Check your azaleas now to see if you find bare stems that have recently been stripped of leaves. Look closely and you may find small azalea caterpillars with insatiable appetites. They can be serious pests of azaleas in the southeastern US ranging from Maryland to Florida and west to Arkansas and Kansas. Azalea caterpillars feed primarily on the leaves of azalea but also have been found on apple, blueberry and Red oak.
There is usually only one generation per year but in some southern states larvae are present from July to October. The young larvae are yellow with seven red longitudinal stripes and a black head and they feed gregariously, skeletonizing leaves. As they mature they become highly colored. Mature larvae are predominately black with a red last segment and eight broken yellow (or sometimes white) lengthwise stripes. The head and legs are bright red and they can measure 2 inches long. Older larva eat entire leaves so take action as soon as possible.
The semi-skeletonized leaves dry up, turn brown, and remain on the plant for several days. If disturbed some of the caterpillars drop one or two inches below the infested leaf and hang by a silken thread. When it is disturbed, the caterpillar raises its front and rear ends into the air.
The azalea caterpillar does much of its damage during the early stages of its larval development, before it grows to its mature stage of a 2-inch caterpillar and is detected. Some describe the fully grown caterpillar as scary looking partially because of the white hair. It is harmless and can be hand-picked and disposed of to avoid further damage and reproduction.
If you do not choose to hand-pick these critters or you have too many to handle, you can treat with Bt or Bacillus thurigiensis, the active ingredient found in Dipel or Thuricide. Bacillus thurigiensis is a microbial insecticide also known as a biological control agent. This product is used specifically for treatment of caterpillars because of its low toxicity to humans and non-target insects. Follow the label carefully when applying to avoid spraying Bt in areas where you are trying to attract butterflies. Other chemicals are available for larger caterpillars including: bifenthrin, lambda cyhalothrin, permethrin, acephate, carbaryl and cyfluthrin. As with all pesticides, read and follow all label instructions and precautions.
Although these caterpillars can be controlled with insecticides or hand-picked, adults can return after overwintering in the soil or a sheltered place and lay more eggs. Female moths deposit masses of 80 to 100 eggs on the underside of leaves. Regular checking your plants can help with critter control.