Armyworms

Armyworms can be serious pests of wheat when populations reach large numbers. Armyworms get their name from their migrating habit, as they sometimes start at one portion of the field migrate to other areas of other fields, eating foliage as they go.

True armyworm larvae are smooth, almost without any hairs, and greenish-brown to reddish-brown with a dark stripe along each side. A broad dorsal stripe runs down the length of the back. This species differs from the fall armyworm by having a dark lateral band on the outer portion of each proleg. Damaging infestations of true armyworm normally occur in the spring. Besides feeding on foliage, larvae will sometimes cut the heads of maturing wheat plants.

Fall armyworms are normally a pest of early planted seedling wheat during the fall. These insects can completely defoliate a wheat field when populations are very large. Fall armyworm larvae differ from true armyworms by having a prominent inverted Y on the front of the head and no dark bands on the outer portion of the prolegs.


Scout 1 square foot of wheat in 10 locations throughout the field during the fall and spring. Armyworms fall to the ground when disturbed, and larvae may also be hidden under debris on the soil surface during hot times of the day.


True Armyworm. For infestations that occur during the spring, use a threshold of 6-8 larvae per square foot if wheat is still in the milk stage. Once past the milk stage, wheat can tolerate higher populations and treatment is not usually recommended unless larvae are cutting wheat heads.

Fall Armyworm. Treatment for fall armyworm during the fall should be considered when four or more larvae are present per square foot.


Management options

Insecticide (Trade Names) for ARMYWORMS (True and Fall)Lb Active Ingredient per AcreAmount Formulation per AcreAcres Treated per Gal or Lb of Dry ProductPerformance Rating
chlorantraniliprole (Prevathon 0.43 SC)0.05 - 0.0714 - 20 oz9.1 - 6.49
chlorantraniliprole, λ-cyhalothrin (Besiege)See label6 - 10 oz21.3 - 12.89
methomyl (Lannate LV 2.4)0.225 - 0.4512 - 24 oz10.7 - 5.37
spinetoram (Radiant SC 1)0.023 - 0.0473 - 6 oz42.7 - 21.39?
spinosad (Blackhawk 36% WDG)0.038 - 0.0741.7 - 3.3 oz9.4 - 4.88
β-cyfluthrin (Baythroid XL 1)0.014 - 0.0191.8 - 2.4 oz71.1 - 53.38
γ-cyhalothrin (Declare 1.25)0.01 - 0.0151.02 - 1.54 oz125.5 - 83.18
λ-cyhalothrin (Warrior II 2.08)0.02 - 0.031.28 - 1.92 oz100 - 66.78
Z-cypermethrin (Mustang Max 0.8)0.02 - 0.0253.2 - 4 oz40 - 328

 

  • Avoid planting before the Hessian fly-free date (Oct. 15) as infestations of fall armyworm almost always occur in early planted wheat, especially for wheat planted in September.