Legend Seeds Blog

Cutworms in Sunflowers

When everything looks great from a distance, don’t forget to get out of the pickup and check your sunflower fields for cutworms this time of year. Sunflowers can have irreversible damage in the seedling stage from several species of cutworms. Damage is caused by cutting off the seedling, sometimes below the cotyledon or before they even emerge out of the ground. As the plant matures, damage moves to the leaves and the plant is typically able to recover (V4-V6 stage).

 

Dingy CutwormsDingy Cutworms
Photo Credit: SDSU iGrow
taken by J. Gavloski, MAFRI
Redback and Darksided CutwormRedbacked Cutworm (left
Darksided Cutworm (right)
Photo Credit: Agriculture Canada
Sunflowers damaged by cutworms at the soil surfaceSunflowers damaged by cutworms
at the soil surface.
Cutworm damage at V4 stageCutworm damage at V4 Stage

Here are some key factors to consider for cutworms in sunflowers:

  • Damage can first be noticed by bare patches in a field or several missing plants in a row.
  • Generally, cutworms can first be found on warmer south facing slopes, areas that border grass/pasture or a spot in the field that has weed issues the year before.
  • Scouting towards the evening can be helpful, otherwise look underneath the soil surface or stubble during the day.
  • When a row is missing plants, start by looking near the next undamaged plant for the cutworm.
  • Take note of the size of the cutworm. Small larvae pose the greatest potential for damage as they continue to feed and grow. Larger cutworms, 1.25” to 1.5” (depending on the species) are close to pupating and feed less.

Action Plan

  1. Economic threshold is when you have a 25-30% stand reduction or when there is one small larva (1 inch or smaller) per square foot.
  2. Several insecticides work well if cutworms are feeding on the surface.
  3. Spraying towards nightfall is best.

Summary

To minimize stand loss in the spring, scout for cutworms through at least the V4 stage. Once a plant is cut below the cotyledon it will not come back.

Sunflowers at V4 and V6 stages

Resources

https://www.ag.ndsu.edu/extensionentomology/recent-publications-main/publications/A-1331-sunflower-production-field-guide
Compendium of Sunflower Diseases, 2016