Locust Borers in Oregon

FS 328 June 1996 Locust Borers in Oregon

J.D. DeAngelis and P. Hamm

The locust borer, it is important to apply insecticides at Megacyllene robiniae just the right time. For high-value (Foster), is a pest of ornamental trees, spray an insecticide on black locust (Robinia the trunk and lower limbs when adults pseudoacacia) and its are flying but before they lay eggs; that several varieties. This is, apply from mid-August through mid- beetle (Figure 1) SeptemberDATE. (Figure 3). attacks the trunk and Sprays must be applied before eggs larger branches (more hatch and larvae are able to bore into than 2 inches in trees. Remember that locust borers may diameter) of its host OFnot be the primary cause of death for tree. The beetle prefers trees that are at least 4 years old, though it less often attacks trees or Figure 1.—Adult locust borer. Colors resembleOUT those of a branches greater than yellowjacket wasp: yellow on black. Note the W-shape about 6 inches in pattern on the back, behind the head. diameter. IS The adult beetle itself causes no harm the sapwood and heartwood, pushing the except to lay eggs that hatch into the boring material (sawdust) out of the tree. wood-boring larvae. This material may accumulate at the As the larvae develop, they riddle the base of the tree and can be the first sign tree with tunnels (Figure 2). Otherwise that the tree is infested. healthy trees can survive a fair amount of locust borer damage, although Identification information: weakened limbs may break in strong The locust borer beetle is about 3 winds. Many times, however, locust /4 inch long, black with bright yellow borers attack trees that already are stripes and very long antennae weakened or dying. Thus, it may seem (Figure 1). A yellow W-shape pattern that the locust borer has killed them. extends across the beetle’s back. You Beetles fly and lay eggs in early fall may find adult beetles visiting golden- (Figure 3). There is only one generation rod flowers to feed on pollen. The locust a year. Eggs are laid in cracks in barkcurrentborer can be confused with the painted along branches and PUBLICATIONin the main trunk. hickory borer, which looks similar. Eggs hatch in about a week, and Figure 2.—Locust limb (split and cross- Control larvae bore immediately into the bark section) with borer damage. until they reach the relatively thin layer Woodpeckers and other birds are of living phloem tissue.most There they feed. important natural enemies of the locust By mid-June of the following year, borer. Jack D. DeAngelis, Extension entomol- larvaeTHIS may have grown to 1 inch in Chemical control of the locust borer ogy specialist; and Phil Hamm, length, while feeding under the bark. At has not been very successful. However, Extension plant pathologist; Oregon this point, theFor larvae begin to bore into if you attempt to protect individual trees, State University. http://extension.oregonstate.edu/catalog

OREGON STATE UNIVERSITY EXTENSION SERVICE J F M A M J J A S O N D

Beetles active

Bark applications

Egg laying DATE. Larvae develop

Trunk tunneling OF

Figure 3.—Life cycle and management of the locust borer (MegacylleneOUT robiniae). IS otherwise healthy trees. More often, Consult the latest edition of the PNW University, 422 Kerr Administration already weakened or diseased trees are Insect Control Handbook for specific Building, Corvallis, OR 97331-2119. overcome. Therefore, it may not pay to control suggestions using chemicals and For additional information, call your treat until you solve the other problems, other means; these suggestions are listed county office of the OSU Extension which could include drought stress, root in the Ornamental Pests section. The Service, or write to Extension Entomol- disease, and other root injuries. Handbook is available from Extension ogy, Oregon State University, Cordley and Experimentinformation: Station Communica- 2046, Corvallis, OR 97331-2907. tions, Publication Orders, Oregon State

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