Plant disease experts at the University of California, Davis, report that they have identified the fungi responsible for a perplexing grapevine ailment known as "young vine decline" and are getting a clearer picture of how the disease spreads. Young vine decline usually appears as a slowdown in vine growth, smaller trunk size and reduced foliage. At one point the fungal disease was nicknamed "black goo" because the sap of infected vines may turn dark brown or black. If the problem is identified early, vines can be coaxed back to health but many growers have found it more economical to remove the affected vines and replant the vineyard. "Young vine decline is very complex," said Doug Gubler, a UC Davis Cooperative Extension plant pathologist who is leading the research effort. "It appears, however, that the fungi that cause this disease are not new and, most likely, have evolved with the grapevines. They can live in a grapevine without causing damage until some type of stress triggers them to cause disease in the vines." Inadequate irrigation, poor planting or producing a crop of fruit on very young vines may make grapevines susceptible to young vine decline, he said. Gubler and colleagues have identified five types of fungi that cause young vine decline. These include one species of a fungus known as Phaeomoniella and four species of a fungus known as Phaeoacremonium. These fungi have been found on grapevines in Italy, South Africa, Australia and Portugal, as well as in California. The disease was first reported in Italy around 1900. The earliest report in California occurred in the late 1950s. The UC Davis research team has: * Isolated the five fungal species that cause the symptoms typical of young vine decline. * Determined that the fungi are generally found on aboveground parts of the plant as well as in rootstock. * Demonstrated that these fungi all are capable of infecting through pruning wounds on the grapevine and are very effective at invading the vines' vascular tissue, which transports water and nutrients throughout the plant. * Trapped air-borne (water-splashed) spores from three of the fungal species on both young and very old grapevines in California's North Coast region, Lodi and Delano. * Demonstrated that the spores can be transmitted by splashed water, including rainfall. *Placed as many as 80 million fungal spores in 9-inch vine cuttings and six months later found the vines grown from those cuttings to be free from symptoms. This suggests that the mere presence of the fungus does not necessarily mean the disease will develop. Because the fungi that cause young vine decline can be found almost anywhere, the UC Davis researchers are not recommending that commercial nurseries and the university's own Foundation Plant Materials Service remove healthy plants that carry the fungi. "It may not be possible to produce vines that don't have these fungi, which have the ability to survive both in the soil and plant tissue and can invade the plant in so many ways," Gubler said. Vineyard surveys by the UC Davis researchers suggest that roughly 1 percent of California vineyards are affected by young vine decline. The disease is most prevalent in Sonoma County. "In recent years many of the vineyards in the Sonoma region have been replanted with new rootstocks that we don't know much about," Gubler said. "Some of those rootstocks have the tendency to actually slow the growth of the vines, which could make them susceptible to the young vine decline fungi." When planting a vineyard, he urges growers to take the following precautions: * Purchase healthy plants from a certified nursery. * Make sure the roots are oriented down during planting. * Provide adequate fertilizer and irrigation water. * Keep fruit off of the vines until the plants are at least three years old. Encouraging a crop earlier may provide income from the vineyard sooner, but could stress the vines so much that they become susceptible to diseases like young vine decline. "If growers suspect a problem, we'd like to know about it," Gubler said, inviting vineyard managers to either contact him or their county farm advisors. "We try to look at all vines that are sent to us or visit the vineyards personally." The UC Davis researchers are investigating the biology of the young-vine-decline pathogens in order to better understand the disease and develop control strategies. They hope to identify the source of the fungal spores and determine what causes the fungi to switch from a latent state to a disease-causing mode.