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How to Manage Pests
UC Pest Management Guidelines
Prune
Shothole Borer
Scientific name: Scolytus rugulosus
(Reviewed 6/06,
updated 6/06)
In this Guideline:
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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.
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.
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.
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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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