NC State Extension Publications

General Information

Azalea stem borers (Oberea myops, aka rhododendron stem borer and blueberry stem borer) are slender long-horned beetles about 12 to 58 inch long with yellowish brown heads and thoraxes. The wing covers are yellowish gray with dark outer margins, and there are 2 black spots on the thorax. The egg has been described as "yellow." The eggs occur under the bark.

The azalea stem borer is a slender, yellow, legless grub found inside the stem. No description is available for the pupa.

azalea stem borer beetle

Figure 1. Adult azalea stem borer laying eggs in a rhododendron stem.

Figure 2. Adult beetle of the azalea stem borer.

Figure 2. Adult beetle of the azalea stem borer. Scale bar indicates 1 cm.

Figure 3. Drawing of the larva (grub) inside a rhododendron stem

Figure 3. Drawing of the larva (grub) inside a rhododendron stem.

grub

Figure 4. Azalea stem borers are slender grubs that tunnel in host stems.

Biology

The azalea stem borer is found throughout the eastern United States wherever azaleas and related plants grow. Azalea stem borers infest azalea, rhododendron, blueberry and mountain laurel. Infested twigs wilt and die as the larvae bore downward inside. At this stage, symptoms may resemble those from aerial phytophthora blight. Later in the season, infested stems often break off at the base leaving the plant lopsided and unattractive. Small plants may break off completely.

Adult azalea stem borers emerge from mid-May through June. Eggs are inserted under the bark between two rows of holes chewed through the bark about half inch apart (Figure 4 and Figure 5).

The larva hatches and bores down the twig into the stem and eventually all the way to the crown of the plant. The stem is greatly weakened at the base. The larvae then bore down into the roots where thy spend the winter. Coarse sawdustlike frass is expelled through holes in the bark of the stem and at the base of the plant. Infested twigs wilt as the larva bores downward inside. The larvae pupate the following spring or two or three years later.

Figure 5. Damage caused to a rhododendron stem.

Figure 5. Damage caused to a rhododendron stem by the egg-laying of the azalea stem borer. Left arrows indicates damage. Right arrow shows a leaf scar. Scale bar represents 1 cm.

tunnel

Figure 6. Rhododendron stem cut away to show tunnel of azalea stem borer.

frass

Figure 7. Azalea stem borers expel frass from their tunnels through holes in the bark.

Control

Cutting off and burning infested stems as soon as they are noticed in the growing season is recommended for control. If shrubs have been reinfested year after year, it may be helpful to protect the plants with a pyrethroid insecticide such as permethrin or cyfluthrin. This should give adequate control if applied in spring after the new growth has emerged and hardened off somewhat in mid-May and again in early June. Consult the North Carolina Agricultural Chemicals Manual for specific recommendations. Look in the Trees and Woody Ornamentals section, under "Any Plant: Borers." Be sure to read and follow all label instructions.

Authors

Professor and Extension Specialist
Entomology and Plant Pathology
Professor Emeritus
Entomology and Plant Pathology

Publication date: Jan. 1, 1994

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