Don Phillips wrote in message ...
[...]
With the exception of the mildew year we have always had an excellent
crop and this year has been no exception, but there is a worry. Many
of the tomatoes have yellow tops around the area where the tomato is
connected to the calyx. [...]

Sounds like greenback to me: it isn't always green! Exceptional
amounts of sunshine can cause it, I believe; and maybe they aren't
getting enough potassium if you've only fed them twice -- they've used
up the nutrients in the growbags by now.

I've heard of a variety which is very prone to greenback, whatever you
do, but the red parts of whose fruits are so good that it's worth the
trouble of cutting the green bit off each one: needless to say, I
haven't a clue which variety it is! Anyhow, the fruits can do you no
harm that I've ever heard of.

Mike.