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Battling the Iris Bud Fly

September 16, 2009

Fall is very much in the air in Maine, and fall is clean-up time in the garden. My primary objective during fall clean-up is to gain ground in my battle with the Iris bud fly.

I have been growing irises just about as long as I have been gardening here, and my iris of choice is the Siberian iris.  These irises, as their name suggests, thrive in cool climates. Flower detail - 'Lavender Bounty.' Photo credit: Jean Potuchek I love the graceful lines and simple flowers of this plant, and the narrow blade-shaped foliage that remains attractive long after the flowers have bloomed. My first perennial flower bed was the iris bed, a half-moon under a bay window at the front of the house that I dug to accommodate five divisions of old-fashioned blue-violet Siberian irises that a friend had given me from her garden. The following June, when the whole area burst into bloom with masses of these lovely flowers, I was hooked. Within a few years, these irises had formed big clumps that needed to be divided, and I planted the divisions on the back slope. During a visit to the home and garden of the legendary iris breeder, Dr. Currier McEwen (more about this in a later blog post), I discovered the great variety of modern Siberian iris hybrids. Over the next few years, I added many of these, in shades of yellow, pink, and blue to various parts of my garden. Today, I have Siberian irises growing in every flower bed except the new fence border.

Siberian irises 'Super Ego' and 'Tiffany Lass.'  Photo credit: Jean Potuchek

For years, my relationship with the Siberian iris was a romantic idyll; here was a trouble-free plant that filled my life with beauty each June. I clearly remember the day that idyll was shattered. It was a perfect sunny Saturday in mid-June, and I was working on building the walkway between the deck border and the blue and yellow border. As I worked, I was keeping my eye on a gorgeous pale blue Siberian iris, ‘Super Ego,’ that was about to bloom. This was the first year that this plant was well established; it was loaded with buds, and those buds had been getting bigger every day. It looked like today would be the day that they finally opened. But, before my horrified eyes, as each bud started to unfurl, it simply collapsed.

The culprit was the iris bud fly, a garden pest of which I had previously been blissfully unaware. The iris bud fly lays its eggs in spring/early summer on the developing buds of the iris. When the larvae emerge, they burrow into the side of the bud to eat its pollen, and in the process, destroy most of the flower. At best, the bud opens into a deformed flower; at worst, it just collapses because there’s really no flower left. When the larva has had its fill of one flower, it travels down the stem to the next bud. Finally, it pupates within the stem over the winter, and then emerges as a fly in the spring to lay its eggs and start the cycle all over again.

For a gardener, there are only two ways to get rid of the iris bud fly. The first is to spray the buds with a chemical insecticide that will kill the larvae. Since I’m a card-carrying member of the Maine Organic Farmers and Gardeners Association, this is something I don’t want to do. The tedious alternative is to remove every stem from every iris once they have bloomed and to destroy them. In a garden like mine, with dozens of iris plants, this is a big job, but it’s the one that awaits me each fall. So far, I have not succeeded in totally eradicating the iris bud fly from my garden; there always seem to be one or two that somehow escape my clean-up efforts and go on to lay their eggs on my plants. But I think I am making progress.  I haven’t had another year as devastating as that original loss of all my ‘Super Ego’ flowers. This year, whether because of my efforts or because June was just too cold for the iris bud fly larvae to hatch, I had very little bud fly damage. Here’s hoping, that if I’m diligent about clean-up, there will be even less next year.

Information about the iris bud fly is available from Region I of the American Iris Society and from Eartheart Gardens, the successor to Currier McEwen’s iris  operation.
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3 Comments leave one →
  1. brenda permalink
    June 10, 2011 8:27 am

    So glad to have found this blog posting, since I just discovered this horrible creature this year.

    You say you have to remove every stem after it has bloomed and you do this in the fall. Do you mean only the flowering stem and not the leaves? And if it’s only the flowering stem, why do you wait until the fall rather than right after bloom?


    • June 10, 2011 12:12 pm

      Brenda, I’m sorry to hear that the iris bud fly has shown up in your garden; it really is a pest. You are absolutely right about removing the flowering stems; it would be far better to do it right after bloom. There are two reasons I tend not to get to it until fall: (1) I’m busy with other things in the summer garden and just don’t get around to it; (2) I like to let the seed pods develop and ripen and to get the resulting self-sown volunteer plants. This year, I am foregoing the buds and trying to remove flowers as soon as I see they have bud fly damage and the flowering stem as soon as I see both flowers have damage or as soon as they finish blooming. Be sure not to throw the spent flowers or stems into the compost; you don’t want to give the larvae any comfortable place to pupate and winter over. I seal everything up in plastic bags (the kind with zippers) and throw them out with the trash. Good luck in eradicating this pest from your garden.

  2. brenda permalink
    July 9, 2011 5:48 am

    thanks for your reply! I love my iris and will gladly remove all staks if it removes this nasty bug!

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