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 (e.g., the fly-safe date), depending on location in the state. Cereal leaf beetle and aphids are usually controlled by beneficial parasitoids or natural pathogens. However, populations of some pests, especially cereal leaf beetle, armyworm, and sometimes aphids, may occur in numbers warranting rescue treatment with insecticides. The following text reviews the insect pests that may impact wheat.
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. Flaxseed pupae are located within the leaf sheaths of plants in the spring, resulting in the broken wheat stems and lodging associated with that damage. Damage by the maggots occurs in the late spring and early fall following activity by adults in early spring and late summer. Under serious infestations, the problem is generally detected after the damage has been done and the fly is in the flaxseed stage protected from insecticides by the plant and pupal case. It is somewhat challenging to control Hessian fly with foliar applications, which is why the major tactic for controlling Hessian fly is planting wheat after the Hessian fly-safe date for your county (see Figure 6-1). Seed treatments are available and have activity against the Hessian fly, but are usually unnecessary if following the fly-safe date.
APHIDS The English grain aphid and the cherry oat aphid may cause limited feeding injury. The greenbug, an aphid which produces a toxin that affects the wheat plant, rarely occurs in Ohio. To determine the need for treatment, first identify the aphid. English grain aphid has black cornicles (tailpipes on the tip of the abdomen), oat-bird cherry aphid has a red-orange spot between the cornicles, and the greenbug has a dark green stripe on the back and the tips of the cornicles are black. Keep in mind that natural predators usually control most aphid populations on small grains. In addition, planting after the fly-safe date also will limit risk of aphid infestation and disease transmission. Greenbug infestations great enough to cause economic damage are rare in Ohio. Aphids also are important in Ohio because they may transmit the barley yellow dwarf virus that causes stunting and yellowing of wheat and other small grains. However, 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.
OVERWINTERING CEREAL LEAF BEETLES appear in the spring and lay eggs, which hatch into larvae that feed on wheat and oat leaves. Damaged fields often have a frosted appearance due to the defoliation. 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. A complex of parasitic wasps generally controls cereal leaf beetle, but treatment of fields may be warranted when mild winters adversely affect natural control. An infestation averaging one larva per stem may result in a loss of 3 bushels per acre.
ADULT ARMYWORMS 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. Detection of larvae is initially along the edge of fields and low-lying areas. When six or more larvae can be seen per linear foot of row, or head clipping is evident and larvae are not fully grown (larvae are predominantly 1-inch long or less), a rescue treatment may be needed.
For more information on managing insect problems and for the chemicals labeled for wheat insects, see the Agronomic Crops Insects website at: oardc.ohio-state.edu/ag/pageview.asp?id=1029.