Tomatoes: leaf problems

Although easy to grow and very rewarding, tomatoes can suffer from a range of easily preventable leaf problems.

Magnesium deficiency shown by the tomato leaves. Credit:RHS/Tim Sandall.

Quick facts

Plants affected Tomatoes
Main causes Imbalances of temperature or nutrient deficiencies
Timing Summer

What is the problem?

Inappropriate levels of water, light, temperature and nutrients can all cause problems with leaves in tomatoes. These are physiological disorders - problems that are caused by the growing conditions rather than by pests or diseases.

Some pests and diseases can also cause leaf problems in tomatoes.

Links

Tomato viruses
Potato and tomato blight
Aphids

Symptoms and causes

  • Curling leaves: This is usually caused by variable temperatures at night or aphid attack.
  • Twisted and distorted leaves, often with a much reduced leaf area: This is often caused by hormone weedkiller contamination, but other cases may be caused by tomato viruses. See our advice in tomato viruses for further information. Mild cases may be caused by variable light and temperature conditions.
  • Mottling of older leaves: This is often caused by a lack of nutrients, usually magnesium deficiency. When present only in the older leaves, there is no cause for concern.
  • Lumps and nodules appear on the foliage: This occurs when the plant contains more water than it can use, resulting in swollen water-filled areas on the leaves. This is called oedema and results from excess atmospheric humidity and/or too much moisture at the roots. Adjust watering and humidity accordingly to remedy the problem.

Biology

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 of tomatoes for temperature, nutrients and light levels. Outdoors, the plant is equally vulnerable to lack of warmth and variable temperatures.

Tomatoes need warmth and will not thrive at temperatures of below 12°C (54°F). Although it is easy in summer to keep temperatures raised in glasshouses, outdoor tomatoes may still require fleece or other additional protection.

In early summer, the nights can be cold and the days very warm. This fluctuation of temperatures is the main cause of what can sometimes be a very alarming degree of leaf curling. The plant is unable to cope with the accumulation of carbohydrates that occurs if nights are too cold for plant physiological functions to occur normally. Fortunately this does not seem to be a serious cause of loss of crop and usually disappears of its own accord as the nights begin to get warmer in late summer.

Small greenhouses and polythene tunnels used by home growers are much more liable to fluctuating conditions than larger greenhouses.

Mottling and discolouration of older leaves usually indicates a deficiency of nutrients, especially magnesium, and is a less serious problem providing the plant is otherwise vigorous.

Tomatoes are particularly sensitive to hormone weedkillers. Even the vapour emitted from loosely-capped bottles, or bags of lawn ‘feed and weed’, is sufficient to cause damage, especially under hot conditions. If this problem is suspected, remove all sources from the vicinity and if hormone weedkillers were the cause, the plants will produce new, normal growth. If symptoms persist the problem is probably caused by virus. These two possible causes of distorted foliage are otherwise very difficult to distinguish without specialised tests for viruses.

Links

Weedkiller in manure
Weedkiller damage
Nutrient deficiencies

Control

Non-chemical control

Control temperature and sunlight levels carefully to avoid extremes, using combinations of heating, ventilation and white greenhouse paint as appropriate. A maximum-minimum thermometer is a very useful tool in managing temperature levels in greenhouses.

Avoid erratic watering and if plants do become too dry, do not flood them, but bring the soil moisture level back up again gradually. If oedema occurs, do not remove the damaged leaves, as they are needed to shed surplus moisture.

Do not store hormone weedkillers or lawn ‘weed and feed’ products in the greenhouse. Avoid bringing tomatoes into contact with lawn clippings (e.g. in garden compost) if the lawn has recently been treated.

Chemical control

Pesticides are not required to treat physiological problems as no pest or disease is involved. There is therefore no chemical control.

Advertise here

We love free entry to our local RHS garden

Lucy, mum, part-time lectureer & RHS member

Become a member

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.

  • Diane64 avatar

    By Diane64 on 24/05/2014

    The leaves on the top of my Tomato plants "Curl" Downwards, not "UP" as is described in symptoms of "Leaf curling" disease. Also the leaves are a healthy shade of green, not yellow. I cannot find this description any where online. Do you think they have the "Leaf Curling Virus" or something else? I'm growing them in pots and in need of transplanting them to larger pots. Should I prune off the "curly tops"? I came upon a 2003 research article from the USDA about "Helping Plants Defend Themselves" against fungus, virus and bacterial infections by spraying them with a 1:10000 solution of aspirin and water. Have you ever heard of this or know of any updated research done? I wish I could upload my photo to attach to this post. Any advice as to a cure or treatment would be greatly appreciated. Thanks, from the deserts of Las Vegas, NV, USA.

    0 replies

    Report
  • Diane64 avatar

    By Diane64 on 24/05/2014

    Forgot to include an important fact about the "Helping Plants Defend Themselves" article. The Salicylic Acid, (aspirin), induces the plant to trigger "Systemic Acquired Resistance" or SAR for short. Fantastic !!!!

    0 replies

    Report
  • Diane64 avatar

    By Diane64 on 24/05/2014

    Forgot to include an important fact about the "Helping Plants Defend Themselves" article. The Salicylic Acid, (aspirin), induces the plant to trigger "Systemic Acquired Resistance" or SAR for short. Fantastic !!!!

    0 replies

    Report