December 6, 2021

Infested Firewood Kills Oaks



Infested Firewood Kills Oaks

Firewood stacked for sale on Topanga Canyon Boulevard. Unfortunately, oak brought in from outside the Canyon could introduce infestation to Topanga’s trees with the Goldspotted Oak Borer.

Do you know where your firewood comes from? This is a really important question.

Imagine what Topanga and the Santa Monica Mountains would look like if all the oaks were gone. While we have long focused on development as a major threat to our oaks, there are some new threats, possibly as close as your woodpile that could be even more devastating to our trees.

Last week, a black oak in Idyllwild died, and the non-native Goldspotted Oak Borer (GSOB) was the cause. This represents a big jump from the previous northern boundary of the infested zone, located about 40 miles further south in Julian. GSOB attack many species of oaks, especially the coast live oak. As of 2010, GSOB has killed more than 80,000 oak trees spread over approximately 140,000 acres of woodlands in San Diego County. As of February 2012, a UC Davis study found that over $8 million in public and private funds have been spent on removing dead trees, disposing of infested wood, and public outreach. Several parks and campgrounds have closed due to hazardous trees.

Originally from northern Mexico and southeastern Arizona, this tiny beetle hitchhiked a ride in some firewood, which was stacked within a few hundred yards of an oak tree.

The tree in Idyllwild had other health issues, was located along the road shoulder, and was found full of beetles that had not yet had time to emerge.

Dr. Tom Scott, natural resources specialist at UC Riverside, noted that it is not clear if this is actually the first tree to be infected, or just the first to die. Efforts are underway to examine other oaks in the Idyllwild area to document how far the insect has spread.

GSOB has few local natural predators to prevent it from burrowing into the trunk of the oaks and laying eggs. When the larva hatches, they girdle the tree by tunneling between the bark and the sapwood, stopping the flow of water, nutrients and food from the roots to the leaves. The trees die as the galleries of hungry larva eat their way around the trunk. It can take between 1 and 9 years to kill the tree, although the average time it takes is 3 years.

Dr. Scott observed that the data suggests that if a tree does not die immediately, it becomes a source of infestation each year that it survives, allowing many hundreds of beetles to be released into the surrounding area searching for more oaks.

Controlling an outbreak usually means cutting down the infested tree and carefully chipping all the bark, and much of the wood itself to ensure that all life stages of the beetle are killed. When hundreds of beetles emerge all at once, than all nearby trees are at risk, even ones that are in well tended landscapes.

Lower mortality is observed only in areas where the trees are spread apart, as the beetles are weak fliers and usually can’t disperse more than a few hundred meters. Thus infection is highest where the canopies connect or are close together.

Thus far, there is no effective way to kill the beetles once they have infected a tree. The only control is to prevent their spread by properly treating the wood from the dead trees. The choices you make on where you obtain your firewood are the best line of defense:

• Buy local wood from a reputable local dealer.

• Make sure that the wood you buy is NOT from the dead trees from anywhere in San Diego County.

• If the firewood seller can’t provide documentation of where the wood came from, don’t buy it. Many firewood vendors are opportunistic and fly well under the radar of any realistic regulations.

Another way to prevent the spread of the beetle is to keep firewood in the place where it was produced.­­­

• Don’t load up your firewood to take camping or to recreational cabins or parks.

• While it may cost a bit more to buy firewood at the camp store, it is one of the best ways to prevent spreading many kinds of pests and diseases that hitchhike in logs.

Go check your woodpile and your oaks. If you find the characteristic D-shaped hole produced by these beetles in the bark, or live beetles between the bark and the wood, PLEASE contact the LA County Foresters. They can be reached at the local Malibu office (818) 222-1108.

Infested Firewood Kills Oaks

The polyphagus shot hole borer leaves a tiny, round hole on an oak at the Huntington Botanic Garden. This pest, recently found in Los Angeles County, attacks more than 200 tree species in addition to oaks.

As if the spread of GSOB was not enough of a problem for our oaks, another new type of ambrosia beetle, called the polyphagus shot hole borer has also recently been found in LA County.

Another tiny beetle, this one leaves only a tiny round hole, about the size of the letter “o” in the bark. Not only does it attack oaks, but seems to like over 200 species of trees found in our area. Unfortunately, oaks are one of the species that dies as a result of the fungus spread by the beetle. Together, GSOB and the polyphagus beetles have the potential to drastically change our local landscape, not to mention the ripple effects on the hundreds of amphibians, reptiles, birds and mammals that rely upon oaks for their survival. Not to be alarmist, but this is really serious!

Our best protection is eyes on the trees and quick reporting. Please consider becoming part of the early detection process by signing up at website and learning how to document what you see. This is also a great place to learn how to treat infested firewood. Keep a close eye on your trees. If you see the canopy starting to brown from the top towards the center of the tree, call the Foresters and have them come and look.

If one of your oak trees dies, don’t give away the firewood. Remove the bark and grind it into mulch to prevent spreading.

Our oaks are such an integral part of the landscape, it is truly devastating to imagine our hills with all the oak trees missing. To keep abreast of the latest news and information on how to prevent the spread of these new threats, check out the UC Cooperative Extension web site at

This is also where you can get information on a workshop for homeowners that is planned for Saturday Jan. 12, 2013 at the Huntington Library, Art Collections and Botanical Gardens in Pasadena. Sign up and spend a day with local experts looking at oak pests and diseases, old and new.