The symptom is a white or gray, powdery growth on leaves and stems. Providing adequate sunlight and air circulation to lower relative humidity and using fungicide sprays for high-profile plants help control powdery mildew. RUST Rusts are also host-specific. They produce masses of easily noticed, orange or dark red spore masses on leaf tissue. Rusts are commonly seen in our region on turfgrass, hollyhocks, snapdragons, hawthorns and the small fruits.
Rusts usually develop during cool weather.
They are spread by wind and splashing water. Rusts require water to reproduce and infect host plants. Controls include watering early in the day and applying protective fungicidal sprays. Scab on crabapple and pyracantha are leaf-spotting diseases that can cause defoliation. Botrytis flower blight occurs on annuals and some perennials during wet seasons.