Watch for cutworms

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Black cutworms are “right-on-time” this year. Trap catches to the south of Michigan have been high (to see what is happening to the south of us, visit the Chat’n Chew cafe web site which links to newsletters from Illinois, Indiana, and Ohio

Adult black cutworm moths migrate into Michigan in early spring. Before the crop emerges, adult moths lay eggs on available vegetation in field margins and ditches, on cover crops within the field, and especially on low, densely growing weeds. When the weeds or cover crops are killed by herbicide, larvae move onto the nearest green plants, often the crop. Small larvae initially feed above-ground, making small pinholes in the leaf or chewing on the leaf edges. Bigger larvae feed near or below the ground, cutting off plants at the base. Cut plants are wilted or simply dead.

Effective weed control avoids or reduces black cutworm infestations. Controlling low lying, densely growing weeds such as chickweed, deadnettle and mustards reduces the areas for moths to lay eggs. If weeds or a cover crop can be killed a week or two before crop emergence, most cutworm larvae will starve. Over the last few years, there have been spotty cutworm infestations in corn, soybeans and sugar beets, perhaps because of earlier planting or changes in production practices to no-till. Also, with the use of herbicide-resistant crops, fields may be weedier early in the season before glyphosate is applied. Scout for cutworms at seedling emergence. Look for wilted or cut plants, and dig around the base of nearby seedlings to find the larvae. If you can’t find cutworms near a damaged plant, move down the row to the next apparently undamaged plant. Larvae feed at night and hide during the day, so the best time to look for larvae is in the early morning.

A general threshold is 5 percent or more of plants showing cutworm damage. Rescue (foliar) insecticide treatments are the preferred way to manage cutworm because few fields will have a significant problem. Insecticides are most effective if sprayed in the evening when the cutworms are active. In crops like corn, beans and alfalfa, pyrethroids such as Ambush, Baythroid, Mustang, Pounce, and Warrior are particularly effective against cutworms (check labels for specific crop registrations and rates). For sugarbeets, options include Asana, Declare and Lorsban. As usual, be careful when adding an insecticide to a micro-rate herbicide application for beets.

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