I do not usually have problems with rot, so now that I have found fungal crown rot among my
irises, I don't know how to get rid of it. I threw out the plants that were affected and dug up the surrounding as yet unaffected plants and soaked them in a bleach solution. But I'm worried that the pathogen is in my soil. Is there some treatment I should give to the soil that the irises were in? They were in a raised bed and the thought that whatever I plant there in the future will rot makes me seriously unhappy.

If your problem is the crown rot caused by Sclerotinia sclerotiorum, then a soil drench of Daconil, or drenching the base of the iris clump with Daconil, will give control, but not a cure, so in other words, treatment will stop the pathogen from spreading to healthy plants. Terrachlor is another treatment recommended for Sclerotinia rolfsii, or Mustard Seed Fungus which sometimes strikes iris in more southern states, especially areas with summertime heat and humidity.
It is important to identify, exactly what the pathogen is, because some sclerotinia strains have developed some resistance to fungicides. Maybe your local extension service can help.

Thanks, Tim. I'm pretty sure it is sclerotinia something, but I'm not sure which. You've given me good information.

I agree with Tim....get your extension agent, as quick as you can, to send in samples for ID....then treat per recommendations.

In the meantime leave the area open to the sun for some solar treatment after loosening the soil [and then washing off the tools well].

Thank you, Arlyn and Dave, for your advice. Arlyn, I know you have had a lot of experience dealing with mysterious pathogens. Dave, I removed the irrigation hoses from the area and am letting it dry out and bake in the sun. I've dedicated one spade to work the area and am keeping the rest of my tools separate.

Fortunately, only a small area was affected (at least so far - gulp).

What does this fungal crown rot look like? I had three of my rhizomes turn in to dry, brown, crumbles early this spring. Is that what happened to them?

The base of the leaves turned yellow and mushy. There was a cottony white growth on the leaves that ate into the leaves and destroyed their tissue. There were also soft spots on the rhizome. Soft spots on the rhizome you can scrape out, but the yellowy leaves mean it's a goner.

For those who haven't seen it....

Yup, Sherry, that's it. What did you do when your iris got it? (I assume those pictures are of your own iris.)

(deleted duplicate post)

thanks for the pictures sherry.

I had read in 2001 a very good, although short, article by the Late Richard Ernst of the famed Cooley's Gardens of Silverton, OR. The article was published in the AIS Bulletin in July of that year. At that time I was plagued with rot problems, especially the kind illustrated in Sherry's pictures above. According to Rick (and others) this disease carries several names, but they are all IMHO the same pathogen. Crown Rot, Southern Blight, Mustard Seed Fungus, etc. etc.

It is titled 'More on Iris Culture' and appears on page 22 in that issue. Also it is in PDF format. Although brief, the points he made have helped me a lot over the years. This is the link if you care to take a peek:
https://archive.org/stream/bul...

This was three years ago. I dug them up and dipped them.. I may have dug the soil out and replaced it, but don't remember. I haven't seen any this year (yet), but it seemed to be an isolated problem that affected only a few Iris.. Nothing at all like the soft rot I dealt with earlier in the year.

In small plantings, prompt removal of the "almost spent" leaves will prevent a lot of the crown rot from developing into a full blown problem. Here, I blame high humidity / dew, which runs down the leaf, to the base, where it's "trapped" by the leaf. The moisture can also make the bacterial rot possible, and, in many cases , here, I see both occurring on the same plant....I think the "fungal" opens up a wound that the bacteria can use to enter the rhizome. The "upside", for me, is that the fungal crown rot pretty much "cures itself"....sun, and airflow will halt it. I do spray fungicides, all year long, mostly for leaf spot, but, they will help with the crown rot, too.

crowrita1 said: In small plantings, prompt removal of the "almost spent" leaves will prevent a lot of the crown rot from developing into a full blown problem. Here, I blame high humidity / dew, which runs down the leaf, to the base, where it's "trapped" by the leaf. The moisture can also make the bacterial rot possible, and, in many cases , here, I see both occurring on the same plant....I think the "fungal" opens up a wound that the bacteria can use to enter the rhizome. The "upside", for me, is that the fungal crown rot pretty much "cures itself"....sun, and airflow will halt it. I do spray fungicides, all year long, mostly for leaf spot, but, they will help with the crown rot, too.

Ditto

Thanks for posting those pictures Sherry. There should be a spot on the website to post the iris related diseases and such.
Hope the stuff clears up Andrea. At least you have some good advice to implement.

Leon, that article was very interesting and informative. So the pathogen is soil borne and thrives in moisture and warm temperatures. I'll look into getting some Terrachlor. Tim recommended that, too.

I must say that what Arlyn said about sun and airflow is really on. I have noticed among my big clumps where the rhizomes have grown close together there is some blemishes on the leaves and it is not leaf spot. I don't get perturbed about leaf spot. I think in the future I am going to thin the big clumps.

Holy bleep, that Terraclor is pricey, more than $100 a gallon, and I see that it is prohibited for residential use. Daconil is within reason.

Oh well, I'm going to see if the crown rot cures itself, as Arlyn says, from the sun and airflow.
If it doesn't and I lose a few more iris, they are replaceable.