It seems as if everyone gets active when the weather turns warmer – including army cutworm larvae in alfalfa and wheat fields.

"In Kansas, the army cutworm is a perennial pest that can damage wheat and new alfalfa fields in late winter or early spring," said Kansas State University Research and Extension entomologist Jeff Whitworth.

Army cutworms have one generation each year. They lay eggs in the fall, which hatch, and the young early instar larvae overwinter. Depending on temperatures, the larvae typically resume feeding in late February or early March. They then grow and complete their development.

"This is the same time of year when wheat and alfalfa start growing, so most economic damage occurs at this time, too," Whitworth said.

Seven to eight larvae were found in late February in a two-foot square area in Kingman County. They varied in size from three-eighths of an inch to 2 inches long, with some migration noted across a county road from a seedling alfalfa field, he said.

Army cutworms feed on almost any vegetation they come into contact with, he said. In Kansas, however, they're usually pests in wheat and alfalfa. The larvae feed above the soil surface, but spend non- feeding time below ground. As they finish developing in the spring, they build "cells" a few inches under the surface and pupate. The adult moths typically emerge in May or June. During "outbreak" years the moths' emergence can occur in huge numbers.

Army cutworm larvae seem to prefer leaves, but will eat other plant parts if no leaf tissue is available and may consume stems – even following them into the soil. Most feeding occurs from late afternoon until dark in late winter/early spring as the weather warms. Infestations may not be apparent under sunny conditions because the larvae seem to be sensitive to sunlight, often hiding in the soil between and around plants. Larger larvae may be readily apparent on cloudy days, however, or they can be found by digging down an inch or two in the soil on clear days.

Indications of small amounts of larval feeding damage can go unnoticed, but when large populations occur, plants often show small or semicircular holes in leaves. The extent of the damage depends on the number and size of larvae, size of the plants, and growing conditions.

Wheat probably is not as susceptible to damage as first-year alfalfa, because it can withstand some defoliation and still survive. Growth and maturity may be delayed, however, if plants are small or there are many worms, Whitworth said. Plus, more defoliation occurs as the larvae grow. If the growing point of the seedling is damaged, the plant may die.

"That's (death) rare, but if food is limited because the plant has had less than ideal growing conditions, larvae may follow the plant down into the soil, which can destroy the whole plant," the entomologist said.

As plants are destroyed the larvae move to other plants until bare spots are evident. Because most larvae are feeding on the outer edges, the bare spots continue to expand.

Feeding continues in this manner until the cutworms mature and pupation occurs. After the food in one field is consumed, they move to a new area en masse. Their mass migrations usually start in the late afternoon on sunny days, with the larvae consuming any vegetation in their path.

Army cutworm larvae may destroy alfalfa seedling plants in early spring or hurt foliage enough to reduce the amount harvested in the first cutting of established stands. Early detection is critical to good control, he said. Seedling fields are most vulnerable and should be treated if two or more larvae per two feet are present. Established stands should be treated if four to five larvae per two feet are detected.

Poor wheat stands that were planted late or drought-affected are most susceptible to army cutworm losses. In such situations, only one to two larvae per two feet may justify treatment.

Wheat fields with good stands probably won't need to be treated until larvae average four to five per two feet. Higher densities may be tolerated in well-tillered wheat with good growing conditions.

Information about insecticides labeled for army cutworm control is available in the Wheat Insect Management Guide (2004) and the Alfalfa Insect Management Guide (2004) at local county Research and Extension offices or on the World Wide Web at: http://www.oznet.ksu.edu.

"Successful army cutworm control is dependent on proper timing. It's important to treat the larvae before they cause economic losses and to make sure insecticides are applied in sufficient quantities to contact the worms," Whitworth said. "K-State research indicates that all tested insecticides seemed to work equally well. Thus, from a practical standpoint, price and availability should be your guideline for product selection of labeled insecticides."

Flocks of birds feeding in wheat or alfalfa fields often are an indicator of the presence of these worms and "often do a remarkable job of controlling them," the entomologist said. "But, don't count on them. You need to look for yourself, as there is no substitution for scouting."