The weather was wonderful for dogwood blooms this spring. But it wasn't so great for the trees themselves.
"We've had a lot of powdery mildew this spring, especially on dogwoods," said Jean Williams-Woodward, a plant pathologist with the University of Georgia Extension Service.
Warm, humid days and cold nights, she said, are ideal for powdery mildew on dogwoods. The fungus usually appears as a white coating on the leaf surface.
"On some dogwoods the leaves may turn gray or have darker blotches on them," Williams-Woodward said. "This, too, is powdery mildew, but just older infections."
However they look, leaves with powdery mildew aren't long for this world.
"Once the leaf is infected," she said, "the fungus moves across the leaf surface and blocks the sunlight. Some leaves may remain on the tree, but most usually fall."
Homeowners become alarmed when the leaves start dropping off their favorite landscape trees. "But the tree will leaf out again," Williams- Woodward said.
Powdery mildew infects almost every landscape tree, she said. But the fungi are host-specific. Crape myrtles, for instance, also get the disease but are infected by a different fungus.
Most powdery mildew fungi will cause the leaves to drop off. The fungus that infects crape myrtles, though, is an exception.
"Powdery mildew is very active in late spring through early summer," Williams-Woodward said. "It peaks in June, then drops off some through the summer."
Once a tree is infected, she said, there's no way to control it. "It helps to rake and remove the leaves that drop off," she said. "That will help protect new growth or next year's growth."
For large dogwoods, nothing else can be done. "There are fungicides you can use to prevent powdery mildew," she said, "but you will never get enough coverage on a large tree."
For young, small dogwoods, homeowners can prevent powdery mildew infections with sprays of Immunex. Daconil will work, too, she said, but will not control the fungus as well.
(Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)