In Defense of the Trees
Invasive Beetle in Ojai
Photo by Brendan Cleak and Caryn Sandoval of One Apparatus
What do beautiful communities, rich wildlife habitats, parks, bird nests, our global climate, and tire swings all have in common? They all depend on trees, a notable symbol representing a healthy environment. Much of the conservation and restoration work undertaken by the OVLC has revolved around the planting and protection of trees. Since 2016, however, a newly arrived invasive beetle has been expanding its range in the Ojai Valley, creating a very real threat to our trees.
The first Polyphagous Shot Hole Borer (PSHB), spotted in the Ojai Valley added Ojai to a long list of affected communities. The PSHB is a small ambrosia beetle thought to come from Viet Nam. It is related to a second similar species (Kuroshio Shot Hole Borer) that together are lumped into the category of Invasive Shot Hole Borer (ISHB), and both are widespread in the southern areas of California from San Diego County up to Ventura County. Ojai is one of the newest infestations. The PSHB enters trees through boring and it brings with it a pathogenic fungus that causes Fusarium Dieback disease. Infected trees may experience branch dieback, canopy loss, and, in some cases, tree mortality.
Unlike many invasive insects that focus on specific tree species or crops, the PSHB can utilize and reproduce in a great many species of trees that include common landscape trees and native trees in urban and wildland areas. So far, researchers have identified 64 tree species that support the reproduction of the beetle and the associated fungus. Of these, 15 species are known to be particularly susceptible to damage and death caused by fusarium dieback including California sycamore, arroyo willow, red willow, black cottonwood, and our prized valley oaks.
The OVLC has been working with university scientists at the University of California Santa Barbara and through the University of California Division of Agriculture & Natural Resources to track the spread of the beetles and fungus. Beetle traps have been set up at a number of OVLC preserves and beetles have been captured on the Ventura River Preserve and the Ojai Meadows Preserve. Follow-up investigations have shown that the beetle is well-established in trees throughout the Ojai Meadows Preserve, and we are beginning to observe our first tree deaths in willows and cottonwoods near the Maricopa Highway. We continue to monitor affected trees and are working with scientists to develop a response strategy that may include treating some trees or possibly the removal of impacted trees to prevent the spread of beetles.
While there has been a lot of scientific inquiry regarding the spread and impact of the disease, little is known about how to effectively treat it. Since the beetles do not need to leave the tree to reproduce, chemical pesticides are likely to be ineffective unless injected directly into the tree (at a very high cost). In some cases, removing trees and chipping them may help control the spread of the beetles. In some species, affected limbs can be removed and chipped if the trunk is not infested.
As we work on a response plan, our community can play an important role in limiting the spread of beetles and the related disease. The most important action is to not move wood around the area and to not move wood out of the Ojai Valley where it can infect other communities. It is thought that moving firewood is one of the main pathways for the spread of the disease, so always remember to buy it where you burn it. Moving green waste is also a threat. If you have a dead or dying tree in your yard and you observe bore holes, consult a licensed arborist for an inspection prior to removal to ensure beetles are not transported off your property where they can infest more trees. When trees are removed, it is recommended that wood be chipped to ½ or one inch and covered with plastic for several months in a process called solarization.
In the coming months, look for community meetings and information sessions that we hope will bring community resources together to address this threat to our local treasured trees. It is unlikely that any one group or agency can address this threat alone, so we hope to build a community network where efforts are shared among many parties as has been done in Orange County and San Diego County. For more information on PSHB impacts and strategies, visit PSHB.org.
