Host: Chrysanthemum, geranium, hollyhock, hemerocallis, rose, salvia, snapdragon, zinnia
Symptoms: Rust causes yellow or pale spots to form on the leaves, leaf stalks, and stems. Within or directly beneath the spot, brightly colored (orange, rust, red, brown or yellow) spores are produced in pustules that rupture through the epidermis. Leaves eventually turn brown and dry up, leaving the plant unmarketable.
Conditions Favoring Disease: Rust occurs when leaves become wet from rain, dew or irrigation, particularly at night when slow drying occurs. Many rusts are worse in cool to warm temperatures.
How Pathogen Survives/Disperses: Spores from uredia are carried by wind or splashing to healthy leaves. When the leaves become wet, spores will germinate and send out mycelium to penetrate and infect the leaf. New rust lesions form within 7 to 10 days, and further uredia are produced, completing the cycle. In some cases, the rust fungi survive the winter as teliospores on leaf debris.
Photo and write up provided by Syngenta Professional Products