Prevent iris borer by removing iris leaves in autumn in WNY

iris with leaves in Buffalo Niagara New York
Photo by Connie Oswald Stofko

by Connie Oswald Stofko

In general, gardeners in Western New York are encouraged to keep perennial leaves and stalks in place to create winter interest, but one plant you should cut down is the iris.

“We encourage folks to cut the iris leaves down after the first heavy frost,” said Marilee Farry, president of the Western New York Iris Society. “What is important is not to throw those leaves into the compost pile but to either burn them or put them into the garbage can.”

The iris borer moth lays eggs on the leaves in autumn, she explained, and the eggs overwinter on the leaves.

In spring, the eggs hatch into larvae and “eat each other, until the winner moves down the iris leaves (fairly rapidly) into the rhizome and usually devours it,” Farry said. (Yes, the iris borer larvae are proven cannibals, with only one surviving in each iris, according to the American Iris Society.)

If you get rid of the eggs, you get rid of the problem.

“I cut my leaves every year, and I have not had the iris borer for the last two years,” she said.

If you haven’t had any problems with the iris borer, should you still cut down your iris leaves?  The answer is yes.

“One never knows where or when those ugly moths will fly,” she said.

See more information on the care of irises here, which has also has photos of the iris borer larva and the damage it can cause.

The meetings of the WNY Iris Society are open to everyone. See their upcoming events here.

5 Comments on “Prevent iris borer by removing iris leaves in autumn in WNY

  1. Hi Glenn, this is from Marilee Farry: Yes. All irises that grow from rhizomes, no matter how small the rhizomes are, are prey to the iris borer moth, including Siberian, Tall Bearded irises, Japanese irises, etc.

    Bulbous irises are usually not affected–such as Reticulata, English and Spanish irises– because they grow from bulbs, not rhizomes.

  2. From Marilee Farry:
    The general consensus at the WNYIS regarding preventing the iris borer–If we have a mild autumn in Western New York, we wait until there is a killing frost before we suggest you cut the leaves of your irises down. The reason is the iris borer moth lays her eggs on the tips of the iris leaves during the fall. If it is mild, she will continue until she is killed by the cold weather. The eggs winter over and when it warms in the spring, the eggs hatch and the cannibalistic larvae eat each other, leaving one larva. It then travels down the leaves and enters the rhizome of the iris in a fairly quick fashion. It eats the rhizome from the inside out. Usually, the iris does not bloom and slowly dies.

    Cleaning the garden bed of all loose debris, following cutting the iris leaves, is an excellent idea because the iris borer larvae can live in the debris.

    When cutting the iris leaves, we suggest that you cut them one or two inches from the base of the leaves, that are growing from the rhizome. Always discard the garden debris and the cut iris leaves in the garbage–not the compost pile. Always, Marilee Farry WNYIS

  3. Interesting, I usually cut the leaves down in late September and clean up any plant debris around the rhizome. They seem to keep healthy this way.

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