Remove any yellowing leaves promptly to help prevent spread of the disease. Iris leaf spot, caused by a fungus, is the most common disease. Remove all leaf and other debris in fall, since diseases and insects often overwinter on old foliage. Iris borer is the most serious insect pest of iris. Bacterial soft rot readily attacks borer-infested plants.
Aphids can be a nuisance problem at times.
USE Most iris, especially bearded iris, will grow best with full sun for at least 6 to 8 hours a day. In very hot areas though, some shade in the afternoon will help keep flower colors from fading in the heat. Iris should be planted in an area with good air circulation to help prevent disease problems. Most iris need very well-drained soil. Japanese and Louisiana iris will grow in wet soil.