western rootworm silks 2 MER copy.jpg

Western corn rootworm adult


  • Adult: Small yellow bug with three black stripes on the forewings.
  • Larvae: Slender, about ½" long and white with a brown head and dark spot on the posterior end.
  • Eggs: White, football-shaped and very tiny. 

Timing of damage: V8 to R5

Type of damage: Larvae feed on and tunnel into roots. Adults feed on and clip corn silks.

Scouting: For larvae, dig up 10 randomly chosen plants and check soil for rootworms. For adults, 
count the number of beetles on five plants each in five separate locations.

Economic threshold: For larvae, treat if two or more are found per plant. For adults, treat if silks are clipped to ½" or less before 50% of plants have been pollinated when beetles are present.

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