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Skaggs: Drought stress can weaken azaleas

POSTED: April 8, 2008 5:00 a.m.

For many people, spring doesn’t truly begin until the azaleas are blooming. It is hard to imagine spring without the vivid blooms of this beautiful flowering shrub.

Azaleas are fairly tough plants when given the afternoon shade they so desperately need.

Due to the drought of 2007, many azaleas went into winter in an already weakened condition. Azaleas are some of the first ornamental plants to experience drought stress, and unfortunately drought stress can make the plant more susceptible to disease and insect pests. As a result, damage from the azalea lace bug could be more prevalent in 2008.

Since its introduction from Japan in the early 1900s, the azalea lace bug has become a serious pest of azaleas.

This bug prefers the evergreen azalea varieties, but also infests native, deciduous azaleas. Mountain laurel may also be attacked by the lace bug.

The smooth, white egg of the lace bug, which is only a few millimeters in size, is flask shaped. It is usually deposited in the underside tissue of a young leaf along the mid-rib or large vein. Each egg is inserted in the tissue with its neck slightly above the leaf surface

Female lace bugs lay groups of eggs on the underside of the leaves in September and October. These eggs overwinter and hatch during March, April and May.

A large population of lace bugs can build up during these months. A second generation develops during the summer.

Because of the extended egg laying period, it is quite possible to find all stages together under a leaf at the same time. Usually two generations are produced in a year.

Lace bug injury is caused by the immature nymphs and the adults as they extract sap from the under surfaces of the leaves. The adult is one-eighth inch long and one-sixteenth inch wide. It has lacy wings with brown and black markings and light brown legs and antennae. The nymph young lace bug is almost colorless at hatching but soon turns black and spiny. It sheds its outer skin six times before reaching the adult stage.

The damage caused by this pest appears as spotted discoloration or bleaching of the upper surfaces of the leaves. In severe infestations, the leaves become almost white, many of them drying completely and dropping off. The underside of the leaves are also disfigured by the black, dry, shiny excrement and cast skins of the lace bug.

Repeated applications of an insecticide are usually needed to effectively control lace bugs. The first application should be made as soon as nymphs appear in the spring, followed by a second application seven to 10 days later. Three or four applications may be needed at monthly intervals.

Thorough coverage of the undersides of the leaves where the insects are found is essential if good control is to be expected. Several readily available insecticides will do a fine job in controlling lace bugs.

Two good options are Ortho Systemic Insect Killer (acephate) and Bayer Advanced Tree and Shrub Insect Control (imidacloprid).

Billy Skaggs is an agricultural agent and Hall County Extension Coordinator. Phone: 770-531-6988. Fax: 770-531-3994.



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