BER is almost entirely a water availability issue; the quality of the water is rarely a factor. If the roots can't take up enough water, then the plant can't push the necessary water-soluble nutrients to the ends of the fruit, and it's only the calcium whose absence has that sort of devastating effect. Studies have shown that calcium levels even in the plant stems are normal in BER cases.

If your soil is alkaline, the calcium is there and available, so focus on root health... you say that soil moisture isn't a problem, but don't mention how much or how often the plants are watered. Frequent shallow waterings can lead to BER, which not many people realize, as can sudden shifts in daytime temperature even if you have a deep, even watering schedule.

Bottom line, shallow or stressed root systems are the problem, as actual calcium deficiency is rare outside of hydroponics and very unlikely in alkaline desert soil. Make sure you're watering deeply every few days and monitor the soil moisture three or four inches down to check that it's evenly moist.

--Alison

Watering is not an issue as I use drip and try to deep water as infrequently as possible. It is 90-100 degrees and less than 15% humidity the first two months the plants are in with near zero rain fall so I do water more than people in most of the country. Usually every 3 days when it is very hot and dry. In July I water no more than once a week when the rain starts if at all. We get clouds every afternoon but only 1-1.5 inches of rain per week.

I do have nematodes but plants with good healthy roots seem to have the same problem with BER. The health of all plants in the garden get much better once the rain starts in July. Could sunlight stress be making it worse?

I was hoping that somehow the calcium was just unavailable because of alkalinity. There is so much in tap water that small pipe leaks seal themselves.