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. Lack of oxygen causes physiological wilting, impaired water and nutrient uptake and, ultimately, root and plant death. Most crops cannot tolerate flooded conditions or high water tables for extended periods without adverse effects. In addition, excessive leaching as a result of heavy rainfall can lead later to nutrient deficiencies in plants, especially nitrogen. With the droughts of recent years, growers have witnessed severe wilting, firing and stunting on many crops.