As the weather begins to warm, and the crops in the field begin to grow, insects start their annual migration into Kansas or come out of their winter hiding places to feast upon the new growth. One such insect that is making its presence felt across Kansas is the army cutworm. The following piece is from the agronomy department for K-State Research and Extension with some information about the army cutworm and the threshold for various crops for possible treatment.
Varying levels of army cutworms have been found on scattered fields of wheat, alfalfa, and canola in Kansas as of mid-March. Generally, the army cutworms have been found coming out of pasture and other grassy areas. Infested wheat fields seem to be very strongly correlated to areas with grass or pasture in close vicinity.
Reports of army cutworm infestations are not necessarily a cause for alarm. So far, many of the infestations in wheat are below the treatment level. But it’s something to watch and, if necessary, consider treating in wheat, alfalfa, and canola. One of the main concerns at the moment is on seedling alfalfa, where the economic threshold is very low – just 2 per square foot. Canola should be treated when there is an average of two or more larvae per foot of row.
Wheat fields infested by army cutworms will look ragged. By late March, the cutworms will probably be larger and damage may be more extensive. Treatment thresholds will depend on the growth stage of wheat, the condition of the wheat, and infestation levels (described below in the “Wheat” subsection).
Army cutworms oversummer in the Rocky Mountains. They fly back to Kansas and surrounding areas in the fall and lay eggs in the soil. The eggs hatch either in the fall or early winter.
Army cutworms feed on a wide variety of plants including weeds, vegetables, fruit crops, oilseeds, and grasses. Plant-use patterns depend on a where a female lays her eggs and what locally available alternatives larvae choose to eat. Despite being broad generalists, larvae may express strong feeding preferences among plant species and even among different wheat cultivars.
Larvae begin feeding whenever temperatures rise a few degrees above freezing. When scouting for army cutworms, it is best to wait until temperatures have warmed up well above freezing. That’s when they will be feeding on plants. When temperatures are near or below freezing, army cutworms will burrow into the loose soil at the base of plants, emerging to feed in the evening if it’s warm enough.
Often, if you see birds feeding in a wheat or alfalfa field this time of year it is probably because of army cutworms. Birds have been known to effectively control army cutworms over a period of a few days.
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-State Research and Extension. You can contact her by e-mail at aboor@ksu.edu or calling 620-793-1910