Tomato Leaf Problems
In many cases leaf problems are physiological rather than pest and disease problems.
Many of these can be avoided by means of proper, feeding, watering, light, ventilation and temperature control.
Other causes could be blight, aphids and or viruses which are discussed elsewhere on the website.
A few of the more common cases are as follows;
Tomato cultivars often curl up their leaves in a response to cool night temperatures.
This is perfectly natural and in itself, is not a problem.
This can be an indication that night temperatures are falling too low, so supplementary overnight heating should be considered.
On occasions leaf curl can be caused by an aphid infestation which will be seen by inspecting both surfaces of the leave/s.
Treat this problem with normal aphid control.
Leaves may become twisted / and distorted due to contamination by hormone-based weed killers, such as lawn herbicides.
Avoid this situation by keeping a separate watering can for herbicide application, not spraying on windy days, and not composting the first grass clippings after lawn herbicide application (particularly if you are using your own compost).
Similarly do not mulch with treated grass clippings.
Mottled old leaves:
This is often caused by a lack of nutrients, if it is only present on older leaves, then there is no cause for concern.
However it can be a lack of magnesium! (see below)
Lumps and nodules appearing on foliage occurs when the plant contains more water than it can use, resulting in swollen water-filled areas on the leaves.
This is called oedema!
It is caused by excessive atmospheric humidity and/or too much moisture at the roots.
Control this by adjusting watering and humidity.
Magnesium deficiency seen as yellowing between the leaf veins, and is often more noticeable on the lower leaves.
It is most likely to occur in tomatoes grown on sandy or acid soils, or where high-potassium feeds have been over-applied.
In severe cases premature defoliation can occur, but mild cases are unlikely to affect yield or quality.
Control this problem by applying fortnightly foliar sprays of 50g Epsom salts mixed with 5 litres (1gall) of water.
If the leaves become both mottled and distorted they should be removed as these may indicate viral infection.