Sometimes the blooms or blossoms on a tomato plant will dry up and fall off before producing fruit. This is known as blossom drop. It is caused by temperature, not a disease.
Tomatoes plants are sensitive to heat. If the temperature is too cold or hot the blossoms can dry up and fall off. Once they have bloomed and set tomatoes, heat doesn't bother them as much.
Temperatures above 85 degrees in the day, above 70 at night, or below 55 at night can cause blossom drop. The blossoms are more sensitive to heat than the fruit.
Too Much of a Good Thing
Another cause of blossom drop is too many tomatoes. When the plant puts out a lot of blossoms and these are fertilized to become fruit, it can be overwhelming. The plant will let the unneeded blossoms wither.
Choose hybrids over heirloom varieties because hybrids are bred to be hardier. If the description of the tomato states, "heat-set" or "heat tolerant" it will be resistant to the problem.
Even though blossom drop is caused by high temperatures, tomatoes like heat. The hotter it is the more watering is required. For temperatures 90 and above they may need to be watered several hours every day.
- Ohio State University: Blossom end rot
- Alabama Cooperative Extension: Blossom drop in tomatoes
tomato disease, growing tomatos, blossom drop