Wherever iris are found there, the iris borer prospers.
An annoying pest considered repulsive by iris fanciers, the adult moth is a drab violet brown with black markings, while the borer at first is slender and pale pink.
As it progresses down the leaf blade and into the rhizome, it becomes fat and darker.
How Borers Emerge
Eggs that are laid in fall on the trash, and old iris leaves hatch in late April or early May, depending on the advancement of spring.
The young caterpillars, or larvae, enter the newly growing iris leaves, making pinpoint holes that appear as translucent dots.
With an insatiable appetite, they eat their way down through the left blade, leaving a ragged, oozing tunnel behind.
Reaching the rhizome, the borer eats out a large area in the center, making that part of the rhizome useless.
Often this is followed by bacterial decay. Some scientists believe the larva transmits the bacterium to the rhizome.
In any case, the evil-smelling decay and the borer are often found together. The borers emerge in August to form brown chrysalids in the soil.
The pupation period lasts four to five weeks, with the adult moths appearing in September or October. After fertilization, egg-laying starts.
Control Plans For The Iris Borer Pest
Knowing the pest’s life history permits control plans to be put in force.
- First, since the borer emerges from the rhizome in August, iris plants should be lifted for inspection and divided in July while the borer can be destroyed.
- Second, since eggs are laid in the fall on old iris leaves and trash near the bed, a complete cleanup should be made before winter sets in.
- Third, because the eggs hatch in late April or early May, a control spray should be applied while still small.
Spraying The Leaves
Malathion, or a combination of malathion and methoxychlor sprayed on the leaves by the second week in May, will kill the newly hatched caterpillars.
Annual pest control measures for the iris must be carried out since the adult moths fly readily from one iris bed to another.
There is no hope of completely eradicating them, but an annual control program is necessary for outstanding iris.
44659 by H. G. Mattoon