I am heartbroken. I noticed this afternoon that the fans of a formerly-thriving four-year-old clump of I. tectorum alba, three feet across, were now lying flat on the ground. Pulling up a random handful, I found the rhizomes completely hollowed out. Now I got focused, and went systematically through the remains of the clump -- I found two two-inch borers, and maybe three plantable fans left. I also dug up the soil for a foot around where the clump had been and found four pupae. Needless to say, I enjoyed skewering the little invaders!

Having planted back the sad remnants, is there anything I can do to prevent this recurring, especially this late in the year?

Also, a large stand of I. foetidissima nearby has also completely died -- are they vulnerable to borers too? I found no borers or pupae among the apparently-rotted remains there...

Thanks!

Lynn