Nitrogen: Too much or too little will stress the plant. Always follow the instructions on your fertilizer. Use an organic, slow-release fertilizer and compost instead of quick-release, synthetic fertilizer.
Temperature: Day temperatures above 90 degrees and night temperatures above 70-75 degrees can interfere with pollination and fruit set. Research indicates that the higher night temperature has more of an influence.
Excessive wind, stress from insects or disease, lack of light and excessive pruning are also reasons to explore if you're experiencing blossom drop. Spend some time in your garden and see if you can identify the reason.