Fall armyworm larvae are commonly found feeding in the whorls of sorghum and also feed on the grain of older plants. Larvae generally have a dark head capsule and a prominent, light-colored inverted Y on the front of the head. The body color is greenish to brownish with dark stripes along its length. It has relatively few tiny spines (setae) on the body, contrasting it with the corn earworm.
Check in the whorls of young plants and the grain heads of older plants. Examine a minimum of 50 plants throughout the field. Sets of 10 heads can be briskly shaken into a bucket or sweep net. Carefully look through the debris for larvae of all sizes. Corn earworm or sorghum webworm will also be found feeding in heads. Frass (worm poop) often accumulates in the collars of upper leaves if large larvae are present.
Treatment is recommended when an average of one or more larvae is found per plant, either in the whorl or head stage.
Management options
| Insecticide (Trade Names) for FALL ARMYWORM | Lb Active Ingredient per Acre | Amount Formulation per Acre | Performance Rating |
|---|---|---|---|
| carbaryl (Sevin 80S) | 1 - 2 | 1.25 - 2.5 lb | 7 |
| carbaryl (Sevin XLR 4) | 1 - 2 | 32 - 64 oz | 7 |
| chlorantraniliprole (Prevathon 0.43 SC) | 0.05 - 0.07 | 14 - 20 oz | 9 |
| chlorantraniliprole (Vantacor 5 SC) | 0.047 - 0.067 | 1.2 - 1.71 oz | 9 |
| chlorantraniliprole, λ-cyhalothrin (Besiege) | See label | 6 - 10 oz | 9 |
| methomyl (Lannate LV 2.4) | 0.225 - 0.45 | 12 - 24 oz | 8 |
| methoxyfenozide (Intrepid 2F) | 1 - 1.25 | 8 - 10 oz | 8 |
| spinosad (Blackhawk 36% WDG) | 0.038 - 0.074 | 1.7 - 3.3 oz | 8 |
| β-cyfluthrin (Baythroid XL 1) * | 0.01 - 0.02 | 1.3 - 2.8 oz | 5 |
| γ-cyhalothrin (Declare 1.25) * | 0.01 - 0.015 | 1.02 - 1.54 oz | 5 |
| λ-cyhalothrin (Warrior II 2.08) * | 0.02 - 0.03 | 1.23 - 1.85 oz | 5 |
| Z-cypermethrin (Mustang Max 0.8) * | 0.01 - 0.025 | 1.76 - 4 oz | 5 |
* Pyrethroid insecticides may not provide adequate control of corn earworm or fall armyworm and are not recommended if infestations are well above the treatment threshold.
- Planting early, before mid-May, will generally help avoid some damage from fall armyworm and corn earworm.