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A survey of wheat fields conducted the past two weeks found several different insects and other pest present in wheat fields. A few of the pest found included slugs, grass sawflies larvae, true armyworm larvae, brown stinkbugs, cereal leaf beetles and a few aphids. The slugs were tentatively identified as brown garden slugs which often occur in fields with high levels of plant residues. They can cause economic damage in field corn and soybean, but are generally not considered a spring pest of wheat in Missouri. Both grass sawfly larvae and true armyworm larvae were present in some fields. The grass sawfly can cause defoliation of wheat, but rarely reaches the high numbers of larvae necessary to do so. In contrast, the true armyworm larvae can cause considerable damage if populations reach or exceed economic threshold levels. True armyworm larvae have four pairs of prolegs (pairs of legs in the center of the body) with each leg displaying a dark brown to black triangular blotch on the outside of each leg. Additionally, the larvae have three distinct dark lines running the length of worm. Grass sawflies have greenish yellow bodies, an amber to yellow head capsule with two distinct black eyespots. The grass sawfly larvae have seven to eight pairs of abdominal prolegs which occur on most of the abdominal segments of these larvae. Brown stinkbugs were numerous in some fields although below the threshold of one stinkbug adult or nymph present per 10 wheat heads when in the milk stage of growth. In Missouri brown stinkbug are not considered an important pest of wheat. Low numbers of cereal leaf beetle larvae are present in some wheat fields, although well below the economic threshold of one or more larvae present per flag leaf. This pest is seen as small brown larvae which slowly moved up and down the flag leaf as it feeds and removes the green layer of tissue from the surface of wheat flag leaves. If you rub the larvae, the outer dark covering will be removed to reveal a small yellowish larva. This dark, moist covering is produced and used by larvae to protect them from parasitic and predaceous insect. Populations of several species of aphids were present in fields, but at relatively low numbers. The greenbug and bird cherry-oat aphids are the most important aphids in small grains with some fields treated during the past two weeks in southwest Missouri. Populations of English grain aphids have been found infesting wheat heads in these areas. Although lady bird beetles were actively feeding on these populations in most fields, some English grain aphid populations exceeded the economic threshold of 50 to 100 aphids per head and were controlled with insecticide applications.

Wayne Bailey
BaileyW@missouri.edu