We received reports this week cutworms reducing sunflower stands in South Dakota. Cutworm caterpillars are an early season pest, and their feeding results in cut young plants and defoliation. Younger plants are at more risk for cutworm injury because their stems are smaller in diameter and may be fed all the way through by the caterpillars. While identifying the cutworm species and size can be important for determining management effectiveness, the management options are similar for all species.
Identification & Scouting
There are three species of cutworms that are reported as pests of sunflowers. These include the dingy cutworm, redbacked cutworm, and the darksided cutworm. All of the cutworm species listed are nocturnal feeders that hide in the soil during the day. These cutworms can be observed by using a hand trowel and digging in the soil near plants that show signs of defoliation or cutting. Cutworms may also be present under plant debris that is in the field. To scout for cutworms, walk in a “W” or “Z” pattern, and examine injured plants in five locations within the pattern. At each location, use the trowel to search a 1 square foot area within the row. Dig approximately 2 inches down, and carefully sift through the soil when looking for caterpillars.
The dingy cutworm caterpillars are approximately 1 inch when fully grown and are generally a grey to dull brown color. They have one observable pale grey line that runs down the center of their bodies (Figure 1). Dingy cutworms have already been observed in safflower and sunflower in parts of South Dakota this year.
These cutworms are approximately 1 inch long when fully grown and are dull gray to brown in color. They have two distinguishing red stripes present on their backs (Figure 2).
The darksided cutworm caterpillars are approximately 1 inch in length when fully mature. They have a pale brown back and lighter underside. These cutworms have numerous indistinct stripes present on their sides (Figure 3).
Insecticide management for cutworms should be considered if an average of 25 to 30 percent of the plants within the five scouted locations are cut, or if one caterpillar per square foot is observed. For cutworms, management after emergence can be achieved through the use of foliar insecticides. Please refer to the current edition of the South Dakota Pest Management Guide: Sunflower & Oilseeds for a list of insecticides currently labeled for cutworm management in sunflower. Management of cutworms often requires evening sprays to ensure residual activity for when the cutworms emerge. Spraying prior to a rain event may also assist in delivering the insecticide to the belowground caterpillars.