The glassy-winged sharpshooter and the Pierce's Disease that it spreads are seen as a major threat to the state's wine industry.
But University of California at Davis plant pathologists say a group of five fungi are also a threat to young grape vines.
The fungi cause what is known as young vine decline. And like the bacterium-caused Pierce’s Disease, there is no known treatment, the pathologists say.
Fortunately, only about 1 percent of the state's vineyards are affected by young vine decline. Pierce's Disease in contrast has infested 13 state counties and threatens the state's $2.8 billion wine, table grape and raisin crops.
Both diseases affect the grapevine’s water conducting capabilities and tissue.
The earliest report of the fungi in the state was in the late 1950s, but has become of some concern in vine growing regions since the early 1990s, pathologists say.
And while Pierce’s Disease affects other crops, such as almonds, citrus, alfalfa and peaches, the fungi affect only grapevines.
Pathologists believe “environmental stresses,” such as inadequate irrigation water or fertilizer, improper planting or producing a crop of fruit on very young vines can trigger the disease. The fungi that cause it are found in most vineyards, pathologists say.
Affected vines may grow more slowly, have a smaller trunk and less foliage than normal, and contain yellowed or wilting leaves.
The fungi can enter the vines through wounds made during propagation or pruning. Only rarely does an entire vineyard show symptoms, pathologists say.
Nurseries can halt its spread by making sure they sell only vines that are otherwise healthy and protected from environmental stresses.