Irises forum→Iris borer, YUCK!

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Name: Cindy Vasko
VA (Zone 6b)
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cinvasko
Jun 30, 2020 5:48 PM CST
Ugh...was going through an iris bed today to clean out weeds and found nearly 1/3 of them with borers. I was able to kill all the ones I found but it's late and I didn't have time to thoroughly clean them. Fortunately I have to move all the iris in this bed before fall so I'll get crackin' on the maintenance. I never had borers before except for the odd one or two - so is this procedure right; remove spoiled foliage and rhizome cleaning the tools in a diluted bleach solution in between cuts, clean dead matter out (and kill the borer) and soak in a 1-to-10 bleach/water bath? Air dry before replanting. How long do you soak for? Thanks!
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Name: Cindy Vasko
VA (Zone 6b)
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cinvasko
Jun 30, 2020 5:53 PM CST
I also just found this advise in another person's thread and wanted to copy & paste it here so I could find it again - "Tom's advise (If you are not averse to using chemicals, you can treat your iris beds in the early spring with Bayer Grub killer, the stuff that's made for lawns) is great advise.

I've been using the Bayer Grub killer for years now. I make sure I apply it before the temperature reaches 70 degrees. That's when the little buggers hatch.

The best way for me to look for borer damage is to pay CLOSE attention to the "center" leaves on the iris fan."
Give me land, lots of land, under starry skies above. Don't fence me in.
Name: Laurie
southeast Nebraska (Zone 5b)
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lauriemorningglory
Jul 2, 2020 9:59 PM CST
Cindy, others can give better advice about what to do. I wouldn't even deal with the rhizomes that have borers--just kill the borer and then toss the rhizome. I'd only keep rhizomes that have not been damaged by the borer.
Name: Sue Petruske
Wisconsin (Zone 5a)
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petruske
Jul 2, 2020 10:28 PM CST
The Bayer Grub Control works GREAT!! I put it on every spring before temps reach 70.

I would agree with Laurie. If you have enough of a particular cultivar, keep the healthy rhizomes. The infested ones, kill the borer and toss the rhizome. If you really need to keep a rhizome kill the borer, clean the rhizome well and soak in the 1/10 (bleach/water) solution as mentioned. I believe I soaked them for 30 minutes, then rinsed in clear water. Let them air dry and replanted into a new location.

I read an article somewhere that said the borers are carnivores when it comes to fellow borers. They eat each other until there is just one left in the iris. I've found that to be true. Way back in 2008 when I found my first iris borer, I very carefully looked through every inch of the iris, there was just one borer there. Just ONCE did I find 2 borers but they were both small and obviously had not run into one another yet.

I do swear by the Bayer Grub Control. It works.

Do NOT compost the infested rhizomes (even if you have killed the borer). Burn it if possible.
Name: Cindy Vasko
VA (Zone 6b)
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cinvasko
Jul 3, 2020 12:57 PM CST
What is the reasoning behind tossing the entire infected rhizome? Is it because it may harbor eggs or bacterial rot? I'd like to try and save them because they are my only rhizomes - all the iris I have I bought last fall, and many are 2018 and 2019 intros. I was planning on cutting a good portion of the rhizome off well ahead of the damaged area prior to treating it - I'm going to try and hope for the best unless that's hugely unwise. Frankly if I have to start all over again I don't think I'd waste the $$ - I live in an area where iris borers are not uncommon. I did bag all the litter from my cleaning things out but I'll have to send it to the landfill as we have a burning ban right now. Thank you for all the advise!
Give me land, lots of land, under starry skies above. Don't fence me in.
Name: Kent Pfeiffer
Southeast Nebraska (Zone 5b)
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KentPfeiffer
Jul 3, 2020 3:18 PM CST

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There's no real reason to destroy a rhizome once you've killed a borer within it. The damage caused by the borer can make the rhizome a bit more susceptible to rot, but rot is ultimately a result of environmental and cultural conditions. Borer damage would be a rather trivial additional factor.
Name: Cindy Vasko
VA (Zone 6b)
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cinvasko
Jul 3, 2020 4:06 PM CST
KentPfeiffer said:There's no real reason to destroy a rhizome once you've killed a borer within it. The damage caused by the borer can make the rhizome a bit more susceptible to rot, but rot is ultimately a result of environmental and cultural conditions. Borer damage would be a rather trivial additional factor.


Thank you - would it be better if I didn't replant the rhizomes until the cut portions hardened off completely? The upside to all of this is that I have to remove all the iris from this bed anyhow because the bed (which is a raised bed) is within inches of my neighbor's stockade fence and he wants to come over and pressure wash/seal the fence this summer. I asked him to wait until July/August so I could move the iris to different locations - so now I will be able to look over everything carefully in the next week or so. I figure if I cut/trim this iris and let them harden off it won't be much different than when a seller is digging & prepping iris to ship out? Of course a little more stressful on the plant but they seem pretty hardy. We've had literally months of nearly daily rain - sometimes flooding - and the last week has been dry. Hopefully our bizarre rainy season is ending and we can get back to more normal weather. I looked at the other iris beds and haven't found any borers yet. Thanks!
Give me land, lots of land, under starry skies above. Don't fence me in.
Name: Kent Pfeiffer
Southeast Nebraska (Zone 5b)
Charter ATP Member I was one of the first 300 contributors to the plant database! Plant Database Moderator Plant Identifier Region: Nebraska Celebrating Gardening: 2015
Forum moderator Garden Sages Garden Ideas: Master Level Irises Million Pollinator Garden Challenge
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KentPfeiffer
Jul 3, 2020 5:13 PM CST

Moderator

I've generally had better luck with irises when they were allowed to harden off for awhile rather than replanting right away. It's a bit counterintuitive. For most plants, digging them up and letting them lie around for a few days, or weeks, is a sure way to kill them. Bearded irises seem to benefit from it.
Name: Lucy
Hamilton, MA (Zone 6b)
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irisarian
Jul 3, 2020 8:15 PM CST
We have never discarded rhizomes after a borer attack. Just cleaned out the area & if plenty of rhizome left replanted.,
Name: Sue Petruske
Wisconsin (Zone 5a)
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petruske
Jul 3, 2020 11:47 PM CST
Absolutely you can keep all the iris's that can be rescued. Especially if you only have one rhizome left. Save all you can.

I once was gifted an iris from a friend who I know had the iris borer. And she cleaned it up nicely. I didn't get it planted right away. And thankfully I didn't. When I got around to planting it I noticed little bit of what looked like wood shavings laying under the rhizome. And sure enough, there the little bugger was inside it yet. Grumbling

I generally have more than I want to keep. Even when I have to thin out some beds I will throw out the small ones because I just cannot plant them all. I have given away, literally, hundreds of rhizomes.

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