Cooperative Extension

Armyworms invade the county

The northwest area of Livingston County has recently experienced an infestation of a voracious plant eater called the True Armyworm, generally called the Common Armyworm.

Armyworms get their name from their behavior of moving across fields in an army-like fashion. As larvae consume available food sources, they migrate as an army to new host plants.

J. Keith Waldron in the Cornell University – Cornell Cooperative Extension Field Crop News Blog presented an alert explaining that Armyworms are primarily a pest of plants in the grass family: forage/pasture/grasses (and lawns)/small grains/and corn. Note: Under hunger stress true armyworms will also attack some legumes and other plants.

This native species does not overwinter in New York, but flies north from states to our south in the spring.

Armyworm moth migrations are somewhat sporadic, cyclic from year to year and difficult to predict. This year timely seasonal storm conditions provided the ideal transport for the emerging moth population, in the south to hitch a ride en masse, at a level not experienced since 2008 when we experienced similar activity.

Moths lay their eggs on weeds and grasses along field margins, on leaves of corn, or on small grains. Larvae hatch about a week later and develop over approximately a three week period, feeding mostly at night.

Commercial crop situations at risk from armyworms are grass as in hayfields and pasture; corn (field and sweet), especially when planted into grass fields, no-till and reduced till fields, fields with crop residue, and planted into grass cover crops and fields with grassy weeds such as quackgrass; and small grain crops like wheat, oats, and rye.

Information from the University of Illinois indicates host material also includes beans, cabbage, carrots, onions, peas, peppers, radishes, sweet potatoes, etc. Larvae feed for over a month and remove notches or large sections of leaf tissue on either side of the main veins.

True armyworm larvae appear smooth, cylindrical, and pale green to brownish when they are still small. Mature larvae are smooth and marked with two orange, white-bordered strips on each side. Larvae range in size from 1/8 inch to 1 1/2 inches long.

Early detection while the larvae are small is important. Large larvae do most of the feeding, are capable of destroying whole stands of crops, and are harder to control.

Armyworm larvae feed at night so look for signs of feeding: chewed leaves, cut stems, lodged plants, pellet-like frass on the ground. Larvae tend to hide during the daytime, often hidden under the plant canopy and surface residue or in corn whorls.

Economic thresholds are indicated for determining when to apply control measures in farm crops. These have been easily met in many situations and farmers have been applying control materials. It hasn’t been necessary to count critters in most cases.

Armyworm can be a problem for homeowners just with their annoying presence. They will crawl up the walls of structures. They will devour lawn grasses.

The need for control can be difficult to determine because while the caterpillars eat the grass and the lawn turns brown, they do not eat the crowns of the grass and the grass should grow back. Water may be needed, but the expectation is the grass will survive. Vigilant observation of ornamentals and vegetable gardens is recommended to make other control determination decisions.

The US Department of Agriculture (USDA) Farm Services Agency (FSA) can now file weather related disaster reports for damage done by armyworms due to the fact that they have arrived earlier than expected and in unprecedented numbers because of the unseasonable warm weather this spring.

Farmers should report their losses to their county Farm Services Administration to begin documenting the extent of the damage.

If the FSA can document a countywide loss of 30 percent or greater for a single crop, they can then submit their data to NYS Department of Agriculture and Markets for a potential disaster declaration – allowing access to low-interest emergency loans.