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.

Request the high-res image.

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.”