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Although easy to grow and very rewarding, tomatoes can suffer from a range of easily preventable problems at the time of ripening.
Blossom end rot of tomato fruit. Credit:RHS/Pathology.
Tomato fruits are in competition with each other, the leaves and stems for water and nutrients at ripening time. Too much or too little warmth and light, as well as variable water and nutrient supplies, can all lead to disappointing ripening and fruit quality.
These problems are usually seen on greenhouse-grown tomatoes, rather than those grown outdoors.
Tomatoes are particularly prone to what are known as physiological disorders: abnormal growth caused by non-infectious factors. This is partly due to the difficulty of controlling the sensitive requirements for temperature, nutrients and light.
Greenback and the internal white or yellowish discolouration (sometimes called ‘whitewall’) are problems caused by excess light and temperature and insufficient potassium fertiliser during fruit development and ripening. They are usually found on greenhouse rather than outdoor tomatoes.
Pale patches that fail to ripen can also be caused by variable water and nutrient levels.
To a large extent tomatoes can balance their nutrition and other physiological factors, but the practice of de-leafing can upset this balance and make tomatoes more prone to fruit ripening problems. De-leafing makes fruits easier to see and harvest and helps to reduce disease levels, but it should be kept to a minimum and be carried out no higher than the lowest truss of ripening fruits.
Control temperature and sunlight levels carefully to avoid extremes, using combinations of heating, ventilation, shade netting and white greenhouse paint as appropriate.
Choosing greenback-resistant cultivars will help avoid greenback and whitewall. Seed catalogues should list current greenback-resistant cultivars. Examples include ‘Alicante’, ‘Shirley’ and ‘Craigella’.
Avoid erratic watering and if plants with ripening fruit do become too dry, do not flood them, but bring the soil moisture level back up again gradually.
Feed tomatoes regularly to maintain high soil fertility. Special tomato fertilisers have high levels of potassium to encourage good fruit development. Adequate potassium nutrition is required to reduce greenback and whitewall, but excessive use of potassium-rich fertilisers can lead to magnesium deficiency and blossom end rot. Use of tomato feeds as directed by the manufacturer should avoid over or under supply of potassium.
Pesticides are not required to treat physiological problems as no pest or disease is involved. Therefore there is no chemical control.
Tomatoes: leaf problemsTomatoes: fruit splitting and crackingTomatoes: stem problemsPotato and tomato blightBlossom end rotTomatoes
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