Cutworms and Wireworms
Saturday, February 2, 2002
filed under: Insects
Cutworms and Wireworms
No-till may increase early season damage potential
Cutworms and wireworms can be a crop pest that growers should watch for early in the growing season, particularly in a no-till system.
Terry Gregoire and Frank Sobolik, area extension agronomists for North Dakota State University and Colorado State University, respectively, write in their online guide to no-till basics (which can be found on the web site of the Manitoba-North Dakota Zero Tillage Farmers Association, (http://www.mandakzerotill.org/) that “economically important insects that may increase in a no-till system are grasshoppers, cutworms, wireworms, and wheat stem sawfly... crop monitoring for insect activity is a necessary part of minimum and no till production.”
This should not come as a surprise, since these insects with often feed or lay their eggs where there is a lot of plant residue. Jan Knodel, crops specialist at the North Central Research Extension Center, Minot, N.D., says she has heard of some producers who suspect Spartan or other pesticides for cutworm or wireworm activity in sunflower, when in reality, it is more likely to be caused by the increased crop residue of a no-till system. Of course, that risk should be taken in context with the benefits of no-till, including soil and water conservation, increased yield potential in arid conditions, and savings in time and cost of primary tillage operations.
Wireworm and cutworm populations in wheat stubble or other crops can carry over to the subsequent sunflower crop, and cause early-season damage. “Cutworm problems are more variable, depending on weather conditions. Wireworms seem to be a problem somewhere every year. We’ll see poor stand establishment somewhere just about every year. Sometimes that’s moisture related, but part of it often too are wireworms,” says Roger Stockton, extension crops and soils specialist, Kansas State University, Colby.
Knodel says wireworm larvae are hard, smooth, slender, and wire-like, varying from 2 to 1½ inches in length when mature. They are a yellowish-white to a coppery color with three pairs of small, thin legs behind the head. The last body segment is forked or notched. Adult wireworms are bullet-shaped, hard-shelled beetles that are brown to black in color and about ½ inch long. The common name “click beetle” is derived from the clicking sound that the insect makes when attempting to right itself after landing on its back.
Cutworm (army cutworm) larvae attain a length of 1½ to 2 inches. They are pale greenish-gray to brown with the back pale-striped and finely mottled white and brown coloration but without prominent marks. Skin texture consists of fine, close-set, irregular granules. They are more plump and softer-bodied than wireworms. The army cutworm becomes a moth as an adult, with a wingspan of 1½ to 1¾ inch. The forewings are dark gray-brown with a number of distinct markings. The hind wings are light gray-brown with a whitish fringe.
Wireworms have a longer life cycle than cutworms, and usually feed on roots and germinating seedlings below ground. Wireworms prefer more moist, cooler soil temperatures (50-55 degrees F) and move deeper into the soil if soil gets too dry and when soil temperatures become too hot (>80 F).
Cutworms usually feed above ground on young plants at night. Cutworm damage consists of young plants chewed off slightly below or at ground level. When checking fields for cutworms during the day, dig down into the soil an inch or two around recently damaged plants, where larvae are likely to be found.
Early-season prevention and scouting is critical for managing both insects. Currently the only insecticide registered for wireworm in sunflower that provides effective suppression is Lindane, as a seed treatment. Several products are available for controlling cutworms: treatment is warranted when one cutworm or more is found per square foot, or when a stand reduction reaches 25 to 30%.
More information on wireworms from NDSU can be found online at http://www.ext.nodak.edu/extpubs/plantsci/pests/e188-1.htm and on the army worm and army cutworms at http://www.ext.nodak.edu/extpubs/plantsci/pests/e830w.htm –Tracy Sayler