RE: Borers - My personal observations

Just thought I would add my two cents on borers, for what its worth. I was plagued for the past several years, even after using the Merit granules liberally sprinkled. However, this year I was almost borer free (I think I found about 8 all season, compared to probably 150+ last year). The only thing different this year was that I sprayed around and right on each rhizome with the Imidacloprid (I also used the granules). I think that the granules can just sit there and not enough dissolves and get into the rhizome. I think in human terms its the same difference between getting a shot from a doctor and taking a pill.
I also noticed that borers prefer the periphery of the iris bed, not the center, although in my case, not necessarily near the bushes. You would think they would be attracted to the heavier concentrations of iris, but not true. This leads me to believe the borer probably need to leave the iris bed (to mate in some exotic borer love ritual?) and later return for egg laying. Not being strong winged, they settle for the first iris they find. As for borer preferring large rhizomes, I am sure they do, but I don't think they have the brains to go house-hunting, so to speak. I have had whole clumps of pardancanda (an irid with very small rhizomes) totally devastated by borer. They probably eat them like you would eat a bag of popcorn. When ready to pupate I think they can travel distances too. I have found pupa in areas 10 feet away from the nearest iris rhizome. I also think they prefer non pbf iris, as they are less frequently attacked. At Presby I have seen whole rows of pbf iris spared and the next row full of borer..so they definitely have their preferences
Laetitia.

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