Help Stop the Polyphagous Shot Hole Borer

It's a small beetle, but it can have a devastating impact on the Arroyo's trees. The polyphagous shot hole borer (PSHB, Euwallacea sp.), which has recently been found across Southern California, burrows into susceptible trees and spreads two harmful fungi: Fusarium euwallaceae and Graphium sp. The fungi form a symbiotic relationship with the beetle, and together they cause the disease Fusarium dieback, disrupting the flow of water and nutrients.

The PSHB infests over 110 host species, including the following common native trees found in Arroyo parks and gardens:

You can help protect our native trees!

The Arroyo Seco Foundation is working with the City of Pasadena Department of Public Works to develop a plan to take on the PSHB and Fusarium dieback. The first step is to survey the extent of the infestation in the Arroyo Seco. We need a crew of dedicated volunteers to inventory trees in Pasadena's Arroyo Seco parks and track the infestation. With your help, we can determine the extent of its local presence and stop it before it spreads to the rest of our woodlands. You can read more about our program and how you can get involved below.

  • We will be surveying the parks along the Arroyo Seco in Pasadena. Each volunteer will be assigned an area that they will be responsible for. Volunteers are free to work on their own schedule, but we are asking for a commitment of at least 10 hours.
  • Volunteers will 1) visually assess trees for signs of PSHB infestation, 2) check the density of boreholes if the borer is present and 3) measure the diameter of the trunk. Data will be recorded and mapped using Esri's Collector for ArcGIS mobile application. The application is free and available for iOS and Android, and we will provide you with a user account tailored to your area. We will also provide tree identification guides and diameter measuring tapes. Volunteers must provide their own mobile device.
  • If you would like to help, contact ASF staff at to schedule a training session. Please include a signed release form (download here) as well. All volunteers must fill this out.
  • We are still determining the best way to address to the PSHB and to keep it from spreading. The data we collect will be crucial for obtaining grant funding and developing response strategies, including restoration projects if necessary. Thank you for your support!