iris root rot

Asked September 21, 2016, 2:27 PM EDT

Much of my iris bed is affected by root rot. I've dug them all out to take get a good look and treat the rotted rhizomes. My question is whether or not the soil needs to be treated before re-planting the treated the rhizomes and how to do it if so. I live in NE Ohio.

Stark County Ohio iris root rot

1 Response

Thanks for your question about iris root rot, also called bacterial soft rot. The American Iris Society has a concise article about the maladies of irises, and this author describes it thus:

"In some years this can be a major problem that can almost wipe out a planting if allowed to spread without remedial action. The pathogen is Erwinia carotovora (yes, it affects carrots) and affects all the bearded irises. It presents as a soft, foul-smelling rhizome rot followed by wilting and dying of the leaf fans. It is prevalent in wet springs with high temperatures. If you observe this and smell it, get busy cleaning it out! Use a spoon and scrape the infected tissue out. The wounds in the rhizomes need to be exposed to the sun. Then powder the wound with a chlorine based cleanser. Instead of the cleanser some people douse the rhizomes in place with Dial antibacterial soap (with triclosan)."

Another iris expert advises this about the soil:

"If the rot is extensive, you should dig up the plant; but if only a portion of a plant is infected, the plant can be treated in place. Since the soil immediately surrounding the infected plant has very high Ec levels, it is best to scrape away and dispose of that as well and replace it with uncontaminated soil. With a sharp knife, Cut off the rotted portion of rhizome and leaves, and put into the trash. Do not add diseased leaves and rhizomes to your compost pile! Make sure you cut back the rhizome to all white healthy tissue."

Hope this helps! Good luck!