University of Maryland: Garden Q&A
Q: Saw your alert about Thousand canker disease on Facebook. How can I protect my black walnut trees?
A: Thousand canker disease was introduced from its natural habitat west of the Rockies into Tennessee. Now, citizens must help to keep it out of Maryland. DO NOT bring firewood into Maryland. Diseased and dying trees are often the first ones cut for firewood. Also, be alert for diseased black walnut wood or lumber shipped in (illegally) for use in building or crafts.
For additional information on the disease go to http://www.ext.colostate.edu/pubs/insect/0812_alert.pdf.
If you suspect you see the disease, notify the Home and Garden Information Center and send us photos, so that we can contact the Maryland Department of Agriculture which will work to stop the spread of Thousand canker disease.
Q: My garden is a mess. A white fungus spead from the peonies to the lilacs to the cucumbers. Then the black spots on my roses spread to the Black-eyed Susans, too. How can I keep these contagious diseases under control?
A: These plants all have different diseases. Disease organisms generally specialize and attack only one plant or family of plants. Though the fungi may look similar and even have the same common name, such as the whitish powdery mildew fungus you saw, they are all different disease types and incapable of spreading from one plant species to another.
Remove the disease spores in your garden this fall to reduce the risk of infection next year. Cut off, rake up, and dispose of all infected foliage, either now or as soon as frost browns it. Next year, keep a sharp lookout for the first sign of disease and call HGIC right away. Each plant will require a different treatment for its particular disease.