Iris: Leaf spot
Photo by: R.S. Byther
Biology
Leaf spot is caused by a fungus which overwinters on dead leaves and other plant material. Spores develop in spring and infect leaves. Several cycles can occur in warm, wet weather, and the disease thrives on plants growing in acidic soils.
Tiny brown spots emerge with water-soaked edges, later turning yellow. Near season’s end after bloom, spots may multiply and run together. Severely infected leaves may die. Older spots reveal grayish centers with red-brown borders.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Remove and destroy dead and infected leaves in fall.
- Maintain adequate plant spacing to improve air circulation.
- Lime to keep the soil pH above 6.
- Change iris planting locations after a few years.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
If the problem has been severe in previous years, fungicide applications may be useful. Make a fungicide application before the disease appears (when plants are 6-8 inches tall) and repeat every 10-14 days while weather remains wet and warm.
Approved Pesticides
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.