What is this worm on my azaleas?
Published 10:59 am Friday, August 12, 2022
It’s that time of year again and the usual suspects are beginning to appear. This very colorful worm (a.k.a. caterpillar) on your azaleas is an Azalea Caterpillar (Datana major). They are very destructive little critters! In large enough numbers, they can defoliate an entire bush. Often, they are not noticed until the damage is already done.
The azalea caterpillar hatches around mid to late-August, earning the name Labor Day Worms. However, this year the calls are already coming in. Typically, we do not notice them until the damage is seen. The eggs are on the underside of the leaf and packed in as a tight cluster of white eggs numbering 80 to 100. The eggs will hatch and the young caterpillars will emerge having a yellow body with black stripes and a red head. As they grow, they will molt to a black body with yellow dots, the red head may or may not, turn almost purple. The way to distinguish caterpillars from other insects, like sawflies, is by the three sets of legs near the head. The azalea caterpillar will raise its head and curl its tail when disturbed to form a shape like the letter “C”. There are a few others that do this but not many.
Upon eating their fill of your azalea, they will crawl down the plant and burrow into the soil to pupate. It is here that they will spend the winter. In late Spring they will emerge as adult moths and begin the process all over again. Do not worry about handling these caterpillars, they are completely safe. They may however, regurgitate yellow juice onto your hand.
In a homeowner situation it is really best to pick the caterpillars off of the bush and smash them or place them in a bucket of soapy water. You can pick them off by hand if there are just a few or, you can shake the bush to remove them. If the infestation is really bad, you may need to go to a product containing B.t. (Bacillus thuringiensis). This is a natural, organic product that will control the young caterpillars. It is marketed under names such as DiPel. Spinosad is another organic insecticide that will work on caterpillars and some beetles. There are insecticides that will work such as Carbaryl (Sevin), Acephate (Orthene), and pyrethrin-based insecticides that end in -thrin. The insecticides are much more harmful to the beneficial insects on the bush, so beware of aphid or spider-mite spikes after using an insecticide. This is due to killing all of the beneficial insects that are predators of these pests.
Azalea caterpillars will only feed on rhododendron species for the most part. There has been documentation of feeding on blueberries however. So, if you have other azaleas, rhododendrons, or blueberries be sure to check them all.
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