Irises forum→Ack! My iris has fungal crown rot - what do I do?

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Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 6, 2018 6:39 PM CST
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. Confused Crying

Name: Timothy
eastern oregon (Zone 7b)
Irises Bulbs Region: United States of America Region: Pacific Northwest Plant and/or Seed Trader Dahlias
Garden Photography Salvias Cat Lover Enjoys or suffers hot summers Hybridizer Region: Oregon
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TBMan
Aug 6, 2018 9:49 PM CST
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.
Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 6, 2018 10:23 PM CST
Thanks, Tim. I'm pretty sure it is sclerotinia something, but I'm not sure which. You've given me good information. Thumbs up
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Aug 7, 2018 6:08 AM CST
I agree with Tim....get your extension agent, as quick as you can, to send in samples for ID....then treat per recommendations.
South central PA (Zone 6a)
Irises Region: Pennsylvania
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DaveinPA
Aug 8, 2018 7:10 PM CST
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].
Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 8, 2018 8:12 PM CST
Thank you, Arlyn and Dave, for your advice. Arlyn, I know you have had a lot of experience dealing with mysterious pathogens. Sad 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).
Name: Lyndylu
Oregon's high desert (Zone 5b)
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LynnDel
Aug 8, 2018 8:15 PM CST
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?

Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 8, 2018 9:48 PM CST
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. Sighing!
Name: Marilyn, aka "Poly"
South San Francisco Bay Area (Zone 9b)
"The mountains are calling..."
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Polymerous
Aug 8, 2018 9:55 PM CST
Sad Sighing!
Evaluating an iris seedling, hopefully for rebloom
Name: Sherry Austin
Santa Cruz, CA (Zone 9a)
Region: California Irises Keeper of Poultry Roses Dragonflies Birds
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Henhouse
Aug 8, 2018 10:14 PM CST
For those who haven't seen it....
Thumb of 2018-08-09/Henhouse/7607e0 Thumb of 2018-08-09/Henhouse/3703a7
Thumb of 2018-08-09/Henhouse/4ed973 Thumb of 2018-08-09/Henhouse/27bc5a
Thumb of 2018-08-09/Henhouse/b29342

The surest sign that intelligent life exists elsewhere in the universe is that it has never tried to contact us.
Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 8, 2018 10:37 PM CST
Yup, Sherry, that's it. What did you do when your iris got it? (I assume those pictures are of your own iris.)
Name: Lyndylu
Oregon's high desert (Zone 5b)
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LynnDel
Aug 9, 2018 10:33 AM CST
(deleted duplicate post)

[Last edited by LynnDel - Aug 9, 2018 10:34 AM (+)]
Give a thumbs up | Quote | Post #1783166 (12)
Name: daphne
san diego county, ca (Zone 10a)
Million Pollinator Garden Challenge
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shizen
Aug 9, 2018 10:40 AM CST
thanks for the pictures sherry.
Name: Leon
Indiana (Zone 5a)
Light is the shadow of God!
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TBGDN
Aug 9, 2018 11:02 AM CST
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...
Even a fool, when he shuts his mouth, is counted (as being) wise.Proverbs 17:28
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Name: Sherry Austin
Santa Cruz, CA (Zone 9a)
Region: California Irises Keeper of Poultry Roses Dragonflies Birds
Bulbs Foliage Fan Photo Contest Winner: 2015
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Henhouse
Aug 9, 2018 11:29 AM CST
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.
The surest sign that intelligent life exists elsewhere in the universe is that it has never tried to contact us.
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Aug 9, 2018 12:45 PM CST
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.
Name: Leon
Indiana (Zone 5a)
Light is the shadow of God!
Charter ATP Member I was one of the first 300 contributors to the plant database! Celebrating Gardening: 2015 Region: United States of America Region: Indiana Vegetable Grower
Garden Ideas: Master Level Peonies Hummingbirder Cat Lover Dog Lover Million Pollinator Garden Challenge
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TBGDN
Aug 9, 2018 12:51 PM CST
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 I agree

Even a fool, when he shuts his mouth, is counted (as being) wise.Proverbs 17:28
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South central PA (Zone 6a)
Irises Region: Pennsylvania
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DaveinPA
Aug 9, 2018 1:40 PM CST
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.
Los Altos, CA (Zone 9b)
Irises
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AndreaD
Aug 9, 2018 5:54 PM CST
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.
Los Altos, CA (Zone 9b)
Irises
Image
AndreaD
Aug 9, 2018 6:10 PM CST
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.

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