You will always get the iris borer. I dig up the plant and dispose of the 'rotted, mushy' parts. BT, bacillus thurengis, is a safe, effective biological control that can be sprayed on foliage. When the larva eats the sprayed foliage it dies within a few days. I think if you spray wqithout cleaning it up, you will leave eggs behind so you would have to do continuous spraying. Marg

Marg, I'm so tickled to see someone else using BT for borer control! I just started using it this year. A hybridizer in S. Illinois who has been using BT for years with great success say he sprays every 3-4 weeks early spring through late summer, because he believes that the moths do not only lay eggs in late summer/fall - they can also lay in spring/early summer. I have discovered that this is true. I have seen many cases this spring where moths laid eggs on iris BUDS and BLOOMS, and I found many borers in spent flowers, eating their way down the stalks towards the rhizomes! (I didn't think to spray the stalks - ack!)

BT is sold under the trade name Thuricide here in the states - not sure if it is the same in Canada.

Diana

This is the answer I've been looking for. The borers are driving me bonkers. Decimating my tubers and making me sick at heart. I'll be shopping for Thuricide.
Thanks.