Symptoms of infection usually appear as light colored spots on the upper leaf surface followed by rusty colored areas of spores either on the upper or lower leaf surfaces (goldenrod and geranium). Rubbing these areas with a finger or onto a piece of paper will leave a rusty colored smudge. Rust diseases can be quite complex and may alternate between hosts in different genera or remain on the same host during their life cycle. Alternate hosts may include weed species. Perennials commonly attacked by rust fungi include aster, campanula, dianthus, hollyhocks, iris, and malva.
either on the upper or lower leaf surfaces
Most foliar diseases can be lessened with proper watering and humidity regulation. Water plants as early in the day as practical to allow foliage to dry before nightfall. Alleviate poor air circulation or crowded conditions with proper plant spacing. Inspect new growth and older foliage regularly for signs of infection to catch infections early. Sometimes simply removing the infected spotted leaves or plants will solve the problem. Selection of resistant varieties will also help to eliminate the application of costly controls.