Types of Blight
Early Blight. Early blight symptoms usually begin after the first fruits appear on tomato plants, starting with a few small, brown lesions on the bottom leaves. As the lesions grow, they take the shape of target-like rings, with dry, dead plant tissue in the center. The surrounding plant tissue turns yellow, then brown before the leaves die and fall off the plant.2 While early blight does not directly affect fruits, the loss of protective foliage can cause damage to fruits due to direct sun exposure. That condition is known as sun scald.
Late Blight. Late blight can affect tomato plants at any point in the growing season and at any stage of growth. Symptoms appears at the edge of tomato leaves, with dark, damaged plant tissue that spreads through the leaves toward the stem. White mildew may grow on the lower leaf surface of the affected area. This type of blight progresses rapidly through plants in humid conditions,3 and if left untreated, can spread to fruits.
Septoria Leaf Spot. Like early blight, the first symptoms of septoria leaf spot often begin on the lowest leaves of plants after fruits appear. Rather than showing as a few lesions per leaf, septoria leaf spot appears as many tiny, brown spots on leaves. Lesions continue to grow and spread before causing leaves to fall off. This type of blight does not usually affect fruits.4
Early blight and septoria leaf spot spores survive the winter in the ground, causing the disease to return next year.1 Late blight does not overwinter in the soil because it requires live tissue to survive, but wind can carry spores up to 30 miles away from infected plants.3
Once blight is positively identified, act quickly to prevent it from spreading. Remove all affected leaves and burn them or place them in the garbage. Mulch around the base of the plant with straw, wood chips or other natural mulch to prevent fungal spores in the soil from splashing on the plant. If blight has already spread to more than just a few plant leaves, apply Daconil® Fungicide Ready-To-Use, which kills fungal spores and keeps blight from causing further damage.
Related Articles in Edible Gardening:
- "Fighting Tomato Blight," Massachusetts Master Gardener Association
- David Whiting,Carol O'Meara, Carl Wilson, "Tomato Early Blight," Colorado State Master Gardener Program, October 2014
- Margaret Tuttle McGrath Ph.D., "Late Blight Management in Tomato With Resistant Varieties," Cooperative Extension System, November 2015
- "Septoria Leaf Spot of Tomato," Missouri Botanical Garden
- Ron Smith, Susie Thompson, Todd Weinmann, Julie Garden-Robinson, "All in the Family: Potatoes, Tomatoes, Peppers and Eggplant," North Dakota State University, March 2012
- "Early Blight on Tomato," Missouri Botanical Garden