Your pictures are definitely disgusting as are those fat suckers. It almost turns my stomach to hunt them out. I spray every year or use granules containing imidacloprid and still have the #%*& things. You did not state what you use to spray on them. I have used Bayer Advance Rose and Flower spray and the kind you mix with water and Season Long granules by them as well as spraying other stuff later on. Nothing seems to work too well. Jim Hedgecock uses something called Fertilome Tree Drench. Others use things I never heard of nor do I have an agricultural card.
Any suggestions? Last year I think I did not use the stuff twice which may be the reason. I do go on the hunt weekly and root out those creepy things.

Jane
Thanks for reading the article. Borers are a never ending fight. If you get rid of one batch there will be others to follow the next year. I do not like to recommend a particular product since what works for one might not work for another. Whatever a person uses must be handled with extreme caution if pets and children are around.

Below is a picture of the two primary products I use faithfully every spring in early April when the first tulips begin to bloom. The Insect killer is "SYSTEMIC", meaning it enters into the plant tissue and attacks the insects from within. The Daconil is a fungicide which I like to use once every summer month, especially when the weather is hot and humid.

I cannot as I said tell someone this will be the "silver bullet": BUT it works for me! And out of about 300+ iris plants It keeps borers in a minority.
Whatever you choose, please follow the complete instruction on the label and wear personal protective clothing. Insecticides can be very toxic and potentially dangerous. Hope this will help, and excuse me for being overly cautious. (P.S. Ortho has modified some of its products recently to comply with federal and state standards concerning environmental issues. So these might not be available now as shown below.)

Just reading these older posts on the dreaded Iris Borer. My story goes like this. After receiving some iris from someone who offered 'pay for postage' ........ I was removing the iris from the box and to my amazement I saw the several Iris Borer 'grubs'. One even jumped out of the box.!! It escaped !!!! Well, as we know these are grubs and the one that escaped was going to cause a BIG, BIG PROBLEM. I would have these grubs in some of the iris the following year.
I found a product called 'Grub-X' and it took care of the situation. I applied the Grub-X the following year also. I haven't seen any more infestation. My Aunt (she also grows iris) and I had discussions on this topic and she told me that it is unlikely that we would have it unless we got iris from someone who had them. She attributed it to the isolated area we live in. " We just don't have Iris Borers here" Judy G.