Irises forum→Rot Advice ... please

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Name: Mary
Tennessee (Zone 7a)
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urania1
May 29, 2020 7:40 PM CST
I do not think trying to treat the rot in situ as I have done in the past is going to work very well this year. So ... what would you do. Dig, cut out rot, and replant immediately. Or dig, cut out rot, and let the rhizome air dry for a few days. Also, I know it is not good to cut green foliage, but I feel like cutting the foliage back would prevent rot from starting on a few of the irises. Is this madness? Should I cease and desist?

Also ... those pesky stalks. I would prefer they dry out before cutting them off because they are so full of moisture and I do not want to spread germs. But ... some of the rot is startIn with the stalks.
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
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crowrita1
May 30, 2020 6:24 AM CST
My best luck at treating bacterial soft rot, without digging the plant, has been to scrape, or cut, the "soft" parts out, pull back the soil, a bit, to exopse the "cut" area, and the top of the rhizome to the sun, and air, and sprinkle it with either Comet cleanser, drench it with a bleach water solution...or, if you can find it, a solution of a biocide (like Agrimyacin...that's spelled incorrectly *Blush* ). Watering the plant , after the soil has dried out from the "drench", with "aspirin water" (4 aspirin tablets dissolved in one gallon of water), will help , a bit, also. Cut back the fans to about 6"-8" inches will also help to let in more "sun and wind". That said, I think it's better to DIG the plant, do all the surgery that's needed, give a good wash, and a short soak, in 10% bleach water (just the rhizome, NOT the leaves !!), dry well for a couple days, until the "wounds" crust over, cut back the fans, and then replant....drenching the soil, or replacing the soil, in the spot "might" be a good thing, as well (I have never really been able to see much difference, whether I did, or didn't Shrug! ). Again, watering the plant with aspirin water seems to help (the acilacitic acid{again, NOT spelled correctly! Sticking tongue out }helps kick start the plants immune system, to help fight the bacteria).
If there are a lot of plants....and a lot of rot.....you have a big job ahead of you, and , I wish you luck ! My "soft rot" issues are usually worse at bloom time.....wet weather, stalks in constant motion from the wind,(and the weight of buds / blooms", bending them over, and shading the plant bases, the extra stress of blooming, all contribute to promoting rot !
Name: Mary
Tennessee (Zone 7a)
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urania1
May 30, 2020 7:27 AM CST
Thanks Arlyn. I really appreciate your advice. That is just what I will do. Thank You! Smiling
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
May 30, 2020 9:17 AM CST
I should add that if you use an agricultural biocide...BE CAREFUL ! It's strong stuff, and you need to follow ALL the directions , carefully !
Name: Derylin
Louisville ,Kentucky (Zone 6b)
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KyDeltaD
May 30, 2020 10:02 AM CST
Aryln,
Very spot on advice.
One added thing :Be sure to rinse your cutting tools in a bleach mixture before going on to the next rhizome in order not to spread disease .
Name: Kathy
Nocona,Tx zn.7 (Zone 7a)
My garden..my "Peaceful Haven"
FAIRYROSE
Jun 8, 2020 7:34 AM CST
I always trim the spent stalk with a sharp knife right down to the rhizome..yes it's full of water, not bacteria (I lost many my 1st year by leaving it on!) I rinse with a small paint brush dripping with a water/bleach solution, let air dry, then cover.
**Note. I've taken a newly planted rhizome out of the soil, when it showed rot (not sure why) sliced away nearly half & treated it,let dry out a day. It actually bloomed the following Spring, so don't underestimate those small rhizomes!
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Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jun 8, 2020 7:40 PM CST
Kathy, thanks for the comment about cutting the stalk. I've gone back and forth about whether to cut the stalk or leave it. Because it is green, it is photosynthesizing and therefore providing food to the developing rhizomes. For an iris that wasn't particularly vigorous, I felt this could help.

But, I also recently read that iris borers can infest the stalk and eventually work their way to the rhizome, so this year I'm considering cutting all stalks back to the base.
Name: Ivor
Middletown, DE (Zone 7a)
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Islandview
Jun 9, 2020 8:23 PM CST
I may be wrong but I think most of the energy to the rhizome is supplied by the fans of the iris plant via photosynthesis, rather than by stalk. The stalk incidentally is attached to the "mother" rhizome which will eventually die off after blooming.
The iris borer climbs up in the blades of the fan early Spring, chews its way in and then travels back down to the rhizome. If you did have iris borers, then by the time you cut down the stalks, it won't make any difference. Also, apparently the iris borer is not commonly found west of the Mississippi River.
However, having said all this, I have found critters that look like iris borers eating their way through in rhizomes. But upon closer examination, they appear to be something else. Has anyone else seen this as well?
Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jun 10, 2020 10:41 PM CST
I do have iris borer, unfortunately, but I try to keep things cleaned up in late fall and again in spring and watch for the signs of the leaves being chewed in spring. I actually have found the borer feeding in buds! (I'll see if I can find pictures).

Yeah, I know the borers mainly get into the rhizomes via the fans, but apparently occasionally can travel through the stalk. But I'm not sure how quickly they move into the rhizomes.

I imagine the stalk provides energy to the developing seed pod if there is one, but if there isn't, I think that the energy has to go somewhere--those stalks seem to stay green for awhile. Seems like it would pass through the mother rhizome to the developing rhizomes. That's my theory, anyway. Smiling
Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jun 10, 2020 10:51 PM CST
Here is a picture I took a few years ago of an iris borer feeding in a bud:

Thumb of 2020-06-11/lauriemorningglory/527e36 Glare

Name: Mary
Tennessee (Zone 7a)
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urania1
Jun 14, 2020 2:17 PM CST
Thanks. Right now, I am having to ration my bleach. Apparently people are still hoarding it here in Tennessee. Heck, maybe they are drinking it. That would explain a lot of things. Kathy, thanks for the advice about the stalk. Do you only do that for the irises that have rot? Or do you do it in situation for all your irises if it has rained a lot. All of my rot always starts with the stalk.
Name: Jane H.
Kentucky (Zone 6b)
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janielouy
Jun 14, 2020 2:44 PM CST
I am having a different problem with my irises. Some are just falling over at the base where the fans attach to the leaves. Looks very dried out, no smell or mushiness. I have read about crown rot and this is maybe what it is. I do not see any mustard seeds or white cottony stuff. We have had lots of rain, lots of early heat followed by freezing temps and now back to heat. I have just sprayed with daconil and Miracle Gro as I read about on Phil Williams Rockytop Iris site. We are not getting much rain now. It seems to pass us by. I have dug up two rhizomes that appeared dried out. The rest are here and there.
Any advice? Some beds are unaffected and others are sporadic in falling fans.
NE Oregon (Zone 7b)
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TBManOR
Jun 14, 2020 11:37 PM CST
.... there are other rhizome or crown rots caused by other pathogens besides Erwinia, and Sclerotium. These may be caused by Boytrytis, Fusarium or Pythium pathogens. Infection by Pythium sp. seems to be a fairly new problem to rhizomatous iris, but it is a threat to many other ornamentals. Its symptoms of infection are similar to what you've described, especially appearing during moist hot spells.
These diseases respond differently to fungicidal treatments, so my recommendation is to have samples sent to your local county extension agent for analysis. Daconil (chorothalonil) is a shield type fungicide thats effective for foliar treatments, but not so much as a soil drench remedy. Captan seems to have more effectiveness as a soil drench in halting new infections of certain soil borne pathogens. There are many effective fungicidal remedies that are beyond the reach of the average gardener, unfortunately, due to either state restrictions or professional applicator only restriction.
But still, to be absolutely sure, please contact your local county extension agent with a sample. They may send it off to a lab where the pathogen can be isolated and identified
Name: Bea Kimball
Little Rock, Arkansas; (Zone 7b)
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Buzzbea424
Jun 16, 2020 3:29 PM CST
At our local meetings of the iris society they mention that you should use bleach without the additive that makes it "splashless" when you soak your rhizomes.

Good luck. I had a lot of trouble in one area of my iris bed last season due to heavy rains. I amended the soil in the bed, trying to improve the drainage. Ironically, rhizomes of the same varieties flourished on a neglected, rocky hillside with poor clay soil, where they had pretty much been tossed. Shrug!




Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jun 16, 2020 4:52 PM CST
TBManOR said:Infection by Pythium sp. seems to be a fairly new problem to rhizomatous iris, but it is a threat to many other ornamentals. Its symptoms of infection are similar to what you've described, especially appearing during moist hot spells.



I just finished watering all of my iris during the hottest "first half of June" on record. I wonder if that could be conducive to this disease?
Name: Kent Pfeiffer
Southeast Nebraska (Zone 5b)
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KentPfeiffer
Jun 16, 2020 5:48 PM CST

Moderator

There's an old saying about bearded iris: 'They can take a lot of water and they can take a lot of heat, but they can't take a lot of water and heat at the same time.'
Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jun 17, 2020 5:41 PM CST
Thank you, Kent! I hope they'll be all right...

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