LYGUS BUGS

A, Normal alfalfa plant; a, undamaged blooms; b, well-developed seed pods; c, nymphs; d, adult lygus bugs. B, Badly damaged plant showing e, relatively short internodes and f, completely blasted flower buds. C, g, Normal alfalfa seeds; h, lygus-damaged seeds. (A and B, about three times,natural size-, C, greatly enlarged.)

LYGUS BUGS

Lygus bugs thrive on a wide range of cultivated and uncultivated plants. They cause severe damage to seed alfalfa. They are active from early spring to late fall. The adults fly freely from one host to another and from farm to farm. They breed continuously during the growing season. In the latitude of Utah there are three to four generations a year, each taking 6 to 7 weeks; in more southern regions, such as Arizona, a generation requires from 20 to 30 days, and the insects breed most of the year.

During cold weather the adults find protection among dormant alfalfa plants or in various crop debris. With the coming of warm weather they seek early-flowering weeds. The females insert their eggs singly in the plant tissues. Later they also deposit their eggs in alfalfa. The eggs hatch in 10 to 15 days. The hatch is usually concentrated during the period when alfalfa plants are budding or blooming. The insects become full-grown and change to adults in about 3 weeks. The new adults usually fly to more succulent alfalfa or other plants and begin to lay eggs in about 10 days.

The young lygus bugs, or nymphs, feed extensively on the buds of alfalfa, causing them to wilt and die. Sometimes such destruction by a large population of nymphs is severe enough to prevent flowering of the plants. At other times the bugs feed on the flowers and cause them to drop. They will also feed on the pods, causing the injured seeds to shrivel and turn brown. Vegetative growth of the plant is also impaired and distorted. The nymphs feed more constantly than the adults and are thus more destructive.

Control: Alfalfa grown for seed can often be adequately protected from lygus bugs by a single application of DDT as soon as the plants begin to bud. Use 20 to 25 pounds of 10 percent DDT dust per acre or a spray containing at least 1.5 pounds of actual DDT per acre.

Sometimes the crop is reinfested during the bloom period to an extent that a second application of insecticide is needed. Generally, excessive reinfestation occurs when the first growth is left for seed or when pollination is deficient and slow. If a second treatment is desirable, toxaphene may be applied to the blooming plants before 7 a. m., or after 7 p. m., when bees are not working in the field. Dust with 20 pounds of 10 percent toxaphene per acre or spray with 1.5 pounds of actual toxaphene per acre. The best time for this application is 3 to 4 weeks after the bud stage treatment with DDT.

Forage or chaff treated with DDT or toxaphene should not be fed to dairy animals, animals being fattened for slaughter, or poultry.