OAK TREE EXPERTS: HOW OAK TREES ARE DYING AND WHAT CAN BE DONE TO SAVE THEM

By Janis Russell

October 10, 2016 (Jamul) - On Saturday, October 1, the public gathered under some oak trees near the Lyons Valley Trading Post in Jamul to hear two experts talk about what has been happening with the coast live oak trees in California.

Pete Harper, who organized the event and works in escrow, gave the welcome. “About five months ago, I bought a place out here,” he said, adding that he liked the beauty of nature in Jamul. Then he found out about oak boring beetles killing oak trees. Harper discovered that his neighbors have tried different things without success. He did some research and invited two experts who have been working on this issue. Dr. Tom Scott is a natural resource specialist with the Department of Environmental Science at the University of California Berkley. Bret Hutchinson is the owner and operator of Green Tree Forest Services and a certified arborist at U.C. Riverside. Scott has dealt with oak tree mortality for the past 13 years. (Cheyenne Borello, a forester at the main Cal Fire Headquarters, was unable to come.)

Scott was the first to speak. “You guys are probably my 300^th meeting.” He has been working with communities a lot regarding the beetle that’s been killing the oak trees. “We sit under coast live oaks capable of growing where no other species of trees are…they are worth saving and worth managing,” Scott added.

Engelmann oak trees aren’t being attacked. Only the coast live oak trees have been ravaged by gold spotted oak borers. “San Diego sits on the edge of the Mediterranean rainfall,” he noted, where rainfall is Oct 15-April 1. “Beetles come from monsoon rainfall,” which occurs when it rains heavily in summer. Because of the extended drought, the trees can’t fight off the beetles.   But they can “compartmentalize and grow faster,” especially those under 10 inches tall.

The longest Scott has seen any tree survive with beetles is 15 years. “What we want to avoid is to lose 90% of trees.” To avoid that loss will take “lots of community action and planning.” He also cautioned, “If you move firewood out of this valley, you move the problem to a new location. One piece of firewood can have 9-10 beetles.” The wood can still leave the community if it’s not infested with beetles. But Scott concluded, “The best thing to do is to manage wood properly. Burn it where you buy it.”

Hutchinson talked about different beetle types. He has dealt with pine trees dying in the 1980s. “

Gold spotted oak borers are a new invasive species spreading in this area for 10-12 years.” These beetles have a one-year life cycle and are ½ inch long. In April-May, they emerge out of the tree. When the trees are infested with larvae, the larvae pupate and then become beetles. They form D shaped exit holes, chewing their way out.

Western oak bark beetles are small, about 1-2 millimeters in length…this beetle itself bores into the tree. It attacks trees under major drought stress, and they start at the top of the tree.

There’s also the polyphagous shot hole borer. It is not species specific. “It tracks down into the center of the wood itself [and] lays eggs…it brings along very specific fungi.” There’s a rapid shutdown of tree circulation.

Someone asked how one can tell when a tree is infested. Hutchinson said you can tell when it’s usually too late.

 “The main reason trees are being attacked is drought stress…most oak trees have crown thinning,” he explained. “A tree that has 65-70% of its canopy begins to go into drought stress.” That’s when leaves start dropping and roots “are withdrawn.” People need to find ways to keep the trees healthy.

The easiest sign to know when trees are being attacked is lesions, which are dark spots on the barks of trees. There’s the oak ambrosia, where beetles can get into dead oak trees and live on fungus. The wood borers feed on the wood itself after the trees are dead.

Mother Nature helps treat trees, like trees being able to get water in their system and attack the larva. Woodpeckers know when the gold spotted oak borers are there and they pull the larva out of trees. Also, parasitic wasps lay their eggs in the pupation chambers.

“Once the tree turns brown, take aggressive action,” Scott advises. “Cut it down and chip the brush.” To save the wood that’s infested, split it down to firewood and cut off the infested bark. Then keep that bark separate.

“If trees are still green and struggling, you need to improve their health…apply a little extra water…don’t put water near the base of the tree. Use a soaker hose to put down slow, consistent water. Start four to five feet away from the tree.” Someone asked Hutchinson how often to water the trees. Hutchinson answered, “If the trees have severe, deep stress, do twice a month.”

There are also insecticides a person can use. The best one is a carbaryl base trunk spray, according to Scott. “Spray trees as high up as possible... to encapsulate the outer bark if there’s already larva. Then the beetles die [and] get a toxic dose… Trunk spray is more efficient, more successful.” This can be found at Home Depot. “It’s intentionally not labeled to use for whole tree spray.” You should only apply it according to the directions. “This stems from knowing what type of beetle the tree has,” he emphasized.

Scott said, “We’d rather have you identify the problem. Then hire an arborist…work with neighbors.” Someone asked how often to apply treatment. Scott said you can apply the carbaryl sprays [every] 150 days. Hutchinson said it’s important to time when to spray with the emergence of the gold spotted oak borer in spring. “Sometimes you can spray more than once a year,” Hutchinson added.

Then there was some more questions and answers with the experts.

Someone asked if the beetles have any natural enemies. Hutchinson named woodpeckers and other beetles. Another person asked if woodpeckers do more damage to the trees when they get the larva out. Hutchinson clarified that woodpeckers do less damage by only chewing the bark. Dr. Scott said he discovered one tree in Idyllwild that had 8000 beetles. He suggested looking for amplifying trees that have lots of exit holes and then “you can knock out a substantial amount of adults (beetles) that are there.” Someone asked if trees act as amplifying trees for more than one succession. Scott replied, “It tends to be trees for two to three years.”

The same person also asked if there were ways to catch trees before you see the exit holes. Hutchinson said, “Wait until January…cut out 6-inch panels. The tree is on its way (to dying) if there are four or five beetles.” But in general, it is obvious that trees are dying because of major crown thinning etc.

Someone asked if velvet ants are predators. Scott said that those ants just feed off the larvae of the tree.

Another person asked where to look for the exit holes. Scott said “Most are within six feet and down…look at the trunk of the tree.” Someone else asked what to do with the main trunk of the tree. Hutchinson said, “Cut it all up into firewood size. Split the bark off the tree. Get rid of [the infested wood].” Once the whole thing is cut down, the actual wood is fine.

A woman asked Scott about chipping versus grinding the wood. Scott said to get a tub grinder that’s three minus.” With a tub grinder, it’s important to “put a fair amount of material through…chippers are much better as long as they’re working right.” Another person asked when to cut the trees down. Hutchinson said, “As soon as it’s brown.” But you can cut it down if it’s still green and there are beetles in the tree.

A woman asked if livestock will be affected if you use the carbaryl spray. Hutchinson said, “Mammals have the ability to detox carbaryl fairly rapidly,” but cautioned, “If you hire an arborist, put pets inside.” Dr Scott added that the carbaryl spray “denatures on soil faster than it does on trees.”

 A man mentioned people have approached him with different products to use systemically and to be sprayed on trees. Hutchinson clarified, “It’s just helping with the health of the trees.” Dr Scott added that when his mother was dying of cancer, different people approached him with products that could cure his mom. “When someone tells you something that’s too good to be true, chances are it isn’t true… Arborists use products we know will work…. Please consult an arborist. Use reputable people.” A woman asked if Hutchinson had a list of recommended arborists. Hutchinson suggested to look around in the community, and check into their backgrounds.

Someone else wanted to know if there were any new products coming out. Hutchinson said it was doubtful.

A woman asked if it’s required to cut the wood down into firewood size. Hutchinson responded, “You don’t have to, but it accelerates the dying process. Put wood into a pile and cover with visqueen. But it has to be completely sealed, and it will kill some beetles. Scott suggested leaving the wood to just decompose on the ground for other animals to use as shelter as long as the bark is off it. A man asked if someone is considering replanting dead trees, is it best to replant coast live oak or Engelmann or a mixture? Hutchinson said a mixture was fine.

Someone asked about mulch. Hutchinson said to get mulch not from the dead trees nearby, but from an outside source, and put two to four inches of mulch around the trees. Scott warned that six inches of mulch “is a fire hazard… It’s good to have oak woodlands around the house” as fire protection. Someone asked if it’s better to keep the oaks trimmed right off the ground. Hutchinson said to trim it near their house and to trim it up off the ground.

Harper concluded by mentioning an email list for people to sign to come up with different strategies to manage the trees and beetles. He wanted to make sure everyone signed the list.

For more information about the gold spotted oak borer, visit: http://ucanr.edu/sites/gsobinfo/.

According to the GSOB preparedness plan outline, ask yourself: 1) Who? Identify responsible and assisting agencies, non-government organizations and community groups that can help, the stakeholders, and who has the resources and skills to help with the problem. 2) What? Determine what actions are needed to monitor. See what steps can be taken to prevent its introduction into the community’s oaks. Determine what steps need to be taken when the first GSOB infested tree is found. See what the contingencies are if this beetle becomes firmly established. 3) Where? Identify where the public can find information and resources. Determine where the infested wood can be disposed of safely if it’s confiscated or voluntarily surrendered. 4) When? Determine trigger points for active GSOB intervention. Establish a protocol to determine when a new isolated intervention will be treated. 5) Why? Map or estimate the number of oaks at risk in the community. Determine their economic and esthetic value and potential cost of removal in order to make a case for intervention. Determine why infested wood in moving in your community. 6) How? How can this be paid for with declining budgets? How can we control the movement of firewood? How can we involve the private sector? 7) Education- How will the internal core group be kept apprised of current research findings and science-based control and prevention strategies? How will community officials learn about the risks and expense of a potential GSOB outbreak? How will volunteers be trained and organized? How will public awareness be increased?

For other readiness and management plans, go to: http://www.emeraldashborer.info/resources.php.