Fortunately, we do not have Iris borers in the west. However, the Iris borer can pose a very difficult problem in the Midwest and along the east coast. They hatch in the spring and chew into the leaves, leaving chew marks on the margins of the leaves. They then bore down through the leaf, leaving long wet looking streaks on the leaves. Once they get into the rhizomes, they gorge themselves. What they don't eat then can rot.

First, always maintain a clean garden. If you see the borers in the leaves, simply squash them. We recommend using the insecticide Cygon 2-E. Spray in two week intervals from about the time the tulips bloom through mid-summer. A 10% solution of Murphy's Oil Soap (one part soap for every nine parts water) can be used as an organic alternative to Cygon.

Neil

It is my understanding that Cygon 2-E has been banned in the U.S. and will no longer be available once current stock is sold out.

The best chemical option I know for borer control is imidacloprid (Merit) applied in very early spring before temps reach 70 degrees. It would have no effect on borers applied this late in the season, however.

Laurie

Neil

Murphy's Oil Soap and Iris Borers
Taken from AIS Region 18 Bulletin -- Spring 2000
Michael Gullo
West Walworth, New York
(This article was recently on Iris-Talk and originally printed in the January 1998 AIS bulletin)

I first heard about the Murphy's Oil Soap method of borer control in the January 1998 AIS Bulletin. The title of this article was "Sand and Soap" written by Marie Gebert. In the article she presented the following advice: "use a mixture of one half cup of Murphy's Oil Soap to one gallon of water. Spray on the iris leaves weekly (or after a rain) from early May to late July. This should be used after any other sprays."
I use the soap that comes in the refill bottles not that which comes in the spray bottles which is already diluted. I feel that a thorough garden cleanup (very later fall or very early spring) is also very important to make borer control even more effective. I have been using this method of borer control for the past two seasons with great success.
I only find a very small number of borers that manage to survive the spraying, which I promptly squish. One could probably combine the oil soap treatment and beneficial nematodes (alternate sprayings) and achieve even more complete protection. With just two sprayings last season I only found a dozen or so borers.

Marie, in her article, mentions that she and others in her area (northeastern Connecticut) have been using it to great effort for five seasons (as of 1998). I don't believe in using harsh chemical treatments to control pests or other problems, so Murphy's Oil Soap has been quite a help. Your climate will dictate how early you need to start spraying. Some years the first of May is early enough, but lately here I have needed to start even earlier, usually mid to late April. If you wait till the borers hatch then it will be too late, at least to stop the early ones.
I won't use harsh chemicals, but for those who do I would suggest trying a test plot for the Murphy's to see if it is as effective as chemical treatments. I know of a number of people who use chemicals like Cygon only out of desperation.

"A dozen or so borers" is a dozen or so more than I want feeding, maturing, and breeding in my iris beds.

Laurie