A spring armyworm infestation of near historic proportions could stretch well into July, when another armyworm species begins arriving and feeding on corn, say Purdue University entomologists Larry Bledsoe and John Obermeyer.
If the scenario plays out, it could be double trouble for Indiana farmers or no problem at all, Bledsoe says. Much will depend on nature's own control measures in reducing both armyworm species.
It's too early to tell whether the spring, or "true," armyworms will overlap with the fall armyworms, Bledsoe says.
"We've got unusually large true armyworm populations, and now we're awaiting the appearance of the fall armyworm," he says. "Our anticipation is that natural controlling agents will keep damage below economic impact levels. This is speculation, because we've never dealt with armyworm numbers this high before."
True armyworms are active from May to early July. Fall armyworms appear in early July and are present until frost.
But this is no typical armyworm year. Waves of true armyworm moths swept across Indiana this spring. Eggs from the first armyworm flight hatched in May, and larvae ate their way from southwest to northeast Indiana. Some crop fields and pastures were so badly damaged no green vegetation was left.
A second generation armyworm has been flying throughout the state. The moths are laying eggs, which could hatch by month's end and begin the process all over again. Larval-phase feeding could go on for a full month afterward.
A true armyworm consumes about 80 percent of its food in its final three to five days as a caterpillar. If the crop is gone and the larvae are still hungry, they'll move as a unit to the next grassy field.
"We haven't seen outbreaks of this magnitude since the 1950s," Bledsoe says.
Fall armyworms have yet to arrive in the Midwest. The pests seek very late planted corn on which to lay their eggs. During July and August the developing larvae feed in the whorls of corn, eventually moving to the tassels and ears as they emerge.
Farmers should inspect their fields regularly for armyworm activity, Bledsoe says. Not all fields with feeding larvae are candidates for pesticides, he claims.
More information about armyworms and pesticide options is available online at www.ces.purdue.edu/hotnews/index.html  .