Answer: There are several diseases and conditions that could be affecting your tomatoes; late blight is one of them. Normally when late blight hits it's swift - one day your plants look fine and the next day they start to wilt, and can die almost over night. Late blight is caused by the fungus Phytophthora infestans. The fungus produces huge numbers of spores which may be splashed by rain or overhead watering. Ideal conditions for development of late blight are cool nights and moderately warm days with abundant moisture.
Tomatoes suffering from blossom end rot have dark, sunken areas on the blossom end. This condition is caused by water stress--a dry period followed by heavy rains. To combat this, mulch your plants with a thick (4-6 inch) layer of straw to help conserve soil moisture.
Be sure to rotate your crops--don't grow tomatoes, or any member of the same family like potatoes or eggplant--in the same spot more than once every 3 years.
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