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
"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
* 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
"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-
-- Doug Gubler, Plant Pathology, (530) 752-0304,