Science: This Summer–DDT

Some commercial DDT preparations available to U.S. householders and gardeners have proved 1) disappointingly feeble, 2) harmful to plants and animals. But the U.S. Department of Agriculture last week declared that DDT, properly used, is still the best insecticide. To help citizens prepare for their annual battle with the bugs, the Department gave out some advice:

For flies, mosquitoes, bedbugs, roaches: Use a 5% DDT solution in kerosene, painted or sprayed on screens, walls, mattresses, under sinks, shelves. It is good up to six months but a fire hazard when first applied. Aerosol bombs are less effective than painting; although they kill all insects in sight, they leave no lasting deposit.

For dogs’ fleas, ticks, lice: Dust with a 10% DDT powder—but don’t use it on cats, because they lick off the dust. DDT solutions are dangerous to animals.

For shade trees: A .1% DDT emulsion destroys tent caterpillars, cankerworms, gypsy moths, elm leaf beetles, boxwood leaf miner and some other pests. Warning: it increases the population of red mites, by killing their parasites.

For vegetables: A 3% DDT dust against cabbage caterpillars, applied no later than 30 days before the cabbage is to be eaten, seems to be safe.

For grain bins and warehouses: Spray walls and woodwork with 5% DDT in kerosene. Don’t get it on the grain; treat bins when empty.

For fruit trees: Don’t use. Because DDT is a cumulative poison and apparently injures some plants, it is unsafe to use on most fruits and vegetables until further tests have been made.

The Department of Agriculture added a reassuring word: the danger of handling DDT has been greatly exaggerated. It is less toxic than other insecticides (arsenate of lead, nicotine), in two years has not injured any of the thousands of workers who have handled it constantly.