The most damaging disease caused by Xylella fastidiosa in California is Pierce's disease of grapevines. Currently, Pierce's disease is most damaging in the north coastal grape-growing regions from Santa Cruz north to Mendocino counties. The disease also occurs in the Central Valley region of the state, which contains most of the state's grapevines. Pierce's disease has not been a major problem in the Central Valley during recent years, but some vineyards in Fresno and Tulare Counties have been severely damaged. Pierce's disease first received notice in the Los Angeles basin more than 100 years ago. Many thousands of acres of vineyards were lost in a major epidemic. These areas in Orange and Los Angeles Counties never returned to commercial viticulture. The pathogen Xylella fastidiosa is still endemic in these areas; homeowners that plant grapevines usually end up with their vines killed by Pierce's disease.
Almond leaf scorch is curiously absent from most of the Central Valley of California, even near vineyards where Pierce's disease is active. Because of this, the identity of the most important vectors for this disease is debatable. The disease has been severe in Contra Costa, Los Angeles and Riverside Counties. Currently the most important losses appear to be in San Joaquin and northern Stanislaus counties. Recently almond leaf scorch was found for the first time in northern Solano and central Tulare counties (A. H. Purcell, unpublished data).
The first reports of 'bacteria-like bodies' associated with a plant caused by Xylella fastidiosa referred to alfalfa dwarf in the 1920s (Weimer 1937). The disease has never been a problem north of Fresno County. The main vectors are assumed to be grass-feeding sharpshooter leafhoppers, the green sharpshooter and the red-headed sharpshooter. The impact of the disease is that alfalfa stands with dwarf disease have to be replanted much sooner than normal. Symptoms of alfalfa dwarf differ sharply from Pierce's disease and other leaf scorch diseases caused by Xylella fastidiosa. Alfalfa plants decline slowly after infection. They are slower to grow after cutting and have smaller,darker colored leaves and stems compared to healthy plants. A diagonal slice of the taproot reveals that the woody tissue of the root has a yellowish color, with streaks of brown dead wood.
A lethal disease of oleanders (Neerium oleander L.) that was first noticed in southern California in the early 1990s.
For more information follow this link Oleander leaf scorch.
We single out California as a separate geographic region for a couple of reasons. First, this home page is coming to you from the University of California. One of our objectives is to provide Californians with information about diseases caused by Xylella fastidiosa. Specifically, there is now a major increase in Pierce's disease in coastal California and a new disease of oleander associated with Xylella in the southern part of the state. Secondly, much of the ongoing field research on Xylella-caused plant diseases applies mainly to the California situation. This is rapidly changing with increased research on Xylella fastidiosa as a result of the spread of citrus variegated chlorosis disease in South America, tree leaf scorch diseases in the eastern US, and new approaches to bacteriological research. If you would like to send us a description of the impact of Xylella fastidiosa in your region, please do so! We reserve the rights and responsibilities of editorial judgement!
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