Fall Armyworm

Fall Armyworm

Fall Armyworm

Fall armyworm is an occasional pest of cotton grown in Tennessee. The caterpillars (larvae) feed on fruiting structures and especially on flowers or bolls. The injury they cause is similar to that of bollworm. Larger larvae can often be distinguished from bollworm or tobacco budworm by having a dark-colored head with a light-colored inverted Y. Infestations almost always occur after flowering has begun and are more likely to cause yield loss in late maturing fields. Bt cotton varieties have reduced the importance of this pest, but insecticide applications may still be justified.

Small larvae are often found in white blooms, pink blooms, or behind the bracts of medium-sized bolls. Large larvae are often seen in blooms or found inside bolls. Scout by examining 25 flowers (white or pink) and 25 mid-sized bolls at a minimum of 4 locations in a field. Alternatively, the number of fall armyworm larvae can be counted while inspecting plants for bollworm or tobacco budworm.

Treat when an average of 4 or more larvae are found in 100 blooms and/or bolls, or treat when 10-20 larvae are found per 100 plants. Timing applications to control small larvae is more effective than trying to control larger larvae. 

 

Management Options

 

Insecticide (Trade Names)*
for FALL ARMYWORM
Lb Active Ingredient
per Acre
Amount Formulation
per Acre
Acres Treated per Gal or Lb
of Dry Product
Performance Rating
acephate 90 (Orthene 90S)0.91.0 lb15
chlorantraniliprole (Prevathon 0.43 SC)0.067 - 0.0920 - 27 oz6.4 - 4.79
chlorantraniliprole, λ-cyhalothrin (Besiege)See label8 - 12.5 oz16 - 10.259
emamectin benzoate (Denim 0.16)0.01 - 0.0158 - 12 oz16 - 10.78
indoxacarb (Steward 1.25)0.09 - 0.119.2 - 11.3 oz13.9 - 11.38
methomyl (Lannate LV 2.4)0.4524 oz5.37
methoxyfenozide (Intrepid 2)0.06 - 0.164 - 10 oz32 - 12.88
novaluron (Diamond 0.83, Mayhem 0.83)0.039 - 0.0786 -12 oz21.3 - 10.78
spinetoram (Radiant SC 1)0.033 - 0.06254.25 - 8 oz30.1 - 167
spinetoram, methoxyfenozide (Intrepid Edge)See label6 - 8 oz21.3 - 169
spinosad (Blackhawk 36% WDG)0.056 - 0.0722.4 - 3.2 oz6.7 - 57

 

*Most pyrethroid insecticides provide some suppression of fall armyworm infestations, and using the highest labeled rates or a tank mixture with products listed above will often improve control.

  • Plant early maturing varieties.
  • Bt cotton varieties provide good but variable levels of control. Insecticide applications may be needed in some cases, particularly in flowering cotton.
  • Insecticide applications can be terminated when cotton has accumulated 400-450 DD60s past NAWF5 (NAWF5 = average of 5 or fewer nodes above a first position white flower).