Earlier in the spring I got my first indication that something was
wrong with my irises when I noticed that a few leaves and stems would
detach themselves easily from the iris rhizome with a gentle pull. The
second clue that something was wrong with my irises was the smell that
emanated from these leaves and stems when they were pulled out, the
smell of rotting plants is unmistakable and very noticeable. I put
things off until I had more time to investigate what the problem was.
Yesterday, as I was transplanting some irises I found the culprit. It
is the larva of the Iris Borer, a moth that lays eggs on leaves of irises
that hatch, tunnel into the plant and down into the rhizome where they
become larva before emerging as moths in the fall. According to my reading: In the spring you'll
notice a brown or wet looking mark on the leaves of your iris, it is
the sign of the Iris Borer traveling down the leaf into the rhizome. To
kill it before it reaches the rhizome you can pinch and squeeze the
leaf. To be honest, I don't remember any of these marks but I do
remember seeing a stem or two that had holes on the buds before they
When I found the Iris Borer larva in some of the
rhizomes I discovered that when I touched it with a stick it looked like
it vomited something up. The second picture above shows the larva of
the Iris Borer covered in whatever substance it kept spitting up, in
what I believe was an attempt to discourage me from bothering it. I
kept nudging it until it seemed to have nothing left to throw up and
then I tossed them on the sidewalk for the birds to eat.
Make sure you clean up the dead leaves of plants in your garden in the fall and spring to avoid problems like this. I hope that my Iris Borer problem isn't so sever that I end up losing my black irises.