Several different insects can be important on wheat in Ohio. Management of insect pests affecting wheat often emphasizes nonchemical control measures. Hessian fly is controlled primarily by delaying planting until late September or early October, depending on location of the field in the state. Cereal leaf beetle and aphids are usually controlled by beneficial parasites. However, populations of some pests, especially cereal leaf beetle, armyworm, and sometimes aphids, may occur in numbers warranting rescue treatment with insecticides.
The Hessian fly passes through two generations per year in which adult flies deposit eggs, maggots hatch on leaves and feed on stems, and then maggots pupate into the commonly recognized flaxseed stage. Adults are active in early spring and late summer. Damage by maggots occurs in the late spring and early fall.
Assessment: Flaxseed pupae are located within the leaf sheaths of plants in the spring. Broken wheat stems and lodging are associated with damage. Under serious infestations, the problem is generally detected after the damage has been done and the fly is in the flaxseed stage. Thus, rescue treatments are not warranted.
Control: Plant wheat after the Hessian fly-safe date for your county (see Hessian Fly-Safe Planting Dates for Ohio Counties).
English grain aphid and the cherry oat aphid may cause limited feeding injury. The greenbug, which produces a toxin that affects the wheat plant, rarely occurs in Ohio. Aphids are important in Ohio because they may transmit the barley yellow dwarf virus that causes stunting and yellowing of wheat and other small grains. It is not economically feasible to control transmission of barley yellow dwarf virus with insecticides because aphids can transmit the virus within six hours of landing on the plant.
Assessment: First identify the aphid. English grain aphid has black cornicles; oat-bird cherry aphid has a red-orange spot between the cornicles; the greenbug has a dark green stripe on the back and the tips of the cornicles are black. Threshold: Aphid populations on small grains are usually controlled by natural predators. Insecticide treatment is warranted when an average of 50 or more greenbugs occur per linear foot of row in the fall or 100 or more per foot in the spring. Greenbug infestations great enough to cause economic damage are rare in Ohio.
Overwintering beetles appear in the spring and lay eggs which hatch into larvae that feed on wheat and oat leaves. Larvae appear as small black slugs due to accumulated fecal matter on their backs. There is one generation per year with new adults appearing in late spring. Cereal leaf beetle is generally controlled by a complex of parasitic wasps, but treatment of fields may be warranted when mild winters adversely affect natural control.
Assessment: An infestation averaging one larvae per stem may result in a loss of three bushels per acre. Count the number of larvae on five stems at each of 10 randomly selected areas within a field.
Threshold: Infestations with an average of two or more per stem warrant insecticide use.
Adults become active in late April and early May and are attracted to grass crops, including wheat. Larvae are active in late May and June and can feed on leaves and emerging heads. Most serious damage occurs when larvae feed on stems and clip heads completely off.
Assessment: Detection of larvae is initially along the edge of fields and low-lying areas. Examine plants for foliar feeding and head clipping.
Threshold: When head clipping is evident, three to four larvae can be seen per linear foot of row, and larvae are not fully grown (larvae are predominantly 1-inch long or less), a rescue treatment may be needed.