Question
Hello,

We live in western Oregon, and have spent two summers in our current home. There are two small-ish magnolias planted on either side of the east-facing front porch. Last summer (2010), they were fine. This past summer (2011), they seem to have been suffering from powdery mildew. (I learned this just recently, as I was researching if the white leaves could be used for mulch. I'll be destroying the leaves.)

Summer 2010 was sunny, warm, and dry. Summer 2011 was gloomy and wet and we were lucky to get about 3 weeks of summer weather in August, so I assume the weather was a big factor in the mildew problem.

Now that winter is just around the corner, I'm not sure what to do and what to expect for next summer. The leaves are off and the buds are developing.

Is there any treatment I should do over the winter/spring? Should I expect the problem to continue next summer, even if the weather is warm and dry?

Thanks for the help!
Pam

Answer
Yes warm humid weather will give the fungi the conditions it needs to grow. No need to treat this winter. Start the treatment early next spring. I would apply a fungicide at bud break and then maybe once a month check and you may need to apply again later into the summer. Whether it becomes a problem again will depend if the conditions are right when the fungi is producing spores to spread the fungi. One year you can have a major problem the next none can be found.

Powdery mildew is a powdery, fluffy white to light gray-colored fungus growth on succulent stems, leaves, buds and flowers is the characteristic symptom of powdery mildew. Young plants and actively growing shoots are more severely damaged than older plants, leaves or branches. Infected leaves may be dwarfed, curled or deformed.

To control use one of the following fungicides according to label instructions:

Propiconazole (Banner Maxx) is registered for control of powdery mildew and numerous other diseases on ornamentals.

Myclobutanil (Systhane, Eagle, and Immunox) is registered for control of powdery mildew and numerous other diseases on ornamentals.

Sulfur as a spray or dust as needed. Sulfur may cause some plant injury if applied when air temperature exceeds 90 F.

Triforine (Funginex) is labeled for use on roses and several other ornamentals. Follow manufacturer's instructions on the label. This product is only available in small packages.

Triadimefon (Bayleton and Strike# is now registered for use on a number of ornamentals.

Fenarimol #Rubigan) is a locally systemic fungicide for the prevention or therapeutic control of powdery mildew of field or landscape grown ornamentals.

In some situations copper fungicides will provide control of powdery mildew.

Check with your local nursery store for a fungicide for powdery mildew on trees and shrubs.