Prevent blights by providing proper care to the potato plants.

Will Daconil Kill Potato Blight?

by Amanda Flanigan

Blights are a serious fungal disease that can attack potato (Solanum tuberosum) plants, leading to loss of vigor, stunted growth and poor crop production. If not controlled, blights may threaten the life of the annual vegetable plant and will spread to healthy plants, infecting them with this damaging disease. Daconil is a fungicide that, if used properly, will treat and prevent potato blight.

Potato Blight

Early blight and late blight are two fungal diseases affecting tomato plants. Early blight (Alternaria solani) attacks the oldest leaves first, resulting in circular dark lesions measuring about 3 to 4 mm in diameter. Rings may form around these lesions, creating a target-board appearance. Infected leaves yellow and drop from the plant, and dark lesions develop on stems. Late blight (Phytophthora infestans) affects all aboveground parts of potato plants, resulting in water-soaked pale or dark green spots on leaves. As the disease progresses, these spots will expand and change to purple, brown or black as it kills the tissue. Blight is prevalent when conditions are moist and humidity levels are high.


Daconil is the brand name of a broad-spectrum fungicide containing chlorothalonil. It controls various fungal diseases on ornamental and vegetable plants, including blights. Daconil is available in concentrate and ready-to-use forms and is applied as a foliar spray for treatment or prevention of fungal diseases affecting plants.


Each type of Daconil fungicide has directions located on the bottle that you should follow to ensure the effectiveness of the fungicide and reduce damage to plants. For example, concentrate Daconil must be mixed at a rate of 1 1/2 teaspoons for each 1 gallon of water. This solution works to control or prevent the fungal disease. For prevention of potato blight, apply the solution when plants reach 6 inches or taller and repeat the treatment at five-day intervals to maintain control. To treat potato blight, spray the infected plant when the first symptoms appear and repeat the treatment every five days as needed.


According to the Missouri Botanical Garden website, chlorothalonil is considered only slightly toxic to humans but does cause skin and eye irritation. Chlorothalonil also has a low toxicity level to bees and birds but is highly toxic to fish. It is important to keep children and pets away from the area until the chlorothalonil is completely dried. Wear protective clothing when using the chemical fungicide, and wash your hands with soap and water after handling Daconil fungicide.

About the Author

Amanda Flanigan began writing professionally in 2007. Flanigan has written for various publications, including WV Living and American Craft Council, and has published several eBooks on craft and garden-related subjects. Flanigan completed two writing courses at Pierpont Community and Technical College.

Photo Credits

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