% of plants cut

For insecticides registered for cutworm control, please consult the 2018 North Dakota Field Crop Insect Management Guide E1143.

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.

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