How to Rid Your Garden of Iris Borers
If you live west of the Rocky Mountains, right now you are scratching your head and wondering what the heck an iris borer is. For gardeners east of the Rocky Mountains, the iris borer is the scourge of the iris garden.
Know your enemy
The iris borer is actually the larvae, or caterpillar, of a brown nocturnal moth which lays its eggs on the dead leaves and other debris surrounding iris at the end of the summer, typically late August through September. A female moth can lay up to 1,000 eggs before she dies. Fortunately, there is only one generation of moths each year.
The eggs over winter in your garden, hatching in the spring when warm weather arrives in April or May depending on your climate. The larvae which are the iris borers, head for the nearest iris, climb to the tops of the leaves and burrow into them. Iris foliage at this time of year is usually only about 6 inches tall making it easy for the iris borer to climb them.
During the spring months, the borers munch their way inside the leaves down to the rhizome which is their ultimate target. Once in the rhizome, usually in July, they take up residence, eating it to a hollow as they grow to their adult size of 1 to 2 inches. Then in late July or early August, they emerge from the now dead rhizome and burrow into the soil to pupate into moths which will begin the cycle again.
Cleanliness is king
Obviously, the best way to rid your garden of iris borers is to keep it very clean. Remove all weeds, plant debris and dead or damaged iris leaves immediately. This makes your garden uninviting to the moths who will look elsewhere for a place to lay their eggs. When the foliage on your iris dies after the first frost, cut it down to the rhizome and remove it. Don't leave anything for the eggs to overwinter in.
Try a natural insecticide
You can try spraying your iris with any spray that contains pyrethrum. Another alternative is a solution of 1 part Murphy's Soap and 9 parts water. Both have been effective in killing the larvae as long as they are used before they have a chance to burrow into the leaves.
Squeeze 'em til they scream
If you examine the foliage on your iris closely, it's easy to see where the borers have entered them. Simply squeeze the leaves between your fingers to destroy these pests.
Kill 'em with kindness
Sprinkle diatomaceous earth liberally over your rhizomes. Diatomaceous earth is made up of the skeletons of diatoms that lived in ancient seas that dried up eons ago. The skeletons are ground into a white powder that has sharp edges that will tear up the insides of the borers when they eat it, killing them.
A good alternatively is crushed eggshells which have the added advantage of eventually breaking down in the soil and adding needed calcium.
If you are vigilant, you can prevent iris borers from destroying your iris.
More on garden pests
© 2015 Caren White