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What is it?

This is a common plant disease caused by the fungus Sphaerotheca pannosa. It is one of the most serious and widespread diseases in rose plants.

What does it look like?

The disease consists of a grayish white material that is powdery covers leaves, twigs and flower buds. The leaves may be discolored or curled, often turning yellowish and purplish and dropping off. Often new growth is stunted, and infected flower buds do not open properly. Late in summer, black dots which produce spores are scattered over the powdery fungal cover.

How does it manifest?

Spores are spread by wind to healthy plants. The fungi multiply and sap the plant of nutrients. When this is left unchecked it will kill canes and entire plants. Powdery mildew may occur anytime when rainfall is low and temperatures are between 70° - 80° F.

What can you do about it?

Apply fungicide containing triforine at the first sign of mildew on rose plants. At intervals of 7 to 10 days respray plants if mildew is present. Repeat applications until mildew is gone. In the fall, rake up and destroy leaves to avoid the chance of spore spread.