Producers go to war against armyworms
Sep. 23—It doesn't take an army to fight this army, as long as the foe doesn't get too big.
Farmers, not just in Iowa, but in other parts of the country are going to war against the invasive pest armyworms as they destroy crops and grass. In Union County, reports are coming from alfalfa hay fields.
"Parts of Union County are pretty bad," said Rob Evans, manager of Nutrien Ag Solutions in Creston. "And this is not typical every year."
Maybe 2 inches long, Armyworms were given the name for how they appear to move in unison as they eat hayfields, lawns and certain other vegetations.
Typically, armyworms do most of their damage during the overnight hours.
"On alfalfa, they eat all the leaves to a bare stem," Evans said. "Then you look for brown spots," as evidence of their work.
According to Iowa State University Extension, fall armyworm is native to the southern U.S. (Texas and Florida), but the adults are strong flyers and capable of migration to northern states. Multiple migration events are possible each summer, and adults can be found in Iowa from June to August. This year, they are more abundant in the Midwest than usual and are causing late-season issues. Evans said the hurricanes and storms in the South have forced the worms to go north. And when they arrived in Iowa, the state's dry summer has benefited armyworms.
"Heavy rains can slow them down," Evans said.
According to Iowa State University, a generation takes about 30 days to complete its life cycle in the summer. Eggs are usually laid in a mass of 100-200 on light-colored surfaces, including fence posts, poles or tree limbs. Eggs often look moldy or fuzzy because they are covered with grey scales. Eggs hatch within four days and larvae (caterpillars) go through six instars before pupation. Young larvae are greenish with a dark head and older larvae are mottled with red and brown. White lines along the top of the body develop along with raised spots and spines. Fall armyworm species have a white, inverted "Y" on the face and four raised bumps in the shape of a square near the end of the abdomen.
Looking for fall armyworm is best in early morning or late in the day, when larvae are most active. The best way to confirm the presence of fall armyworm in pastures or hayfields is to use a sweep net. The net will pick up larvae that are too small to find other ways. If fall armyworm larvae is n the sweep net, determine how many caterpillars are present per square foot by looking on plants and in the litter on the soil. Without a sweep net, check areas that look dead, wilting or drought-stressed, or where birds are congregating.
Iowa State University Extension states armyworms prefer corn, sorghum, bermuda grass, tall fescue. They can also feed on alfalfa, barley, oats, ryegrass, vegetables and soybean. Armyworms tend to move quickly into new areas in large numbers. Damage can be extensive, especially to young plants, and can destroy the growing point. Damage ooks like hail damage. Fall-seeded grasses can be severely impacted; larval feeding can cause plant stunting or death.
Evans said there are insecticides that eliminate armyworms.
"I'd say we sprayed at least 1,000 acres," Evans said.
He has heard reports the chemicals don't waste any time. He said one field was sprayed last Friday afternoon. After Creston's football game that evening, the farmer could already see evidence the spray worked.
For hay fields, Iowa State University Extension suggests baling the hay quickly to ensure the armyworms won't continue to feed. If plants are used as ground cover, it may not be necessary to spray an insecticide. If an application is warranted, timing is critical for effective larval suppression. Insecticide applications for control of fall armyworm larvae are most effective when the caterpillars are small (less than 1/2 inch long) and when made late while fall armyworms are actively feeding.
