I have gotten a lot of questions about powdery mildew and rust on roses. The questions I have received have all focused on roses but these problems can affect lots of plants, including squash and lilacs. These airborne fungi are the result of moist conditions combined with warm temperatures. The mildew looks like someone fiendishly sprinkled flour all over your plants. It stresses the plant and lowers its immune response, weakening its resistance to other diseases and weather conditions. If enough of the leaf surface becomes covered with powdery mildew, photosynthesis is impaired.
Rust is another fungus that can affect a wide range of plants, when given the right warm, moist condition that it loves. It appears quite different, however, making yellow-reddish or brown spots and splotches on leaves that appear to be more raised or bumpy than powdery mildew. Rust also prevents photosynthesis and stresses plants to the point of diminished growth and production.
Our Penetrate product, comprised of live beneficial soil bacteria and their food, will actually eat and eradicate the bad airborne fungi such as powdery mildew and rust. The product is not listed for this use, but it works very well. It is listed for soil applications, so as you apply you can spray generously on the plants and the soil. Our other products, Optimize, Maximize, Nourish-Biosol, don’t have a direct effect on the airborne fungi like powdery mildew and rust, but they have a very strong indirect effect that is at the heart of all pest and disease prevention. Our products maximize complex beneficial soil microbiology, which is the key to growing healthy plants that produce lots of sugars and metabolize at a high, vigorous rate. All plants will be best able to fight pests and disease if their health is being maximized by the soil in which they grow. In addition to just being healthy, there are compounds and exudates produced by lively soil and strong plants that can positively impact pest and disease resistance.
For powdery mildew and rust, in addition to proper application of our products, it is best to provide good air circulation through the plants by thinning and making sure spacing is proper. Sun exposure is another strong deterrent and should be at least six hours per day so be sure your susceptible plants are in a sunny location. Weather can create garden challenges and properly conditioned soil will address many of those challenges with amazing natural adaptations. Our four-part John & Bob’s system, pre-packaged in proper ratios based on garden size in the Nature's Gardening Kit, is the easiest and most effective way to make your soil lively and full of productive energy.