The “US8” isolate of Phytophthora is a very aggressive pathogen of most potato cultivars, but only moderately aggressive with tomatoes. This won’t guarantee that your plants won’t become diseased. Different varieties of the fungi have different degrees of aggressiveness and may favor certain cultivars of the crops. Preventing late blight and early blightĬhoose disease-resistant varieties of tomatoes and potatoes that have been developed over the last few decades. See this decision tree to tell whether your plants have late blight or early blight. Tubers develop small, black, sunken spots that render the potato unusable. Underground potato tubers do not escape the disease because spores are washed into the soil from aerial plant surfaces. The spores of Alternaria produce a black, velvety texture in the centers of the spots.

Maturing tomato fruit develops sunken, blackish circles that also resemble targets at first. Stem lesions are usually black and may kill a branch or the entire plant. (This symptom is not seen in late blight infections.)Īffected leaves then turn yellow and either dry up or fall off. Leaf spots are dark brown to black, enlarging in concentric rings that give the lesion a target-like appearance. The disease can rapidly spread from plant to plant and to adjacent fields.Įarly blight symptoms are likely noticed on lower leaves first. Purple/black spots on the leaf stalk and stem, and grayish green, greasy or water-soaked lesions on green or maturing tomato fruit become visible. The tomato fruit or potato tuber rots, has a foul odor and is inedible. White spore masses and cells of the water mold typically develop on the underside of the affected leaf. Discoloration usually begins on the margins of leaves and soon the entire leaf is covered and dies. Dark brown/green water-soaked lesions appear on the leaves. Late blight symptoms progress rapidly and the entire plant may die in a day or two. Melanson, Mississippi State University Extension, Early blight has lesions with concentric rings. Symptoms of late blight and early blightįortunately, the symptoms of the two blights are fairly easy to tell apart.

During World War I, more than half a million people starved to death in Germany because supplying the war effort took away all available control measures to fight the pathogen. or Canada from Ireland or Germany in the 1840s and 1850s, most likely it was because of the potato famine, brought about by the loss of that important and nutritious crop due to late blight. Historically, Phytophthora infestans was responsible for the deaths of millions of people from starvation. World-wide, the pathogen causes billions of dollars’ worth of crop losses annually. Of the two diseases, late blight is more devastating. However, both diseases can occur during any part of the growing season as long as environmental conditions are favorable for reproduction and spread of the pathogens. To confuse the matter further, late blight often occurs early in the growing season when cool, wet weather conditions allow for the rapid spread of swimming spores, called zoospores, to spread from plant to plant.Įarly blight, on the other hand, often occurs later in the growing season and is typically first manifested on older leaves and maturing tomato fruit and potato tubers. It was identified in Chautauqua County last year.Įarly blight, caused by the true fungus Alternaria solani, can be a significant cause of plant mortality and crop loss, but it usually doesn’t spread as fast. Late blight was found in Onondaga County (the Syracuse area) in the middle of June. Late blight, caused by the fungus-like water mold, Phytophthora infestans, is a devastating disease that can quickly wipe out many acres of crop. There are two very different blight diseases that affect tomatoes and potatoes (and some of their relatives in the plant family Solanaceae). There are two blights to watch out for: late blight and early blight. Gardeners love growing tomatoes, and losing them to disease can be disappointing. Photo courtesy Gerald Holmes, California Polytechnic State University at San Luis Obispo, īy Steven Jakobi, Allegany County Master Gardener Volunteer Late blight progresses rapidly and the entire plant can be dead in a day or two.

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