Iris Diseases
Gary W. Moorman, Professor of Plant Pathology
| 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. Apply iprodione, chlorothalonil, triadimefon, or mancozeb when leaves are 6-8 inches long. Remove and destroy infected bulbs |
| 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 chlorothalonil, propiconazole, thiophanate methyl, triadimefon or mancozeb when leaves are 6-8 inches long. |
| 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.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group No. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. No.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 2 | 3 | Dicarboximide | iprodione | 12 | Chipco 26GT (100-1138), Chipco 26019 (264-481), Iprodione (51036-361), Sextant (51036-361-59807) |
| 3 | 2 | Triazole | propiconazole | 24 | Banner MAXX (100-741), Propiconazole (51036-403), Spectator (62719-346-10404), Kestrel (66222-41-81943) |
| triadimefon | 12 | Strike (3125-436), Bayleton (432-1360) | |||
| M | 1 | Chloronitrile | chlorothalonil | 48 | Daconil (50534-9), Exotherm Termil (70-223) |
| 12 | Echo (60063-7), PathGuard (60063-7-499), Concorde (72167-24-1812), Pegasus (72167-24-1812) | ||||
| Dithiocarbamate | mancozeb | 24 | Dithane (707-180), FORE (707-87), Pentathlon (1818-251) | ||
| manganese + zinc | 24 | Protect T/O (1001-65) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
DISCLAIMER
Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
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