| Iris Problems | |
|---|---|
| Symptom | Probable Cause |
| Leaves Mined; Rhizomes Damaged | Iris Borers |
| Ragged Holes In Leaves | Slugs and Snails |
| Leaves Discolored; Roots Damaged | Thrips |
| Leaves Curled And Distorted | Aphids |
| Rhizomes Soft; Odor Present | Bacterial Soft Rot |
| Rhizomes Gnawed; Unearthed Or Eaten | Rodent Injury |
Leaves Mined; Rhizomes Damaged Caused By Iris Borers
This is the most serious pest of iris. 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 bearded 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 you see in leaf mines. For more information see the file on Controlling Borers
Leaves Discolored; Roots Damaged By Thrips
Several species of thrips could potentially damage inner folds of Iris leaves. Adult thrips are tiny, narrow, 4-winged insects, about 1/16 of an inch long. They hide between new leaves and flower petals, and injure tissues by rasping at them and lapping up the sap that oozes out. Larvae are usually wingless. The pests feed from May to November, turning the foliage brown or black. Growth is stunted, and tops usually die. In older clumps almost all of the roots may be killed. Adults overwinter in leaf buds, protected by bases of older leaves. As soon as you spot thrips on the iris, spray them with insecticidal soap every 3 days for 2 weeks. If you can not see the thrips to spray them, spray the leaves and flowers with a neem insecticide 2 or 3 times at 7 to 10 day intervals. For more information see the file on Controlling Thrips
Rhizomes Soft; Odor Present Caused By Bacterial Soft Rot
Soft, pulpy rhizomes accompanied by an offensive odor and withered leaf tips are the most obvious signs of this disease. Bearded 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,Rodent Injury
During the winter months, small rodents such as mice or voles 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 your planting holes with small baskets of 1/4-inch hardware cloth cut to fit.
