April 27, 1994|By ANN EGERTON

People aren't sure when or why their flowering dogwoods (Cornus florida) started looking sick; as best the experts can remember, it was in Long Island, spring of 1979.

The dogwoods' disease is called discula anthracnose, a fungus; it currently ranges in the eastern U.S. from Massachusetts and northern New York along the Allegheny mountains to Georgia and South Carolina. According to a spokesman for the Home & Garden Information Center of the Cooperative Extension Service of the University of Maryland, the Tennessee nursery industry, which accounts for approximately 80 percent of all the dogwoods sold in the country, has been particularly hard hit.

Last month, while traveling in the Florida panhandle, I saw a large dogwood on someone's lawn that was quite dead, so it appears that discula anthracnose is moving right along. Suggested causes include several dry summers followed by cool moist springs, but no one knows for sure. The Pacific dogwood is being hit by the same fungus, which produces small tan spots with dark purple borders on leaves, causing the leaves to droop. It works its way into the branches and the trunk and eventually kills the tree.

Cornus florida is considered by landscapers, nursery people and gardeners alike to be one of the great small (25-40 feet) trees of the eastern and central United States. It blooms in late April and early May, producing, in uniform groups of four, creamy white (or pink cultivated) bracts or modified leaves, which any one else but a botanist would call petals. Its true petals are very small and yellow.

Since its leaves don't come until after its flowers have bloomed, it has a unique airy look while in blossom. Its heart-shaped leaves provide shade in the summer and turn a magnificent deep scarlet in autumn. In the fall, it produces red berries whose high fat content provides excellent nourishment for birds during the winter. The tree's loose, free-wheeling shape is pleasing to the eye in the winter, with or without snow, and it's easy to propagate; it even self-seeds. The hardy Cornus florida is just about the all-purpose tree.

Perhaps those all-purpose qualities got it into trouble. Cornus florida is an understory tree, meaning that it is naturally meant to grow at the edge of the woods in partial shade, not as a specimen in the middle of a sun filled lawn. Of course, people couldn't resist plunking such pretty things in the sun, and we got away with it for generations, although Cornus florida has been plagued by borers for some time.

Scientists have been trying, since 1969, to produce a hybrid that is resistant to the borer. Elwin Orton Jr., a plant breeder and research professor at Cook College of Rutgers University, leads a team which has produced about six hybrids of the Cornus florida and Cornus kousa, the smaller Japanese and Korean dogwood that blooms about three weeks later. The new dogwoods are resistant both to the borer and to discula anthracnose; they bloom later than the Cornus florida and earlier than the Cornus kousa but all, like the kousa, bloom after their foliage has grown, so none has the airy look of Cornus florida.

Nursery people say that it's a bit early to judge these new patented hybrid dogwoods, which are only six or seven feet tall. They're not available for landscaping yet, and they'll be both expensive and limited; only 14 nurseries in the U.S. are licensed to sell them.

In the meantime, many nursery representatives and scientists say not to give up on Cornus florida, although they admit that the native flowering dogwoods in the woods, especially in higher elevations where the soil is poorer, will probably succumb to discula anthracnose. Homeowners should be able to fight it with luck, sensible care (light fertilizing, watering during dry weather, mulching, pruning damaged limbs) and fungicides if necessary.

If they're determined to plant Cornus florida, they should buy a healthy proven variety. They can tolerate the sun now, indeed, there's a Catch-22 to all this: While some say that too much sun stressed the dogwood and made it susceptible to the fungus, sunshine slows the fungus down.

Two great trees, the American chestnut and the American elm have been all but wiped out by fungus diseases. Sara Stein points out in her book ''Noah's Garden'' that ''from 1800 to 1950, 90 native species of plants became extinct in the U.S. and that it is projected that in the period between 1950 and 1998, another 475 native species will be lost.'' Let's hope that Cornus florida will not be among them.

Ann Egerton is a Baltimore writer.

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