Treating healthy oaks can help

<p>Treating healthy trees with phosphonate can stem the spread of sudden oak death for up to two years, while a commonly used alternative may be worse than doing nothing, according to a new study by UC Berkeley researchers.</p><p>Initial research showed the preventative fungicide, commonly sold in California under the brand name Agri-Fos, was effective for an undetermined length of time.</p><p>But this latest round of trials confirmed that it provided protection for 18 months and in some cases up to two years, good news for larger property owners facing the prospect of treating many trees, said Matteo Garboletto, an adjunct professor of soil pathology whose lab conducted the studies.</p><p>Even when property owners band together to buy the fungicide in bulk at wholesale prices, it can end up costing them $25 a tree.</p><p>"The good news is, if you start treating trees, although you have to treat them forever, you don't have to treat too frequently. One treatment a year is sufficient, and if you live in an area where the level of infestation is moderate to low, one treatment every one to two years would be enough," Garboletto said.</p><p>Conversely, a separate examination of a popular alternative treatment comprised of azomite soil amendments and a lime bark wash was ineffective at stopping the spread of the deadly pathogen that has devastated California's oak woodlands, including some 60,000 acres in Sonoma County in the past several years.</p><p>Garboletto likened the alternative to "treating pneumonia with orange juice."</p><p>"A lot of people have bought into it, including cities and municipalities and whole neighborhoods," he said of the azomite treatment, which is complicated and calls for putting a large amount of lime on the ground and another matter on the tree and bark. "If you're going to spend a lot of money, it might as well be spent on something that works."</p><p>Researchers conducted a direct comparison of the two treatments -- phosphonate versus azomite soil amendment with a lime bark wash -- on potted oaks in greenhouses. They also did a field study measuring the efficacy of treatment by using in the laboratory branches from infected trees. That way no living trees would be placed at risk.</p><p>"Azomite appeals emotionally to a lot of people," said Janice Alexander of the California Oak Mortality Task Force. "Now we'll be able to tell them it doesn't work."</p><p>The studies, paid for by the U.S. Forest Service, are published in the current issue of the University of California's California Journal.</p><p>Phosphonates applied to healthy trees are only effective as a preventative measure to stop the spread of Sudden Oak Death. Researchers have yet to come up with a cure for the disease, which is caused by the exotic water mold P. ramorum. The pathogen is thought to be carried by more than 100 plant species. It is deadly to tanoaks and four types of oaks: black canyon, coast, live and Shreve's. California bay laurel trees also are a major source of transmission.</p><p>The study results come at a critical time. If property owners apply a treatment now, trees will be protected if and when a winter wet season returns, or if the spring months of April and May prove rainy, Garboletto said.</p><p>Although the last couple of years have been dry, slowing the spread, the pathogen is like "a ticking time bomb," he added. When the drought breaks, a large number of trees can be infected very fast.</p><p>Workshops are being held monthly at UC Berkeley to teach people how to apply phosphonate the easiest way -- by injection.</p><p>For more information, go to matteolab.org or suddenoakdeath.org.</p><p>You can reach Staff Writer Meg McConahey at meg.mcconahey@ pressdemocrat.com.</p>