Bacterial soft rot enters plants through wounds caused by the iris borer. Infected leaves have a watersoaked appearance. Healthy leaves fall over when the rhizomes rot. Rotting rhizomes have a foul odor. Cut off leaves showing the water soaked areas. Destroy rotted rhizomes and control the iris borer. Plant rhizomes shallow and disinfect tools with 70% denatured alcohol. No chemical control is listed.
Bacterial leaf spot causes translucent spots of irregular shape. These appear dark green in reflected light. The spots may merge in rainy weather to involve the whole leaf. Remove and destroy spotted leaves early in the growing season. Remove and destroy the tops in fall. No chemical control is listed.
Blossom blight causes blossom spots and blights in rainy seasons. Remove blighted blossoms. The disease is also called leaf blight and is caused by Botrytis cinerea. Applications of benomyl or chlorothalonil control the problem.
Leaf spot causes irregular spots which vary in size and may run together. The spots have grayish centers with dark brown borders. The disease is usually in the upper half of the leaves and is more serious after the plants have bloomed. Premature death of the leaves weakens the rhizomes. The causal organism is Didymellina macrospora and it can be controlled with sprays of chlorothalonil.
Plants infected with rhizome rot fail to grow in the spring. The fungus develops in cool wet weather. No chemical control is listed for this disease caused by Botryotinia convoluta.
Crown Rot is worse when plants are crowded. The leaf and flower stalk bases are attacked. The infection spreads to the rhizome causing a rapidly developing dry rot. Remove infected plants. The disease is caused by Pellicularia rolfsii and no chemical control is listed.
Mosaic infected plants have yellow striping or mottling on the leaves and flowers. The flowers are smaller then normal. Discard infected plants and control aphids which spread the disease.