blight

blight

[blahyt]
blight, general term for any sudden and severe plant disease or for the agent that causes it. The term is now applied chiefly to diseases caused by bacteria (e.g., bean blights and fire blight of fruit trees), viruses (e.g., soybean bud blight), fungi (e.g., chestnut blight), and protists (e.g., potato blight). Other plant afflictions (caused by insects or unfavorable climatic conditions) that display similar symptoms are also called blights. See diseases of plants.

Plant disease caused by the fungus Endothia parasitica. Accidentally imported from East Asia and first observed in 1904 in New York, it has killed almost all native American chestnuts (Castanea dentata) in the U.S. and Canada and is destructive in other countries. Other blight-susceptible species include the European chestnut (C. sativa), the post oak (Quercus stellata), and the live oak. Symptoms include reddish brown bark patches that develop into sunken or swollen and cracked cankers that kill twigs and limbs. Leaves on such branches turn brown and wither but remain attached for months. Gradually the entire tree dies. The fungus persists for years in short-lived sprouts from old chestnut roots and in less susceptible hosts. It is spread locally by splashing rain, wind, and insects, and over long distances by birds. Chinese (C. mollissima) and Japanese (C. crenata) chestnuts are resistant.

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Any of various plant diseases whose symptoms include sudden and severe yellowing, browning, spotting, withering, or dying of leaves, flowers, fruit, stems, or the entire plant. Usually the shoots and other young, rapidly growing tissues of a plant are attacked. Most blights are caused by bacteria or fungi (see fungus); some result from drought. Fungal and bacterial blights are most likely under cool, moist conditions. Most economically important plants are susceptible to one or more blights. Measures taken to fight blight include destroying the infected plant parts; using disease-free seed or stock and resistant varieties; rotating crops (see crop rotation); pruning and spacing plants for better air circulation; controlling pests that carry the fungus from plant to plant; avoiding overhead watering and working among wet plants; and, where needed, applying fungicides or antibiotics. Maintaining sanitary conditions is the most important measure for stopping the spread of the infestation. Seealso chestnut blight.

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Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. It is simply a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this symptom are called blights. Several notable examples are:

On leaf tissue, symptoms of blight are the initial appearance of lesions which rapidly engulf surrounding tissue. However, leaf spot may, in advanced stages, expand to kill entire areas of leaf tissue and thus exhibit blight symptoms!

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