PESTS OF SMALL GRAINS


Extracted from INSECT and related PESTS of FIELD CROPS (AG-271)
Dated 5/82
Placed on the Web 6/95 by the Center for Integrated Pest Management, NCSU

The production of small grains in North Carolina is concentrated in the Piedmont and Coastal Plain counties. Approximately 212,550 hectares (525,000 acres) of rye, oats, wheat, and barley were planted for grain in 1980, wheat being most prevalent. In addition, some small grains are utilized as cover crops. Acreage and production, however, are erratic and respond quickly to variations in weather, pest populations, and economic conditions.

Key to Pests of Small Grains

A. Insects and mites that pierce tissues to extract sap.

  1. Aphids - These winged or wingless, pear-shaped insects are usually less than 3 mm long and feed in colonies. They are basically green, yellow, or pink and have a pair of appendages on the abdomen known as cornicles. The extent of damage caused by these aphids varies, but nearly all aphids cause some discoloration or mottling of the foliage.

    1. Corn leaf aphid - Up to 2 mm in length, this pale bluish-green insect has a dark area around the base of its cornicles and a fine, powdery film over its body. This aphid causes a yellow mottling of the foliage.

    2. English grain aphid - Up to 2.5 mm long, this aphid is usually pale green (though sometimes yellow or pink) with a dark blotch on its back. The insect feeds on the foliage but causes more damage when it feeds on ripening kernels, causing them to shrivel.

    3. Greenbug - Up to 2 mm long, the wingless form of the greenbug has a pale yellow to bluish-green abdomen with darker green, longitudinal streaks. The head, which is often a pale, strawlike color, is lighter than the rest of the body. As it feeds on the foliage, this aphid causes red spots which gradually enlarge. Eventually leaf tips turn brown. Circular areas of yellow plants with dead plants in the center, known as "greenbug spots," may continue to enlarge.

  2. Chinch bug - This 4 mm-long, black bug has opaque wings, each marked with a black triangle. Feeding anywhere from the roots to the upper leaves, the smaller, wingless, red and black nymphs cause dwarfing, lodging, and yield reduction. Young plants may wilt and die.

  3. Hessian fly maggot - This 2 mm-long, white to tan, legless larva feeds along with other maggots behind the leaf sheath where the leaf joins the stem. Leaves become thickened and weakened stems may break when the grain heads.

B. Chewing insects that feed above ground

  1. Armyworms - Reaching a maximum length of 30 to 40 mm, these smooth-skinned caterpillars are voracious foliage feeders. They have 5 pairs of prolegs.

    1. Armyworm - This pale green to brownish-green caterpillar is 30 to 35 mm long when fully grown and has three dark longitudinal stripes. Its head capsule has markings like those of the fall armyworm but they are lighter or less intense

    2. Fall armyworm - This green, brown, or black larva (up to 40 mm long) has a dark head capsule usually marked with a pale, but distinct, inverted "Y." A darker, curved marking occurs on each side of the "Y" (Fig. B). A black, longitudinal strip runs down each side of its body and a yellowish-gray stripe runs down its back. The larva attacks small grains only in the seedling stage during late summer or fall.

  2. Cereal leaf beetle adult - About 6 mm long, this beetle has a blue-black body, brownish-yellow legs, and a reddish-brown thorax (area behind the head) (Fig. A). The beetle chews leaves, leaving longitudinal holes between the veins.

  3. Cereal leaf beetle larva - About 6 mm long when fully grown, this soft-bodied, yellow larva is usually coated with black, fecal material (Fig. B). It has three pairs of legs near its head. The larva feeds between the leaf veins on surface leaf tissue, leaving longitudinal gray or white patches instead of holes. Infested fields may have an overall whitish cast.

  4. Grasshoppers - Many species of variously colored grasshoppers, ranging in length from 19 to 38 mm, feed on leaves and stems of small grains, eventually causing the heads to fall to the ground.