Best Mildew Prevention For Roses

Powdery mildew present on rose foliage. Note the small, flour like white spots.

A frequent question that I get from my customers is “How do you keep your roses looking great with no sign of mildew?” Prevention is the easiest way to keep the upper-hand on powdery mildew,  which can be the bane of rose lovers and gardeners alike. My nursery is located in Eastern Oregon which has beautiful hot and sunny summers, but spring and fall are typically wet and cold. It’s the cold, wet and overcast skies that create the perfect environment for mildew spores to proliferate

What Is Powdery Mildew?

There are numerous species of the fungal disease know as powdery mildew, and each species targets a distinct genus of plants. Therefore the fungal disease that attacks roses is different from the powdery mildew that targets your cucumber plants in the late spring. Unlike most fungal diseases, powdery mildew can lie in wait until the environmental conditions are right before infecting a plant. It does not require direct moisture to activate. The ideal conditions for powdery mildew are when temperatures are between 55 degrees – 75 degrees and the humidity level is high. Don’t be fooled into thinking that your garden is safe if you have yet to have an outbreak, powdery mildew is a traveler, and can travel up to a mile through the air or farther when attached to a leaf or other yard debris.

Identifying powdery mildew is easy due to its distinguishing powdery look on foliage. The disease starts off with very small circular white spots, almost as though the leaves have been dusted with flour. As the disease progresses it can cover entire leaves and flower buds. Powdery mildew will either first appear at the base of the plant on older leaves or at the tip of new foliage and buds. If it is left untreated the foliage will turn yellow, then brown, then eventually drop off. Flower buds will become distorted and in many cases will fall off before opening.

The good news is that treating and preventing powdery mildew is relatively easy. My favorite preventive and curative (if needed) treatment is GreenCure. I have used GreenCure for several years at my rose nursery with stellar results. I’m not a paid representative, so this recommendation is just based upon my use of the product.

What is GreenCure®? It is a potassium bicarbonate-based fungicide that has been proven to cure and prevent powdery mildew, black-spot, downy mildew, blights, molds and other plant diseases. GreenCure’s active ingredient potassium bicarbonate is a naturally occurring compound that is widely used in food is an integral part of humans, animals, plants and virtually all living organisms. It is safe for the environment!

The key to controlling powdery mildew with GreenCure is to use it before you need it. It works wonders as a preventative treatment when used every 10-14 days. If you do have a mildew outbreak you can treat with a heavier dose per the included directions. Typically in 1-2 treatments the powdery mildew will be eliminated and your prize roses will be saved, Yeah!

healthy rose
Healthy Henry Kelsey own root rose. Note the dark green foliage, uniform flower shape and buds free of mildew.


Leave a Reply