Home Gardening

Dogwood diseases abound in springtime
The Coast Gardener Newspaper and Web Column - March 30, 2002

Congratulations are in order for those individuals and businesses that helped make the Herb and Garden Fest in Ocean Springs last weekend a success. I enjoyed meeting and talking with many gardeners and exhibitors. I even found some nice herbs for my patio!

Despite the cold, dreary weather of late, the flowering trees are beginning to greet the Coast with their beautiful sights and smells of a new spring season. One of my favorite native trees is the flowering dogwood. These spectacular specimens are beginning to fill area landscapes and woodlands with cheery white flowers and bracts. Bracts are those modified leaf structures that look like flower petals.

Unfortunately, the wet and cool conditions of spring sometimes encourage a leaf spot disease to attack dogwoods. This disease, dogwood spot anthracnose, detracts from the overall appearance of the tree. This disease infects trees in the forest as well as those in home landscapes. Moist conditions are necessary for the fungus that causes this disease to thrive.

White tree varieties are usually the ones affected; however, some of the other varieties of dogwoods can become victims of spot anthracnose. Flower buds that are infected with the fungus may become stunted and malformed. In severe cases, buds may even die completely. Fortunately, this disease will not kill your tree.

Spots on the bracts and leaves are circular and may be pinhead-sized or larger. The edges of the spots (margins) are reddish-brown to purple with the centers being yellowish brown. Infected foliage and bracts may appear smaller and have distorted shapes. Severe anthracnose infection can blend together to form large blighted (wilted) areas of dogwoods. New spring leaves and berries also become infected with the fungus.

While the disease does not kill dogwoods, repeated infection from year to year can cause the plant to suffer more extensively environmental stress such as drought and high temperatures.

Ornamental fungicides can be used to combat the problem. One must start the fungicide application at bud break in the spring and repeat every ten to fourteen days until bracts fall. Spraying trees after spot anthracnose symptoms have appeared is of little value.

Another fungus disease that affects dogwoods is powdery mildew. This disease likes sunny, warm days and cool nights. It usually appears later in the spring season when daytime temperatures get warmer.

This disease is easily identified with its grayish-white powdery growth. It looks like someone took talcum powder and sprinkled it on the leaves.

Leaves infected early in the season by the powdery mildew fungus become curled and distorted as they expand. Infected younger leaves have blister-like areas, which quickly become covered with the mildew.

This disease also affects crape myrtles and roses. Fortunately, it will not kill your plants, but it is quite unsightly and results in fewer blooms for gardeners to enjoy. Powdery mildew is also treatable with fungicides; however, good sanitation and pruning practices are good defenses against this disease. Always choose resistant varieties when looking for crape myrtles, roses, or dogwoods at your favorite lawn and garden center.

These archived gardening columns were written by Chance McDavid, former Harrison County Extension Agent.