Scouting for Cutworms in Winter Wheat Back »

Written collaboratively by Adam Varenhorst, Ruth Beck, Patrick Wagner, and Amanda Bachmann.


Winter Wheat: Common Cutworm Pests

We have not received any reports of cutworm issues in winter wheat yet this spring. However, it has been a cooler spring compared to 2016 when cutworms were causing issues as early as mid-March. It is possible that cutworm emergence may still occur and scouting for these pests may be necessary. There are two species of cutworms that feed on winter wheat in South Dakota. The first species is the army cutworm (Figure 1) and the second species is the pale western cutworm (Figure 2). Both species are capable of causing economic injury to wheat if large populations are present in the spring. The caterpillars of both species are favored by warm spring weather. Extreme cold temperatures and limited snow cover during winter months can reduce the survival of these pests.


Army Cutworm

Profile
Caterpillars of the army cutworm overwinter in alfalfa and winter wheat fields. In the spring, the caterpillars emerge and begin feeding once temperatures warm up. Young caterpillars are small and generally a light gray-brown color with relatively few markings. As the caterpillars mature, they develop a dull gray or gray-brown body that may have mottling (spots or smears of varying colors). The older caterpillars will have several pale stripes that run the length of their bodies. Regardless of age, the caterpillars all have a dark brown head that may have some mottling.

Behavior
The army cutworm caterpillars feed at night and hide just below the soil surface during the day. Because scouting for the caterpillars can be time intensive due to sampling soil it is generally recommended to make management decisions based on detection of the characteristic plant injury. The feeding is characterized by “clipping” where the caterpillars feed on the plant near the soil surface. This type of feeding can result in patches of plants that appear to be cut or clipped. For winter wheat, the caterpillars tend to feed on the tender blades. Army cutworms generally do not feed on the stem, crown, or meristematic tissues, which allows regrowth of the plant to occur. In areas where caterpillars are abundant, they will move from food source to food source in large populations that appear to be marching in “army style”.

Management
Management is recommended if patches of the field have been clipped, or if 2-4 army cutworm caterpillars are observed per square foot. For insecticides that are currently labeled for army cutworm caterpillar management please refer to the current version of the South Dakota Pest Management Guide: Wheat.


Figure 1. Army cutworm caterpillar. Courtesy: F. Peairs, CSU, Bugwood.org
 


Pale Western Cutworm

Profile
As indicated by their name, pale western cutworm caterpillars have light gray-white colored bodies. The heads of pale western cutworm caterpillars range from light to dark brown with two distinct vertical lines present. The caterpillars also have characteristic dark spots on each body segment.

Behavior
The pale western cutworms overwinter as eggs and hatch in the spring when temperatures are favorable. The developing caterpillars feed on plants near the soil surface. Unlike army cutworms, pale western cutworms feed through the stem and cause plants to die. Pale western cutworms are not usually observed until later in the spring, causing them to be considered more of a pest of spring wheat. However, they can be an occasional pest of winter wheat if the weather permits.

Management
Management is recommended if 1-2 pale western cutworm caterpillars are observed per square foot.


Figure 2. Pale western cutworm caterpillar. Courtesy: F. Peairs, CSU, Bugwood.org


References:

  • Blodgett, S. and J. Kieckhefer. Insect pests of wheat. In Clay D. E., C. G. Carlson, and K. Dalstead (eds). iGrow Wheat: Best Management Practices for Wheat Production. Pp. 191-205
  • Michaud, J. P. and R. J. Bauernfeind. 2014. Kansas Crop Pests: Army cutworm. MF3150. K-State Research and Extension, Kansas State University Agricultural Experiment Station and Cooperative Extension Service.
  • Varenhorst, A. J. 2017. Foliar insecticides in wheat. In Bachmann, A. (ed). South Dakota Pest Management Guide, Wheat: A guide to managing weeds, insects, and diseases. Pp.
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