UC Nursery and Floriculture Alliance
University of California
UC Nursery and Floriculture Alliance

Spring 2014 Field Observations: Polyphagous shot hole borer detected in Santa Cruz County

by Steve Tjosvold

A new invasive pest, the Polyphagous shot hole borer (PSHB), was recently detected by the California Department of Food and Agriculture (CDFA) in a survey trap in Santa Cruz County along Highway 17 close to the Santa Clara County border.  The tiny beetle is part of a new insect-disease complex that is threatening avocado, coast live oak, box elder and other trees in Southern California. The newly identified beetle penetrates the bark of many hosts and carries a symbiotic fungus (Fusarium species) that the larvae feed on. The fungus can then cause branch dieback in susceptible hosts. The same beetle and fungus have also been found in Israel, where the complex has caused severe damage to avocado trees since 2009.

The situation in Santa Cruz County is being sorted out by CDFA. The one beetle detection in the survey trap is only an indication that it is in the area, and it is not currently considered established.  Delimitation traps may be installed and potential hosts may need to be inspected in the oak and California bay woodland where the trap was placed.

PSHB is a Q-rated pest, which is a temporary designation of a pest that is suspected to be of economic importance. Information needs to still be gathered before any determination might be made if or how regulatory action would be enforced. So far, no quarantine has been established. PSHB could be transported in firewood, solid wood packing or shipping material, and possibly nursery stock with at least 2-inch diameter trunk diameter.

For more information see John Kabashima’s article in this issue of UCNFA News,  and the following links:


Thank you to Marylou Nicoletti, Santa Cruz County Agricultural Commissioner, for providing information about CDFA efforts in detection and delimitation for PSHB. 

Steven A. Tjosvold
Farm Advisor, Environmental Horticulture
UC Cooperative Extension Santa Cruz County
1432 Freedom Boulevard
Watsonville, CA 95076-2796
(831)763-8013 phone, (831) 763-8006 fax



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