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Iris Diseases

Informational table showing disease name, symptoms, pathogen/cause, and management of Iris diseases.
Disease Symptoms Pathogen/Cause Management
Bacterial Leaf Blight Faint water soaked spots on leaves enlarge along the leaf when weather is wet but cease activity when it is dry. Xanthomonas campestris pv. tardicrescens Remove infected leaves. Avoid overhead irrigation.
Botrytis Rhizome rot Few leave emerge in the spring. Leaves are yellowed, turn brown, and die. Gray masses of fungal spores form on infected leaf tissue. Rhizomes have a dry, mealy rot. Large, shiny, black, granule-like structures (sclerotia) form on the surface of infected rhizomes. Botrytis convoluta Do not plant infected rhizomes. Destroy infected plants.
Crown Rot Leaves die slowly from the tips. White fungal threads can be found at the leaf bases. Tan, spherical structures (sclerotia) form between rotting leaves. Corticium rolfsii Discard infected bulbs.
Ink Spot (Bulbous Iris) Tiny spots and streaks on leaves enlarge and become dark reddish brown. Spots may become gray in the center. During wet weather, dark masses of spores form in the spots. The plants yellow and die prematurely. Heavily infected bulbs may rot before flowering occurs. Drechslera iridis Destroy leaf debris. Remove and destroy infected bulbs. Apply a fungicide to protect plants.
LEAF SPOT Small brown spots with water soaked margins turn yellow, ehlarge and develop reddish-brown borders. Leaves die. Dark fungal spores can be seen within the spots with a magnifying glass Mycosphaerella macrospora (Didymellina) Remove and destroy infected leaves and leaf debris. Apply a fungicide to protect plants.
Nematodes Black streaks develop along the veins of outer leaves of bulbs. The basal plate is gray and separated fro the outer scales by a dark sunken groove. Ditylenchus destructor Destroy infected bulbs. Plant in nematode-free soil
Soft Rot Leaves collapse suddenly or die gradually from the tips. The base of infected leaves and infected rhizomes have a foul smelling soft rot. Erwinia carotovora pv. carotovora Destroy infected rhozomes. Control iris borers which often cause the injury where the bacteria initially gain entry.
Virus Mild mosaic on flower stalks and spathe (mild mosaic virus). Yellow green stippling and stunting (severe mosaic virus). Flower color breaking and puckering can occur. Iris mild mosaic, iris severe mosaic, cucumber mosaic (all aphid transmitted), broad bean wilt, tobacco ringspot, tobacco rattle, bean yellow mosaic, narcissus latent virus, bearded iris mosaic, beardless iris mosaic. Most iris cultivars tolerate viruses. Destroy severely affected plants.

Leaf spot symptoms
Leaf spot symptoms.

Prepared by Gary W. Moorman, Professor of Plant Pathology

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Iris Diseases

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