Cutworms (for sweet and high-biomass sorghum)

Julien Beuzelin, Attaway, Denise, Ensley, Carlen  |  9/8/2014 9:42:09 PM

Cutworm larvae feed on existing winter vegetation until it is removed or decomposed to a point no longer adequate as a food source. If present at planting, cutworm larvae may threaten stands of emerging crops.

Biology

The eggs are round, pearl-white, laid in mass on the ground or on the surface of the leaves and covered with yellowish brown hairs. The newly hatched larvae are greenish with a dark longitudinal band on each side. They gradually turn brownish black as they mature. The fully grown larva is stout and cylindrical measuring 30-50 mm in length. The pupae are reddish dark brown. The adults are brown moths with greyish brown forewings patterned with wavy markings, and the hind wings are transparent with a brown narrow band along the outer margins.

Damage
Cutworm damage occurs most frequently following legume cover crops or in reduced tillage systems. Cutworms may become established on existing vegetation and move to emerging plants once this vegetation has been killed. These insects can greatly reduce the stands of seedling crops by cutting down young plants at the base.

Management
Pest managers and producers should scout fields and identify those situations that may result in pest problems. Fields should be considered “high risk” and managed with preventive pest management methods if winter vegetation remained in the field until just prior to planting. Destroying all green vegetation at least 21 days prior to planting reduces the likelihood of cutworm attack. Treat when cutworms are damaging stand. Infestations may be spotty within a field and only require treatment where damage and live cutworms are found. At-planting insecticides applied in a band (no less than 10 inches) may be justified if vegetation has not been burned down at least 21 days prior to planting.

LSU AgCenter entomologists recommend that winter vegetation be completely dead at least three to four weeks prior to planting. Cutworms are able to feed on decaying vegetation; therefore, herbicide application five to six weeks prior to planting is preferred.

An effective IPM strategy for cutworms should include weed-free seedbeds well in advance of planting, optimal application dates for agronomic practices, and discriminate use of preventative and reactive chemical control strategies for pest problems.

Insecticide Options
Contact your local LSU AgCenter office, or go to www.lsuagcenter.com, for insecticide options for your region. Or check the LSU AgCenter's 2014 Louisiana Pest Management Guide.

Sources:

Leonard, B.R. (2012). Louisiana Conservation Tillage: Chapter 5: Arthropod Pest Management. LSU AgCenter.
Guidry, K., Kruse, J., Boquet, D. & Leonard, B.R., Levy, R., Miller, D., Overstreet, C., Padgett, B., Stephenson, D. & Williams, B. (2010). Louisiana Crops Newsletter: Cotton, Corn, Soybeans, Sorghum, 1(1).
Stewart, S., & McClure, A. (2013). PB1768 2013 Insect Control Recommendations for Field Crops.
Vasquez, E. & Amante, V. Armyworms and cutworms.
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