Iris Disease: Crown Rot
Iris leaftips dying off? Leaf bases dry and brown? Could be iris crown rot. Find out what it is and what to do about it.
What is it?
A widespread plant disease caused by the fungus, sclerotium rolfsii. The fungus decays or destroys the leaf and stem bases, bulbs and rhizomes.
What does it look like?
Plants grown from rhizomes die starting at the leaf tips and progressing ever downward. Leaf bases may be dry and brown, or rotted. Irises grown from bulbs will be stunted, yellowed and die prematurely. Leaves and stems are rotted at the soil level and bulbs will be soft and crumbly.
White fungal strands may cover the crown and soil in both types of plants, and tan to red or brownish pellets will cover the infected plant tissue and be present on nearby soil.
How does it manifest?
Crown rot is spread by moving diseased transplants, infested soil and water and tool contact with contaminated species. Fungal pellets may survive many years in dry soil and reinfect healthy plants when soil becomes moistened. The fungus spreads decay and kills the leaf bases, bulbs, leaves and stems and often many rhizomes.
What can you do about it?
Any plants, which show signs of infection, must be discarded including bulbs, rhizomes, plants and infected soil six inches around each infected plant. Then coat the area with a fungicide containing PCNB. At the start of planting the next year, redrench the soil as soon as new growth begins to show. Always plant in well-drained soil with rhizome tops showing at the soil line, and roots covered. Thin out overcrowded plantings, as this is the quickest way to spread the disease.