The American plum borer, Euzophera semifuneralis, damages trees by feeding between the outer bark and sapwood much like the dogwood borer does to dogwood. The larval galleries are filled with frass (a dark, granular waste material). The caterpillars bore holes to the outside through which frass is expelled and through which sap sometimes oozes. With young trees, early season infestations can be detected by the wet spots on the bark where sap oozes from the cambium in response to feeding. These borers overwinter as caterpillars in white cocoons under the bark. In April, they mature into small, grayish- to reddish-brown moths that have two dark spots near the tip. These spots may be large enough to form a dark band across the wings. The moths fly at night, mate and lay eggs for a new generation. Females lay tiny pink to white eggs on bark, and after hatching, tiny new caterpillars crawl about looking for a way to bore under the bark. American plum borers are greenish to pink to almost purple caterpillars that grow to about an inch long. The head is dark brown. These borers often attack wounds, cankers or rough spots in the bark. Mature caterpillars spin a white cocoon inside of which they molt into a fusiform, brown pupa about half an inch long.

American plum borer caterpillars are about an inch long and pink to purple.

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American plum borer caterpillars are about an inch long and pink to purple.

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American plum borer moths are about an inch long.

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American plum borer moths are about an inch long.

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The hind wings of American plum borer moths are plainish.

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The hind wings of American plum borer moths are plainish.

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The American plum borer, is a sporadic pest of ornamental plums, cherries and maples and has been called a "minor" pest of peaches and apples in North Carolina. It also infests the black knot fungus galls on wild cherry as well as galls of a wide range of other hardwoods, especially in the rose family and walnut family. Extensive boring by the caterpillars can ruin fungus galls that would otherwise be used by wood turners to turn bowls and other objects.

At least two kinds of wasps parasitize the American plum borer and woodpeckers and other predators also help to moderate the population. One method of treating the borers inside a tree is to inject the tree with an aromatic solvent such as finger nail polish remover using something such as a oil can as an injector. As long as the solvent is not a registered pesticide, this is legal. Specimen trees can be protected by spraying with a pyrethroid insecticide in May and August. When used as directed, pyrethroids are very toxic to insects but are not particularly hazardous to humans and pets (other than fish-avoid using pyrethroids around pools, ponds, and streams). These insecticides are available in the garden sections of most big box stores as well as nurseries and garden center.

• American Plum Borer, Euzophera semifuneralis (Walker). Anonymous. No Date. Virginia Tech.
• American Plum Borer. Krawczyk, G. 2017. Tree Fruit Production, PennState Extension.
• NC State Extension Plant Pathology Publications
• NC State Extension Horticultural Science Publications
• North Carolina Agricultural Chemicals Manual

For assistance with a specific problem, contact your local N.C. Cooperative Extension center.

This Factsheet has not been peer reviewed.