Iris Leaf Spot -- Didymellina macrospora (Heterosporium iridis)
Symptoms: Iris leaf spot causes spots that are small and grayish-brown to brown in color with water-soaked yellowish, red or dark brown margins. This border does not appear in bulbous iris. The spots typically enlarge and coalesce, causing the leaves to die from the tip downward. Spots can also occur on stems and flower buds.
Conditions Favoring Disease: Iris leaf spot thrives in rainy conditions in cool to warm temperatures.
How Pathogen Survives/Disperses: In moist latitudes, the fungus over-winters as mycelium in diseased leaves and other plant parts.
Photo and write up provided by Syngenta Professional Products