Fall Armyworm Egg Mass

A fall armyworm moth caterpillar emerges from an egg mass. The masses have popped up around Iowa and Iowa State Extension recommends removing the egg masses by wiping or scraping before hatching can occur.

OSKALOOSA — Property owners in Mahaska County may notice a new type of uninvited visitor hanging around railings, bird feeders or even on the side of vehicles: eggs of the invasive fall armyworm moth.

Thousands of the insect were blown into the region by storm fronts from the southeastern United States in what entomologists are calling an unprecedented event. Egg masses have been reported in Iowa on trees, house siding, playground equipment, golf carts and more.

“Fall armyworm egg masses are tan-to-buff in color, of various shapes, and appearing fuzzy or furry,” Iowa State Professor of Entomology Donald Lewis said. If looked at closely, the mass will reveal 100-500 shiny, round eggs. Each female moth can lay 1500-2000 eggs in her lifetime.

Lewis expects that the caterpillars may begin emerging “any day now,” as the egg stage can be as short as two to three days in summer.

Once hatched, the fall armyworm will be a tiny green caterpillar with a black head. They darken with age and older worms may be green, brown or black with stripes. A fully-grown fall armyworm caterpillar will be 1.5 to 2 inches long.

Though harmless to humans, high numbers of the caterpillar feeding in one area can destroy lawns if ignored.

“All of my entomology colleagues in the eastern united states are saying this is unprecedented. They have never seen this much damage from fall army worms in the past,” Lewis said. “This is new to us too. We’ve documented fall armyworms in Iowa, but the widespread existence of egg masses is new to us”

If someone notices a patch of eggs, they should remove it by scraping or washing them off of the surface.

“Wiping them off eliminates any threat that the caterpillars will develop and feed on your lawn,” Lewis said. He emphasized that insecticides will not work to control the species, as they are immune to most common insecticides found in Iowa.

“Treating the egg masses with an insecticide is not advised, it will not work,” Lewis said. “Spraying your entire lawn at this point is too much insecticide too early. Wait. Watch. Spray only when and where the armyworm caterpillars appear. Try to hold back on unnecessary spray application.”

The caterpillars are known to consume over 80 plant species, but turf and pasture grasses, corn and wheat face the biggest threat.

Right now, it is too early to tell what effect the species will have in the state, but Lewis expects that Iowa will miss out on the extreme damage suffered in states such as Ohio and Indiana where drought also played a role in the death of many crops and grasses.

Brought in with the late August storms, the fall armyworm outbreak extended northward and westward with heavy populations and severe damage to turfgrass from Oklahoma to Georgia and Indiana to Maryland.

“Pretty much the eastern half of the united states was inundated to the point that fields were destroyed and lawns were completely ruined,” Lewis said.

Shannon Rabotski can be reached at srabotski@oskyherald.com.

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