What’s Bugging My Azaleas?
One of the more popular spring flowering shrubs in the landscape is the azalea. Most avid gardeners love azaleas because they come in a variety of sizes, shapes and colors, and because they can plant varieties, which will bloom from April through June.
While azaleas are one of the most colorful shrubs this time of year, they can easily become disfigured or destroyed by a number of insect pests. This includes azalea lace bugs, spider mites, azalea bark scales, azalea twig borers, azalea leafminers and azalea caterpillars.
The most prevalent insect attacking azaleas is the lace bug.
They are so named because of their lace-like wings. Both adult and immature bugs are usually found on the underside of leaves during April and May. They also produce a second cycle (brood) from July through September. Adult lace bugs are 1/8 inch long and 1/16 inch wide. This insect overwinters on your azaleas in the egg stage, and will hatch the following spring when the temperatures begin to warm.
Lace bugs damage azaleas by removing or sucking the sap from the plants as they feed. Damage is recognized by a blotched or spotted grayish appearance of the upper leaf surface. Eggs and spots of excrement resembling dark varnish will appear mostly on the underside of the leaves. Heavily infected leaves will turn yellow, then brown, and drop off prematurely.
A second insect pest of azaleas is spider mites or southern red mites. Spider mites are dark red and very small (0.4 mm long), and most active from January through June. Their damage closely resembles that of lace bugs. Spider mites feed on the lower leaf surfaces causing infested leaves to turn gray or brown and drop prematurely.
If you examine the leaves very carefully, you can usually see the mites or their webbing on the underside of the leaves. Another method of detection is to place a piece of white paper under several leaves. Tap the leaves on to the paper. If you have spider mites, then you’ll most likely see tiny red specks moving around on the white paper.
Azalea bark scale is a third insect pest of azalea. This insect produces a white or cottony sac that is often found attached in the axils of twigs and leaves during May to June and September through October.
Infested azaleas usually appear chlorotic, and severe infestation of azalea bark scale can weaken or kill your azaleas. Often the leaves are covered with a black fungus (sooty mold), which thrives on the honeydew or sugary substance excreted as the scale insects feed.
Another insect pest that can do substantial damage to those beautiful azaleas is the azalea stem borer. Stem borers are the immature stage (larvae) of the adult longhorned beetle. They are slender, yellow and legless grubs that bore inside the stems. This pest is most active from May through September.
Infested twigs will wilt and die as the larvae bore downward inside the twigs. Later in the season the infested stems break off at the base leaving the plant one-sided and unattractive. With small plants you may even find the entire plant falling over from borer damage.
As the stem borer larvae bore down through the stems into the roots to overwinter, coarse sawdust like frass is expelled through holes in the bark of the stem and at the base of the plant. Infested twigs wilting then follow this.
Using an approved insecticide can easily control all the insect pests discussed up to this point. With the stem borer, you should cut off and burn any infested stems as soon as they are noticed during the growing season. If the shrubs are reinfected year after year, it will then become necessary to protect the azaleas with an approved insecticide.
The azalea leafminer or leafroller is another pest of azaleas. This leaf-mining larva is yellowish and 1/2 inch in length. As the young larvae mine and feed within the leaf, they cause the formation of brown blisters on the leaf surface. At this point the leaf can be held up to light, and you’ll actually see the leafminer inside of the brown blister.
As the larvae mature, it emerges and moves to a tip of a new leaf. It will then roll the tip up for protection as it feeds and grows. When the leafminer has finished growing, it rolls up the leaf margin and spins a cocoon. Adult moths will later emerge from the cocoon, mate, and then deposit eggs for another generation or cycle.
Azalea leafminers are usually active from April to June. Seriously injured leaves turn yellow and drop prematurely, resulting in an ugly plant.
A final pest that I would like to mention is an azalea caterpillar. These insects usually defoliate most of your plant before they are ever detected. This usually occurs during the months of July through September.
The azalea caterpillar feeds in groups, and can easily be detected as the plant’s younger leaves are literally “chewed up”. Azalea caterpillars vary in length from 1/2 to 2 inches, and are reddish or brownish black in color with white and yellow stripes and a reddish head.
There are other insect pests that occasionally attack azaleas. In general, all that infest azaleas can be controlled with an approved insecticide. If you find that the pest population is out of control on your prized azaleas, then you can contact any Extension Center for the safest and most recent method of control.