The mighty oak can be felled by a fungus.
Sudden oak death is caused by a fungal infection in trees. As a mortal disease, it affects oaks primarily tanoaks and live oaks. The disease has deforested large natural oak stands in coastal areas of California and Oregon. It is caused by the fungus Phytophthora ramorum and its presence requires moist, cool air. The fungus causes leaf and twig diseases in other species of woody plants. The bay laurel acquires a leaf spot when it contacts Phytophthora ramorum. The leaf spot disease doesn't kill bay laurel, but it can affect the health of the tree by leaf loss and stress.
History
The fungus first became a serious problem in the mid-1990s when it caused the death of wild oak trees and then spread to nursery trees. The leaf and twig diseases affect the coastal redwood, Douglas fir and bay laurel among others. The fungus is also found in Europe, Canada and the Netherlands. The presence of bay laurel is a predictive indicator of the fungus.
Effects on Oak
The fungus affects the vascular system of trees and prevents adequate water from being transported to the entire tree. Adult oak trees are the ones most affected. Juvenile trees are not impacted by the fungus. Adult oaks present red cankers on the trunk as an early sign of the disease. The cankers begin just a few inches off the ground and ooze red or black sap. It takes only two to four weeks for an infected oak tree to die, but some other trees last as long as 11 years.
Effects in Bay Laurel.
Phytophthora causes leaf lesion in bay laurel. The lesions appear where water remains on leaves and are brown surrounded by a yellow area. The leaf tissue dies in the area infected and often the leaves drop. The fungus doesn't cause death in bay laurel but loss of surface leaf area restricts photosynthetic activities, which are crucial to plant survival.
Controls
Removal of the bay laurel is recommended. Containment practices are in place where firewood is prevented from crossing state lines in infected areas. The disease remains in dead wood and can infect a previously healthy area. Disinfection of tires, dog paws and shoes is requested. There are no totally effective fungicides and tree removal is the optimum response to infected trees. The wood should be burned or composted. The spores do not spread in burnt wood and effective composting destroys the fungus.
