Two years ago, the State of California decided it didn’t have the budget to support individual oak-owners’ efforts to save their trees from Sudden Oak Death. We’re on our own, folks, but we can get help from the University of California, in particular from Matteo Garbelotto’s lab at Berkeley.
The lab’s free workshops are supported by grants from the U.S. Forest Service and state and private forestry organizations.
Aside from attending one of these and learning more than you ever could from reading here, there are a few things you can do if you have a susceptible oak. These are only oaks in the “red oak” group: coast live oak, black oak, Shreve oak, and recently, canyon live oak. Valley oaks, so far, are not infected. The bad news is that you’ll have to do some triage. Criteria: trees that mean a lot to you and your landscape—go ahead; be subjective—and trees that have a defensible perimeter.
Now that the infectious agent is here, our native bay laurels have become Typhoid Marys. Phytophthora ramorum infects their leaves and multiplies, then moves on via water drops. Splashing from the soil, running downhill: whatever water does, the spores ride it. We can’t wipe our laurels out; all else aside, they stump-sprout with great determination.
First place in the triage line goes to oaks that aren’t within 30 feet of bay laurels. You can prune back overhanging laurels, especially if they’re downhill or on the same level with your oak, and that cuts the chance of SOD considerably. Bay laurel leaves show signs of SOD in a patchy manner; not all leaves show the irregular line of darkening near the tips or the black line and yellow “halo” of Phytophtora—even then, those might not be P. ramorum, the dangerous one.
Look for lesions where water runs—on the tips of downward-hanging leaves and at the base of upstanding leaves. The hitch is that bay laurel leaves can have spots and lesions from all sorts of things from infections to momentary water shortages to insects and even adventurous animals, especially if they’re in the shade. Gray fuzz, for example, looks alarmingly like but isn’t SOD.
Tanoaks get really sick with SOD and can spread it—a scary thing for the many critters that live on them—and even redwood needles can spread it. You might see it on rhododendrons; again look for it where water sits. It infects plants of all sorts; it’s just that many don’t get sick from it.
If you see ambrosia beetle signs (e.g., sawdust) or lots of black “charcoal balls” (fruiting bodies of the fungus Hypoxylon) on the trunk, then the tree’s doomed. Opportunistic infections like this follow SOD; you don’t see them until it’s too late.
Next: A remedy or two, maybe.
SUDDEN OAK DEATH
1–3 p.m. Wednesday, Nov. 4, and Wednesday, Dec. 9, 2009, at the Tolman Hall “Portico” on the UC Berkeley campus. Admission is free, but registration is required. E-mail your name, preferred date, and affiliation (if applicable) to firstname.lastname@example.org, or call 847-5482. Register ASAP, as registration is on a first come-first serve basis, with a 20-person limit per session.
Next workshop: Sudden Oak Death Syndrome: What to look for and what to do.