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How to Manage Pests

UC Pest Management Guidelines


Sap leaking from shothole borer holes.

Prune

Shothole Borer

Scientific name: Scolytus rugulosus

(Reviewed 6/06, updated 6/06)

In this Guideline:


DESCRIPTION OF THE PEST

Shothole borers are tiny brown or black beetles; their white legless grubs mine the tree's cambium layer (sapwood). 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 can girdle the tree, causing tree or branch death.

MANAGEMENT

Shothole borers invade trees that have been previously damaged or weakened from disease. Maintain trees in a sound and vigorous condition, with sufficient fertilizer, water, and sunburn protection to prevent attack by this beetle. Prune to eliminate areas in older trees infested with shothole borer. Remove severely infested trees. Shred or haul to the dump 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 populations can emerge from these materials before they dry out, and beetles will then migrate into orchards. There are no insecticide treatments recommended for this insect.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Prune
UC ANR Publication 3464
Insects and Mites
C. Pickel, UC IPM Program, Sutter/Yuba counties
F. J. A. Niederholzer, UC Cooperative Extension, Sutter/Yuba counties
W. H. Olson, UC Cooperative Extension, Butte County
F. G. Zalom, Entomology, UC Davis
R. P. Buchner, UC Cooperative Extension, Tehama County
W. H. Krueger, UC Cooperative Extension, Glenn County
Acknowledgment for contributions to Insects and Mites:
W. O. Reil, UC Cooperative Extension Solano/Yolo counties

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