Toronto Globe and Mail, August 29, 2007

WAR BEING WAGED AGAINST DEVASTATING FUNGUS

[Rachel's introduction: Sudden oak death has made Ontario growers much more wary of their sources of plants, says Michael Celetti, a plant pathologist with the Ontario Agriculture Ministry. He worries that insufficient rigour south of the border could allow the pathogen to slip in through the back door. "What happened to the precautionary principle?" he asks.]

By Kate Harries

The botanical term is Phytophthora ramorum, but among foresters and nursery growers -- who know it as sudden oak death -- it's viewed as the equivalent of the Black Death: a deadly alien disease that owes its name to the devastating speed with which it has rampaged through coastal oak forests in California.

It's an insidious invader that can hitch a ride on popular garden plants and even stick to shoes or tires that pick up spore-infested soil.

Laboratory tests have found that both the eastern red oak and the sugar maple are very susceptible to P. ramorum. If the pathogen -- it's a fungus-like water mould of the same family as potato blight -- were to escape into the landscape, it could lay waste to the hardwood forests of the Great Lakes-St. Lawrence region, already stressed from other exotic pests and diseases.

Federal authorities in Canada and the U.S. have been waging a continent-wide battle to contain P. ramorum since 2004, when a southern California grower shipped infested plants to 40 states and B.C.

In Ontario, where it hasn't been detected, fear of the highly contagious disease has prompted some growers to erect biosecurity defences much like those used by farmers against foot-and-mouth disease.

An outbreak would be "absolutely devastating," says Peter Zwaagstra, manager of Blue Sky Nursery in Beamsville, Ont. "The whole place would be shut down, they'd burn all your plants, you may be out of business for two years."

Mr. Zwaagstra, who supplies around 70 garden centres across the Greater Toronto Area, is also conscious of the threat to the forest. "We try to do what we can to meet our customers' needs and protect the environment in Ontario."

He implemented protective measures two years ago and got a full program in place this year. He buys two-inch tissue-culture plantlets - grown separately from the plants -- rooted in sealed, sterile containers and has adopted other biosecurity practices from his Washington State supplier: restrictions on the movement of visitors, off-site incineration of plant debris and minimizing standing water.

Sudden oak death has made Ontario growers much more wary of their sources, says Michael Celetti, a plant pathologist with the Ontario Agriculture Ministry. Even though growing conditions on the West Coast make for a cheaper plant, many are looking at alternatives. "Some of them have decided to bite the bullet and produce it here at a higher cost," he says.

So far, the North American outbreak into the wild has been limited to California and Oregon. In B.C., two nurseries remain under quarantine because spores persist in soil and a few infected plants are still being found in landscape projects.

Sudden oak death is insidious: It infects many species without killing them so they become effective carriers; symptoms can take weeks to show up; and there's no chemical defence. An ever-expanding range of host plants, now numbering 120, includes garden favourites from magnolia to oleander. Five -- rhododendron, camellia, viburnum, pieris and kalmia -- have been designated as high risk in the U.S. Canada has designated six, adding lilac to the list. Trees include beech, fir, dogwood and variety of fruit trees such as cherry and peach.

The response by governments to the threat on both sides of the border has been a heightened attention -- sampling and testing -- to shipments of host plants and destruction if the organism is found. Plants from infected areas, which include most of Europe, must be certified disease-free.

There's one key difference between Canada and the U.S. Here, if a species is a host, the whole genus becomes suspect. In the U.S., only a species that becomes naturally infected is considered a host. Thus, the only maple of concern in the U.S. is the bigleaf maple, native to the West Coast. Here, all maples are listed.

Laboratory tests have found that both the eastern red oak and the sugar maple are very susceptible to P. ramorum.

"It grew much faster on the eastern red oak than it did on the western species that are dying by the hundreds of thousands in California," says Mr. Celetti. And "it grew faster on the trunk of the sugar maple than it did on the oak."

But laboratories foster infection. Would the same happen in the landscape? American scientists suggest that Ontario's minus-28-degree winter temperatures would kill off the spores. Mr. Celetti disagrees: under two feet of snow, the temperature only dips to minus 3, and that's not cold enough.

He worries that insufficient rigour south of the border could allow the pathogen to slip in through the back door.

"From my perspective, what happened to the precautionary principle?" he asks. "Particularly when you're dealing with something with such a wide host range."

But Shane Sela, who's in charge of the Canadian Food Inspection Agency's battle against the disease, says there's a rigorous surveillance program to stop the disease at the border.

"I'm confident we are doing a good job to manage the risk," Mr. Sela says. "We have to be protecting our forest situations, but at the same time we can't be overprotecting... presenting unnecessary barriers to trade."

Meanwhile, those responsible for managing the risk in eastern seaboard forests are pushing for more research to determine whether tougher controls on plant movement are warranted.

Both Richard Wilson, plant pathologist with the Ontario Ministry of Natural Resources, and Steve Oak, who co-ordinates the U.S. P. ramorum early detection program from his office in Asheville, N.C., have asked California experts to plant eastern species in infected forests.

"We have models that tell us that eastern species are somewhat susceptible," says Mr. Wilson.

"We can't validate these models."

But the Californians won't do the study. Mr. Oak, a forester with the United States Department of Agriculture, says that, in the absence of field evidence, "we have to assume that it could be a serious problem. It would be irresponsible to act otherwise."