Do a search for iris borer. There's also a current discussion, one of the top few on the list about what to do with these things. 'Lost Most Beard Iris Rhizomes this Year' is the title of the discussion. I hate them.

If it were me, and I I knew the borers were active in the rhizomes, I would dig and cut back flags to 3 or 4 inches. Clean ALL iris plant matter from the bed and dispose of it. Soak the rhizomes in a bleach solution - there are directions for this online - most say to soak them at least a day since these things are hard to kill. From most of the recommendations I've seen, it is recommended that every fall, even when not digging them, it is best to cut back and dispose of the flags since the eggs for these things are laid in summer on the tips of the leaves. And remove all old plant debris from the beds.

The pesticide option you will see the most is for Merit or a similar systemmic product. I hate this option because the pesticide is absorbed into the plant tissue (and actually any plant tissue it comes in contact with). I grow my iris close to where I grow things to eat, fruit trees, and more. Also, iris are flowering plants, and any time you are flowering you attract bees. It is the systemmic pesticides that have been identified as one of the most significant killer of bees.

The amazing thing is that at a similar price point, beneficial nematodes can be applied next spring when temperatures get to about 50 degrees F, the same time those borers get into motion, and they will kill them all far more effectively than the systemmic. I provided a little more info in the other thread. My iris are starting to recover over the last year, but certainly not so many nice blooms this year because I was starting with such small pieces of rhizomes when I went through my treatment. I'm hoping by next spring and summer things will start looking nice again. Good luck.

Here is a link that might be useful: Lost Most Beard Iris Rhizomes This Year

Thank you. We don't use systemic pesticides here in Ontario but you've given me lots of information and possible solutions. I hate to have to dig up these plants but that's what I'll have to do.

Just can't believe how destroyed my plants look.

Ianna

Probably best to go through the digging and soaking thing once (of course they need to be divided about every 3 years anyway) to make sure you get things cleaned out well. Also a good time to add compost or other organic enrichment to the bed. Just make sure to throw out all iris debris. It seems to me that with treatment early with the nematodes in the spring and then trimming and disposing of leaf tips in the early fall we can keep these things at bay.