The polyphagous shot hole borer (PSHB), a forest pest from Southwest Asia, is attackingPest_PSHB and killing hundreds of California native tree species, including coast live oak, western sycamore, and red willow.
While most bark beetles feed on the tree itself, PSHB feeds on a fungus it introduces and transports from tree to tree. The fungus spreads throughout the tree, damaging the tree layer that carries water and minerals up the tree from the roots. The tree is effectively starved. The resulting damage varies from tree to tree and can include:
- Discolored wood
- Leaf discoloration and wilting
- Weakened structural integrity
- Dieback of limbs from the tree’s tips and roots inward
- Increased susceptibility to other pests and disease
- Tree death.
PSHB infestation has contributed to the decline of native woodlands, reduced canopy cover near river and stream banks, and reduced habitat for several threatened and endangered species. Additionally, the devastation has resulted in millions of dollars of damage to native restoration efforts and agricultural production.
Gold spotted oak borer (GSOB) and Kuroshio shot hole borer (KSHB) are also presenting serious threats to California native trees.
Managing the Threat
Treatment methods being researched at the University of California, Riverside are are not available for public use. Current management programs for these pests are focused on limiting their spread into new areas and protecting healthy trees.
Spread limitation measures of infected/infested trees include:
- minimizing firewood transportation (“Buy Where You Burn”)
- disposing infested material by chipping, grinding, and tarping which uses heat generated by the sun to kill beetle larvae (USDA 2013).
Protecting healthy trees includes:
- practicing appropriate cultural practices (irrigation, mulching, pruning, and fertilization at optimal levels)
- using plants and soil known to be free of pests and pathogens
- cleaning/sterilizing tools that come into contact with infected plant material.
Dudek certified arborists certified provide ongoing pest inspection monitoring. Monitoring efforts include identifying pests through rapid woodland assessment monitoring, ongoing pest trapping, and visual woodland and urban forest assessments. Once pests are found, Dudek arborists record the location and extent of the outbreak, establish an action threshold, and provide management options and treatment recommendations.