Need help figuring out what caused this......

Hopefully, I can post a pic in a few days, but maybe a verbal description will help, as I need to replant these freshly dug iris and don't know what caused this:

One rhizome has row upon row of tiny (about the size a small nail would make) holes. The holes are in straight rows about 15 holes across and 6 holes down--looks man made, but that couldn't be possible as this iris has been in the ground two years.... The holes are smaller than iris borers (though, unfortunately, I have those, too), and each hole is, perhaps, a 1/4 centimeter from the next. The plant itself was pretty healthy. I've looked online, and can't find anything. All you experts, please help!! Thanks

Long way from being an expert but you are possibly looking at dead roots. I
have seen this type of dotted holes in dug rz's. If you pull a dead root it will
leave what appears to be a small hole.

Wow....hadn't thought about that---but would they be so symmetrically arranged? These are perfectly ordered, row upon row...

That is your key to the solution. I can't think of any insect or larva that has
any symmetry to its eating habits. If the plant is healthy it is apparently not
a problem.

Hmmm....good thought. Can't wait to post a pic, but guess I'll go ahead and replant it tomorrow, based on that thought! I'm just so perplexed by it....

Yes, I think you're describing holes left by dead roots... freaked me out the first time I saw them on old rhizomes. I thought for sure they were infested by the dreaded iris borer!

Oldgardenrose is correct. Assuming the holes are on the bottom of the rhizomes, they are leftover from old roots that have died. No big deal and no problem for the rhizomes. Go ahead and replant.

dead roots ,
eons ago i took a plant to iris club and asked the same question . i became a member same day ^_^

Ok, thanks all you guys---and I have to say...what a smart group! Yes, it is dead roots. I pulled it out today to replant it and noticed how very symmetrical all the live roots are. Amazing! I never noticed....I wonder if any other plant/bulb grows its roots in such perfect order???? Now....about those iris borers....got a cure for THOSE???!!!

The only cure for borers at this point in the season is manual destruction whenever you find one. Early next spring there is more you can do to effectively minimize or eliminate next year's crop of borer larvae, but none of that will help you right now.

Thank you, thank you! I just split my Iris yesterday and found this same problem. My husband and I both thought borer and threw out over 1/2 of my iris. He kept nagging at me to find out how to control the borer before replanting any of the good rhizomes. Luckily I found this post this morning. I sprinted out back to the burn barrel to retrieve my "diseased" rhizomes before hubby burned them. Thank goodness he is a procrasinator.

I, too, have noticed these spots on old iris rhizomes. I knew they weren't a sign of illness, but I never figured out what caused them. I, too, thought it was bugs. Thanks for clearing up a mystery.