Scouting for Fall Armyworm

Pest Importance

  • Fall armyworm, Spodoptera frugiperda, is a minor pest of corn in the United States.
  • Economic damage is sporadic from year to year.
  • Fields at highest risk from injury are:

  • Fields planted to non-Bt hybrids without Lepidoptera control
  • Fields in the southern U.S. and Texas
  • Late-planted fields
  • Late-maturing hybrids
Photo: Early-stage fall armyworm larva

Early stage fall armyworm larva

Injury Symptoms in Whorl-Stage Corn

  • Early stage larval feeding:
    • Causes “windowpane” and shot holes in leaves
  • Late-stage larval feeding:
    • Causes elongate, ragged holes (see photo below)
    • May cut leaves in half
    • Injures developing tassel in VT stage
    • Plugs whorl with wet, yellowish-brown frass
Photo: Whorl-stage corn injury from fall armyworm

Whorl-stage corn injury from fall armyworm

Scouting for Fall Armyworm

  • Only larvae in whorl-stage corn can be controlled with insecticides; larvae in corn ears are protected
  • Scout for larvae in whorl-stage corn:

  • Select 20 consecutive plants in a row.
  • Inspect plants for feeding injury.
  • Confirm identity of pest species as fall armyworm.
  • Repeat 20-plant sample at 4 additional locations.
  • Determine percent infestations based on 100 plants.
  • Consider insecticide application when 20% of whorl-stage plants are infested with live larvae.

Identification of Fall Armyworm

Dark spots (tubercles) on dorsal surface arranged in "trapezoid" or when near the tail, in a "square" pattern. Spots are darkened in photo for emphasis.

Fall armyworms can be distinguished from similar corn caterpillars by 2 physical characteristics:

  • Inverted “Y” pattern on the front of a dark head (see next 2 photos)
  • Dark spots (tubercles) on dorsal surface arranged in “square” or “trapezoid” pattern (see third photo)
Photo: Similar caterpillar species found on corn (armyworm, fall armyworm and corn earworm.)

Similar caterpillar species found on corn (left-right): armyworm, fall armyworm
and corn earworm. The fall armyworm has an inverted "Y" pattern on the front of a dark head.

Photo: An inverted “Y” pattern on the front of a dark head identifies the fall armyworm.

An inverted "Y" pattern on the front of a dark head identifies the fall armyworm.

Photo: fall armyworm caterpillar on corn ear.

Dark spots (tubercles) on dorsal surface arranged in "trapezoid" or when
near the tail, in a "square" pattern. Spots are darkened in photo for emphasis.

Photos and Text
Marlin E. Rice; Reviewed by Susan Moser, Herb Eichenseer and Laura Higgins

Reference
Bessin, Ric. 2003. Fall armyworm in corn. University of Kentucky Cooperative Extension Service. ENTFACT-110.