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Size Matters for Cutworm Control (06/13/19)

Cutworm damage is starting to show up in the emerging field crops including alfalfa, canola, chickpea, field pea, lentil and sunflower.

Cutworm damage is starting to show up in the emerging field crops including alfalfa, canola, chickpea, field pea, lentil and sunflower. Cutworm larvae are difficult to scout for since they feed at night and hide underneath clumps of soil during the day. Cutworms are feeding more with the warm temperatures, causing cut plants, defoliation and stand loss. Now is the time to get out and scout for cutworms when crops are young, the most susceptible stage.

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. A mature dingy cutworm is about 1½ inch and the size of a pencil in width. The next life stage, pupa, can also be found in the soil and is a non-feeding stage. The adult moth will emerge from the puparium.

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Scout fields regularly by looking for freshly damaged (or cut off) plants or defoliation, digging 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, field pea and sunflower, are more susceptible to cutworm damage than small grains, because cut plants do not grow back (grains compensate by tillering). If a ‘rescue’ 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
  • Pea / Lentil – 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

Before pulling the trigger, look at the size of the cutworm larvae. If the majority of the larvae are small, <¾ inch, they still have a lot of crop feeding to do before maturity, so an insecticide treatment will be necessary when you are at or above the action threshold. If you are finding a mixture of some small cutworms, many large cutworms and some pupae, it may be too late for a foliar insecticide application since the majority of the larvae are mature (finished feeding) and/or pupating (non-feeding stage). 

For insecticides registered for cutworm control by field crops, please consult the 2019 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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