Malformed fruit is more likely to appear early in the harvest. This malady, which produces fruit with dark, sunken and leathery bottom ends, is caused by calcium deficiency during pollination. Ferretti recommends proper liming, not cultivating around plant roots and taking care not to over-fertilize. Too little or too much moisture also can upset calcium nutrition, so be sure to mulch and irrigate properly. Good color fails to develop if temperatures are too high or too low during ripening.
Higher temperatures speed up ripening, but the final color is more orange than red.
Ferretti says tomato color will be affected if summer temperatures rise above 85 degrees F or below 50 degrees F for prolonged periods. Affected areas of tomatoes with these disorders have poor flavor and off-color. Because these problems can be caused by viruses, nutrition, light intensity, moisture and variety characteristics, no one solution exists. It appears as yellow or white patches on the exposed section of the fruit. It is common during rainy periods when temperature and humidity is high.