The black cutworm, Agrotis ipsilon Hufnagel (Lepidoptera: Noctuidae), is a common insect pest in turfgrass throughout Louisiana. It does the most injury to turfgrass in the larval stage as a caterpillar before maturing into an adult moth. Larvae emerge from underground burrows in the soil at night to chew on grass leaves and stems. Injury occurs as small, sunken dead patches in the turf. Black cutworms can be active all year, and turfgrass injury is commonly observed in early spring.
In Louisiana, the black cutworm can complete five to six overlapping generations in a year. Females lay eggs on the tips of grass blades, and larvae hatch from eggs within several days, depending on the temperature. The larval stage lasts 20 to 40 days until pupation occurs and the pupae become adult moths. Mature larvae are thick and robust, measuring about 2 inches in length. They range from gray to brown to black in color and have a light-gray underside. It is common for cutworms to curl into a C-shaped ball when disturbed. They can spread through the lawn by crawling.
Cutworm adult moth
Black cutworms are burrowing, nocturnal insects and are rarely seen during the day.
Turfgrass injury typically occurs as small, sunken circles of dead grass.
Cutworms can be active all year long in Louisiana, but injury typically begins to appear in April.
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Use the flush test to determine whether certain insects are present in the lawn. Mix 1 tablespoon of lemon-scented soap per 1 gallon of water. Slowly pour the soapy water onto healthy grass surrounding the injured areas. In wet conditions, drench a 1-square-foot area with soapy water. In dry conditions, drench a 4-square-foot area. Then, for five to 10 minutes, closely watch the area to see if insects come to the surface. Repeat as desired in other areas to better determine insect presence.
One way to reduce insect injury and accelerate turfgrass recovery is to maintain a healthy lawn through proper cultural practices. Never apply more than 1 pound of nitrogen per 1,000 square feet per application, and always follow soil test recommendations for proper fertility. Irrigate as needed while taking rainfall into account. Mow regularly, but never remove more than one-third of the leaf blade height at one mowing. Thatch can develop over time and may need to be reduced through vertical mowing. Compaction can form more quickly on finer texture soils and in areas where there is high traffic. Dethatching or aeration need to be performed in late spring to summer when the turfgrass is actively growing. Properly maintaining a lawn through these cultural practices promotes dense and vigorous turfgrass and can increase tolerance to insect injury.
In addition to cultural practices, insecticide applications may be required to achieve effective insect control. Treat with insecticides when cutworm injury is excessive or large numbers of larvae are found during the flush test. When using any insecticide, you must follow the manufacturer’s labeled directions concerning all application parameters.
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For more information regarding insecticides for turfgrass insect pests, please reference the Louisiana Insect Pest Management Guide.
Download here: Louisiana Home Lawn Series: Black Cutworm 3624-L
Figure 1. Merle Shepard, Gerald R.Carner, and P.A.C Ooi, Insects and their Natural Enemies Associated with Vegetables and Soybean in Southeast Asia, Bugwood.org
Figure 2. James Kalisch, University of Nebraska, Bugwood.org
Figure 3. Adam Sisson, Iowa State University, Bugwood.org