University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

Iris problems

4 (1 = rare 5 = annual)
4 (1 = very little damage 5 = plants killed)

Plants Affected

Iris sp. (Iris) get a leaf diseases caused by Mycosphaerella macrospora which causes lesions that appear to have greasy margins and bacterial rot that decays the rhizome.

The more serious problem is the iris borer that allows the bacterial rot inside the leaf and rhizome that the borer carries in on its body.

Life Cycle

The fungal disease likes wet conditions.

The borer enters the leaf when the leaves are about 4-6 inches high. The insect works its way down the leaf into the rhizome. The bacterium follows.

Use a preventative insecticide and sanitation (dig up and remove borers, scrape out decay, dip in 10 percent chlorine bleach solution, dry for several hours in sunlight). Replant so that top of rhizome is visible after watering the rhizomes in. Cut leaves to 4-6 inches in height.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic