Certified GKH Gardening Expert
This issue is due to a lack of calcium in the blossom end of fruits. It is also more prevalent on the first fruits to ripen. Improve the soil quality around your tomato plants, cut spots off the affected tomato fruits (or simply discard them), and salvage what you can of the crop. To improve the soil and prevent future problems, maintain adequate, consistent soil moisture through proper mulching and watering. This article will also help:
I've been reading much on preventing this problem & am trying things as preventative measures, rather than applying Band-Aids. Baby powder & powdered milk look promising in multiple ways. The talc fights bad bugs (a bit), sugars in the milk feed bad bugs what they can't digest & process, resulting in dead bugs & their moving.
Allegedly, these also fight blossom end tot & kill or drive away aphids. Bonus points there. away