Mediterranean Oak Borer

City staff are taking aggressive steps to mitigate two pests threatening to destroy significant trees and fundamentally alter the City's treescape, Emerald Ash Borer (learn more here) and Mediterranean Oak Borer (MOB). 

Unlike Emerald Ash Borer, which arrived in the US in 2002, MOB is a newer, emergent threat first discovered in the United States in California in 2017, and in Oregon in 2018.  The first Oregon white oak tree confirmed to have declined because of MOB infestation was identified in May 2023 in Troutdale.  In August 2023, several Wilsonville trees displayed symptoms of MOB infestation, which was confirmed in one 55' Oregon white oak (since removed) in the Frog Pond West neighborhood.

Upon confirmation of the MOB diagnosis, the City immediately began collaborating with ODA, ODF, Metro and the City's consulting arborists. The state, which is still developing best practices to help local jurisdictions identify and mitigate MOB’s presence, is providing assistance, as are consulting arborists at Bartlett Tree Experts and Morgan Holen & Associates, LLC.

In September 2023, arborists began injecting insecticides and fungicides into the trunks of publicly-owned large Oregon white oak trees, while City staff began reaching out to homeowners associations and land owners to discuss efforts to preserve trees located on private property. 

Resources

• Oregon Department of Forestry: MOB Fact Sheet
• Oregon Department of Agriculture:
  • MOB Fact Sheet
  • How You Can Help Stop the Spread of Invasive Pests
  • Report suspicion of MOB to ODA
• Identifying MOB: ODA Images of EAB and look-alikes

Tips

• To avoid spreading insects and diseases, don't transport firewood.
• Dead and dying oak trees may become hazardous; consult City Planning about emergency tree removal permits. 
• Trees suffering from drought may be more succeptible to infestation; supplemental watering and mulching during periods of drought are encouraged.
• Share information about MOB with others