'Beloved' dogwood threatened by fast-spreading fungus Trees in forests are most at risk

April 29, 1991|By Luther Young

The springtime spectacle of dogwoods in full bloom is threatened in Maryland and throughout the East and South by an incurable, fast-spreading disease that has killed millions of the native hardwood trees in the past decade.

Known as dogwood anthracnose, the lethal fungus thrives in the cool, wet highlands of the Appalachians, including the Great Smoky Mountains, the Blue Ridge Mountains and in Catoctin Mountain Park near Thurmont, where 85 percent of the dogwoods have succumbed since 1983.

But the disease -- first detected in New York during the late 1970s -- has turned up in widespread areas of 16 Eastern states and surged within Maryland during last year's rainy spring into all counties, according to the Maryland Department of Agriculture.

"There's a lot of concern. This is just so dramatic," said Ann Sindermann, a plant pathologist for the department's plant protection division. "Although the majority of the problem for us is still in the mountains, all native dogwoods are vulnerable."

The four- to six-week blooming season for Cornus florida is in full stride in Central Maryland, with the familiar white or pink flowers -- actually a form of leaf known as a bract -- bringing welcome spring color to lawns and the understory of taller trees in the woods.

"This is an incredibly beloved tree," said Jay Stipes, an expert on the disease and professor of plant pathology at Virginia Tech in Blacksburg, Va. "We depend on it as a harbinger of spring, one of the things that reminds us it's time to wake up after winter."

The dogwood is the state flower of Virginia and North Carolina and the state tree of Missouri. Cities and towns in the South hold gala dogwood festivals every spring, and the tree is an economic mainstay of the Southern nursery industry.

The cross-shaped, red-tipped blossoms have important religious symbolism for some Christians, and its fall crop of red berries provides food for birds and other wildlife.

"Unfortunately, the dogwood could become extinct," said Dr. Stipes. "The outlook is very bleak in the highland areas, and we don't know how trees in other areas will manage the disease. This is a pretty deadly beast."

The U.S. Forest Service identifies the dogwood's entire 26-state Eastern U.S. range as vulnerable to the disease, but it currently infects Alabama, Georgia, Tennessee, North and South Carolina, Kentucky, Virginia, Massachusetts, Connecticut, New York, New Jersey, Pennsylvania, Ohio, Delaware, Maryland and West Virginia, plus the District of Columbia.

Threats to the dogwood are nothing new. A minor leaf disease known as spot anthracnose is a frequent problem, and the trees can be destroyed by borers that enter through wounds in the bark.

But the new anthracnose is more virulent, causing infected leaves to spot, curl and hang limply on their branches, forming numerous "watersprouts" or shoots on the lower branches and eventually producing cankers that girdle the trunk and kill the tree.

Frank Santamour, a research geneticist at the National Arboretum in Washington, conducted a test planting at the Catoctin Park, near Camp David, with dogwood seedlings from 17 states to search for a strain with natural resistance to the disease.

The results? All of the trees died where they were grown between October 1985 and June 1988. "Once a tree is infected, it's only a matter of time before it dies," he said. "I don't see much hope that Cornus florida can be bred to resist this anthracnose."

Scientists are at a loss about the origins of the disease, which has never been detected in the United States before. One theory suggests it is a native fungus that mutated and became deadly (( after a series of wet, cool springs.

Most feel it's an Asian import, since a relative of the U.S. dogwood -- Cornus kousa, known as the Chinese, Japanese or Korean dogwood -- shows resistance. Also, the disease appeared almost simultaneously in the Northwest, where the Pacific dogwood, Cornus nuttallii, is the native species.

"It's a fungus; it loves shaded areas where cool, damp conditions keep moisture on the leaves longer than in open sun," Dr. Stipes said. "Forest dogwoods are most threatened, and well-tended landscape trees have a pretty good chance of surviving."

Although fungicides can help control the disease's spread, aerial application is impractical over large acreage in the wild, since dogwoods hide beneath the leafy canopy of oaks and other hardwoods prevalent throughout the Appalachians.

"I don't see it becoming extinct," said William Jackson, a plant pathologist with the U.S. Forest Service in Morgantown, W.Va. "But we may lose the dogwood in the wild areas where it's always been so abundant and beautiful."

Some researchers disagree that dogwood anthracnose is a major threat. Elwin Orton Jr., a professor of horticulture at Rutgers University, thinks the disease is an opportunistic phenomenon that took advantage of dogwoods weakened in a cycle of drought and borer damage.

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.