Voracious Bug Feasts On Leaves

USA Today (Society for the Advancement of Education), June, 1999

Gardeners beware! There is a bug called a leafminer at large that can cause serious injury to plants by destroying leaf tissue, cautions entomologist Dale Pollet, Louisiana State University, Baton Rouge. Leafminers and other insects harmful to vegetation seem to appear in hordes, almost overnight. "Dry weather conditions, along with the heat stress on many plants, make us try to compensate by watering them, and that provides a windfall food source....

"The eggs are deposited in the leaf tissue, and the hatching larva feeds between the upper and lower surface of the leaf. creating a mine or gallery, which gives this pest its name. As the larva matures, the mine gets wider and longer. In some cases, it appears swollen."

With heavy infestations, controls are necessary. These pests are managed by killing the adults on emergence and preventing egg deposits or re-infestation. What is used depends on individual needs. "PH [the ratio of acidity to alkalinity] is critical when you try to control a pest like this because it is imperative that the material is available when the pest is there. PH should be between 5.5 and 6.5, otherwise the material will be short-lived and have little to no residual effect. Without some residual, you will have to repeat the spray and have greater potential for harm to the environment and the natural beneficial insect populations." Insecticides used by homeowners to control such pests include malathion, diazinon, dimethoate, cygon, and thiodan-plus. "It is important to read the labels because some plants should not be sprayed. Others have long harvest intervals, while others are only a day or two."

Most people bring these pests in from the nursery or store where they bought the plants, Pollet notes, so it is important to check the leaves before purchasing them. In many cases where only one or two leafminers are seen, several could be in the egg or early larval stages. "So be aware. Many leafminers are naturally occurring. Check plants early and often (at least once a week). When insects are detected, remove and destroy tunneled leaves. Preventive maintenance sprays should be made once or twice to control the problem."