Ed Stuart said:

Hi,

Currrently, one third of my tomatoes are red but they have an
unripened green circle three quarters of an inch around the stem.
I've never seen this before. Why is this and should I pick them now?

Green shoulders is a cosmetic problem in tomatoes. These areas may
turn yellow but will never fully ripen before the rest of the tomato gets
over-ripe and rots.

This sort of uneven ripening is more common in older varieties than
modern hybrids. It's often associated with high temperature in the fruit
and especially likely to happen in sun-struck fruit. Maintaining a good
foliage cover will help to limit the problem.

--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)