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Tomato Care: Leaves

Tomato seedling There can be many reasons why the leaves of your tomato plants are in poor health or just look strange. This article looks at different causes of poor leaf health by first describing the symptom, then the cause and where relevant possible solutions.

This is the third in the series on tomatoes, the first looked at strategies for healthy tomato plant growth and the second on tomato root health.

Leaves Small compared to normal but colour is okay.

Small leaves are usually due to the same reason as a small thin stem on your tomato plant, so if you have one you will usually have the other.

Common causes for small leaves are:

  • Dry growing conditions due to a low relatve humidity level in the day, this resultsin the plant using its energy and time in transpiring water through the leaves to maintain a suitable leaf temperature. This is then at the expense of the plant using some of the water in maintaining an adequate moisture content which aids cell expansion. So raise the relatve humidity where possible by overhead damping/misting and or adding shading if in a greenhouse.
  • A heavy fruit load compared to leaf area will result in the fruit being a strong sink for the sugars from the leaves. Try to pick lower trusses, raise night temperature if possible to encourage ripening if need be. Often in commercial growing greenhouses they will have only 5 to 6 fruit per truss in winter and say 6-7 in summer. In some areas in the depth of winter, close to the shortest day, it may help to have 4 tomato fruit per truss.
  • Root damage. See tomato root care article for information.
  • Stem Borer in the lower stem just above the soil surface.

Small compared to normal. Colour not okay.

There are various causes for small miscoloured leaves.

  • A stem infection will reduce uptake through the plant and so result in reduced top growth which is often miscoloured.
  • Check for botrytis fungal infection round the stem wounds where deleafing has been done or round lateral wounds.
  • Broken stem. (fatal usually) take a leader if possible from below the wound to replace the leader.
  • Collar rot around the base of the stem just above the pot soil surface. This will usually appear as a soft wet brown area. Causes vary from physical damage from sciarid fly followed by a secondary fungal infection of fusarium or rhizoctinia. Collar rot can also be various other fungi such as pythium, Phytophora or botrytis. Weak tomato seedlings can develop a stem infection if damaged at a young age.
  • Root damage. See tomato care root article for more information.
  • Viral diseases can result in reduced top growth. Thrips transmit a virus called Tomato Spotted Wilt Virus (Bronze Top). There is no cure for this just remove the plants as the symptoms occur.

Large compared to normal. Colour OK.

  • If the plants are very strong and taller than the others of the same variety then it may be a rogue plant (also known as Jacks). These are genetic variants which usually have little or no fruit and big leaves. The leaf colour is darker green and usually hairless. Remove.
  • No fruit set may have resulted in improved vegetative growth so check for setting of the fruit. Bees?
  • Are the other plants just shorter. is a lack of heat or poor irrigation resulting in reduced growth on some plants.

Funny Leaf Colour

Silver appearance

Silver appearance of the individual plants is due to a genetic fault called Silvering. This is a natural chimera and results from the cells producing one row of cells less than normal and the row of cells not there usually contains the chlorophyll (the green pigment in cells). No cure so remove the ofending leaves. The fruit is usually poorer.

Purple colouring

Purpling is typically put down to phosphate deficiency and typically appears in the growing points of the plants, underneath the young leaves (the veins turn purple) and on the young trusses and also around nodes. Some purpling of the nodes is considered to be a good thing but excessive is not so OK.

Phosphate deficiency is brought on by…

  • Low phosphate in the nutrient solution / fertiliser mix . It should be greater than 40ppm in summer and 50 to 70ppm (parts per million) in winter.
  • Cool temperatures in the solution (if using hydroponics) or sooil/pot and the air temperature can lead to reduced phosphate uptake. Hydroponics solution historically have been recommended to be above at least 16 (preferably 18-21 degrees over a 24 hour average). Less than 16 degrees the uptake of phosphate drops off. What is the air temperature. It typically should be greater than 14 at night and greater than 18 in the day all year round.

Yellowing of the leaves

Can be due to a nutrient deficiency which will be part of the next upcoming article

Orange leaves

Main cause is Tomato Russet Mite which causes an orange ‘glaze’ to appear on the stem bases and lower leaves. The lower leaves wilt and the from the inside out as the mites chew the leaves. The fruit go black if infected.

Black leaves.

Causes for black are

  • Sooty mould caused by white fly infection, try to remove the white fly using local recommended treatments.
  • More serious pathogenic infection with the two main ones are bacterial infection from pseudomonas and a couple of other fungi usually due to cold and wet conditions. Such as plant under a drip in winter.

White leaves

  • Severe whitening of the centre of the top leaves is often a very severe case of iron deficiency.
  • White centres and green margins is a typical symptom of glyphosphate (round up) damage.
  • White edges of leaves can be damage from spraying too heavier a concentration or in a the middle of a sunny day.
  • White extreme edges of the compound leaflets can also be due to calcium scorch. This is due to high humidity condition + warm weather causing limited water movement within the plant. The rapidly expanding edges of the new leaves therefore suffer from a lack of calcium so this deficiency symptom occurs. Increasing air movement within the greenhouse by increasing ventilation is required. This is condition usually occurs due to a mix of conditions during a time period and may well stop occurring the next day as the weather improves.
  • White circles can be septoria leaf spot (but this is not so common in NZ)
  • Very small white spots like pepper is the result of two spot mite damage which is more common in dry areas such as Nelson and Blenheim.

Strange leaf shape

  • Strange shaped leaves including half of the leaf (divided down the midrib) being distorted, large bubbles, are often just signs of epinasty which is due to a hormonal imbalance within the plant. Nothing to do about it.
  • Whippy (thin (2-5mm thick) with no actual leaves just thin strands if any) looking top leaves is often due to virus infection (cuumber mosiac virus) which is transmitted by insects usually. Remove the damaged plants.
  • Severe infections of insects can distort leaves including whitefly or thrips.
  • A curled older leaf is due to the age or can be cooler temperatures. Not really known.

Young top leaves.

Yellow between veins, but the veins are green is usually due to manganese or iron deficiency.

In hydroponics often a direct addition of iron or manganese will fix low levels, after a nutrient analysis has been done analysis. High iron or high manganese levels can cause an antagonism between the two; so the high one level of one will suppress the uptake of the other. A direct addition of the low nutrient will alleviate the situation. In media based growing systems or in a garden garden it can just be a sign of general low fertility in the soil so add some fertiliser or mulch for long term root/ soil zone health.

Check root health as root death can limit nutrient uptake hence deficiency symptoms appear.

Heavy fruiting tomato varieties (beef steak) often have yellow tops when first fruit are about to be picked. (plus root death at this time) and this should clear self when first truss or two are picked.

Check pH if above 6.5 -7. Drop below 6 for improved iron uptake.

In hydroponics if a rule of thumb is for the manganese level to gernally be about 10% of the iron total level. So if iron is 10ppm then a manganese of 0.4 to 1ppm is suitable.

General yellow splotches

  • Growth spots due to rapid plant growth in vegetative growth conditions. Should clear in time.
  • Check root health
  • Virus symptoms especially yellow green rings. This will not be so common. Fruit will especially reveal this with concentric rings of pale – white red on the fruit. Growth is also typically stunted and fruit small and stunted in sizing.

Old base leaves

Yellowing between the veins in old leaves can be caused by magnesium deficiency as the plants remove translocatable elements from the old leaves before they are dropped. Usually not a major cause of concern if it is just the lower 2-4 loeaves and these are often just removed with periodic deleafing. If it spreads up the plant then it could be due to low nutrient levels in the media (ie Magnedium) so alterations to the feed / fertiliser is required. The mg level is recommended to be 16% of the total cation concentration. So ([mg+]/ [Mg + Ca + Na + K]) should = 16%.

There is two types of calcium deficiency the second being about at the stage of the 8th truss and will appear as a yellow band through the middle of the crop. This is more severe and can cause some drop in production due to the localised truss not producing very well. In hydroponics the preventative solution is to have a high concentration of magnesium and calcium in the initial feeds and a low level of potassium so that the young plants can absorb calcium and magnesium easily with minimal competition from the potassium. As plants age their ability to absorb magnesium decreases so enabling the plant to store these two nutrients at a young stage is a good idea.

Twisting leaves

Due to cool weather perhaps. No great trouble.

General yellowing.

Usually just due to shading. Causing the leaves to lose green colour or age as plants remove nutrients. Leaves should be deleafed. Keeping leaves, which are too old, can have two effects of altering the taste of the fruit by being an absorber of sugars which should be going to the developing trusses. Also possible reducing the shelf life of the young fruit.

Small translucent bumps under the leaves usually along the veins are a sign of a condition called oedema. This is caused by high humidity conditions so if you have this you will also have calcium scorch. Increase ventilation and general air movement to reduce the relative humidity in the greenhouse. This is usually not a fatal disorder just the plants reaction to unsuitable environmental conditions. Similar to measles in cucumbers which are raised spots on the fruit due to humid conditions, probably preventing transpiration of water through the cell fissures on the fruit skin.

Scorched (brown and dry) at the end of the leaves.

Calcium scorch

Spray damage due to a high damage of sprays on leaf say in hot conditions. Spray when over clouded or in late afternoon.

Interveinal scorching and death.

  • Severe toxicity if some elements can cause this or severe wilting.
  • Small brown necrotic (dead) spots on leaves could be due to water from the overhead sprinkling system landing on the leaves and the meniscus of the water droplet which develops acting like a magnifying glass and so burning the leaf tissue.
  • Necrotic spots can also be fungal with a couple of likely causes
  • Stemiphyllum in cherry tomatoes due to a relative humidity which is too high.
  • Botrytis spots where a dead flower infected with bot spores has landed on a leaf and the rh has been high enough (>90% for greater than 4 hours).
  • Black spots can be due to bacterial infections such as bacterial speck and scorch (pseudomonas… due to cool wet conditions)

Leaf veins funny colour.

  • Purple is due to phosphate deficiency
  • Green veins and yellow between veins (see deficiency page)

Top Leaf Wilting

If there is a sunny day after a period of cloudy humid weather the sudden increase in leaf temperature can cause rapid evaporation of water from the leaves which is greater than the plants ability to supply water. Overhead misting or wetting with a hose can be a quick fix but the plants have a short memory and healthy plants should be adjusted by the next day and so be ‘hardier’.

A fertiliser concentration which is too high for the relative humidity and air temperature will restrict water movement through the leaves into the plant and so cause wilting. Try to lower the nutrient level.

If this is not the case then obviously check for stem damage or root damge reducing water uptake Usually will be botrytis of the stem or a root rot which has traveled up the stem such as pythium. Splitting the base of the plant in half may reveal some vertical staining within the stem up the sap flow which kills the cells hence the blocking. The fungal infection produces toxins which cause the death of the cells in the plant sap cells.

Inner leaflets wilting at the top of the plant.

This is not a good sign and can be due to bacterial canker which is a caused by a nasty bacterial called clavobacter michiganensis. This virus will also affect the fruit also turning them white and streaky and small. This disease when it infects a plant it is very lethal with the plants succumbing to wilt after a short time dependent on season.

In summer with the heat and low relative humidity the life of an infected plant is shorter. Easily transmitted by hand through plant sap on hands infecting wounds such as deleafing and picking. Careful management is required with separate gloves used for infected rows and those plants pruned last to prevent cross contamination with clean rows. There is no spray to cure the plants once infected only copper sprays to harden the plants and so hopefully kill any bacterial spores which are sitting on the outside of the plant surface. Plants are usually removed to limit the spread.