Okra is warm-season vegetable crop grown throughout the southern United States in temperatures ranging from 75 to 90 degrees Fahrenheit. Valued for their edible immature seedpods, okra plants are susceptible to several fungal leaf diseases that threaten crop yield and plant vigor. Prevention, identification and early control are vital for reducing damage to okra from these devastating fungal diseases.
Okra leaves are subject to three fungal diseases: cercospora leaf blight, powdery mildew and wet rot. Fungal growth on okra leaves are parasitic, which means they sap or take away nutrients from the leaves and stems. These leaf diseases cause similar symptoms to soilborne fungal infections. However, the color of fungal buildup on leaf surfaces identifies the particular pathogen, while soilborne fungal infections do not cause fungal growth on leaf surfaces.
Cercospora leaf blight also known as cercospora leaf spot produces an olive green to sooty colored fungal growth on leaf surfaces. As the diseases progresses, symptoms consist of leaf wilt, leaf curl and leaf drop. While symptoms may appear severe, the disease rarely causes serious damage to infected okra. Powdery mildew infections of okra cause visible white powder coating on leaves, leaf curl, leaf yellowing, distorted leaf growth and leaf drop. Wet rot affects okra blossoms, fruit and wounded leaves. The fungus produces white fungal buildup on infected areas. However, it differs from powdery mildew because the fungal heads turn purple to black as the disease matures. Infected leaves rot and drop off the plant.
Cercospora leaf spot and powdery mildew infections are severe during warm and humid weather conditions. However, the cercospora fungus favors moisture on leaf surfaces for infections, while powdery mildew does not require moisture on leaves. Both diseases favor poor sunlight for development. Wet rot favors warm and wet weather conditions as well as wounded leaves for infection. Water droplets from rain or irrigation spread wet rot fungal spores to non-infected areas.
Avoid okra stress with regular fertilization and watering to prevent cercospora leaf spot. However, avoid freestanding moisture on leaf surfaces during irrigation by avoiding canopy watering and watering during the evening. Plant crops with adequate spacing so that leaves can air dry to prevent fungal leaf infections of okra. No chemical fungicides are available for cercospora leaf spot. Chemical fungicides are effective for treating severe powdery mildew and wet rot infections. Avoid poorly drained soils and moisture on okra leaves to prevent wet rot. Always check with state laws before applying chemical fungicides as a treatment for these fungal diseases.
- Clemson University; Cooperative Extension; Okra; Powell Smith, Bob Polomski and Debbie Shaughnessy; April 2003
- University of Florida; IFAS Extension; 2006 Florida Plant Disease Management Guide: Okra; Richard Raid and Aaron Palmateer; 2006
- University of Florida; IFAS Extension; Okra; Mark A. Moosler and Esther Dunn; 2009
- University of Florida; IFAS Extension; Powdery Mildew of Vegetables; Ken Pernezny, Don Maynard and W.M. Stall; 2009
- University of Florida; IFAS Extension; Cercospora Leaf Spot; M. L. Elliott and P.F. Harmon; 2009