Armyworms are small green, brown or black caterpillars with an inverted "Y" on the head. Armyworms are about 0.5 to 1.5 inches long. Armyworms feed continuously, but are army worms are most active and easily seen during the early morning and late evening.
Row covers and hand picking are the organic method that works the best to eliminate this enemy. But your fight will go on for days in the fall if you choose the organic non-chemical attack on the armyworms.
Bt (Bacillus thuringiens) does the job of killing armyworms.
Attack of the Armyworms
As if landowners haven't had enough problems in the summer with drought, high temperatures and grasshoppers, as fall comes they now have something else to worry about — fall armyworms.
Damaging populations of the pests have been reported and specialists warn the worms are doing significant damage to newly established pastures and in bermudagrass fields.
"In several instances, entire small grain fields are having to be replanted because the armyworms have eaten the seedling leaves as they emerged from the soil," said Hugh Aljoe, NF forages specialist.
"A fall armyworm infestation can devastate a new small grains crop within hours," Aljoe said.
Watch for the presence of small white or pale gray moths in fields just before dark. This moth lays eggs from which armyworms hatch. Fall armyworm damage is often first noticed around the field margins near fence rows with overgrown vegetation or wooded borders, Aljoe says.
Fall armyworms will likely be present from August until frost. Army worm populations can reach damaging proportions following fall rains, while temperatures are relatively warm. As temperatures decrease, the life cycle of armyworms slows. The destructive caterpillar stage of the army worm lasts two to three weeks. Although prefering immature growth on grass, armyworms will eat new growth on most any plant. Chemical treatment may be the only option to destroy the armyworms when armyworm populations reach 4 to 5 armyworms per square foot, or two to three armyworms per row foot on plants 2 to 4 inches in height. However, chemical treatment may not always be economically feasible.
Two types of chemical treatment for armyworms are available: 1) treating the plants where the armyworms will be feeding, and 2) killing the caterpillars on contact.
Among the most common leaf-treatments for armyworms are Sevin and Lorsban SG. Sevin is labeled for both wheat and pasture, and does not have a grazing restriction. Lorsban SG kills on contact and by ingesting the chemical, and is labeled on wheat only.
Chemical treatments that kill armyworms on contact include Lorsban SG, Karate, methyl-parathion, parathion, and malathion. Lorsban SG has a grazing restriction of 14 days, methyl-parathion and parathion both have 15-day grazing restrictions, Karate has a 30-day grazing restriction, and malathion has no grazing restriction. Most contact pesticides have little or minimal residual affect after initial application.
The insecticide Confirm has been allowed under Section 18 for fall armyworm control in pasture. It provides excellent armyworm control and a 21-day residual with no grazing restrictions.
Significant numbers of armyworms may reappear within five to seven days after treatment. Regular monitoring of armyworm presence in treated and untreated fields should continue until the cooler temperatures and plants mature.
Info courtesy of Uof N.