What's eating my Bearded Iris?

Iris Borer:
In areas where Borers live (we do not have Iris Borers here in the Western United States), they can pose serious and frustrating problems for the Iris grower. Borers begin life as eggs, laid on garden debris in the fall. Each spring, about the time tulips bloom, these eggs hatch into larvae.

These 1/4 inch long larvae crawl onto the Iris and up the leaves. Near the top they chew into the leaves and then down to the rhizomes, where they gorge themselves until they reach a size of about 1 1/2 inches in length. Borer injury often appears as notched wounds or slimy wet looking areas on the leaves. Borers often will hollow out whole rhizomes causing the fans to collapse and the remaining tissue to rot.

Keeping a clean garden is the fist step in minimizing Borer problems. A sharp eye for signs of Borer entry allows some gardeners to catch the Borer in the leaf before it travels to the rhizome (simply squash them in the leaves). The most effective control relies on an understanding of the Borer's life cycle.

Sometime in the summer the Borers change into pupae. These pupae reside in the soil for about a month and then a moth emerges and lays eggs. As pupae, moths and eggs, the Borers do not feed. Only as larvae do they eat and do their damage. At this stage they are most vulnerable to our efforts to control them.

Systemic insecticides are considered to be the most effective control of Iris Borers. Always take care to follow the manufacturer's recommendation when using agricultural chemicals. (Imidacloprid has proven effective against Iris Borers. Check with your local garden center about systemic insecticides that contain this chemical.)

A 10% solution of Murphy's Oil Soap (one part soap for every nine parts water) can be used as an organic alternative to commercial chemicals. Diatomaceous Earth is also effective in ridding plants of caterpillars. It shreds the inside of caterpillars when they ingest the dust, but you do have to reapply after a rain or watering as it loses its effectiveness when damp. Recent research has given us another organic approach to borer control. Read the article here on the use of nematodes to combat the Iris Borer.

Slugs, snails and other pests around Bearded Iris: 

In early spring, or when you notice damage from slugs and snails, bait for these pests using whatever method you prefer. Aphids, thrips, and whiteflies can be controlled by a variety of insecticides readily available at garden centers. Insecticidal soaps can also be effective.


We suggest you make a homemade insecticidal soap, a low-toxicity bug control solution that will desiccate the soft bodies and kill the aphids without doing harm to your plants. Simply mix a few teaspoons of liquid dish soap with one quart of water, then spray or wipe the solution onto the leaves, stems, and buds of the plant. (Don’t forget: These bugs like to hide beneath leaves, so take care to thoroughly coat the underside of the leaves, too.) Repeat the process every two or three days for the next few weeks, until you no longer notice aphids on the plant. If your aphid infestation is not eliminated by the use of insecticidal soap, you may need to use a systemic pesticide. Consider using a product containing Imidacloprid. Mix and apply according to the manufacturer’s directions.