Sudden oak death (SOD) is a forest disease affecting oak trees provoked by an exotic pathogen that has killed hundreds of thousands of native trees in California. The disease is caused by a deadly microorganism called Phytophthora ramorum, which was first discovered in California in 1995. In numerous North American and European countries, the virus has been found in bays, blueberries, horse chestnuts, rhododendrons, camellias, and other ornamental and landscape plants. The fungus is so dangerous that the recent outbreaks of SOD on Japanese larch have required cutting thousands of trees. The only completely reliable way to confirm a P. ramorum infection or sudden oak death is to take a sample and analyze the tissue of the affected plant in laboratory conditions.
Sudden Oak Death Treatment
Signs of damage
- The trunk of the tree begins to bleed; a dark red-brown liquid flows out of it;
- Dark spots appear on the leaves;
- The buds are white or light-colored, then turning black and crusty with age;
- Cisterns on stems and branches;
- Leaves in the crown turn pale green, then yellow, then brown during 2–4 weeks, with no long period of visible deterioration;
- Subsequently, the leaves dry and fall off;
- Causes non-fatal leaf spot or twig death in alternative species instead of the bleeding ulcers it causes in oak trees.
How to prevent
The best defense against SOD is to avoid transporting host plant material over long distances and pinpointing the disease. The treatment of this disease is entirely aimed at preventing and protecting susceptible oaks. For prevention, always allow 15 feet (4.6 m) between the oak trunk and other susceptible species such as bay and rhododendron. To protect oaks, you should also spray a preventive fungicide, a complex, concentrated liquid foliar fertilizer containing liquid-form phosphorus, potassium, and trace elements (Mn, Cu, Zn, Fe). Remember that you should never plant new oaks in areas with known infections. Also, be attentive and do not allow the trees to be weakened by drought stress, injury, or other damage, as trees are the most vulnerable.
Heal
SOD has always been fatal to susceptible oaks, and there is no cure. There are very few mechanisms to control this disease, mainly involving early detection and proper disposal of infected plant material.
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