Tomato Greenback and Whitewall
Greenback is a physiological condition where the stalk end of the fruit fails to ripen.
The problem is usually found on greenhouse rather than outdoor tomatoes.
It is seen as distinct green, hard area on the fruit shoulder, visible before ripening.
These areas remain hard and unpalatable as the rest of the fruit ripens.
The cause is usually a result of excessive heat, and or light, or possibly insufficient potassium uptake.
Do not be tempted to over-feed your plants other factors could be the cause of this defficiency.
Excessive use of potassium-rich fertilisers can lead to magnesium deficiency and blossom end rot.
A regular feeding and watering regime should suffice.
Use of tomato feeds as directed by the manufacturer.
Ensure that there is adequate shading and ventilation to reduce light and temperatures in your greenhouse.
Choosing greenback resistant cultivars will help.
Blotches and Whitewall
This is similar to greenback and it is seen where the skin of ripened fruit develops irregular yellow patches, with hard, white patches inside.
Avoiding overuse of nitrogen fertiliser will help prevent these.