Professional Management of Invasive Shothole Borers (ISHB) in Sonoma County
What Are Invasive Shothole Borers?
Invasive shothole borers (ISHB) are a group of cryptic species of ambrosia beetles within the genus Euwallacea. The term "cryptic" is used to describe species that are visually indistinguishable from each other and can only be identified through DNA analysis. The two species of ISHB present in California are the polyphagous shothole borer (PSHB) and the Kuroshio shothole borer (KSHB).
Female ISHB are approximately 2 mm (0.08 in) long and range from brown to black in color. Only females can fly and disperse to other trees. Males are smaller, around 1.6 mm (0.06 in), and range from light brown to black with no wings.
Both males and females spend most of their lives inside trees within channels called galleries that the females create by boring into trunks or branches. Once the larvae grow into adults, the beetles mate inside the galleries. Females then disperse to start their life cycle over again.
Invasive shothole borers do not eat wood. Like other ambrosia beetles, they feed on symbiotic fungi that they "farm" inside trees. These fungi infest the tree tissue, causing a disease called Fusarium dieback.
For more detailed information regarding this pest, visit UC Agriculture and Natural Resources.
Why Are Invasive Shothole Borers a Problem?
The invasive shothole borer is known to kill Sycamores and Valley Oaks, which are common trees in our urban and riparian habitats. The death of these trees will drastically reduce our canopy in the Bay Area and carry the added risk of turning healthy trees into fire hazards that threaten people's safety.
Rather than directly killing trees, ISHBs bore tunnels and introduce a fungus that disrupts the tree's vascular system, hindering water and nutrient flow. This weakens the tree, causing branch dieback, loss of leaves and, ultimately, tree death. The dead trees become brittle and more susceptible to breaking apart, posing a danger to people and property.
Increased Fire Danger Posed by ISHB
Forests and landscapes with a high number of dead trees become tinderboxes, as dead trees dry out faster and burn more intensely, fueling wildfires. This creates a dangerous situation, especially in populated areas where fires can easily spread to homes and buildings. The dead material serves as abundant fuel for wildfires, exacerbating their intensity and spread. Additionally, the loss of live trees reduces the moisture content and windbreak capacity of forests, further increasing the susceptibility of these areas to fires. Consequently, effective management and control of shot hole beetle populations are crucial to mitigating fire hazards and protecting forest health.
Here in California, ISHBs are a particular concern. They've infested many urban and native trees, increasing fire risk near communities. As it currently stands, there are no known natural enemies or pheromone lures to help manage the pest. In fact, there are many areas in the Bay where treatment will not be made due to access or economic challenges. These realities will keep this pest active in our region for the foreseeable future.
How to Manage Invasive Shothole Borers
This pest is best managed with the use of trunk-injected insecticides and fungicides. Injections at the base of the trees using Emamectin Benzoate and Propaconizol are the only recommended course of treatment. When trees die, they must be chipped and stumps ground to 1 inch in diameter for 100% control, including any surface roots. Be sure to dispose of chips at a recycling facility. Do not move chips around and dump them unless sterilized under clear plastic for 6 weeks at temperatures averaging 95°F.
Contact Image Tree Service today for fast help. Dial (707) 723-1214 or fill out a quick formto get started now.
Host List
Susceptible to ISHB-FD (may cause tree death)
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