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Blight control methods can be preventive or used when blight has been identified on a plant. Preventive steps to blight control include rotating crops, using seed certified to be free of disease, and in some case choosing blight-resistant varieties. Other methods of blight control can be employed after blight has been identified. They usually include using sprays that work against the various forms of blight. In some cases, heavy pruning is necessary and affected plants may need to be destroyed, usually by fire.
There are various forms of blight, specific to certain plants, which are caused by a number of pathogens. All blights cause leaf spots or a change in color, followed by wilting and death of affected parts. Organic gardeners may prefer to remove infected leaves, wait to see if the disease spreads, and then choose a less toxic copper fungicide if blight persists. Otherwise, chemical sprays are available and usually require applications every seven to ten days throughout the season.
Early blight is a potato plant disease, causing brown or black spots on the leaves and damaging the tubers. As early blight usually doesn't kill the plant, harvest may proceed, but affected leaves and tubers should be destroyed after harvest. Late blight affects both potatoes and tomatoes, causing leaf spotting before killing the leaves. Regular spraying should slow the spread of disease. With both blights, harvesting potatoes after the plants die naturally gives underground spores time to be killed by spraying.
Flowering plants are also vulnerable to certain types of blight. For flowers, blight control usually consists of cutting out affected shoots or pieces and destroying them. Flowers affected by blight include clematis, lilacs, and peony plants. Various chemical sprays or organically derived copper fungicides can also be used when blight appears on flowering plants. In places where blight is a recurrent problem, spraying when leaves appear in spring can reduce it.
Regular crop rotation can aid in blight control. For potatoes and tomatoes, which share vulnerability to late blight, it is recommended plants not be planted in the same bed more often than every third year. Buying disease-free seeds and seed potatoes can be helpful if blight is not a regional problem. Plant breeders continue to work at creating blight-resistant varieties of crops, although resistance levels vary for each plant type. Irrigating crops or watering at the base of the plant, rather than overhead, may also prevent or slow the spread of blight.