If you're buying a Christmas tree you can plant in your landscape after the holidays, look closely. A University of Georgia expert says one popular dual-purpose tree may not survive in your yard.

A new disease poses a deadly threat to Leyland cypresses, said Jean Woodward, a plant pathologist with the UGA College of Agricultural and Environmental Sciences.

Seiridium, a fungus, causes fast-spreading cankers that limit Leylands' water uptake, she said.

Many people consider Leylands perfect Christmas trees. Georgia growers have about 400,000 Christmas trees this year, and about 240,000, or 60 percent, are Leylands.

Most Georgia growers offer Leylands only as cut trees, said David Moorhead, a UGA forest regeneration scientist. And they're still an excellent choice for shoppers.

A few Christmas tree growers and a number of nurseries offer them in containers so people can plant them outside after the holidays. If the tree is infected with Seiridium, though, its outlook isn't good.

"With the stress of being in that dry environment in the house over the holidays, it's unlikely to survive in the landscape," Woodward said.

Seiridium has erupted in Georgia. Woodward said it attacks Leyland cypress and Atlantic white cedar. It may infect arborvitae, too.

"We just started finding it in Georgia in the past couple of years," she said.

Another fungus, Botryosphaeria, causes similar cankers and has plagued Leylands since the early 1980s.

Seiridium had appeared in neighboring states by 1993. It may have been in Georgia longer than anyone knows for sure. UGA pathologists may have diagnosed the earliest cases as Bot canker, as Botryosphaeria is known.

"We just got used to the problem being Bot canker," Woodward said. "For 10 or 12 years, that's all there was. We started seeing Seiridium in '97 and really got to looking at it this year."

In the summer, Woodward studied a collection of Leyland cypress samples that showed canker symptoms. "I found Seiridium in about 90 percent of them," she said.

The fungus spreads in the wind and in splashes of rain or irrigation water. It moves through wounds or natural openings in the tree bark into the critical cambial tissue underneath the bark.

Botryosphaeria typically causes only a single canker that eventually girdles a branch and kills it. Seiridium, though, causes many cankers throughout the tree.

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Bot canker damage in a Leyland cypress.

The most obvious sign of Bot canker is the foliage of a tree branch turning reddish brown. Seiridium affects a tree from the bottom up and from inside out. In time, the tree begins to look thinned out, with off-color foliage.

Woodward said Seiridium is much more serious than Bot canker. "When you see signs of Bot canker, you can prune out the infected branch," she said. "By the time you see signs of Seiridium, it's too late to do anything to save the tree."

The tree won't die right away. But it will eventually. No fungicide will kill the fungus once it has infected the tree.

From the first infection, the tree will begin oozing from the entry point in about two weeks. Within a year, the foliage will start dying back. In another year or so, much of the tree may die.

Keeping the tree watered enough to relieve moisture stress will prolong its life, Woodward said. She recommends providing drip irrigation to slow the fungus's spread.

"We don't have a cure for Seiridium," she said. "It spreads fast and attacks the whole tree. It's a serious problem for Leyland cypresses."

If Seiridium becomes the widespread killer Woodward thinks it can be, it could hurt Christmas tree growers.

"It would be a problem on the growers' end," Moorhead said. "Leyland cypresses were thought to be practically insect- and disease- free. This could make growers have to put a lot more work into keeping their trees healthy."