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Please help with Iris borer

Posted by kousa Zone 6 (My Page) on
Tue, Jun 11, 13 at 19:50

Can someone help me with iris borers? All of my iris is infested with borers. I have only started growing bearded iris last year, so I do not know where they come from, I have been going around and trying to kill them by hand(they hid in the leaf fold). I doubt that I have gotten all of them. Do I need to dig up all of the bulbs and replant them? Is there a spray I can use?


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RE: Please help with Iris borer

It is too late to get really good control for this year other than by hand, but this fall and winter practice very clean gardening by clearing away any dead leaves and cut back the live leaves to about six inches. Also trim and clean up any other nearby perennials that borer moths may have laid eggs on. Get the trimmings far away from your iris, or burn them. Carefully inspect the rhizomes and clear out any that have rot which sets in because of the borer damage. Clean up the garden after the first hard frost, if you have one.

Insecticides used are systemic ones, since the borers are inside the leaves and rhizomes where you can't really spray them. These are either imidicloprid (Merit) or orthene applied in the spring when leaves are 4-6 in. high. If you want an alternative to insecticides, some professional growers have burned their fields with a flame weeder type device to destroy the debris and burn it in place. You might want to read up on this before you try it, sounds to me like you'd really have to know what you were doing, and is a kind of last resort thing you would do if you had way more iris than you could possible clean up by hand. Also you could let loose parasitic nematodes, which do prey on the iris borer. But these are things to do next spring. Do the best you can now to squish the borers in the leaves before they get down to the rhizomes. Good luck.


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RE: Please help with Iris borer

  • Posted by kousa Zone 6 (My Page) on
    Wed, Jun 12, 13 at 17:01

Thank you for your advice, aseedisapromise. I hope that I got to all of them.


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