Is it borers?

11 years ago

I noticed yesterday all my yellow iris (a well established patch) lying on the ground. I assumed at first that they had been trampled by deer or the dog. Closer inspection revealed that the fans were not broken off at the base, but looked chewed and rather rotten there. The fans themselves were still green and healthy looking. Googling led me to pictures of borer damage that looks just like this, with the exception of the fans not showing stress. But the information found leads me to think that this is the wrong point in the season to be seeing this if it is borers.

Do they ever strike this late n the season, and what can I use to control them now? I didn't see any slugs or larvae, but I didn't dig up the rhizomes.

Featured Answer

cecily

11 years ago

Chewed rhizomes with healthy looking fans can be vole damage. Borers form a tunnel into the rhizome with conspicuous frass. Soft rot is slimy & stinky with fans laying on the ground and the rhizome is mushy.

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Comments (12)

raee_gw zone 5b-6a Ohio
Original Author
11 years ago
I will dig them up today and look more closely.
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raee_gw zone 5b-6a Ohio
Original Author
11 years ago
Well, I went to dig the rhizomes and... there were no more rhizomes. Found a stub of one, and 2 small hollowed out shells. The rest totally gone -- eaten by the big fat white grub of some sort that I also found. A few of the fans still had a root attached so I replanted those but figure that entire stand is lost.
keswick_sniders
10 years ago
Are you sure the grub you found was the culprit. I don't think a single grub could eat all the rhizomes in one fell swoop. The fact that you indicate this happened suddenly and that you found the fans looking healthy, suggests a larger culprit. I am betting on voles.
raee_gw zone 5b-6a Ohio
Original Author
10 years ago
Really, I have no idea! It sure seemed to be the likely culprit. It was on the remains of a rhizome. That would indeed be fast work. It was quite a large grub -- bigger around than my little finger.
petalique
10 years ago
Iris borers -- you can seach images to see what the damage looks like. And here's a video (fat ones, not the wire like worm. Ugly!

https://m.youtube.com/watch?v=Lnp1Bs6nC5Y

How to prevent them?
keswick_sniders
10 years ago
Usually, when you discover an iris borer or even two in a clump, the leaves will look quite ratty and yellowed (because the little bugger has tunneled his way down to the rhisome eating as he goes. The rhisome itself will usually have a cavity in it, where you will find the borer, bloated and ugly. If the borer is there for any length of time before being discovered, the rhizome will be rotting and smelly. Not pleasant. But all this takes time, and you are not usually left with healthy looking leaves and no rhizome whatsoever. The leaves would need to show evidence of boring - that's the route to the rhizome. I have seen much borer damage in my day, but I have never seen healthy leaves and no sign of the rhizome except where an animal has been involved - usually voles.
raee_gw zone 5b-6a Ohio
Original Author
10 years ago

This is what the fans looked like the day after I first posted. I did not see an entry hole from the green to the rhizome on any of them. They were seemingly just eaten away from the root.
raee_gw zone 5b-6a Ohio
Original Author
10 years ago
keswick_sniders
10 years ago
Your pictures don't show the leaves. Were they yellowing, streaked, with holes in them?
raee_gw zone 5b-6a Ohio
Original Author
10 years ago
No. By the time I found them they were browning at the tips, but otherwise intact.
lmmunro1
10 years ago
When you have full foliage and minimal rhizome, this does not look like borer damage, nor is it borer season (mid August). You have a different critter.