Iris rot

hilltopviews(z7 SE)August 14, 2005

We've had a wet summer this year. As I'm cleaning and removing weeds, I'm finding almost all of my iris are rottening.

When I say rot - its really - mush !! I'm having to remove them as I find the decaying tubors.

These are old plants I've had for years, moved them when I've relocated. Is it the rain or is there something else going on?

Plants have good drainage, but we have had a lot of rain this season.


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marvine(z7/8 GA)

I'm having a lot of rot too - first time ever. It must be the rain. I'm digging them up, cleaning out the rot and laying them in the garage to dry. I don't know what else to do.

    Bookmark   August 14, 2005 at 8:23AM
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cantstopgardening(Zone 4/5 WI)

could be excessive rain, or could be the dreaded iris borer. I have to get out there and start digging up my iris and searching for those bad guys. I know they are out there. Grrrr....

I did a search on this forum for iris borer for you. I hope my link will work.


Here is a link that might be useful: search of iris forum for iris borer

    Bookmark   August 14, 2005 at 10:32PM
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njiris(z 5 NJ)

If you have borers, you should be able to see either chewed leaves, holes in rhizomes, or borer droppings. However, borers are pretty much gone to pupate by now. You won't see the pupa, unless you dig up your iris beds and search for shiny brown dormant capsules about one inch long.
If you have rot from excess rain, you will see fans flopped over, yellowing foliage, and in bad cases, stinky mush where your rhizome used to be. This is much worse than borer damage.
Once you kill the borer, clean out the wound, the iris does just fine. But rain...but by the time you realize your rhizomes are suffering, alot of damage has been done already.
Best cure for water damage, is dig up, clip, dry in the sunshine...a sunny window is the best, then replant when totally dried out (a week or so).
You can have rain-rot even with good drainage. I've had potted iris with drainage holes in 2003-2004 when the rains would not stop, rot out right in the pots, elevated high off the ground. I think the rot is a result of the duration of contact with water. An iris can take only so much, good drainage or not, before it rots.
Sorry to hear about your loss. Hopefully you can salvage many of them.

    Bookmark   August 14, 2005 at 10:50PM
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marvine(z7/8 GA)

This is definitely ROT. We have no problem with borers in this part of the country. I'm on top of a mountain with very porous ground, and they are still rotting. Fist time in I've seen rot in my 9 years growing iris. I'm digging them up, cleaning out the rot (it does stink bad) and have them on the garage floor for drying. We are over 20 inches ahead of normal for rain.

    Bookmark   August 15, 2005 at 6:30AM
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"We are over 20 inches ahead of normal for rain"

So you're the one stealing all our rain this summer...... I just found a new one beginining to rot and we haven't had rain in a month..... I'm blaming it on getting an iris from the northwest and expecting it to adapt quickly to our humid weather. Get out the Comet Cleanser (with bleach) and generously coat the rhizome after you've scraped off the soft rot and the soil around where it was growing. Check every few days to see if you need to scrape more rot away and recoat with Comet cleanser. I've had good luck saving many iris that way.


    Bookmark   August 15, 2005 at 9:49AM
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njiris(z 5 NJ)

A rhizome that has been subjected to alot of rain, but looks OK, may still rot when replanted. I don't understand why, but apparently the 'rot' organisms are alive and well right under the rhizome skin.
I have never had much luck with Comet or Dial soap, I think because of this hidden germ problem.
My best success in treating these rhizomes was to thoroughly dry them out in the sunlight and hope for the best. Sunlight has some UV qualities that kill rot germs.

    Bookmark   August 15, 2005 at 1:51PM
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I find it interesting what does and doesn't work for people. I think if you're going to put iris back in the same area, you're going to have to treat the soil also. With my hot humid summers and mild winters, I think the Comet has definitely helped me save many iris.


    Bookmark   August 18, 2005 at 11:33AM
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suzie_q1542(z6 PA)

I've never heard of using Comet to treat rot. Please explain further.

    Bookmark   August 18, 2005 at 1:06PM
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klavier(Z7 Baltimore)

Comet has worked great for me. Saved plenty of iris this year. The spring was pretty bad for rot, but the summer here has been dry and rot has not been an issue. Garden cleanliness is the largest factor in preventing rot (and borer) any leaf that is brown or wilted (not browning at the tip; that is normal)and may not be attached to the rhizome in all places, or has become soft should be removed and quickly in wet places like New York, Georgia etc. NO MULCH IN THE IRIS BED. Completely decayed compost is fine to put in your iris bed, but anything that may still be decaying is a big no no. I believe rot has to do with suffication. It is my thought that iris rhizomes expose themselves to the air because of some need for survival that air fills. From what I have seen rot begins mostly at the base of the crown where the tissue is soft and vulnerable (rot starting on the thickly protected rhizome surface is rare). All that is needed is a cut, too much water and the tissue dies/ sufficates and then rots. the rotting then sufficates more tissue and the bacterial excretions ( acidic; that is why teeth rot)burn other tissue creating (in the words of Fat B.) a "vicious cycle", which travels into the rhizome where the tissue is mostly starch (which bacteria thrives in)and is soft (now that the access is provided under the protective outer layer. If one notices, the newer cultivars have larger more fleshy rhizomes and broader more fleshy leaves than the older historics. Makes perfect sense why the historics are more rot resistant than the newer ones.
Again, this is all coming out of my rear, so correct me if you observe otherwise.

    Bookmark   August 18, 2005 at 11:24PM
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I don't know if Comet will work on all kinds of rot. But the kind I get is as described by klavier above that begins at the base of the crown. Probably any bleach treatment would work, but the grittiness of the Comet may help it stick to the rhizome and help dry it out.

I scrape all the soft parts of the rhizome off with my fingernail and even some of the firm parts ( you can use a knife or spoon or whatever, but I like to feel with my fingernail when I'm hitting firm rhizome). I then cover the whole rhizome top and bottom with Comet (using my fingers to make sure all the scraped parts get covered). I cover the ground around the rhizome with it also out to a couple of inches. I check it every few days and may have to scrape additional rot and reapply the Comet. Or if it rains, I reapply the Comet. I also dig a little ditch around the rhizome so if it does rain, no run-off will run over the rhizome (mine are on a slope).

I'm trying Laetitia's method right now with a new one that's rotting. It's been out of the ground drying for a few days, coated with Comet. When there's no chance of rain for a few days, I'll put it back in the ground.


    Bookmark   August 19, 2005 at 9:57AM
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rootedinreadyville(Zone 7)

I've never tried "Comet" on them, but I do have a tried and true method for treating them that has been working very well for me. I also use this method on every new rhizome I receive before I plant it.

My method is just to bathe the rhizomes in a sink of cold water with one to two capfuls of Ortho Disease Control liquid added to the water. I scrub the rhizomes thoroughly, removing any mushy and dead parts from the rhizome, then I let them dry a little while before planting them. I don't wait long to plant or replant, usually just a couple hours to twenty-four hours at most.

The Ortho fungicide has sulfur in it which actually kills the bacteria that causes iris rot. It works better than household bleach.

    Bookmark   September 15, 2005 at 6:27AM
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joan_me_coast(z5 ME)

Two years ago, we dug all the irises in our two 4' X 40' iris beds because I found some iris borers. We divided the irises, discarded any with rot or holes, soaked the good ones in a bleach solution, and then in a insecticide. We treated the beds that year and last year with nematodes. This year we have found a lot of mushy, smelly rhizomes. Is this Iris Rot or bores again? I have started a lot of day lily seeds, and have oodles of seedlings needing a home. I need to know if I can take all the irises from one bed, put them in the other bed, and use the clear bed for the daylilies? If I have iris rot, and it is in the soil, will it affect the daylilies? If it is borers, will they attack the daylilies? Any help and/or suggestions will be very appreciated. Thanks, Joan

    Bookmark   May 30, 2006 at 10:07AM
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Joan, it could be borers, it could be rot, or it could be both. Borers consume the rhizomes, leaving wounds that are then susceptible to erwinia attack (bacterial soft rot). Of course lots of things can leave iris rhizomes vulnerable to erwinia infections (overwatering, too much rainfall, poorly draining soil, mulch covering the rhizomes, late freezes, physical injury, pretty much any other sort of stress), so you may or may not have borers as a precipitating cause. Erwinia bacteria seems to be endemic in many (or most) soils, so it's more important to figure out what is weakening or wounding your iris rhizomes than it is to worry about the erwinia in the soil.

As far as iris borers are concerned, I'm afraid I don't know whether they'd be likely to attack daylilies. My guess is that they would not, but I really don't know.


    Bookmark   May 30, 2006 at 12:53PM
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cbfindlay(z6 OH)

New posts to an old and very useful thread. I've got lots of rot going on unfortunately. Leaves keep dropping over and I find nothing but mush in the soil where its rhizome was -- but parts of the plants are still healthy. They haven't bloomed yet in our neck of the woods.
1. If I don't dig them up now and bleach/anti-fungus them, is this going to spread and they'll all croak?
2. I take it I should just dig the plant up wholesale, leave the fans on, and replant wiht fans?
3. Is there any chance they'll bloom if I treat them right now?
Cindy in Columbus

    Bookmark   May 2, 2007 at 4:35PM
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This is my first year with almost wholesale rot issues in the iris. I am blaming our early warm spell followed by three days of hard freeze. It zapped the leaves and I let them stay until they totally died down. By the time I got around to some of them, the rot had begun. I just pulled all dead leaves from the clumps, but didn't dig up the clumps and separate out the good rhizomes.

Question: Should I?

Some are in nursery rows in the garden, but others are in beds....they are now fully exposed to hot sun and I have cleaned around them so they get lots of air.

Question: Is there any treatment to the clumps in situ?

I would apreciate your expert advice. I sure hate to loose any has taken me several years to accumulate what I have and some are great passalong iris from older homesteads. BTW, these are least affected...could just be where they are located.

    Bookmark   May 5, 2007 at 7:44AM
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Thank you for all those suggestions. We are soooo soaked after much too much rain and they say more is coming on for the next seven days. It's beyond amazing.

I have already treated numerous ones with surgery and comet and they are laying on the ground in the rain. If getting them all out by the roots would help I would do that in the rain and totally replant later. This bloom season isn't going to happen. Should I take them all out of the ground today? I read the history of Superstition when they were in Oklahoma and boy did it sound like what I am about to go through. I would rather replant than deal with rot.

I have about a hundred different cultivars that I have never seen in anything but pictures. I bought and planted them last Summer and wonder if I will ever see them in bloom. We now have had Summer, Winter and Spring extremes and there is no end in sight.Perhaps I just need to visit Napa Gardens each year and let someone else have all the work and worry. My Wishful Thinking is a goner, nothing would save it, and I am thinking it may be symbolic!!! Are they usually this much worry? I know the weather man better than my husband now.

    Bookmark   May 7, 2007 at 10:15AM
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allieok(7a Oklahoma)

Last fall I despaired that rot would take all my irises, because I lost one after another to the mushies. I decided to let nature have its way after way too much worry over the issue. This spring (after a wetter than normal winter and early spring), I've seen none of it. My irises are beautiful. Yes, I lost some really nice ones last fall, but the ones that persevered seem healthier than ever. And I have some empty places to plant new acquisitions. Often with problems in the garden, doing nothing is better than doing too much.

    Bookmark   May 8, 2007 at 4:15PM
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