American Plum Borer—Euzophera semifuneralis
Larvae of this moth (Pyralidae) occasionally bore in fruit and nut trees, mountain ash, olive, and sycamore, mostly in young trees.
American plum borer attacks some of the same hosts as other borers, including clearwing moths, flatheaded borers, and shothole borer, but their cultural and physical controls differ. Before taking control action, distinguish among these pests, such as by using a hand lens to examine the arrangement of small hooks on the bottom of larval prolegs.
American plum borer adults are gray moths with brown and black wing markings. Larvae are dull green, pinkish, or white. Both are up to about 1 inch long.
Beginning in about April, adults emerge, mate, and the female moths lay eggs in bark wounds. The newly hatched larvae immediately enter the wound to chew and feed on the underlying cambium. Larvae develop through several increasingly larger instars. Mature larvae pupate in a silk cocoon in bark crevices or damaged wood in trees. They overwinter as mature larvae in a cocoon within the tree. American plum borer has three to four generations per year.
Larvae feed in cambium around main branch crotches, the lower trunk, and root crown, causing extensive gumming, reddish orange frass, and webbing. This weakens limbs, which often break during windy conditions, and sometimes kills young trees.
Avoid bark wounds; larvae can enter cambium only through relatively fresh bark wounds. Pruning cuts, injuries from sunburn or weed trimmers, and bacterial galls and canker fungi make trees highly susceptible to infestation. Take protective measure, such as whitewashing, or painting lower trunks of young trees with interior white latex diluted with an equal amount of water to prevent sunburn.
Where damage is unavoidable or already present, a residual, contact insecticide can be applied from about 1 foot above the main lower branch crotch to the soil line. A professional applicator usually must be hired to apply an effective product and rate for trunk application.
Peak egg laying during the first generation is an optimal treatment time. Use pheromone-baited traps to determine the peak in adult flights, which coincides with the peak egg laying. Reapplication during peak flight in later generations may also be warranted. Alternatively, monitor young trees in spring and summer for frass and gum pockets. If larvae are found, spray trunks two or three times during the growing season at 6-week intervals starting in mid-April.
Plum borer larva
American plum borer adult
Frass from larvae
Damage to scaffolds