What Causes Brown Spots on Iris Plants?

Cut iris blooms and place in water-filled vases for a cut floral arrangement.


The iris (Iris) genus consists of over 300 species of perennials that grow from a bulb, producing medium or large blooms in bright, vivid colors atop tall flower stalks. This versatile plant grows in both dry and wet soils, and works well in rock gardens or as a border plant. Irises grow in U.S. Department of Agriculture plant hardiness zones 3 to 10, depending on the species. When brown spots appear on the iris, it is a sign that something is amiss and immediate action is required.

Ink Spots

Caused by the fungus Drechslera iridis, ink spots are a fungal disease prevalent in moist, mild weather conditions. Ink spots present themselves as reddish brown streaks or small spots on the iris foliage. The spots will enlarge and older leaves may develop a grayish hue in the middle of the spot. Spore masses will begin to grow on the spots during wet conditions. In extreme infections, irises yellow, die and rot before flowers appear. Ink spots cause black, ink-like stains on reticulated irises (Iris reticulata) bulbs. The ink spot fungus can survive on and spread through infected plant debris.

Leaf Spots

Leaf spots are a fungal disease that cause brown to yellowish spots to appear on the foliage. These spots will begin to enlarge and the centers develop a tan hue. These spots are most often near the leaf tip but stems, bulbs and flower buds can also develop the infection. Fungal spores may begin to grow on the spots but may not be visible without a magnifying glass. Leaf spots occur in moist conditions when the temperature is between 50 and 70 degrees. Fungal spores are airborne and can be spread via the wind to other plants.

Treatment and Control

Healthy irises can generally tolerate both ink and leaf spots without treatment but preventive measures should be put into place to protect the plant from these diseases. If chemical treatment is desired, apply a fungicide containing chlorothalonil, iprodione, mancozeb or triadimefon to the iris when its leaves measure about 6 to 8 inches long. Fungicides contain harsh chemicals that can cause more harm than good if not used properly. To prevent injury to the iris, always follow the instructions printed on the fungicide label. In addition, the fungicide should be applied on a day when the temperature is between 40 and 90 degrees, the wind is calm and there is no chance of rain for at least 24 hours.


Proper care and maintenance will help keep fungal diseases such as leaf and ink spots from attacking the irises. Remove and destroy all infected plant debris including the plant matter that has fallen off the iris onto the ground below and around the plant. If possible, dig up the bulbs annually when they go into their dormant period and store in a wooden crate placed in a dark, cool and dry location until ready to plant. To reduce the amount of moisture of the irises foliage, water around the plant’s base and not from above.

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