Hi I garden in New England, and I have a terrible problem with iris borer. Some irises will do fine for several years until the borers get them and decimate the clump. They leave others alone for a while until they find them eventually too. Any ideas for natural treatments?
The most natural treatment is Parasitic Nematodes they seek and destroy moth larvae, which is what the Iris Borer is. Steinernema carpocapsae and Heterorhabditis bacteriophora either of these two has an very good track record for cleaning up the problem. You will have to check with a local nursery or garden center to see if they have or can get them for you. The nematodes will not live through cold winters so you will have to reapply in the spring. Also, before winter be sure to cut back and throw away (not in the compost) all Iris leaves and other fallen debris from the Iris bed. The Moth lays it's eggs in the Iris foliage or nearby plants so keeping the area really clean will help slow down the problem come spring. In spring keep an eye on the Iris leaves and if you see a borer making a home there, cut the leaf off and squish it. I have also read that if your rhizomes are infected, dig them up, cut off the decaying parts and look for holes the borer has made. You can make a solution of 10 parts water to 1 part bleach, put the rhizomes in the solution, it may only take a few minutes or a couple of hours but the borers will back out of the hole and die. When they are cleaned out let them dry thoroughly then replant.
Hi toni--Thanks for the advice. I am guessing my best bet is to wait until spring to buy the nematodes? I will clean up the foliage this fall as you suggest, and I think I will also dig up 7 treat the one clump most affected. It is such a shame, it was such a healthy gorgeous clump.
