Gray substance on dogwood is lichen

Garden Q&A


After our dogwood dropped its leaves this fall, we noticed a gray powdery substance on the bark. Is this mold? The tree is in clay soil and part shade.

You're seeing lichen, an organism composed of algae and fungi living in a symbiotic relationship that benefits both. Because the algae provides its own nutrients through photosynthesis and the fungi protect the algae from drying out, lichens can grow harmlessly on tree trunks. No control is necessary. In fact, lichens indicate good air quality. They are extremely sensitive to sulfur dioxide and are not usually found in industrial areas. Lichens rarely develop on rapidly growing trees, perhaps because bark expands too fast. It lives on healthy mature trees, but also can appear on declining trees that have a slower growth rate (though lichens do not cause the decline).

Should I prune my rose bushes before winter?

It's best to wait until just before leaves bud out in the spring to do yearly pruning of roses. If you prune now and Maryland has extreme weather this winter, your rose bush could lose additional branches to winterburn. A poorly placed stray branch can be removed at any time.


Check houseplants for signs of whiteflies, fungus gnats and spider mites. The latter can be controlled by a spray of water. The first two pests can be treated with a pyrethrum and soap insecticide labeled for houseplants.

Prune out dead and diseased branches from deciduous trees and shrubs. Snow and ice loads can cause these branches to come down unexpectedly.

Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at Maryland Cooperative Extension's Home and Garden Information Center, which offers Maryland residents free gardening information. Call the center's "hotline" at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail plant and pest questions through the Send a Question feature at

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