How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PEST

Shothole borers are tiny brown or black beetles. Their white legless grubs mine the sapwood of the tree and often reduce it to powder. Adult females bore tiny holes in the bark and lay eggs in the cambium layer of the tree. When the eggs hatch, young larvae feed and excavate secondary galleries at right angles to the egg gallery. The outline of the gallery system resembles a centipede. There are from one to three generations each year.

DAMAGE
Normally a number of shothole borer adults invade a tree at the same time. Healthy trees exude resin, which usually kills the insects. If the tree has injured or weakened areas, this resin buildup does not develop and the invasion is successful. Ultimately, larvae may girdle the tree, or tree part, and cause its death.

MANAGEMENT

Shothole borers invade trees that have been previously damaged. The nature of this damage dictates the course of preventive action. To prevent attack by this beetle, maintain trees in a sound and vigorous condition, with sufficient fertilizers, water, and sunburn prevention to keep uninfested tree limbs from becoming damaged. Pruning can be helpful in eliminating areas in older trees infested with shothole borer. Severely infested trees should be removed. Burn or remove all infested wood from the orchard before the growing season starts. Do not leave pruned limbs or stumps (healthy or infested) near orchards (for example, in woodpiles) as beetles can emerge from these materials before they dry out and migrate into orchards. Spraying for this insect is not recommended.

IMPORTANT LINKS

• Photos of borer damage

PUBLICATION

UC IPM Pest Management Guidelines: Apricot
UC ANR Publication 3433
Insects and Mites
W. W. Coates, UC Cooperative Extension, San Benito County
R. A. Van Steenwyk, Insect Biology, UC Berkeley
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
K. R. Day, UC Cooperative Extension, Tulare County
K. A. Kelley, UC Cooperative Extension, Stanislaus County
J. L. Caprile, UC Cooperative Extension, Contra Costa County
Acknowledgment for contributions to Insects and Mites:
L. C. Hendricks, UC Cooperative Extension, Merced County

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