| Solving Japanese Iris Problems | |
|---|---|
| Symptom | Probable Cause |
| Holes In Seed Pods | Iris Weevils |
| Leaves Mined; Rhizomes Damaged | Iris Borers |
| Ragged Holes In Leaves | Slugs and Snails |
| Rhizomes Soft; Odor Present | Bacterial Soft Rot |
| Rhizomes Gnawed; Unearthed Or Eaten | Rodent Injury |
Holes In Seed Pods Are Caused By Iris Weevils
Iris weevil adults are 1/5 inch long, black with white and yellow scales. They\'re locally abundant wherever iris grows. When the weevils breed in the seed pods, the pods show many small holes. Control them by discarding the flower heads as they fade. For more information see the file on Controlling Weevils
Leaves Mined; Rhizomes Damaged – Caused by Iris Borers
Iris borer moth larvae enter iris leaves a few inches above the ground, when the leaves are 5 or 6 inches high. They excavate slender feeding channels that resemble burrows of leafminers. Areas of the leaves may also appear water soaked. In mid-summer, the borer larvae attack iris rhizomes, becoming fat, pink and 1-1/2 to 2 inches long. In August, they leave the rhizomes to pupate in the soil. Tall German irises, are the most susceptible to these insects. When dividing irises, cut out all infested portions and discard or burn them. In the fall, cut faded iris bloom stalks and leaves at the base and burn them, as they are the primary overwintering site for these pests. Spread pyrethrum dust around the base of the plants in the spring to kill the hatching larvae that emerge to seek out the roots. Pinch the larvae visable in leaf mines. For more information see the file on Controlling Borers
Rhizomes Soft; Odor Present – Cause is Bacterial Soft Rot
Soft, pulpy rhizomes accompanied by an offensive odor and withered leaf tips are the most obvious signs of this disease. German irises, especially the tall ones, are most likely to become infected. Crowded conditions and shady locations increase susceptibility, as does a borer infestation. Dig up infected rhizomes, cut out and discard badly affected portions and dip the healthy parts in dilute chlorine bleach solution. Planting irises on a slope reduces the chance of infection. While occasionally reducing plant vigor, bacterial soft rot rarely kills plants.
Rhizomes Gnawed; Unearthed Or Eaten – Caused by Rodent Injury
During the winter months, small animals such as mice, voles, and muskrats sometimes eat iris rhizomes. Moles tunnel through beds in search of earthworms and insects, but mice also use their tunnels to get at bulbs and rhizomes. Discourage rodents by lining planting holes with small baskets of 1/4-inch hardware cloth cut to fit.
