Rhododendron Borer

Rhododendron Borer moth has a black head with green and white markings. The thorax is black and blue with a broad patch of pale yellow or shiny white on each side.

The abdomen is also black and blue with segments two, four, and five trimmed with yellow dorsally; legs are yellow and white apically and dark with some light color markings basally. The wings are transparent with a rusty-black fringe and some yellow scales. There is a tuft of black and yellow scales at the tope of the abdomen. The female has broader bands on segments two, four, and five than the male does. The female’s anal tuft is short and rounded, whereas the male’s is fan shaped. The moth has a wingspan of 10 to 15 millimeters. Larvae are yellow-white caterpillars approximately 13 millimeters long.

The adult is a clearwing moth that somewhat resembles a wasp. The adult female lays eggs on the bark of the plant. The borer is pale yellow with a dark head and about ½ inch long. It chews a hole to the inner bark and forms long tunnels in the branches. By late fall, it enters the sapwood where it survives the winter.

Life cycle:This species overwinters in the larval stage that is located shallowly in a gallery in the host sapwood. Pupation occurs in the spring, and adults begin emerging from pupal cases during the morning from mid-May through June. Adults do not feed and live for only a day or two. Females attract males with their pheromone during late morning and early afternoon.

Females contain an average of 40 eggs, and lay them at old pruning sites, narrow branch crotches, and bark crevices from mid-May through June. Young larvae hatch and bore into cambial tissue and then sapwood. Larvae continue to grow until they prepare to overwinter. They resume feeding in late March, undergoing seven instars until they are fully grown. Mature larvae cut exit holes through the bark, then retreat in the gallery, plugging it with frass. Pupation lasts about two weeks. One generation occurs each year in Pennsylvania.

Damage:Injury caused by this key pest in ornamental plantings of rhododendron tends to increase from year to year if an infestation is not effectively managed. Small host plants are susceptible and may be killed by a light infestation. Branches may be girdled, causing the leaves to turn yellow, then brown and die. Areas of the bark are killed and sawdust-like castings may exude from holes. Growth of infested plants is restricted and fewer blooms may be produced. Infestations can be detected by the presence of shallow, longitudinal scars in the bark on twigs and branches.

Scales insert their piercing-sucking mouthparts into the plant and feed on the juices. A large population will cause leaf discoloration, some dieback and an overall unthrifty plant appearance. These scales excrete a sticky, sweet liquid called “honeydew” which promotes the growth of black sooty mold fungus on contaminated surfaces.

Control:Nonchemical control is limited to pruning and destroying wilted branches. Chemical control with permethrin is directed at the adults. Treatment should take place in May and June. Thoroughly spray bark and repeat three times at 10 to 14 day intervals.

Beneficial insects often control this pest. Dormant oil spray can be applied to kill overwintering nymphs prior to new plant growth. Summer oil, acephate. carbaryl or diazinon can be used in mid-June or early July for the crawlers. Examine the bark of host plants to determine when or if the crawlers are active to help in the timing of any needed treatments.

If you have any questions about how to get rid of borer check out the rest of our website or go to our blog at http://nypestpro.blogspot.com.

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