Marin IJ Articles

How to Protect Your Oaks

How to Protect Your Oaks

Julia Flynn

I've always loved the impractical spot where my mother built her home. After parking in a garage at the bottom of the hill, you climb a steep pathway bordered by fortnight lilies and rosemary to reach the house. At the end of the path, you come to a graceful gate and trellis, arched by an old and beautiful coast live oak. The way I figured it, my reward for climbing that hill was being greeted by this magical tree.

This past summer, my husband and I bought my mother's property. And since the first cases of Sudden Oak Death Syndrome were discovered not far from our new home, I urgently wanted to find a way to protect this special oak, as well as the redwoods, bays, buckeyes, and madrones on the property. In Marin and elsewhere, all of these species of trees have been found to have been infected by the pathogen Phytophthora ramorum. Some, such as bays and madrones, seem to be hosts which are relatively unaffected by it. Others, such as tanoak, coast live oak, black oaks, and Shreve's oak, may sicken and die rapidly after being infected. Already, Sudden Oak Death Syndrome has killed tens of thousands of oaks and tanoaks along the northern coast of the state.

Although there is still no known prevention or cure for the disease, researchers seem to be getting closer to finding one. Until that happens, though, there are a number of practical steps you can take to try protect your trees. Since some individuals of the same species seem to be less vulnerable than others, it's important to make sure your trees are as healthy as possible. One way to do that is to reduce such stresses as over watering, root disturbance, and pests. You can also take simple steps to avoid infection, such as washing off the dirt and mud you might otherwise track in from areas where the disease has been found before reaching home.

Scientists now know, for example, that the pathogen can spread through moist soil and water, whereas it seems to "rest" or become dormant in drier conditions. So one of the first things I did this summer was to adjust the irrigation system so that streams of water would no longer hit the trunk of our entrance oak. Most oak trees do not need any irrigation, since they are well-adapted to normal summer drought conditions.

I also learned that it is vital to protect the oak's root zone. Avoid compacting the soil around the roots or disturbing them in any way. I decided to add about five inches of mulch under the canopy of our special tree, making sure to start two feet away from root crown, or the area where the trunk fans out to the roots. While some people say you shouldn't plant anything under an oak, I planted a few drought-tolerant plants, such sword ferns and hand-watered them to get them established. I'll avoid irrigating the area entirely next summer. The dry months are also the right time to prune oak trees, since insects and fungus are less active then.

I also called in our trusted arborist, who had been trained to spot the symptoms of Sudden Oak Death Syndrome. He examined all the trees and shrubs on the property for any sign of the disease. Luckily, we seem to be disease-free for now. But if he had seen dark, viscous bleeding from the trunk of our oak – one symptom of the disease – and diagnosed Sudden Oak Death Syndrome, we would have sought confirmation by a lab. If it came back positive for the disease, we would have cut down any trees that were dying and left the wood in place on the property. Beetle and fungus infections may occur after a tree is infected, but researchers don't recommend using pesticides before infection or infestation occurs, as a pro-active measure.

One step we are taking to be be pro-active is making sure that we don't pick up any pathogenic hitch-hikers during our trips out into the woods. My family likes to mountain bike in an area where a number of trees have been infected, so we're always careful to wash the mud and dirt off our shoes and bikes before we reach the house. If we were really careful, we'd also go to the car wash before heading home. My husband teases me that I've got Phytophthora on the brain, but I'd rather be cautious than risk losing our magical tree.

For more information on Sudden Oak Death Syndrome, please check www.suddenoakdeath.org or http://cemarin.ucdavis.edu/index2.html

This article appeared in the Marin Independent Journal on November 11, 2002.