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