By Wayne Farnsworth, BrightView Tree Care Services and Randall Oliver, UC ANR IPM
Tiny tree killing beetles that have become well-established in several Southern California counties are now showing up in CAI’s Channel Islands Chapter communities. Unlike many insect pests, invasive shot hole borers infest a wide variety of tree species, including many common ornamentals, avocados and California natives. Sycamores and box elders are among their favorites, and they also attack live oaks, valley oaks and alders, all of which are abundant in our area.
Invasive shot hole borers (ISHB) don’t actually eat wood, but they do cause structural damage when they tunnel into trees and create galleries where they introduce and “farm” a fungus to feed their larva. This fungus causes a tree disease called Fusarium dieback. Over time, as the fungus spreads within the tree’s inner layers, it disrupts movement of water in the tree. Deprived of water and nutrients, the tree suffers from branch dieback and breakage. Eventually, many infested trees die.
Those dead and dying trees pose potential risks to homeowners and their properties due to falling limbs and adding fuel for fires. They also represent a liability risk to HOAs and their management companies and contribute to the ongoing spread of the beetles to other trees in the area.
Supported by a grant from CAL-FIRE, the Ventura County Agricultural Commissioner’s Office recently began removing dead trees in Ojai, the first step in a plan to remove as many as a few hundred dead or dying trees in the county. Deputy Agricultural Commissioner John Beall notes that current funding for this project requires a focus on “leading-edge” areas toward Ventura County’s northern border with Santa Barbara County. Additionally, the Agricultural Commissioner’s Office will work with cities and communities in other parts of Ventura County to develop their own programs to address this growing threat.
In late June, the Agricultural Commissioner’s Office contracted with BrightView Tree Care Services to remove three large trees infested with ISHB (two in Ojai and one in Santa Paula). Dr. Ben Faber of University of California Cooperative Extension Ventura County is currently working with the Agricultural Commissioner’s Office in studying the infested woodchips from these removals. Brightview also performs tree inspections periodically for various customers, and we have GPS tree inventories of most of the properties we maintain in Ventura and Santa Barbara Counties. The inventory software we use has significantly improved our ability to monitor and track changes.
We advise HOAs and property managers to have a conversation with their tree care provider or landscape provider to ensure they are monitoring for this pest. If caught early, it is far easier to manage. Most reputable tree care providers should be able to identify it and make recommendations based on the condition of the infested tree.
Monitoring, removing infested branches, and treating trees when necessary are the best option currently since there are no natural predators or parasitoids for this pest. We have had pretty good success in managing this pest through chemical treatments. The method we use most is trunk injections, which gives two years of control and is safer for the environment than other methods.
Preventing the spread of this pest by only using mulch from known sources and not moving firewood is also critical to prevent it from moving into northern Santa Barbara and San Luis Obispo counties. Currently we dispose of infested wood by chipping the debris and hauling the woodchips to local approved processing facilities. Our crews also take special care to sanitize tools in between trees of known infection.
If you are not already familiar with ISHB, it is also helpful to learn how to identify some common signs of infestation. The University of California has published some great information on its website www.ishb.org, which also offers an updated list of susceptible tree species, resources on how to monitor and manage infested trees and a comprehensive online course.
Wayne Farnsworth is an Business Developer for BrightView Tree Care Services and is also a ISA Certified Arborist and Licensed Pest Control Advisor
Randall Oliver is the ISHB Communications Coordinator for University of California Agriculture and Natural Resources Statewide Integrated Pest Management.