How to Manage Pests
UC Pest Management Guidelines
The adult moth is gray with a wing expanse of 0.75 to 1 inch (19–25 mm) and brown and black markings on the wings. Adult females lay eggs near where callous tissue has developed, such as at pruning wounds, crown galls, or scaffold crotches. Larvae bore into the tree to feed on vascular tissue. Mature caterpillars are dusky white or pinkish and are about 1 inch long. American plum borer overwinters in a protective cocoon spun in a sheltered location on the tree; pupation takes place in spring. There are three to four generations each year.
Larvae attack soft, spongy, calluslike tissue, which occurs at graft unions, tree wounds, and in olive knots. They can continue to feed into normal tissue, girdling limbs, which can cause small branches to break. Gummy frass and liquid exudate may occur around injured wood.
Monitor trees in spring and summer for frass and gum pockets. The borer can be detected by brownish frass and webbing at feeding sites. If larvae are present, remove and destroy infested wood if possible. If wood cannot be removed, spray trees with a hand held sprayer from one foot above the scaffold crotch to one foot below, two to three times during the growing season. The first application should be mid- to late April and subsequent applications at 6-week intervals. Efficacy is improved if the trunk is painted immediately following a trunk spray with a latex paint to protect against sunburn. The paint helps to preserve the insecticide and give protection over a longer period of time.
UC IPM Pest Management Guidelines: Olive