Just to be clear, Milky Spore may also work on Iris borers but only in the pupae stage when they are in the soil later on in the Summer.
A better solution for Iris Borers appears to be an organic bacterium solution called Spinosad. I haven't tried it but it appears to last 4 months and not only treats borers, but sowbugs, thrips, slugs, spider mites, fleas and a host of other predators. It should be sprayed before blooming but not on blooms, to avoid killing pollinators. Here's a link from Texas A&M and I see it is also for sale on Amazon:
https://aggie-horticulture.tam...
Now, I don't have them here but since iris borers start out as moths, I think a bug zapper would help alot if it was put out in April and May to get a lot of these before they start laying eggs. I've used it for tent caterpillar moths, but be prepared to clean it out daily because it can really clog fast this time of year.
