Furious growers, facing tens of thousands of dollars of expenses and lost revenues per acre, are joining some consultants in blaming nurseries and the University of California at Davis for propagating unfit vines. The University's Foundation Plant Materials Service tests vines for diseases, then sells them to nurseries, which in turn pass them along to growers.
Estimates of the extent of affected vineyards are difficult because many of the disease symptoms resemble other vine maladies. Tests indicate that the condition is caused by three species of the phaeoacromonium fungus, which have been found in healthy vines as well as the air and soil. "We have to find out why some vineyards get the disease while others with the fungus don't," said Deborah Golino, FPMS director. "We have limited knowledge about the biology of the pathogens or when to intervene to disrupt the [fungus'] life cycle and control the disease."
It does seem clear that stressed or feeble vines are more susceptible. Young vines require years to develop root and vascular systems sturdy enough to withstand dehydration and the demands of fruit production, according to Dr. Doug Gubler, plant pathologist at UC Davis. He said that production schedules that cause vines to fruit prematurely divert energy from vine and root growth and could be an exacerbating factor.
While phaeoacromonium has been in California for at least 60 years, Black Goo has become a major problem only within the last decade. Many observers suspect that the disease is linked to the massive vineyard replanting caused by the phylloxera louse, which attacks unresistant roots, eventually killing the vine.
As California wineries replanted phylloxera-stricken vineyards, nurseries ramped up production to supply tens of millions of resistant vines. "People propagated new, different rootstocks using the old methods," says Peter Opatz, director of viticulture at Clos du Bois Winery in Sonoma Valley. "The old techniques weren't always suited for the new varieties, so there were fundamental nutritional shortfalls, and the results were not ideal."
Growers tend to attribute Back Goo to inferior, infected vines, while nurseries blame unsound production methods. In any event, it will take time to sort out who is truly to blame, as well as a solution. "I understand how frustrating this is to growers, but the scientific evidence doesn't support quick answers," said Golino.
Black Goo is not limited to California. An international conference that addressed the problem, held last October in Siena, Italy, had 120 participants from 20 countries.