Sunscald in many vegetables occurs when fruits are exposed to direct sunlight in hot, dry weather. Fruit cracking in melons and tomatoes is most severe when soil moisture fluctuates from dry to wet extremes. Blossom end rot in tomatoes, peppers and watermelon is most severe when soils are too wet or too dry. These conditions slow calcium movement in plants, resulting in the collapse at the end of fruits. Moisture fluctuations also can lead to secondary growths on root and tuber crops such as potatoes.
Excessive heat can affect pollination in most flowering crops, resulting in reduced yields.
High temperatures also may affect crop quality, producing bitter, tough and starchy vegetables, or ones with reduced sugar content. Temperature extremes or fluctuations can induce premature flowering in some crops. High temperatures in lettuce and cold exposure followed by warm conditions in some spring-planted greens and cole crops can bring on bolting. Excessive moisture can lead to other crop problems. When soils are saturated or flooded, plant roots cannot function.