Leaf Strip

Basic Borer Information

The Iris Borer Lifecycle

The most effective control relies on an understanding of the borer's life cycle. Borers begin life as eggs, laid on garden debris in the late summer and fall. Each spring, the borers larvae begin to hatch after the first two days of temperatures greater than 70 degrees. New England gardeners also have observed that hatch begins about the time the tulips bloom and it continues into June. The inch long larvae crawl up the iris leaves. Near the top they chew into the leaves. Then they eat their way down inside the leaves to the rhizomes, where they gorge themselves until they reach a length of about 1 to 1 inches. Borers often will hollow out whole rhizomes causing fans to collapse and the remaining tissue to rot.

Some time in the summer the borer larvae change into pupae with a chestnut brown chrysalis or cocoon. These pupae reside in the soil for about a month and then a moth emerges and lays eggs. Borers in the pupae, moth and egg stages do not feed. Only as a larvae do they eat and do damage. At this stage they are most vulnerable to our efforts to control them.

The Signs of Borer Infestation

In an article the September, 2000 issue of "Tall Talk", Barbara Nicodemus gives a great description of how recognize borers in your iris. "The presence of the iris borer may first be recognized by the wet stains along the leaf edges, notched out leaves, small pinholes, fine silk threads left from their spinning, and 'sawdust' looking remains at the base of the plant from their waste. Later, the newly developing central leaves will have larger, more ragged, "saw-toothed" edges, due to the growing borer feeding inside the lower base of the leaf sheaths. The outside base of the plant will become slimy and look water-soaked due to the "bleeding" of the leaves. In the advanced stage, the central leaf may yellow and will be easily pulled out, sometimes even the whole fan. Bloom stalks will topple over and, upon inspection, the base will show the slimy, riddled work of the borer. The preceding two signs might be all that is noticed on smaller rhizomes, like MDBs, etc. This is especially true on some beardless irises, like Siberians."

Basic Borer Control

Keeping a clean garden is the first step in minimizing borer problems. In the summer and fall, the borer moths lay their eggs on the iris foliage or on the foliage of nearby plants. In the fall, cut back the iris leaves and remove them from your property if possible. This will reduce the number of borers hatching next spring.

In the spring, watch for the signs of borer infestation. A sharp eye for borer entry allows some gardeners to catch the borer in the leaf before it travels to the rhizome (simply pinch them in the leaves). If the borer has chewed its way further down the leaf, it maybe easier to remove a portion of the leaf then search for and destroy the borer.

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