Departments of Plant Pathology and Entomology
North Carolina Cooperative Extension Service
North Carolina State University

ORNAMENTALS
AND
TURF

North Carolina Pest News
Volume 11, Number 14, July 19, 1996
Stephen J. Toth, Jr. and Thomas A. Melton, editors

The information and recommendations in this newsletter are applicable to North Carolina
and may not apply in other areas.

From: James R. Baker and Stephen B. Bambara, Extension Entomologists

Stem Borers on Azalea, Rhododendron and Dogwood

Borers in the genus Oberea include the azalea stem borer and dogwood twig borer. These are small, slender longhorned beetles that emerge from damaged azaleas, rhododendrons, blueberries, dogwood and other woody ornamentals in late spring after the new vegetative growth has matured somewhat. These beetles fly to the new growth and chew a series of holes around the stem, then another series of holes 1/4 to 1/2 inch away. Between these rows of holes the beetles insert an egg into the bark. Within a few weeks this egg matures and a slender, white grub hatches and begins to feed within the stem. As the grub bores downward, the stem dies and wilts above the area girdled by the beetle. In shrubs, the grub continues to bore downward and eventually reaches the base of the plant where sawdust and other waste products are pushed out of the holes onto the ground. The dogwood twig borer usually kills back 30 to 40 inches of the branch. The grub usually overwinters in a cell excavated inside the plant close to the ground. The following spring the grub matures and molts into a pupal stage. A few weeks later, a new generation of beetles emerges from infested plants to continue the life cycle. Infested branches often die or they are weakened to the point that they break off easily.

For control of azalea stem borers, the plants can be sprayed in late spring with lindane or Dursban to prevent the beetles from laying eggs. Since this season has already passed, infested stems can be pruned out as soon as wilting is noticed (the stems have to be pruned off below the grub, otherwise the grub continues boring down toward the roots). These stems should be burned or otherwise destroyed. Ornamentals and Turf Insect Note No. 76 provides additional information on the azalea stem borer. Copies should be available in each county extension center in North Carolina.

Leaves damaged by phylloxera galls drop prematurely throughout the summer. It is too late to spray for these phylloxera now. There is additional information on the biology and control of phylloxera in Ornamentals and Turf Insect Note 49. Copies should be available in each county extension center in North Carolina. The best time to treat with pesticide for phylloxera is in early spring as the new growth is emerging, but before the galls close around the phylloxera and protect them from the pesticide.

Twolined spittlebugs are small (1/4 inch), dark insects that resemble overgrown leafhoppers. They have two orange lines across the wings. In late summer and early fall, the adult twolined spittlebugs fly to hollies (and other plants) to feed. They cause hollies to become splotchy and yellow and cause the leaves to drop prematurely. There is additional information on this pest in Ornamentals and Turf Insect Note No. 97, available in each county extension center in North Carolina. I recommend that heavily infested hollies be treated with Orthene, Dursban, Decathlon, lindane, or some other contact insecticide when the twolined spittlebugs become abundant enough to cause some alarm.

Peachtree borers are caterpillars of a clearwinged moth. The moths closely resemble paper wasps, but of course the moths do not sting. These moths emerge throughout the growing season, but the great majority of them are in flight between August 15 and September 15. Consequently, most of the borers can be preventively controlled by spraying with Dursban around September 1. The moths lay eggs at the base of peaches, plums and ornamental cherries. From these eggs hatch tiny, white caterpillars that bore into the bark and form a tunnel in the cambium at the base of the tree. If many borers infest a tree, the cambium may be completely girdled beneath the bark and the tree will die. The borers pupate inside the infested tree during late spring and summer and then emerge as moths a few weeks later. The only control at this time of year is to try to remove the borer from under the bark without injuring the tree excessively.

Termites are not usually a pest of living plants except during dry weather when they sometimes feed in the roots of living plants to obtain moisture. In trees, if there is a wound through the bark or through a dead root, they may invade the inner wood which is not really living tissue. For chemical control, I recommend Knox-Out brand of diazinon or Dursban. Fortunately, termites are not particularly resistant to pesticides. Termites seem to be difficult to kill because they occur naturally just about everywhere in North Carolina and they may migrate in from surrounding woods year after year.

Wheel bugs are predaceous insects that feed on various types of caterpillars and other insects; they immobilize, kill, and digest their prey by injecting them with powerful enzymes. Some predaceous bugs feed facultatively on plants as well if there are no insects around, but such feeding does not result in noticeable plant damage. If humans are unfortunate enough to be bitten by wheel bugs, the resulting wound is quite painful and takes a long time to heal. In the county extension centers in North Carolina are copies of Ornamentals and Turf Insect Note No. 65 which explains some of the biology and possible control of wheel bugs.

The hemlock woolly adelgid is also called the hemlock chermid, the hemlock chermes, the hemlock woolly aphid, and other names. They are small (about 1/32 inch), dark reddish-purple insects covered with a white, fluffy secretion. Some adults have two pairs of wings. Their mouthparts are thread-like and about 1/16 inch long. The eggs are brownish-orange. As the embryo inside matures, the eggs darken. The eggs are also hidden in the white, fluffy secretion. Hemlock woolly adelgid crawlers are very small, flat, naked, reddish-brown insects that move about actively. Settled crawlers are black with a white fringe around the edge and down the center of the back. Young adelgids live on twigs or at the bases of old needles. They soon secrete a white, fluffy wool that completely covers the body. Nymphs resemble adults but are smaller. At first naked and yellow, nymphs soon darken and secrete fluffy, white threads. Infested branches become covered with 1/8 inch round, fluffy white blobs. It only survives on hemlock. This is an extremely damaging pest of hemlock. The hemlock woolly adelgid is thought to have originated in the Orient. It has been known in the Pacific Northwest since 1927. In recent years, hemlock woolly adelgid has been found in the Northeast and as far south as Virginia; it was first found in North Carolina in 1995. Infested hemlocks become covered with dirty white globs of cottony puffs. Infested trees defoliate prematurely and may dieback completely.

The hemlock woolly adelgid overwinters as females within the fluffy masses. They begin laying eggs in February. From the eggs hatch tiny crawlers that settle down and feed. Older nymphs secrete the fluffy, white wool. Some nymphs develop into a winged form which leaves hemlock to lay eggs on an alternate host (spruce, although no native spruces seem to be suitable hosts). The rest of the nymphs develop into wingless females that lay eggs in a fluffy mass on hemlock. The second generation of adelgids on hemlock settle down as young nymphs in July to spend most of the summer as tiny black insects with a white fringe. In October or November they molt and begin to grow, producing the fluffy white mass.

The hemlock woolly adelgid is a difficult insect to control because the fluffy white secretion protects the eggs from pesticides. One good time to try to control it is in October when the second generation is beginning to develop. Insecticidal soaps and horticultural oils seem to be very effective for adelgid control. In addition, diazinon, Mavrik, Merit and Dursban are labeled for the hemlock chermes or adelgids, and all will give very good control if applied thoroughly. Trees that are heavily infested and show symptoms of decline should probably be sprayed for hemlock woolly adelgids. Horticultural spray oil can be applied during the winter and before new growth emerges in spring. Oil sprays may damage hemlock during the growing season, especially in dry weather.

Web page last updated on 22 July 1996 by Stephen J. Toth, Jr..