Irises forum: Iris borers

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Name: Kim
iowa (Zone 5a)
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kimmer
Jun 18, 2016 11:55 PM CST
Angry I hate Iris borers. I have been trying to keep the beds clean. But l just found several of those nasty things. But these are small compared to what I had a couple years ago. Help, I love Iris' but I feel like I am fighting a loosing battle. Confused Confused Angry Angry Does anyone have any ideas?? Kim
Name: Tom
Southern Wisconsin (Zone 5b)
Irises Vegetable Grower Butterflies Region: Wisconsin Keeps Horses Cat Lover
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tveguy3
Jun 19, 2016 4:17 AM CST
If you aren't apposed to using chemicals the best thing would have been to treat them with a grub control. I use one made by Bayer in the spring after there's been several days without freezing, as that's when they hatch. You could use it now I think, but if they are already in the rhizome, they have made wounds that could cause rot later. It's the same one used on lawns for grub control.

If you are apposed to chemicals, then I'd recommend digging up all your irises and checking them over for borers, killing the ones you find, letting the wound dry out and then replanting them. Removing the dead leaves and burning or disposing them helps reduce them as the eggs are laid on them. Some people do a spring burning of their beds if they are planted alone and it's legal in your area. You can feel them in the leaves as they are eating their way down to the rhizome and can squash them too I hear.

The numbers of irises I have, over 600, makes it difficult to go the non chemical route. But if you only have a few it's easier. Good Luck!
I am not afraid of an army of lions led by a sheep; I am afraid of an army of sheep led by a lion. - Alexander the Great
South central PA (Zone 6a)
Irises Region: Pennsylvania
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DaveinPA
Jun 19, 2016 7:29 AM CST
Tom is right for a large garden area. The grub killer treatment and some natural treatments work for the larger areas, mostly in prevention, as once they are into the rhizome it is harder to kill them these ways. For small gardens you can examine the clumps and see if "frass" is there, the little drops of excrement, a sure sign of borer activity, then use the "squish" method when they are in the foliage. If in the rhizome already you can dig it out, clean the wound letting it dry in the sun and replant. I have also left the roots in the ground exposing the rhizome and doing the same. When wound is dry recover with soil. If it is a large clump just toss the rhizome into the trash to save the time and work.

A chemical "cure" is the Bayer Long Season Grub Control or something similar as Merit. For a more natural approach you could try bacillus thuringiensis [BT] but follow the instructions as it may need 2 treatments due to weather.
[Last edited by DaveinPA - Jun 19, 2016 9:31 AM (+)]
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Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Jun 19, 2016 10:20 AM CST
Tom, and Dave pretty well have it covered, although I will add that the "Bayer" product.....with Merit....is a systemic type poison. It's absorbed into the plant, through the leaves, and taken up through the roots (I'm speaking about the "liquid" grub killer), so anything that takes a bite of ANY part of the plant....is gonna' die ! The spring application will remain active for *about* 3 months....depending on rainfall amounts, and the corresponding growth rate of the plants.....and then needs to be re applied. Bayer also makes a "granular:' form of the same product....this only enters the plant via the root system, AND it also contains a fertilizer....which *may* , or *may not* be desirable for you, depending on existing soil fertility. IMHO, it will do some good against your borers, until they pupate....if they take a bite...they die. Downside to these products is that every part of the plant is "poison"...leaf, stalk , root, and rhizome....and that includes the pollen....so any insects...like honey bees....that gather pollen will probably be affected.
The "BT"....which is a "natural" product....works by killing the borer grubs with a "bacterial disease", and again, any grub, caterpillar, or worm that eats it , is going to sicken, and die. It's NOT systemic, and any rains, or heavy dew, will wash it off the plant....so it needs to be re applied quite often.....I do it after a rain, or about every 10 days,- 2 weeks. It also doesn't work as "fast" as the other product, and you will see more signs of borer activity.....they don't die as quickly, so they have a chance to eat more! The "jury is still out" on BT's affect (if any) on pollenators...it won't kill the honey bees, but WILL kill their larva...as far as I know, they still are unsure if it can be taken back, with the bees, into the hive, where it would harm the larva.
There have been a few people using diatomaceous earth....actually injecting it into the plant, at the base, to see if that helps ( The "DE" has sharp edges, and spines , on a microscopic level, that actually "cut" the borer grubs, as they crawl over and through it) I've never tried it on iris, but HAVE tried it on summer squash, for "squash borers"....lots of time consuming work, and I couldn't see many positive results Shrug! .
The "beneficial nematodes "DO work, but , IMHO are WAY to pricey....applied at the rates they recommend , it was going to cost me about $800 to treat my 3500 sq ft of iris beds Blinking .And , in my climate, they aren't expected to "winter over"...so would need reapplied, every year Crying .
The "Milky Spore" disease would also work on iris borers, but I have no idea how you would get it "into" the plant...so it would only kill the ones in the soil, or "on" the leaf.
Good luck with whatever method you use !

caitlinsgarden
Jun 19, 2016 2:11 PM CST
I was overwhelmed by borers years ago, that I never knew I had. When I realized what the problem was I was about to throw in the towel. It was supposed to be very safe and effective, so I used the grub control chemical for a couple of years and was happy to have found the answer. Well, you know what happened then. This chemical was found to cause bee deaths, and other nasty side effects. So I don't use it any more, (although I do have an unopened package of it that I guess I am saving for emergencies!) I am seeking out any suspicious activity and find a little here and there each year, but nothing horrendous. I don't know if I could have got to this low incidence of borer activity without the chemical though.
Name: Ivor
Middletown, DE (Zone 7a)
Irises Cat Lover Garden Photography Region: Delaware
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Islandview
Jun 21, 2016 4:42 PM CST
I recommend using a spinosad based spray such as Bonide's Captain Jack's dead bug brew. It's a semi natural product derived from a soil bacterium. Supposedly it is even safe to use on edible plants and affects primarily caterpillars, borers, etc. To avoid any effect on bees, you should spray early evening when the bees are away and since it is ideally used in the Spring, there are no flowers to attract them in the first place. It may have an effect on worms but probably because it used as an topical application, I haven't seen any effect on the earthworms. I applied once late April and I have yet to see any borers. I'll find out for sure in a few weeks when I dig up my rhizomes to divide them!
Name: Tom
Southern Wisconsin (Zone 5b)
Irises Vegetable Grower Butterflies Region: Wisconsin Keeps Horses Cat Lover
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tveguy3
Jun 21, 2016 5:33 PM CST
Keep us posted on that! Smiling
I am not afraid of an army of lions led by a sheep; I am afraid of an army of sheep led by a lion. - Alexander the Great
Name: Lucy
Hamilton, MA (Zone 6b)
irises
Charter ATP Member Cottage Gardener Enjoys or suffers cold winters Region: United Kingdom Region: Northeast US Irises
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irisarian
Jun 21, 2016 9:21 PM CST
Keep an eye out for borer pupae. they are small brown cases, when you dig & replant irises.

caitlinsgarden
Jun 23, 2016 5:29 PM CST
There are other small brown pupae in the ground that look similar but aren't borers. I don't know if they belong to a helpful insect or if you should just get rid of all of them. I am having a real problem with leaf rot starting at the base of leaves and I don't know if it is borer related or not. By the way, there is an interesting article with pictures about iris borers that I just "dug up". Not sure how I can share the thread here.

caitlinsgarden
Jun 23, 2016 5:31 PM CST
This is the name of the thread, you could probably search for it: Growing Irises in Spite of Borers
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Jun 23, 2016 7:27 PM CST
this article has pictures of both the pupal stage, and the larval stage:
http://www.irises.org/About_Irises/Cultural%20Information/Pe...
South central PA (Zone 6a)
Irises Region: Pennsylvania
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DaveinPA
Jun 26, 2016 6:28 AM CST
For those iris you want to save that have borers inside a lady I know from New York digs the rhizome and uses a long pin [hatpin anyone?] to pull the borer out. Then wash the rhizome and let it air dry before replanting.
Thumb of 2016-06-26/DaveinPA/5fab33 cut rhizome with borer

Thumb of 2016-06-26/DaveinPA/060f5f the critter after "convinced" to leave its dinner

Thumb of 2016-06-26/DaveinPA/3c5889 same rhizome next season with nice healthy fan

Name: Lucy
Hamilton, MA (Zone 6b)
irises
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irisarian
Jun 26, 2016 3:00 PM CST
very ingenious
Name: Pam
Pennsylvania
Irises Keeps Horses Cat Lover Dog Lover Region: Pennsylvania
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Snork
Jun 26, 2016 4:35 PM CST
A skewer for roast chicken works very well for this. I use one with a circular bend at one end. Tie a long btight piece of string to it so I don't loose it in the garden.
South central PA (Zone 6a)
Irises Region: Pennsylvania
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DaveinPA
Jun 27, 2016 7:14 AM CST
Roasted borer anyone?
Name: Jane H.
Kentucky (Zone 6b)
Irises Birds Region: United States of America Region: Kentucky Clematis
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janielouy
Jun 27, 2016 3:05 PM CST
Generally if you have a wire or hatpin handy, you can just stab them and get them out. Gross little buggers and it is often hard to squish them inside the leaves if you find them as if they are not really fat, they are tough. Fat ones squish well but they are usually in the rhizome by the time they get fat.
I have actually found a borer in my LA irises and did not know they would get them. I guess I will have to include them in my chemical treatments next year.
Name: Gabriel/Gabe Rivera
Charlotte, NC (Zone 7b)
German imported, Michigan raised
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Cuzz4short
Jun 27, 2016 3:17 PM CST
My question is. Do they only enter through the leaves only and down to the rhizome? I know myself and I believe Leslie noticed some sort of worm around our plants. The one I found was actually curled up at the base of a fan curled up, but doesn't look like all the other pics I see.
Thumb of 2016-06-27/Cuzz4short/c3ab4d

Gimme it and I'll grow it!
Name: Arlyn
Whiteside County, Illinois (Zone 5a)
Irises Beekeeper Region: Illinois Celebrating Gardening: 2015
crowrita1
Jun 27, 2016 3:42 PM CST
That's not an iris borer, Gabe. That's not to say that the little rascal wouldn't chew on your iris, though ! The way I understand the iris borer life cycle.....the moth lays her eggs on the iris leaves (or surrounding vegetation) and, when they hatch...if the borer is on an iris leaf, he starts eating his way down to the rhizome....if he's NOT on an iris leaf....he has a little silken "thread" that he can use to "para sail" with, hoping to land on an iris. I *think* they always start "high" on the fan (or , at a "leaf tip"....probably because that area is more 'tender" for their little baby borer teeth Sticking tongue out ! After he eats his way into the rhizome....where the pickin's are really good, he either pupates there, or, eats his way out of the rhizome, and pupates in the nearby soil. When the moth emerges from the pupa, the cycle starts all over again.
Name: Jane H.
Kentucky (Zone 6b)
Irises Birds Region: United States of America Region: Kentucky Clematis
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janielouy
Jun 27, 2016 5:40 PM CST
That one Gabe, looks like a tent caterpillar. Several have fallen out of trees near my irises but I have not seen them eat anything. Could be anything but it is not an iris borer.

My new problem which I have never had before is that mustard seed looking thing. I found my Another Woman (one I have dreamed of owning and did not bloom this year) was fallen over and yellowing. I tried to get inside the leaf to see if it was a borer and the whole set of leaves fell off. When I checked for frass, there were those mustard seed things. I will have to research that unless y'all have some info. Should I remove it from the bed? Treat it with something? No clue....
Name: Greg Hodgkinson
Hanover PA (Zone 6b)
Charter ATP Member Irises I was one of the first 300 contributors to the plant database! Region: Pennsylvania Region: Japan Garden Photography
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Misawa77
Jun 27, 2016 5:43 PM CST
More than one "Iris Borer" can enter a Fan/rhizome; but only one shall survive (yes Virginia, they are cannibalistic!).

I have a very small "infestation". I got my systemic granules out late, so I am happy with the borers low voter turnout!!

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