• Four species of adult corn rootworms can affect kernel fertilization
• Adult corn rootworms feed on green silks and can prevent silks from capturing pollen
• In commercial corn fields, large beetle populations (≥ 20 per plant) are necessary to cause economic damage and to justify an insecticide application
• In seed production fields, as few as 1 to 5 beetles per plant feeding on green silks and kernels can reduce seed quality and grain yield (see economic thresholds section below)

• Adult corn rootworms feeding on green silks and immature kernels:
    
  • reduce number of kernels per pound
  • reduce number of kernels per acre
  • increase round kernel fractions
  • decrease flat kernel fractions

Interesting Fact: Adult western corn rootworms live an average of 52 days (maximum 86) in the field

• Hybrids (commercial production fields)
• To justify the cost of chemical control and application:
  • Average of 20 beetles per plant, or
  •  Silks clipped back to within ½ inch of husk prior to 50% pollen shed
• Inbreds (seed production fields)
  • Plants drought or heat stressed
    •  1 to 3 beetles per plant feeding on green silks
  • Plants with optimum moisture and moderate temperatures
    • 5 beetles per plant feeding on green silks

*Reference: Culy, Edwards & Cornelius. 1992. Journal of Economic Entomology 85: 2440-2446.

• Crop Rotation    
  • Rootworm populations can be greatly reduced with rotation (except western corn rootworms in the “Red Zone” of northern Illinois and the southern corn rootworm in the southern U.S.)
• Planting Time
  • Plant early; late-planted and late-silking fields, (even first-year corn fields), can attract large numbers of beetles from neighboring fields
• Bt Corn
  • Hybrids and inbreds expressing a corn rootworm Bt trait will greatly reduce the number of larvae that survive to the silk-feeding adult stage; Bt corn does not affect the adult corn rootworms
• Insecticides
  • Numerous broad-spectrum and long-residual insecticides are labeled for beetle control