what time of year did you dig and clean. Everything I've read is that eggs are laid on iris leaf tips in late summer, while it is still warm. So I've started trimming down to 5" or so in Fall once a little cold weather starts as well as cleaning every single bit of iris leaf debris from my yard. In the next few weeks, as temps are consistently above 50 F, I'm going to apply the correct type of nematodes for combating iris bores. I know some of the poisons, like Merit and some of the Ortho products sound like a good idea, because they are systemics, incorporating themselves into the plant tissues so that whatever eats them are poisoned. But realize, they are systemics - bees and other beneficial insects that visit the flowers will also be impacted by the poisons. If any of it gets over to where you grow food crops, you will also be affected. The nematodes work just as well if applied about now (in Zone 7), and aren't completely unreasonable. I'm thinking, with doing the trimming every Fall I shouldn't have to keep doing the nematodes. So far this spring it is looking like my iris beds have recovered significantly and I have lots of blooms. I really haven't had many the last three years or so since the borers wiped out so many.

The damage was from last year. I cleaned out the old iris bed early last fall.

I'm afraid even with all the bleaching, cutting, some may still stayed in. Also, the old iris bed is not too far away from the new ones.

So just for precaution. The new iris bed is clean of the tall weeds, which I think was the problem before.

The iris bores don't care about the weeds - they lay their eggs on iris leaf tips and dead iris debris toward the end of summer or early fall when still warm, to hatch out the next spring when temps are 50 F or greater. From everything I've learned, they do not overwinter as the caterpillar in the soil or in the rhizomes. So if in the fall you trim all the tips (I trim the flags down to about 5 or 6 inches, and remove absolutely every single bit of old iris debris from the garden, you will have just about guaranteed removal of all the possible borers. Right about now (here in Zone 7 the temps are about getting to and staying above 50F), the borers start hatching and moving, boring small piercing holes in the leaves then eating there way inside the leaf down into the rhizome. This year I am treating with the appropriate variety of nematodes to attack the vine borers, and I have it getting here any day now. I've determined that under no circumstances do I want to be treating a plant that flowers and attracts pollinators with a systemic pesticide like Merit or other similar product because of the damage it can do to things I like.