Iris flowers are a beautiful addition to any garden, but they can be susceptible to pests and diseases. In Minnesota, the most destructive insect pest of irises is the iris borer (Macronoctua onusta). These caterpillars cut holes in the leaves and tunnel through them, causing significant damage. Other common pests include aphids, iris thrips, and iris borers.
Common diseases of irises include flower or leaf blight, bacterial soft rot, crown rot, rhizome rot, leaf spot, and mosaic virus. All of these diseases cause the tips of the iris leaves to turn brown and the plants to weaken. Plant pathogens are responsible for these diseases and can spread through insects, water, soil, air, people, and other animals. To prevent future problems with iris borers, it is important to properly trim and clean your iris plants in the fall.
The University of Minnesota Extension provides detailed instructions on how to identify iris borers when inspecting your plants in spring and summer. Irises should be watered deeply every 3-4 weeks during periods of drought (longer than three or four weeks). They should also be fertilized in early spring, about 6-8 weeks before flowering and again after the flowers have disappeared. At your local garden store, you'll likely find some iris bulbs or rhizomes for sale.
Bearded irises have some problems such as bacterial infections (bacterial soft rot) and fungal infections (rhizome rot and leaf spots). Rhizome-type irises produce larger flowers and include bearded and beardless varieties. Bulb-type irises produce smaller flowers and are often used in rock gardens or in the front row of borders to provide color early in the year. The Nordic Blue Flag (Iris versicolor) is a member of the iris family that is seen more frequently in the wild than in family gardens.
It grows in wetlands and coasts. The Siberian iris is more tolerant to the attack of the iris borer than other types of irises. If you're ready to bring the elegant perennial beauty of lilies to your garden, you can order many types of iris flowers online. To extend the flowering season, consider planting more than one cultivar.
Learn more about several species and cultivars of irises by visiting the Missouri Botanical Garden Plant Finder.