Polyphagous Shot Hole Borer (PSHB) Detected in Sierra Madre

City staff has been alerted to a number of new tree wounds in public trees in the downtown and Canyon areas. Investigations and consultations with local arborists have concluded that the Polyphagous Shot Hole Borer (PSHB) has very likely found a host in the trees on the eastern side of Mary’s Market Parking Lot, and could very possibly be existing in a number of private trees in the area. The downtown trees, however, do not appear to have been infected by the pest at this time, and will continue to be closely monitored. Staff is arranging to conduct laboratory testing on various samples to further confirm the borer and test for its associated and destructive fungus.

The PSHB beetle and its associated fungus is a very destructive pest that has recently been found in parts of Los Angeles and Orange Counties. It is also a very unique pest in the variety of tree species that have been shown to be hosts. At this time, known hosts include Sycamore (detected in Sierra Madre), Box Elder, Castor Bean, Avocado, Black Locust, English Oak, Liquidamber, Coast Live Oak, Persimmon, California Bay Laurel, Mimosa, Goldenrain, White Alder, Big Leaf Maple, Olive, and Wistaria Vine.

There are no known treatments for infected trees at this time. Staff is in contact with a number of agencies that are conducting experimental treatments. Containment of the infestation is the priority right now.

  • Species show various signs of the PSHB; in general look for a newer wound and look for a very small hole that would indicate boring activity. In most cases loose bark can be removed to locate the small hole.
  • Avoid movement of any infested wood out of the area. It is very important to purchase firewood where you intend to burn it.
  • Dead infested wood should be chipped and tarped for no less than 1 week before movement.
  • Tree trimming and landscaping equipment should be sterilized after each location with 25% household bleach or 70% ethyl alcohol.

Additional information will be provided as often as possible, including possible treatment and containment recommendations as well as locations of infestations.

For additional information contact the City of Sierra Madre Public Works Department at 626-355-7135.