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The Black locust borer is one of the few borers that attack the trees in late summer or early fall. Black locusts were at one time an almost perfect tree for Utah. They tolerated hot dry conditions. They tolerated heavy clay alkaline soils and they grew easily from seed. In spite of these adaptations, they are not widely planted anymore because of these borers. Host: Black locust (Robina pseudoacacia) and Idaho locust. May also attack honeylocust, (Gleditsia) and willow (Salix). Life Cycle: One generation per year. After overwintering as an immature larvae under the bark, it resumes feeding about the time buds begin to swell. Sap oozing from the bark surface in the spring indicates the resumption of feeding, which continues until late July. After pupating in the tunnels, adults emerge late July to the end of August. Eggs are laid near wounded bark. The adult is about 18 mm in length and a jet-black, long horned beetle with bright yellow bands. Mature larvae are round headed borers, white, about 25 mm long and cylindrical. The adult borer seems to prefer trees that are at least four years old. Once trunk diameter has exceeded 15 cm, it becomes less susceptible. Damage: The feeding tunnels of the grubs weakens wood and trunks becomes swollen in areas where feeding occurs. Control: Destroying infested trees and branches during winter and spring will control overwintering larvae. Probing the insect holes with a sharp wire may destroy larvae. The adults are active now and are visible crawling on the branches of the trees. Apply chemical controls to the bark to control hatching larvae before they bore into the trunk. Use a registered chemical to control the pest. Thiodan is the best choice for most applications. Read and follow all label directions. Spray the branches that are four years old and less than six inches in diameter because they are the ones that the insects will attack. This is a life threatening pest that will kill the trees if it is not controlled. Larry A. Sagers Regional Horticulturist Utah State University Extension Thanksgiving Point Office
