Rust diseases are a common fungal infection that affect a wide range of floricultural crops, including Aster, Carnation, Fuchsia, Florist’s geranium (Pelargonium X hortorum)Gladiolus, Lilium, Marigold, Poinsettia, Snapdragons, Statice and Viola (including pansy). Rusts have the potential to negatively impact floriculture production because these pathogens often cannot be detected on infected, but symptomless propagation material entering the United States or moving state-to-state. Rust fungi are obligate parasites, dependent upon alive host for growth and development, and seldom kill plants. However, rust infection reduces plant health and vigor, flower production, and aesthetic value.
Aster is affected by several rust diseases-Coleosporium campanulae, Puccina asteris, P. campanulae, and other Puccinia species. Orange-red pustules develop on the leaf undersides; heavy infections can cause leaf yellowing and necrosis. C. campanulae requires pine as an alternate host, while Puccinia species have various sedges and grasses as alternate hosts. The removal of alternate hosts is a good management strategy.
Purchase only disease free plants or cuttings. Carefully inspect all incoming plant shipments for rust symptoms. Keep new plants isolated from established plants for up to three weeks to allow rust diseases to develop, if present. Scout regularly for rust diseases. Frequently remove all rust-infected leaves and badly infected plants and destroy by burning, rapid composting, or burying. At the end of the growing season, carefully clean up and destroy all crop debris.Sterilize benches and propagation rooms with an appropriate greenhouse disinfectant. Keep the humidity within the greenhouse at less than 80%. Iincrease air movementby adding fans which will prevent moisture from condensing on the foliage. Practice only surface watering and avoid splashing water onto foliage. If overhead irrigation is necessary, water in the early morning when plants will dry quickly. Space plants far enough apart to allow for good air circulation.
Cultural and chemical controls can be combined to control Rust diseases. Fungicides registered for ornamentals include Banner Maxx, Eagle, Heritage, Stature, Strike 25 WP, and Systhane 40 WP. Check labels for host appropriateness.