Tom is right, they sometimes leave chewed leaf edges. Also look for frass near the base. In my case the chewed leaves gave it away as frass was only inside the leaf fan. Another clue can be an outside leaf that falls over and is soft on the bottom, but this is also a clue to bacterial rhizome rot as well.
When discovered I removed that particular rhizome, trimmed leaves, started cutting into the rhizome following the path of the borer. Once removed, with damage to its "face" since it did not want to come out, I treated the rhizome with chlorine cleanser powder and replanted it but with no watering in until the cut area was able to skin over for a day or so to reduce chances of bacterial rot. If there are lots of the infested variety I just toss the rhizome.
About 3 cm., just over an inch.
About 3 cm., just over an inch.
