There are small, brown spots on the foliage of my bearded irises. What is the problem?


There are small, brown spots on the foliage of my bearded irises. What is the problem?


The small, brown spots are likely due to iris leaf spot. Iris leaf spot is a common disease of bearded irises. The disease is caused by the fungus Mycosphaerella macrospora. The first symptom of iris leaf spot is the appearance of small yellow-brown spots on leaves that are surrounded by water-soaked borders. The spots eventually turn grayish brown, develop reddish-brown borders and grow in size. As the spots grow, several spots may coalesce and destroy entire leaves. Iris leaf spot is most severe when the weather in spring is cool and wet. 

Good cultural practices will reduce the severity of iris leaf spot. Remove all diseased leaves and flower stalks in fall or early spring. (The causal fungus survives the winter on infected plant parts.) Plant bearded irises in full sun, space plants adequately, control weeds, and avoid wetting plant foliage when watering. 

Fungicides will likely be necessary to control iris leaf spot on plants that were severely infected the previous year. The first application should be made when the leaves first appear in spring. Continue to spray as directed on the product label. Effective fungicide products include those that contain chlorothalonil and myclobutanil. Since bearded iris leaves are waxy, add a spreader-sticker to the fungicide to make sure the fungicide adheres to the iris foliage. 


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