Test Your Knowledge - September

A red-headed azalea caterpillar
A red-headed azalea caterpillar
Chris Evans, River to River CWMA, Bugwood.org

Yes, this is a red-headed azalea caterpillar!

The red-headed azalea caterpillar (Datana major) is a major pest of azaleas in the Southeast from Louisiana to Florida and north to Virginia. Azaleas are the preferred host, but Datana major have been reported on apple, blueberry, red oak and andromeda. Most damage occurs in August and September.

The adult moth is light brown with a 1¾-inch wing span.

An adult moth of the red-headed azalea caterpillar
Natasha Wright, Florida Dept. of Agriculture and Consumer Services, Bugwood.org

In the spring, the female moth will lay 80 to 100 eggs on the lower surface of leaves.

Eggs that will hatch into red-headed caterpillars
Eggs on underside of azalea leaf
Chris Evans, River to River CWMA, Bugwood.org

Later that season the first instar caterpillars will emerge and feed in groups on the undersides of leaves.

First instar caterpillars
First instar caterpillars
James Baker, NCSU

The first instar (youngest caterpillar stage) caterpillars quickly reach about 3/8 - inch long and 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.

The typical u-shape of the azalea caterpillar when it is disturbed
Characteristic u-shape of azalea caterpillar when disturbed
Chris Evans, River to River CWMA, Bugwood.org

Young caterpillars will skeletonize the leaves, but consume the entire leaves as they mature. Many azaleas are greatly defoliated before the red-headed azalea caterpillars are detected.

Azalea caterpillars eating leaves
Red-headed caterpillars eating azalea leaves
Chris Evans, River to River CWMA, Bugwood.org

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 young (less than ¾-inch long). Brands of B.t. that are available for homeowners to purchase include, but are not limited to: Green Light Worm Killer Concentrate, Safer Caterpillar Killer, American Brand Thuricide, 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.

Millie Davenport
HGIC Extension Agent

Page maintained by: Home & Garden Information Center

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.