Sanitation is important in controlling iris leaf spot. Remove all diseased leaves and flower stalks in the fall or early spring. Space plants adequately, keep down weeds, and avoid wetting the foliage when watering. Do not work among plants when the foliage is wet. Plant iris in full sun in a rich, well- drained soil.
Fungicides are effective where cultural practices fail to check the disease.
Fungicides such as Daconil 2787 or Bordeaux mixture can be applied at seven to ten day intervals to protect young growth. A spreader sticker or surfactant can be used to make the fungicide adhere to the foliage. Prepared by Paula Flynn , Department of Plant Pathology Iowa State University , Ames, Iowa. This information subject to a usage policy .