One of the favorite plants in the landscape is the azalea. In April, these plants produce some of the showiest flowers in the landscape.
But care needs to be taken now so they will flower at their best. One way to help retain the flowers is to properly prune the plants. This needs to be done in the spring or early summer. The best time is immediately after the flowers are shed. Proper fertilization and irrigation are needed as well.
One thing gardeners can do now is to control insects that feed on these plants, such as the red-headed azalea caterpillar and azalea lacebugs.
The red-headed azalea caterpillar (Datana major) is a considerable azalea pest in the Southeast. In our area, most of the damage occurs in late August and September, with mid-September being the time when they are most often seen.
The adult is a light brown moth with a 13/4-inch wing span. In the spring, the female moth will lay 80 to 100 eggs on the lower surface of leaves. Later that season, the first instar (youngest stage) caterpillars will emerge and feed in groups on the undersides of leaves. The first instar caterpillars quickly have a yellow body, seven red longitudinal stripes and a black head.
When mature, the caterpillar will reach 2 inches in length and have a black body, red head and legs, and broken yellow (occasionally white) lengthwise stripes. When disturbed, the caterpillars raise their heads and tails into a U-shape.
Young caterpillars will skeletonize the leaves and consume the entire leaves as they mature. Many azaleas are greatly defoliated before the red-headed azalea caterpillars are detected. This is the main problem with these insects. This defoliation will reduce the vigor of the plant and will cause it to use energy to put on new leaves.
Even though the caterpillars are hairy, they are harmless to humans and can be picked off by hand. It is best to remove the caterpillars as soon as an infestation is detected.
Bacillus thuringiensis (B.t.) is a low-toxicity biological control that is very effective if the caterpillars are found when small (less than 3/4-inch long). Brands of B.t. available to homeowners include Green Light Worm Killer Concentrate, Safer Caterpillar Killer and Bonide Thuricide.
If there has been an infestation of red-headed azalea caterpillars this year, make a note on next year's calendar to check for young caterpillars in late spring or early summer. Larger caterpillars will require a more toxic pesticide for control, such as carbaryl (Sevin 50WP) or cyfluthrin (Bayer Advanced Garden Multi-Insect Killer). As with all pesticides, read and follow all label instructions and precautions.
Another major pest of azaleas is the azalea lace bug (Stephanitis pyrioides ). Lace bug adults are about 1/8-inch long. The wings are highly sculptured, giving them a lacy appearance. The adults also have some dark markings on the back and wings. Their markings make them difficult to see on the leaf.
Both adults and nymphs have needle-like mouthparts they use to suck plant sap from the leaf's underside. As a result of the feeding damage, leaves develop pale speckling on their upper surfaces, giving them a grayish cast. When damage is severe enough, the whole leaf appears white and drops early. This early leaf drop can make the azalea susceptible to some of the dieback diseases.
Because the lace bug feeds on the underside of the leaf, most people do not see them until damage is visible.
Black, shiny bits of insect waste and cast-off skins from immature worms also can be found on the undersides of leaves.
There are two generations of this insect each year. The first generation occurs March through May, and the second is in September. I have seen a number of samples with lace bugs on them lately.
If the insect is controlled in April, there is a smaller chance it will be a problem in September.
Lace bugs have several natural enemies that feed on them, including lacewings, assassin bugs, spiders and predaceous mites. However, when lace bug populations get out of hand, chemical controls must be used. Insecticidal soaps may give some control of young lace bugs, and complete coverage of all leaf surfaces is essential.
For adult lace bugs, recommended insecticides include malathion, carbaryl, cyfluthrin and imidacloprid. The imidacloprid is mixed with water and used as a soil drench around the plants.
If imidacloprid is used in the spring, it will give season-long control.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at email@example.com.
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