• There are more than 200 different types of irises. It is a perennial plant that is most commonly grown outdoors and used for landscaping. There are several diseases that affect iris plants. Most are easily treated at home or by using chemicals that are found in garden centers or nurseries.
  
  

Iris Leaf Spot

• The main symptom of iris leaf spot is the appearance of brown spots that are surrounded by yellow. This is first seen on the leaves of the plant. These spots will continue to grow if left untreated and will eventually kill the plant.
  Chemicals such as mancozeb, thiophanate-methyl and mycobutanil are used to treat iris leaf spot. The chemicals may be labeled to treat Didymellina leaf spot but will treat an iris plant.
  
  One of the main causes of iris leaf spot is overcrowding of the plants. Thin the infected plants enough to allow sufficient airflow between each plant.
  
  

Iris Borer Caterpillars

• An iris plant that has pinhole sized holes or tunnels in the leaves is usually infected by Iris Borer Caterpillars. The caterpillars leave streaks on the leaves that appear tan or water streaked. This is caused by feeding. Eggs are laid by the caterpillars in the fall in the roots and soil surrounding the plant.
  
  The main chemicals used to kill the caterpillars are acephate and spinosad. Treat infected plants in the spring when new growth is 4 to 6 inches tall. Repeat the treatment 10 to 14 days later. To prevent further infection, remove all debris from dead plants each fall by burning or burying.
  
  

Iris Scorch

• The main symptoms of Irish Scorch are browning and dying of the leaf tips that eventually spreads to the roots. Irish Scorch is not contagious and most commonly occurs in early summer.
  
  Treatment is best accomplished by digging up the infected plants. Store the bulbs in a warm dry location. Replant the bulbs in fall in the same way they were planted before. The new plants will most likely not bloom the first year but will otherwise be unharmed.
  
  

Bacterial Blight

• Signs of Bacterial Blight include elongated lesions that may appear water soaked. The spots begin at the base of leaves. The lesions will spread rapidly and cause the leaves to turn yellow and collapse.
  
  There is no way to save a plant that is infected with Bacterial Blight. Dig up infected plants and burn them in a separate location. To prevent a recurrence of the disease, space plants far enough apart to allow for sufficient airflow and avoid overhead watering.