From the Viette's Views Gardening Blog
Last September, we received an e-mail from a fellow gardener in Richmond, VA who had noticed that caterpillars were devouring the current season’s growth on his azalea bushes. After some research, he determined that they were azalea caterpillars (Datana major). He had neither seen nor heard of these caterpillars before and was wondering if they were native to Virginia or an introduced species.
I have never seen these colorful (but destructive) caterpillars either but apparently they can be a major pest of azaleas, especially in the southeast. They are native to the continental US and Canada, but are most common in the southeastern US and the Mid-Atlantic States.
The azalea caterpillar (aka the red-headed azalea caterpillar) prefers to feed on azalea foliage but will also attack blueberries, apple trees, and red oak trees. They tend to feed in large groups and can quickly defoliate their target plants if they are not controlled.
The adult stage is a rather nondescript brown moth but the larval caterpillars are quite colorful. They have a black body with several broken yellow stripes along its length. The head and legs are red. The mature caterpillars are about 2 inches long.
Adult female moths lay up to 100 eggs on the underside of the host plant leaves. The eggs hatch later in the season and the tiny caterpillars begin to feed on the foliage.
The caterpillars go through several instars, growing larger during each stage, and usually continue to feed together in large masses. Because of this tendency to group together while they feed, they can strip a plant of most of its leaves in a short period of time.
Major damage from these caterpillars is usually observed in August and September when they are larger and eating voraciously. Though the damage from their feeding does not kill the shrub, it is certainly not aesthetically pleasing!
Controlling azalea caterpillars can be as simple as picking them off the shrubs. These are not stinging caterpillars despite the sparse hairs that cover their bodies, however, the problem is that there can be LOTS of them.
If you have a large infestation, you may need to resort to another form of control.
When the caterpillars are young and small, a liquid formulation of the bacteria Bacillus thuringiensis (Bt) (such as Bonide Thuricide) applied to the foliage will kill them when they eat the leaves. Bt is less likely to harm beneficial insects.
Bonide Captain Jack’s Deadbug Brew, another naturally derived organic insecticide, is effective in controlling the larger caterpillars when it is sprayed on the foliage. The trick is to cover the foliage that the caterpillars will be eating. Always read and follow the label directions when spraying any pesticide.
Special thanks to Walter Forkey for bringing this caterpillar pest to my attention and sending me some photos. He was able to successfully get rid of them with an approved pesticide and hopefully his azaleas will recover nicely in the spring.