
                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: THURSDAY, May 25, 1995                   TAG: 9505250037
SECTION: CURRENT                    PAGE: NRV-8   EDITION: NEW RIVER VALLEY 
SOURCE: JOE HUNNINGS
DATELINE:                                 LENGTH: Medium

KNOWING MORE ABOUT THESE INSECT PESTS WILL TIP THE SCALES IN YOUR FAVOR

Beside the hemlock wooly adelgid, the next most common insect sample I've seen this spring is scale. Scale insects are a peculiar group and look quite different from the more typical insects we encounter. Small, immobile, with no visible legs or antennae, they resemble individual fish scales pressed tightly against the plant on which they are feeding.

More than 150 different kinds of scales exist in Virginia. Many are common and serious pests of trees, shrubs and indoor plants.

Damage

Scale insects feed on plant sap. They have long, threadlike mouthparts (stylets) six to eight times longer then the insect itself. Feeding by scales slowly reduces plant vigor. Heavily infested plants grow poorly and may suffer dieback of twigs and branches. Occasionally, an infested host will be so weakened that it dies.

Control

Adult scales are protected from insecticides by waxy coverings. Therefore, any control measures must be aimed at unprotected immature scales (crawlers) or the overwintering stage.

Dormant oils are effective on the overwintering stage of most species, but they can only be applied in early spring before leaves appear. During the summer, control requires accurate identification of the pest species so that hatching dates of crawlers can be determined. Once the pest is identified and proper timing known, any one of several common insecticides can be used, such as diazinon, malathion, carbaryl and pyrethrin. These products can injure some house plants, so be sure to check the product label.

Armored scales

Scale insects can be roughly divided into two groups: armored scales and soft scales. Armored scales are so named because they secrete a protective cover over their bodies.

Most species overwinter as eggs beneath the female cover. In spring, eggs hatch into tiny mobile crawlers which migrate to new feeding sites. After a few days, crawlers settle, insert their mouthparts, and begin feeding. Soon they secrete a protective cover and lose their legs.

Large populations can build up unnoticed before plants begin to show visible symptoms. Some of our most common armored scale pests include San Jose scale, oyster shell scale and evonymus scale.

Soft scales

In general, soft scales are larger and more convex than armored scales. Many resemble miniature tortoise shells. Soft scales usually cover themselves with wax, but they lack the detachable protective cover for which armored scales are named.

Most soft scales overwinter as immature, fertilized females. In spring, they resume feeding, mature, and lay eggs. These hatch into tiny crawlers. After locating suitable feeding sites, crawlers settle and begin feeding. Some species lose their legs once they've settled, but others retain them and are able to crawl short distances to find suitable overwintering sites in the fall.

Except for soft scales, which infest indoor plants, most have only a single generation per year at our latitude. Our most common soft scale pests include lecanium, hemispherical and brown soft scale.

Plant clinics

If you'd like someone to look at a plant sample to determine if it is infested with scale, visit Lowes in Christiansburg Saturday, May 27, 9 a.m.-3 p.m., when Extension Master Gardeners conduct a plant clinic to assist home gardeners with their horticulture questions.

Master Gardeners are individuals who have received intensive horticulture training from Virginia Cooperative Extension. In exchange for this training, they share their gardening knowledge in their communities through projects such as the plant clinics. Look for Extension Master Gardener Plant Clinics at other local businesses and local libraries each Saturday, May through September. Call your Extension Office for a schedule and information about Master Gardeners.

Joe Hunnings is the Virginia Cooperative Extension agent for agriculture in the Montgomery County Extension office in Christiansburg. If you have questions, call him at 382-5790.

by CNB