- Pruning the affected leaves on your rosebush will stop the spread of powdery mildew and, in some cases, remove the fungus entirely. Examine each leaf for the telltale signs of the fungus, which may include a white crusty coating, a hardening of the leaf, discoloration due to disrupted photosynthesis or lifelessness. Put on a pair of gardening gloves and remove all affected leaves from the bush using pruning shears.
- Rosebushes are most susceptible to powdery mildew in dark or shaded areas lacking in sunlight, since humidity and moisture can become stagnant with no sunlight to evaporate it. If possible, remove any barriers to sunlight or uproot your rosebush and move it to a sunnier location. If your rosebush resides in an area crowded with plants or otherwise lacking in air circulation, you should also move it to an airier location and prune the affected leaves.
- Cornell University tested the effects of baking soda and horticultural oil on plants and on roses specifically, and found the solution useful in killing powdery mildew. Mix 2 1/2 tbsp. of horticultural oil with 1 tbsp. of baking soda and 1 gallon of water. Mix the ingredients well and pour into a spray bottle. Spray your entire rose bush once every 7 to 14 days until the fungus disappears.
- A report from the Colorado State University Extension recommends the use of neem oil as a powerful horticultural fungicide. Marketed commercially under names like Rose Defense, Shield-All and Triact, neem oil can kill powdery mildew if applied from a spray bottle every 7 to 14 days; never use any fungicide more than once per week when attacking powdery mildew. Follow the manufacturer's directions for best results.
previous post