Managing Iris Leaf Spot: Identification and Control

Symptoms and Cycle

Iris leaf spot (caused by Didymellina macrospora) appears as small brown spots with water-soaked borders. Spots coalesce, killing the upper leaf. The fungus overwinters on dead foliage and spores spread in spring.

Control Measures

1. Sanitation. Cut and discard (do not compost) all diseased leaves at ground level in October.
2. Fungicide (for valuable collections). Spray chlorothalonil (Daconil) or mancozeb when leaves are 4–6 inches tall. Repeat every 10 days. Add ¼ tsp liquid detergent per gallon to wet waxy foliage.

iris leaf spot