Iris: Leaf spot
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.
Use Integrated Pest Management (IPM) for successful plant problem 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.
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
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.
Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.