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Wine grapes infected by Flavescence dorée, showing brown, shrivelled fruits.

Wine grapes infected by Flavescence dorée, showing brown, shrivelled fruits.

The discovery of the disease Bois noir in a South Okanagan vineyard late in 2006 was a wake-up call for British Columbia grape growers of the need for vigilance against a host of new diseases.

During the B.C. Wine Institute’s annual viticulture conference in Penticton last summer, Dr. Chrystel Olivier of Agriculture and Agri-Food Canada’s Saskatoon Research Centre told growers that Bois noir and other diseases known generally as "grapevine yellows" could give them the blues if they become established in the region.

Vineyards around the world have reported grapevine yellows, caused by microscopic pathogens similar to bacteria known as phytoplasma. First identified in 1967, phytoplasma are parasites of plant phloem tissue and insects that serve as carriers of the disease.

Affected vines grow more slowly and have discolored and downward-rolling leaves. Fruit is lower quality.

Canada is concerned enough about the possibility of grapevine yellows that it adopted strict new requirements last year governing the import of vines and rootstock from France and Germany, where Bois noir and a related disease, Flavescence dorée, have had a crippling impact in some viticultural areas.

Remove vines

That didn’t stop a shipment of 1,965 Grenache vines from France being planted in the Okanagan before the Bois noir infection was identified, however. The Canadian Food Inspection Agency is investigating the source of the infection in cooperation with the government of France, and plans to remove the vines before bud break this spring.

Depending upon the final results of this investigation, more vines could be removed, said Chuck Lemmon, an officer with the agency. The CFIA knows the locations of other possibly implicated vines, as 2006 plant health import requirements required documentation, tracking, and mapping of all grapevines imported from European sources.

The good news is that Bois noir spreads more slowly than Flavescence dorée. It is not yet regulated in Europe, though it has become more common in the last five years.

Olivier’s presentation to growers last summer highlighted the dangers, however, noting that Flavescence dorée has been "a catastrophe" for growers in Europe.

First identified in the south of France in 1957, Flavescence dorée spread north during the 1970s and 1980s. A warmer climate has allowed the vector, the Cicadellid leafhopper Scaphoideus titanus, to move further north in Europe than had been thought possible. Since the leafhopper originated in North America, it lacks natural predators in Europe.

Flavescence dorée is especially destructive because it often escapes detection, Olivier noted. A plant can be affected and have loss of production even if there are no visible symptoms, Olivier said.

Once a plant does manifest symptoms, whether in a few weeks or a few years of the original infection, a wide range of symptoms may indicate the disease. This is possible because the phytoplasma works to suppress normal gene expression.

Quarantine

Once the disease is detected in a vineyard, the vineyard is quarantined for a minimum of two years, and growers must spray and submit to monitoring. Removal of all vines is common in vineyards where more than 20 percent of vines are infected.

Year-round spraying against the leafhopper is mandatory for nurseries.

Olivier said the best strategy growers in North America can pursue to protect their vineyards against phytoplasma diseases, in addition to respecting import requirements, is to avoid introducing new pathogens to a region.

Since the leafhopper is native to North America, growers have added reason to be careful.

"FD phytoplasma could, if introduced, easily become established and spread in many Canadian vineyards," Olivier said. "There is no such thing as zero risk. The best thing you can do is minimize your risk."