Several species of cutworms can irreversibly affect sunflowers from slightly below the soil surface through the V4 stage by cutting off the tender plant below or right at the cotyledon. If the damage is limited to only leaf tissue above the cotyledon, the plant can usually escape without any yield loss.
FACTORS TO CONSIDER
• Check south facing slopes first because cutworms like warmth.
• Check areas that border grass/pasture first or areas of a field with weed issues from the fall.
• Look for bare patches in a field or a line of missing plants.
• Look for cutworms during the day below the soil surface or underneath stubble.
• Take note of the size of the cutworm (larger ones close to 1½ inches will pupate soon).
1. The economic threshold is 25-30 percent stand reduction or one small larvae per square foot.
2. Many insecticides work well, and spraying towards nightfall is more effective.
Make sure to check your sunflower fields this spring shortly after planting for cutworms. Once a plant is cut below the cotyledon, it will not come back.