It is possible you have 2 problems.
BER problem sounds like BER. Dissolve pellet lime in water then water the plants for quick results. You can buy a $2 bag of cement mix at Home Depot put 1 cup of cement in 5 gallons of water and stir well. Give the plants 1 pint of water every day. BER should be gone in a week.
Squash, cucumbers, bell peppers, and other crops can all have BER.
Leaves falling off the bottom of the plants could be several things. Assuming you have a blight problem. Mix 1 tablespoon of copper sulfate, 1/4 cup of lime or cement, in 2 gallons of water. Spray the plants and give the plants 1 pint of water. The whole USA has suffered from blight for 6 years, blight usually runs its course in 5 to 6 years then it is gone. I have not heard of anyone having blight yet this year.
Leaves turning yellow and falling off can be several things, too much water, not enough water, not enough drainage in the soil water soaked roots, not enough fertilizer, blight.
I have read a dozen reasons why plants have BER, too much rain, not enough rain, uneven rain fall, soil is too cold, roots are water logged, etc. Having lived in MI, IL, TN and AZ I have had BER in all those places. TN has 300 days of rain per year I always planted my tomatoes by April 15 if the garden was not a mud hole swamp. I had tomatoes by July 4th and the soil was plenty warm by then in the 100 degrees summer heat. I had BER in AZ soil is 8ph, all my plants had BER. Cement water fixed the problem in 1 week, not rain since November, no humidity, temperature was in the 80s March 1st did not plant tomatoes until April 1st temperature was I the 90s then. By the time I had tomatoes in AZ temperatures were up to 108 every day, no rain in 9 months, soil was warm as toast, still had BER until I watered plants with cement water.