Q How do I know my tomatoes have greenback?

A  As greenhouse tomatoes ripen, a ring of unripened greenish flesh appears around the
stalk end of the fruit. The rest of the fruit ripens as usual and the plant itself looks normal. Greenback is a genetically controlled problem that tends to be more common when conditions
are very hot and bright in the greenhouse. Low levels of potassium and phosphorous may also exacerbate the symptoms. 

Caption: Greenback is more common when the weather is sunny and hot

Q How can I help tomato plants with greenback?

A The ripe part of affected fruits can still be eaten. Improving the growing conditions should soon
reduce the problem.

Q How can I prevent greenback on tomatoes?

A Add shading and avoid removing too many of the leaves, as these also provide vital shade.
Ensure good ventilation and keep roof vents open to reduce the risk of damaging high temperatures. Most modern F1 hybrids are less prone to greenback, but 'Cristal' and 'Cossack'
are particularly resistant.