By: Alison Pokrzywinski | Nuseed Sunflower Product Manager
Now that the seed has been planted, fields have been fertilized, a pre-emergent is applied and the perfect amount of rain has fallen to activate it, this means you can finally go fishing now!? Wrong.
Sunflowers can have irreversible damage in the seedling stage by cutworms if you are not monitoring your field until they reach 4 to 6 inch leaf stage. They cause damage by cutting off the seedling, sometimes below the cotyledon or before they even emerge out of the ground. Dingy, red-backed and dark-sided cutworms can all damage sunflowers and each reaches a different maximum length before pupating. Damage can first be noticed by bare patches in a field or by walking in a field and noticing missing plants in a row. For scouting check south facing slopes first (the soil warms up faster) and fields that border a lot of grass or that had weed problems in the fall. They feed at night so checking fields closer to dusk is often more productive. If you can’t make it out to the field at 9 pm, no worries, try looking underneath the soil surface near the plants or underneath stubble. I find bringing along a little garden shovel can help. Economic threshold is when you have 25-30% stand reduction or when there is 1 small larvae per square foot (1 inch or smaller). Several insecticides work well (see your local agronomist) and spraying towards nightfall is best.
Dingy cutworm: Larvae are dull brown mottled with cream color. A pale stripe runs on the middle of the back with diagonal markings on either side.
Redbacked cutworm: Larvae are dull brown to gray with two dull reddish stripes along the back.
Cutworms can cut the sunflower below the cotyledon, killing the plant. This can occur either above or below the soil surface.