Blossom end rot. (Remove that tomato now -- no point in wasting the plant's energy on something that will be nasty by the time you can pick it.)

Insufficient calcium is transported to the blossom end of the tomato.

Most commonly caused by uneven water supply.

Is/are the plant(s) in the ground or containers.

What output is each dripper?

How many per plant?

And how long do you run the system?

Even though the soil (or potting mix) may be adequately moist, a heat wave can remove water from the plant faster than the roots can absorb it.

Jean,

who gardened in Long Beach, CA, for 30-some years.

Thanks for your response Jean. the plants are in a raised bed. The drip irrigation is via a 1/4" emitter line with flow rate of .65 GPH every 9 inches. http://www.homedepot.com/p/DIG-Raised-Bed-Garden-Drip-Irrigation-Kit-ML50/202614215

Some of the sprinklers also end up watering the raised bed. It runs for about 10 minutes every other night.

I also noticed many of the flowers dry up and fall off. I haven't gotten many fruits on the plants.

In order to know if adequate water is in the soil, probe with a finger or a trowel about an hour after you irrigate.

Howlongdo you unthe rip.

Frankly, I've had drip inmy raised beds too.

But I find that the loose texture of the planting mix allows the water to go straight down rather than to also spread sideways.

So I now use soaker hose, 4 runs in a 4-foot wide bed. Only enough pressure to sweat, not spray. Runtime will vary according to your growing mix.

I am in NJ zone 6B and if I start my tomatoes too early and they are under stress when they are first transplanted (lots of wind, too cold weather) mine get BER. Its not a calcium or watering issue for me.

Cold temps can be an issue or contribute, as the cold can seriously decrease transpiration, which means less circulation of water in the plant, which is the mechanism that transports nutrients, including calcium. Too much heat and not enough water can also cause a problem, since transpiration through the leaves increases dramatically but transport into the fruit remains low, and all the nutrients including calcium can end up there instead of going to the fruit. So BER from temperature extremes is both a calcium issue and a water issue but not due to anything you're doing or can do much about.

I also suspect that cold temps also coincide with less developed root systems, since cold temps coincide with earliness of the season in NJ, so that's probably a factor as well, since a smaller root system is less able to cope with water fluctuations.