(Megan Kennelly, KSU Plant Pathology)
Irises are a popular plant, often grown in large groups. Iris leaf spot is a fungus that can cause mild spotting to severe dieback.The fungus spreads by spores that are dispersed in wet weather.
Red-brown spots with yellow halo:
A closer view – the black bumps are spore-producing structures:
Spots can coalesce to cover a large area
More significant dieback:
Where does that fungus spend the winter? In old infected leaves. Get those outta there to reduce your risk of infection in the new year. Clearing out old infected plant tissue breaks the life cycle.
More information about managing iris leaf spot is available in a recent article by Ward Upham in the KSU Horticulture News