ELM LEAF BEETLE

ELM LEAF BEETLE

The elm leaf beetle feeds on all species of elms. Repeated defoliations cause a weakening or death of the trees. The beetle lives over winter as an adult. In the spring it eats holes in the young leaves and lays its eggs on the under sides of them. The eggs hatch in about a week, and the young larvae skeletonize the foliage, causing it to dry, turn brown, and fall to the ground. Full-grown larvae pupate in the ground or in crevices in the bark of the lower trunk. In about a week they become adults and emerge. Around Washington, D. C., there are two generations a year; in Oregon there may be three.

The beetle occurs in the United States from Maine to North Carolina and westward to Arkansas and Michigan. It occurs also in Idaho and along the Pacific coast from Washington to California.

Control: Pupae and young beetles can be killed by soaking the ground and the trunk of the tree with a spray containing nicotine sulfate. For small amounts, mix 1 pint of summer oil and 4 tablespoonfuls of nicotine sulfate (40 percent) in 6 1/4 gallons of water. For larger amounts, mix 2 gallons of the oil and 1 quart of nicotine sulfate in 100 gallons of water.

The foliage of elms can be protected by spraying the under side of the leaves, when they are about two-thirds grown, with either lead arsenate or DDT. Lead arsenate spray is prepared by mixing 1 1/2 level tablespoonfuls of the powder in 1 gallon of water (or 3 pounds in 100 gallons) and adding three-fourths teaspoonful of linseed oil per gallon, or three-fourths pint (12 ounces) per 100 gallons of the spray mixture. DDT spray is prepared by mixing 2 teaspoonfuls of a 25 percent DDT emulsion concentrate, or three-fourths teaspoonful of a 50 percent DDT wettable powder per gallon of water. To make 100 gallons, use 1 quart or 1 pound, respectively. These sprays are applied with hydraulic equipment.

For mist-blower applications, a concentrated lead arsenate spray is made up of the following materials: Lead arsenate, 1 1/2 pounds; cottonseed oil or fish oil, 4 1/2 ounces; and enough water to make 1 gallon. A DDT spray is prepared for application by mist blowers by formulating the following: DDT 1 pound, xylene 2 1/2 pints, Triton X-100, 1 1/2 ounces (3 tablespoonfuls), and water to make 1 gallon; or DDT 50 pounds, xylene 15 2/3 gallons, Triton X-100 5/8 gallon, and water to make 100 gallons. The Triton X-100 acts as a spreader. Only 2 quarts of a 6-percent emulsion of DDT are needed to treat a 50-foot elm tree with a mist blower.