What is Blight?

Blight is a general term for a symptom of plant disease characterized by a yellowing and browning of plant tissue and a subsequent drying up of tissue without rotting. The term can denote the symptoms of a specific disease such as late blight of potato, early blight of tomato, or fire-blight; more commonly, however, the term is used for any unattractive condition of plants, irrespective of cause.

Generally, leaves are the most severely affected in blight diseases. In some cases the blight may be localized or confined to leaf spots; however, these spots may be so numerous that the overall appearance becomes unsightly. Blights are not restricted to leaves but can affect flower parts, stems, and leaf stalks as well.

Blight diseases result mainly from pathogenic causes, such as fungi and bacteria, but can also occur from physiogenic causes, such as drought or other unfavorable environments. Pathogenic-caused blights commonly occur during cool, moist weather, and frequently fungi can be observed growing on the affected plant parts. Blights may be serious problems in greenhouses if the causal organism is present and the proper environment exists for disease development.

Treatments for blights depend on their causes. Physiogenic-caused blights may disappear when the environment again becomes favorable for plant growth. Fungal-caused blight diseases have been controlled commonly with copper-containing fungicides. Since the 1940's, the organic dithiocarbamate fungicides have become important materials for blight control. Antibiotics are used for the control of some bacterial-caused blights. Protectant sprays are required for many food crops as safeguards against blights.

Sanitation is important in reducing the occurrence of many blight diseases. For example, the late blight fungus can survive from season to season on discarded potatoes. One control measure is to remove the cull piles from the vicinity of the potato fields. Varieties of crop plants with greater blight resistance have been developed as a means of blight control.

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