The goldspotted oak borer, an invasive insect known for targeting oak trees, has been found in Placerita Canyon and other areas of the Santa Clarita Valley, becoming a growing threat that officials are attempting to mitigate.
In October, the UC Agriculture & Natural Resources assisted the Los Angeles County Parks and Recreation Department to form an organized effort with the local community to observe 20-30 oak trees at Placerita Canyon State Park for any GSOB larvae, Cristhian Mace, an L.A. County natural areas biologist, said in a recent phone interview.
Signs of the oak borer were found in Whitney Canyon and East Canyon by members of TreePeople, Mace said, and knowing how near it was to Placerita Canyon,biologists wanted to get ahead of the challenge. TreePeople is an environmental nonprofit focused on creating a climate-resilient Southern California through research and implementation of sustainable solutions to protect and restore natural resources, according to its website.
Among their findings, which consisted of looking closely at the oak tree bark for D-shaped exit holes, signs of GSOB larvae and canopy thinning, two trees came backpositive while another handful were flagged as suspicious.
“What this tells us, GSOB has probably been here for a while. Not a long while, but it looks like it’s starting to establish itself in this landscape,” Mace said, adding that experts in identifying GSOB taught members of the community how to identify signs of the invasive insect so they can search open spaces near their homes and “share what they learned and be eyes and stewards for the landscape.”
“With GSOB in the environment it means that we have to act now,” Mace said. “Because it’s just the early days of GSOB here at Placerita Canyon but there is an extreme opposite end to this story.”
Marshall Canyon in the San Dimas area was discovered to have an infestation and it contributed to the ongoing oak tree mortality rate, Mace said. In August, part of the Marshall Canyon Trail had to be temporarily closed for tree removal and trimming of the affected oak trees to ensure public safety and help reduce GSOB movement into new areas, according to L.A. County Trails.
In Placerita Canyon there are thousands of oak trees, and in the broader SCV there are tens of thousands, Mace said, and the level of infestation determines the next steps on how officials choose to mitigate the problem.
If a tree has more than 25 D-shaped exit holes, it would be considered an amplifier tree, or in other words, has a larger breeding population and a higher chance of spreading the pest to other nearby oaks, and is labeled as a hotspot, she said.
“Sometimes the only solution is to chop the tree down,” Mace added, but many factors come into play, and it’s observed through a case-by-case basis. “Pesticide treatment is a viable option for even an amplifier tree.”
How fast the invasive pest can kill an oak tree depends on what the oak tree’s health looked like prior to the infestation. If the tree was already stressed, like humans, it means it’s fighting chronic illness and when a new disease enters the body, it has a faster decline compared to a healthy tree, Mace said.
Through findings, biologists have noticed that the oak borer likes to target healthier trees because it gives the insect a better chance of survival. The pest thrives in a cycle, where the beetle will lay its eggs and, when hatched, the larvae will dig under the bark and live there until it’s fully grown to lay its own eggs.
“So you have generations of GSOB kind of just creeping up the same oak year after year,” Mace said.
The oak borer isn’t native to Southern California. It was first discovered in 2004 in San Diego County, with its origins known to be Arizona and parts of northern Mexico.
How exactly the insect could travel thousands of miles and across states was something biologists questioned, because “they’re terrible flyers” Mace said. Through their findings, researchers found infested firewood to be the answer.
When people purchase firewood for camping trips, or other outdoor activities that may require travel, people usually take home firewood that wasn’t used, which is the No. 1 way the pest is spread.
“If you have leftover firewood from a camping adventure, leave it behind. It’s all about buying local and using it all up wherever you are,” Mace said.
In some areas of San Diego County, the invasive species has affected 90% of its oak woodlands.
Due to early detection, not all is doomed and gloomy for the SCV and its oaks, Mace said. L.A. County and other agencies have looked at greenery throughout Sand Canyon all the way up to Green Valley to detect the oak borer. GSOB was found in Green Valley years ago, and has since been mitigated, Mace said.
“As long as we arm ourselves with knowledge, and keep our hearts open, all is not lost … L.A. County’s team is so passionate, tiny, but mighty in their efforts of trying to confront this issue,” Mace said. “We want to save every single tree that we can.”
