Bearded iris plants blossom every spring, adding a profusion of color to any landscape. Though bearded irises are relatively hardy, these plants can sometimes fall victim to a fungal disease called rust. Symptoms of rust include oval brown or red spots on the plant's leaves and stems, according to Cornell University. If left untreated, the disease can kill your iris and spread to other plants. Eradicate rust immediately to help protect your landscape's health and beauty.
Remove the environmental factors that encourage rust growth on bearded irises. Prune back surrounding foliage to expose the affected plant to more air and sunshine, thus helping to dispel humidity. Change your watering practices so you're only applying water at the iris plant's base instead of getting its foliage wet.
Trim off any infected stems and foliage using pruning shears. Dispose of the infected plant parts immediately to avoid spreading the rust spores to other vegetation.
Treat the bearded iris with a fungicide spray labeled for use on ornamental plants. Such products are available at most garden stores and nurseries. For iris plants, North Dakota State University recommends chlorothalonil, thiophanate-methyl or triadimefon fungicides. Apply the products according to their labeled guidelines, as toxicity varies by product.
Retreat the plant four to six weeks after the initial fungicide application if the rust growths persist.