BOLLWORM

a. Eggs; h, egg ( 15 times natural size); c, young larva on square; d. damaged square; e, full-grown larvae showing color differences; f, pupa in soil; g. adult. (a, c, d, e. f, and g, about natural size.)

THE BOLLWORM

The bollworm, also known as the tomato fruitworm and the corn earworm, damages cotton wherever it is grown in the United States, but the losses are usually greatest in Texas, Oklahoma, and Louisiana. It also feeds on many plants besides cotton, especially corn and tomato. Cotton is not the preferred food plant. Bollworm infestations usually develop rather late in the season.

Each bollworm destroys a large number of squares and bolls. When bollworms are numerous a crop of cotton can be ruined in a short time. Damage often occurs so late in the season that the plants do not have time to mature another crop of bolls.

The bollworm moths prefer rapidly growing, succulent cotton in which to lay their eggs. The eggs are laid singly on the tender growth and newly formed squares. They are smaller than the head of an ordinary pin, and pearly white when first laid, but change to a dark color before hatching. The small larvae, or "worms," feed for a few days on the tender buds or leaves and on the outside of squares before burrowing into squares or bolls, usually near the base. Large worms feed almost entirely inside the bolls, so that it is very difficult, if not impossible, to control them. Full-grown larvae enter the soil and change to the pupal, or resting, stage. There are several broods a year. The last brood passes the winter in the underground pupal cells.

Control: When it is about time for bollworms to appear, examine the tops of the plants frequently for eggs and small worms. When 20 to 25 eggs that are beginning to hatch (or that number of eggs and very small worms) are found per 100 plants, it is time to begin applying insecticides. Successful control of bollworms requires heavy applications of dusts or sprays while the eggs are hatching and before the worms enter the bolls.

At 5-day intervals apply 10 to 15 pounds per acre of a 10 percent DDT dust or the equivalent in spray form; a dust containing 5 percent of DDT plus sufficient benzene hexachloride to give 3 percent of the gamma isomer; or a 20 percent toxaphene dust. Calcium arsenate, lead arsenate, and cryolite are less effective. Whenever the spider mites must also be controlled, any mixture containing organic insecticides should include at least 40 percent of sulfur or some other suitable miticide. Use more pounds per acre when the infestation is heavy and the plants are large. Two or three applications will usually control a brood of bollworms, but there may be more than one brood or a steady movement of egg-laying moths to cotton from other crops, with no distinct broods. In such cases several additional applications may be needed to keep the plants covered with insecticides to kill the newly hatched worms. Lady beetles and other natural enemies or extremely hot, dry, windy weather often destroy enough eggs and young bollworms to control a threatening infestation without the use of insecticides. Nicotine or benzene hexachloride may be added to the insecticides to prevent aphids from becoming injurious.