It infects a wide variety of roses, but especially those grown in dryer climates as the fungus has the rare characteristic that not only does it not need water to germinate and reproduce, it can be inhibited by it.

[1] The disease cycle of rose powdery mildew starts when the sexual spores, ascospores, of the pathogen survive the winter in a structure composed of hyphae called an ascocarp.

In fact, if there is too much water present on plant surfaces for a prolonged period of time the fungal growth is inhibited and the spores can actually die.

[1] In fact, increasing the exposure of rose powdery mildew from 18 to 24 hours of light per day reduced the production of conidia, the asexual spores of the fungus, by as much as 62%.

[8] Chemical fungicides are not always necessary, however, it is possible to use more environmentally-friendly solutions such as a water-vinegar spray, or mixtures of baking soda and insecticidal soaps.

Research shows that total yield loss from powdery mildew on cereal crops alone can vary anywhere between 2 and 30% depending on the host and the environmental conditions.

[12] Additionally, the wholesale value of roses annually exceeds $100 million in the United States, so the national economic impact from the flower industry cannot be ignored.