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Rallying Around the Flowering Dogwood

By Adrian Higgins
Washington Post Staff Writer
Thursday, April 21, 2005; Page H01

Look into the concerned faces of Northern Virginia seventh-graders Amy Howard, Jennifer Grottle and Karina Goodman and you see reflected the fragile nature of nature.

In their own time, no more than 13 years, we have seen the flowering dogwood go from the iconic tree of spring to a native plant under virulent assault from a new and exotic disease.

Dogwoods in Tennessee, where new disease-resistant varieties such as 'Appalachian Spring' have been introduced. (Eric Parsons / AP)

As part of a science project at Frost Middle School in Fairfax, they are trying to raise awareness of the plight of the Virginia state tree, a spring beauty that has cheered Jamestown settlers, Founding Fathers, Civil War campaigners and winter weary Washingtonians through the ages.

The dogwood, now coming into full bloom, will grab the limelight for the next two weeks, though as a diminished star on the spring stage. The number of trees has dropped markedly in the past decade in city and suburban neighborhoods, and particularly in the Appalachian woods, as yet another lethal tree disease has appeared out of the blue to alter the shared landscape.

One imposing specimen, with its distinctive blocklike bark and tiered architecture, still stands in the corner lot of Jennifer Grottle's Annandale home, but it is now the last on the block. "My neighbors down the street have taken them out [as they died]," said Leslie Grottle, Jennifer's mother. "Since ours blooms every year, we are hanging on to the bitter end."

The dogwood anthracnose disease is caused by a fungus named Discula destructiva, and it can kill beautiful mature specimens in as little as two years. Scientists speculate it arrived with the Asian kousa dogwood. The disease is apparent in leaf spots, some that are small and ringed with a purple halo and others that spread to kill leaf tissue in a tan-colored blotch.

Typically, the problem is noticed when lower branches die. The disease can spread fast because a tree under attack responds by growing young shoots from the bark, called water sprouts. These then become infected and spread the disease directly into the main branches of the dogwood. The resulting, sunken canker often girdles the branch, and it dies off.

One control method, therefore, is to examine the tree regularly for water sprouts and cut them off.

Plant pathologist Ethel Dutky recalls walking the woods around Camp David in the early 1980s. "It was absolutely shocking. Ninety-plus percent of the trees were killed," said Dutky, director of the plant diagnostic laboratory at the University of Maryland.

But despite the precipitous decline, the dogwood persists, and perhaps the Grottles' tree will be around for a few more decades. In the past five years, the effects of the disease seem to have diminished. Trees soldier on in the wild and in people's gardens. Dutky believes the dogwood is making a comeback.

Experts say three factors may be at play:

• The blight may have weakened, and be the victim of a pathogen itself.

• The surviving trees may be naturally more resistant to the disease.

• The weather in recent years has cooperated.

Margery Daughtrey, a plant pathologist at Cornell University, said the disease is at its worst when a dull, wet spring follows a summer that was dry. More than most trees, dogwoods dislike drought and face the following growing season stressed. In recent years, summers have been moist in much of the East Coast.

Dutky also is encouraged to see more dogwood seedlings growing in the vicinity of their mother plant. Early in the crises, she noticed that there were none of the customary seedlings found beneath dogwood trees -- the disease spores landed on them and killed them. In recent years, however, she has watched new seedlings survive and grow, suggesting these chance seedlings are naturally resistant.

Dutky and Daughtrey say the dogwood is still a great ornamental tree and should be planted, though as a different player in the landscape -- no longer a tree for the shade garden, but for a spot that is sunny, at least in the morning. An exposed site will bring the sunlight, air movement and warm temperatures that help suppress the disease.

Indeed, although the dogwood is thought of as a forest tree because it has the capacity to grow in deep shade, it prefers far lighter shade or full sun, where it will grow better, and flower and fruit more, said Dutky.

The problem with raising dogwoods in sunlight, however, is that they need greater care, particularly a soil that retains some moisture in drought. This is achieved by planting in a deep loam, amended as needed, and then mulching the root zone. The roots should receive an occasional deep soaking during periods of drought.

Another tactic is to spray the leaves with a fungicide preventatively, though this takes knowledge and effort, not to mention the use of pesticides. "Most people in the landscape are not spraying them," said Dutky.

In fact, as the three seventh-graders discovered, few people seem even to know that their state tree is under threat. Only one of 13 adults they surveyed was aware of the anthracnose disease, they said. They also polled classmates at Frost. None knew of the disease. "Some students didn't even know what a dogwood tree was," said Jennifer Grottle.

The disease, incidentally, was identified and named by an Agriculture Department scientist named Scott C. Redlin working in Beltsville for the Agricultural Research Service. He now works for the department in Raleigh, N.C., where the dogwoods flourish, he said, because the spring there gets warm in a hurry. "I suspect the leaves develop more quickly here and the temperature is too high for the spores," he said.

Another scientist, Bob Trigiano of the University of Tennessee, said he doesn't share the view that the disease is any less virulent or that most trees are any more resistant to it, and believes that the key to survival is placement in a sunny location. He also suggests using an anthracnose-resistant variety introduced by the university called 'Appalachian Spring.'

Meanwhile, the Frost Middle School students continue their crusade. Should dogwoods still be sold and planted?

"Yes," said Amy Howard.

"Yes," added Karina Goodman. But gardeners "should take the right precautions."

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