Description
These fungi are aptly named: most rusts produce rust-colored or brown powdery pustules on the leaves and stems of their host plants. Rusts infect all kinds of plants, but most rust fungi infect only 1 or 2 plant species, or only certain varieties of a species. Some rusts, such as cedar-apple rust (see Cedar-Apple Rust), must alternate between 2 specific host plants. Diseased plants are usually weak and stunted, and severely infected plants may die. Spores may be blown hundreds of miles to infect healthy plants. Some rust fungi cannot infect their host unless the foliage remains wet for at least 6 hours. Most rusts require a living host to survive the winter; others can survive on plant debris.
Control
Many methods can be used to control or prevent rust infection. Spray infected plants with a fungicide containing triforine, chlorothalonil, mancozeb, maneb, or zineb. Make sure your plant is listed on the product label. Pick off and destroy badly infected leaves as long as the practice doesn't damage the overall beauty of the plant. Keep the foliage as dry as possible. One way to do this is to water in the morning, which gives the plant a chance to dry out quickly, reducing the chance of infection. The best way to avoid rust infection is to plant resistant varieties of grasses, flowers, vegetables, and woody ornamentals, which may be found in local nurseries or through seed companies.
