Key Features
- Water-logged streaks on leaves
- Brown leaf tips
- Fewer or smaller blooms
Symptoms
Larvae tunnel from the leaves to the brown bulbous roots (rhizomes) at the base of plants. Leaves become streaked with tan lines (often appearing water-logged) and tips of leaves turn brown. Severe damage occurs as a result of rhizome feeding. Bacterial soft rot is often a secondary pathogen that infects the host after or during larval feeding. Pillbugs and sowbugs may also enter the diseased rhizomes. Other diseases can cause similar symptoms in irises. To confirm the presence of iris borer on a declining plant, slice open a suspected leaf or cut open the rhizome and look for the caterpillar.
Biology
Eggs hatch in early spring and caterpillars chew very small holes to tunnel into leaves. Larvae remain within the plant and move down toward the rhizomes. Borers pupate in the soil in July or August. Adults emerge, mate and females lay eggs on iris leaves where they overwinter.
Management Recommendations
Some irises like the Siberian iris are more tolerant to iris borer. Planting this type of iris may reduce damage from this pest. In early spring, check the leaves of iris plants for brown streaks along the leaf for early signs of infestation. Any infested leaves should be removed. Discard any rhizomes containing larvae or showing signs of tunneling. To reduce infestations from occurring the following growing season, remove all above-ground plant material. This will get rid of all eggs laid for the following year. Insecticides can be applied prior to egg hatch when new growth is approximately 6 inches tall. This will kill the small larvae as they chew their way into the leaves.
Effective Pesticides
Active Ingredients include: Acephate, Spinosad
Resources
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
