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Symptoms of plum pox virus include chlorotic (yellow) rings on the leaf surface or chlorotic blotches  and vein clearing.

Symptoms of plum pox virus include chlorotic (yellow) rings on the leaf surface or chlorotic blotches and vein clearing.

A concentrated growing area is complicating efforts to eliminate plum pox virus from the main peach-growing region in Ontario, Canada.

The virus was expected to be eliminated in the provinceCanada’s biggest peach producerby the time current funding expires on March 31, 2011. But federal plant protection specialist Eric Wierenga of the Canadian Food Inspection Agency said that won’t happen, because of a number of factors, including the tight concentration of at-risk orchards in Ontario’s Niagara Peninsula.

“With the Niagara area being one of the prime peach and plum growing areas, it does present some challenges,” he said.

The high concentration of trees in the area facilitates spread of the disease and has resulted in a greater incidence of the virus in some parts.

The Niagara Peninsula is the sole growing region left to achieve eradication. Two regions in Nova Scotia and four in Ontario have already done battle with and eliminated the virus, which reduces yields and the marketability of fruit.

The disease was first identified in Ontario and in Pennsylvania in the United States in 2000. Michigan and New York both reported the disease in 2006.

Pennsylvania announced itself free of the disease last year, but the most recent round of testing in Ontario identified the virus in 108 orchard blocks as well as at four residential properties. Wierenga said the virus was easier to combat in Pennsylvania because of a lower density of plantings, but Ontario will echo Pennsylvania’s efforts as it seeks to wipe out the virus.

One element of the elimination strategy is the establishment of buffer zones around infected trees, within which all trees will be removed. Pennsylvania established a buffer of 500 meters, but the breadth of that buffer would decimate the close-packed Ontario industry.

“Removing large buffers like that won’t help the industry. We would eradicate the disease but at the detriment to the industry, which we don’t want,” Wierenga said.

Ontario will likely follow New York State’s lead and adopt a buffer of 50 meters, though industry’s opinion will be sought before the agency mandates any measures. Those discussions are set to happen this spring.

The buffers will not be used in every case. An international panel of experts drawn from the United States, the United Kingdom, and Spain point to two methods of virus transmission to frame the two-pronged strategy Ontario plans to pursue.

While buffer zones work well in the case of transmission by aphids, blocks where the disease is thought to have been introduced by infected plant material will be removed altogether. This will eliminate the risk that any other trees which may be harboring the virus will pass it on.

To date, 354,798 trees have been removed. The Canadian government will have spent approximately Can.$180 million (U.S.$174 million) on the disease’s eradication by the end of March 2011.

The cost to the industry has also been significant at a time when shifting production and consumption trends in the local processing industry have declined while the farmgate value of all Prunus species has risen more than 15 percent since 2000.

While processing fruit was initially targeted, today, fresh-market varieties are the focus of eradication efforts.

Wierenga said a commitment to eradicating the plum pox virus means CFIA is seeking funds to support the fight against the disease past March 2011.

“We’re currently looking at securing funds beyond that date,” he said. “Eradication is still the push for the government of Canada. But, of course, the money has to come before we can continue.”