Brooke Edmunds, a horticulturist with the Oregon State University Extension Service, troubleshoots the following common problems that might be afflicting tomatoes.
Blossom drop – It's usually caused by dry soil and dry winds, but also may be caused by a sudden cold spell, heavy rain or too much nitrogen. Usually not all blossoms will fall off, so be patient for the next set of flowers.
Blossom-end rot – The end of the fruit farthest away from the stem turns brown or black – a condition caused by irregular watering practices and calcium deficiency. It is most common in western Oregon. Water deeply and regularly. Add lime to the soil in the fall to increase the calcium level for next year’s crop.
Leaf roll – A physiological problem that is most often the result of heavy pruning or root injury. Some tomato cultivars display leaf rolling as a normal growth habit. Plants may lose leaves but will recover. Learn more in this guide on leaf roll from OSU Extension's online catalog.
Sunscald – Green tomatoes can get sunburned if exposed. There is no cure, only prevention by reducing foliage diseases that can cause leaf loss. Take care when pruning to protect the developing fruit.
Early and late blight – These are fungal diseases, characterized by spots on lower leaves and stems that appear water-soaked. Avoid overhead watering, and remove diseased leaves.
– Temperatures above 85 degrees can slow the ripening of tomatoes, which ripen quickest at 70 degrees to 75 degrees. Wait for cooler weather to allow for vine-ripening to occur. Fruit just showing color changes can be picked and stored at room temperature to ripen.