What are these worms on my azaleas?

Published 7:51 pm Thursday, September 27, 2018

These are not “worms;” they are azalea caterpillars. These caterpillars are a common pest that we see in late August and throughout September. However, often these little pests have gone unnoticed until they cause a good bit of damage. Azalea caterpillars, Datana major, emerge from eggs on the underside of leaves in late June to mid-July. The caterpillars then go through several stages of growth. When first hatched, they are very small and green, roughly 3/8 of an inch. As they mature to a medium size, roughly 1-inch long, they become purple-colored caterpillars. The final stage of the caterpillar is roughly 2 inches and will have a black and yellow stripes with a red head.

The Azalea caterpillar is a prolific feeder that can really cause foliar damage to Rhododendron Spp. They are typically host-specific but will feed on blueberries as well. These caterpillars will be found feeding in groups; when disturbed, they will raise their heads and tails in unison, assuming a C-shape. The mature caterpillars will burrow in the soil to pupate. Adults emerge as a species of handmaid moths in early summer and deposit eggs on the underside of leaves in egg masses that number 80–100 eggs each. Adult handmaid moths have darker lines across the forewings and a cinnamon colored thorax.

As with most pests in the garden and around ornamental plants, the best control can be achieved by scouting for eggs on the underside of leaves in mid-June. Picking young caterpillars off of plants and dropping them in soapy water provides good control and is as organic as you can get! If caterpillars are caught in the earliest stage, a product containing Bacillus thuringiensis (B.t.) can be used with good results. One product with B.t. is Dipel, which is OMRI approved for use on certified organic plants. Another product is one containing the active ingredient Carbaryl (such as found in Sevin). As with all chemicals, make certain to read and follow the label. If azaleas are in bloom, do not use products containing Carbaryl, as they are very toxic to bee populations.

Register for the “What You Need To Know So You Can Grow” educational series taught at the Beaufort Extension Center this October to learn more about Soil, Growing Vegetables, Growing Fruit, Turf Management, Diseases and Pests of Ornamentals. This series will be taught on Thursdays beginning Oct. 4 from 6 p.m. to 8 p.m. The cost is $10 per class; those attending all of the classes will earn the Blacklands Area Friends of Horticulture “HomeGrown” certification and a free gardening guide published by the Extension master gardener volunteers in Beaufort County.  To register, contact Sam Bowden at the Beaufort County Extension office by calling at 252-946-0111.

This series answers real questions from eastern North Carolina. If you have a question to submit, please email to Gene Fox at gene_fox@ncsu.edu. Learn more on Facebook at the Blacklands Area Horticulture page or visit the Extension Office located at 155 Airport Road!

Gene Fox is the area agriculture and consumer horticulture agent for Beaufort, Hyde, Tyrrell and Washington counties.