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Tomato blights appear

Learn how to recognize and manage fungal blights on tomato vines.

Early blight on tomatoTomato vines are starting to suffer from disease. The most active fungus on tomato vines is early blight (Alternaria solani). This fungus comes from the soil and starts on the lower leaves. Brown spots with dark borders grow to over ½ inch in diameter. You will notice a pattern of brown concentric rings in the lesions (top photo). Surrounding tissue turns yellow.

Monitor the fertility of your soil. Early blight is especially aggressive on pale, hungry vines. Most tomato plants, infected or not, benefit from a light fertilization after first fruit set.

Keep your eyes open for Septoria leaf spot disease (Septoria lycopersici). Septoria appears as tiny 1/8-inch brown spots with dark borders (bottom photo). It also starts from the soil and works its way up the plant. Numerous lesions can appear on each leaf.

Management strategies of both diseases are similar. Remove infected foliage. Protect the healthy foliage by applying a fungicide. Chlorothalonil (Daconil, Bravo) and mancozeb (Dithane) are most often used. Copper products are organic options. Sprays can continue every 10–14 days if needed.

Keep the foliage dry when watering to prevent the splashing and spread of fungal spores. Irrigate in the morning so any water that gets on the foliage can dry before nightfall.Septoria leaf blight on tomato

Mulch your plants; this can serve as a barrier between your vines and the disease-infected soil.

Staking can help to maximize air flow and sunlight in the planting.

After frost, remove all infected vines to prevent fungal problems next year. Next year, don’t crowd your plants in the garden. Varieties resistant to early blight are available.  


Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Published in the NDSU Yard & Garden Report, July 21, 2014. Photos were made available under Creative Commons licenses specified by the photographers: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org; and Bruce Watt, University of Maine, Bugwood.org. The information given herein is for educational purposes only. References to a commercial product or trade name are made with the understanding that no discrimination is intended and no endorsement by the North Dakota Extension Service is implied.

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