WHEAT JOINTWORM

Background, wheat lodged and broken by wheat jointworm. Insert, the insects and damage (greatly magnified) ; a, adult; b, pupa in cell; c, larvae; d, external appearance of infested stem.

WHEAT JOINTWORM

The wheat jointworm does damage that in some years amounts to millions of bushels of wheat. It is widespread throughout most of the wheat-growing regions east of the Mississippi River and in Missouri, Iowa, and parts of Utah, Oregon, and California.

Heads of infested wheat plants have fewer and smaller kernels and heavily infested fields show many broken straws and much lodging.

The adult jointworm looks like a small black ant with wings. It lays eggs early in the spring in the succulent plant stems. The larvae, small footless grubs, soon hatch and form cells in the wall of the stem, usually just above the second or third joint from the ground. By harvest the larvae are yellowish in color and about one-fourth inch long. Their cells or "galls" have now become hard and woody. Sometimes they appear as wartlike swellings, and the wheat stems are badly twisted and bent. In winter the larvae change to pupae, which are pale yellow at first but turn black later. In the spring the adults emerge through small circular holes which they gnaw through the walls of their cells. Mating soon takes place and the females leave the old stubble fields to find and infest green wheat fields in the vicinity. There is only one generation a year.

Control: The wheat jointworm may be controlled by plowing under the infested stubble, preferably late in the summer or early in the fall, to prevent the emergence of the adults during the following spring. When this is done the wheat should be cut as high as practicable so that most of the jointworms will be left in the standing stubble to be plowed under. Objections to control by plowing, because of its interference with the growing of red clover and other crops useful in soil conservation may be met by the temporary substitution of soybeans, sweetclover, and other crops for forage and green manure. For those areas infested with jointworm in Oregon it is recommended that winter barley or Winter Turf (Oregon Gray) oats be substituted for wheat as a nurse crop for red clover.

In Southern and Southeastern States, where double-cropping systems are in general use, and in Western States, where summer fallowing is practiced, it would be desirable to plow the stubble under throughout large areas and thus secure effective community control.

Where infested stubble has not been plowed, the wheat should be sown as far as practicable from such stubble fields. This will make it more difficult for the jointworm adults emerging from the old stubble to reach the new crops.

In areas where severe losses from the jointworm have occurred during the preceding season, land sown to wheat should be top-dressed only with manure containing straw that has been well rotted or thoroughly trampled. This helps to insure the death of jointworms that might otherwise emerge from the straw to reinfest the field.

If jointworm attacks are especially threatening it may be advisable to substitute temporarily other crops such as rye, barley, oats, or buckwheat for wheat. This can be done safely because the wheat joint-worm attacks no other crops except wheat.

Insecticidal control of the wheat joint-worm is not practical.