What’s Wrong With My Tomato Plant? A Quick Diagnostic Guide.
Tomato plants can change quickly. Leaves may curl, flowers may fall, fruit may develop dark patches or an apparently healthy plant may suddenly begin to wilt.
The same symptom can have several possible causes. Yellow leaves, for example, may result from natural ageing, watering problems, nutrient stress, root damage, pests or disease. Accurate diagnosis therefore begins by examining the whole plant rather than reacting to one damaged leaf.
This quick diagnostic guide will help identify whether a tomato problem is most likely to be caused by environmental stress, a physiological disorder, a pest or a disease.
Start by Looking at the Whole Plant
Before removing leaves or applying any treatment, inspect the entire plant and its growing conditions.
Ask:
Is the problem affecting one leaf, one plant or several plants?
Did it appear suddenly or develop gradually?
Are the oldest leaves affected first?
Is the new growth distorted?
Are there spots, rings, holes or trails on the leaves?
Are insects, eggs, webs or droppings visible?
Are flowers falling before fruit forms?
Is the fruit damaged while the foliage remains healthy?
Has the weather recently been unusually hot, cold, wet or windy?
Has the soil dried out or remained saturated?
Was fertiliser recently applied?
Have roots, stems or leaves been physically damaged?
A problem affecting several plants immediately after extreme weather is more likely to be environmental than infectious. A problem beginning on one plant and gradually spreading may indicate a pest or disease, although this is not always the case.
Four Main Types of Tomato Problems
Most tomato problems fall into one of four broad groups.
Environmental Stress
Environmental stress is caused by the plant’s growing conditions.
Common causes include:
Extreme heat
Cold nights
Strong sunlight
Inadequate light
Drought
Waterlogged soil
Irregular watering
Wind damage
Transplant shock
Root restriction
Environmental stress cannot spread from one plant to another, although several plants may show similar symptoms because they have experienced the same conditions.
Physiological Disorders
A physiological disorder occurs when part of the plant or fruit does not develop normally. It is not caused by an infectious organism.
Examples include:
Blossom end rot
Fruit cracking
Sunscald
Uneven ripening
Leaf roll
Nutrient-related growth problems
These disorders are often connected to water availability, temperature, root health, nutrition or rapid changes in growing conditions.
Pest Damage
Pests feed on leaves, stems, roots, flowers or fruit. Some also spread plant diseases.
Signs may include:
Holes or missing leaf tissue
Chewed stems
Distorted new growth
Sticky leaves
Fine webbing
Pale stippling
Tunnels within leaves
Visible insects, larvae or eggs
Droppings near damaged areas
Inspect both sides of the leaves, particularly the tender growth near the top of the plant.
Disease
Tomato diseases may be caused by fungi, fungus-like organisms, bacteria or viruses.
Possible warning signs include:
Spots that enlarge or multiply
Dark lesions on stems
Concentric rings within leaf spots
Water-soaked patches
White or grey fungal growth
Rapidly spreading leaf death
Sudden wilting despite moist soil
Unusual mosaic patterns
Severe distortion of new growth
Some diseases spread through splashing water, contaminated tools, infected plant material, soil, wind or insect vectors.
Tomato Leaves Are Curling
Leaf curl does not automatically mean the plant has a disease.
Leaves Curling Upwards
Upward rolling of otherwise green leaves is often a physiological response to:
High temperatures
Intense sunlight
Dry soil
Irregular watering
Root damage
Heavy pruning
Transplant shock
The lower leaves may roll inwards while remaining firm and green. If the plant continues growing and the new leaves look normal, this is often temporary physiological leaf roll.
Check the soil moisture and recent weather before taking further action. Avoid removing more foliage from a heat-stressed plant because the remaining leaves shade the fruit and support photosynthesis.
Leaves Curling Downwards
Downward curling can be associated with:
Excessive nitrogen
Overwatering
Root stress
Chemical injury
Sap-feeding pests
Certain diseases
Look for unusually dark-green foliage, thick stems, distorted new growth or insects on the undersides of leaves.
Twisted or Severely Distorted New Growth
Distorted growing tips may indicate:
Aphids or other sap-feeding pests
Mite damage
Herbicide exposure
Viral disease
Severe environmental stress
Damage from drifting weedkiller or contaminated organic material can produce narrow, twisted or cupped leaves. The pattern may appear on several plants exposed at the same time.
Tomato Leaves Are Turning Yellow
The position and pattern of yellowing provide important clues.
Lower Leaves Turning Yellow
A small number of older leaves may yellow naturally as the plant grows. Remove them when they are mostly yellow or no longer functioning.
More extensive lower-leaf yellowing may result from:
Overwatering
Prolonged drought
Root restriction
Nutrient shortage
Poor soil drainage
Lack of light within dense foliage
Early stages of disease
Check whether the yellowing is uniform or accompanied by spots and lesions.
Yellow Leaves With Green Veins
Yellow tissue between greener veins may indicate difficulty obtaining or using a nutrient. However, visible symptoms alone do not always reveal which nutrient is responsible.
Possible causes include:
Unsuitable soil pH
Damaged or waterlogged roots
A genuine nutrient shortage
Excess of another nutrient interfering with uptake
Cold soil
Container compost that has become exhausted
Adding more fertiliser without identifying the cause can worsen the imbalance. First check moisture, drainage, root space and the recent feeding history.
Yellow Leaves With Spots
Yellowing accompanied by brown, black or grey spots may indicate a leaf disease, particularly when the spots increase in number or the problem moves upwards through the plant.
Remove badly affected leaves, improve airflow and avoid splashing soil onto the foliage. Examine the shape and pattern of the spots before deciding on further action.
The Whole Plant Is Pale
A uniformly pale plant may be affected by:
Inadequate nitrogen
Restricted or unhealthy roots
Waterlogged soil
Insufficient light
Cold growing conditions
Competition from nearby plants
An unsuitable container
Compare the plant with others of the same variety. Natural leaf colour differs between tomato varieties.
Tomato Leaves Have Brown or Black Areas
Brown leaf tissue is dead tissue, but the cause may be environmental, physical or infectious.
Brown, Dry Leaf Edges
Dry edges may result from:
Drought
Hot, drying winds
Excess fertiliser
Salt build-up in containers
Root damage
Leaf scorch
The damaged tissue will not recover, but healthy new growth may continue once the cause is corrected.
Brown Spots With Rings
Spots containing visible concentric rings can be associated with certain fungal diseases, including early blight.
Look at where the symptoms began. Early blight commonly affects older foliage first and may progress upwards under favourable conditions.
Dark, Water-Soaked Patches
Rapidly expanding dark or water-soaked patches on leaves or stems require prompt attention. They may indicate a serious infection, particularly during periods of mild, humid or wet weather.
Inspect nearby plants and remove clearly infected material carefully. Do not handle healthy plants immediately after touching wet, diseased foliage.
Bleached or Papery Patches
Pale, bleached or papery areas may be sunscorch rather than disease. This can occur when indoor-grown plants are moved into strong direct sunlight without adequate hardening off.
Affected leaves will not become green again, but the plant can recover if enough healthy foliage remains.
Tomato Leaves Have Holes or Missing Sections
Missing leaf tissue normally indicates feeding damage or physical injury.
Possible causes include:
Caterpillars
Beetles
Slugs or snails
Grasshoppers or locusts
Leaf-cutting insects
Hail
Wind damage
Leaves rubbing against supports
Inspect the plant at different times of day. Some pests hide during daylight or drop to the ground when disturbed.
Small holes do not usually threaten an established plant. Extensive defoliation, damage to the growing tip or repeated feeding requires quicker action.
Tomato Leaves Are Sticky or Covered in Black Growth
Sticky deposits are often honeydew produced by sap-feeding insects such as aphids or whiteflies.
A dark surface growth called sooty mould may then develop on the honeydew. The mould is not feeding directly on the tomato plant, but a heavy coating can reduce the light reaching the leaves.
Check the undersides of leaves and tender growing tips for insects. Managing the pest responsible for the honeydew addresses the underlying cause.
Fine Webbing or Pale Speckling Appears on Leaves
Fine webbing combined with many tiny pale dots may indicate spider mites.
Mites often become troublesome during hot, dry conditions. They usually feed on the undersides of leaves and may be difficult to see without close inspection.
Leaves can become bronze, dry and brittle as an infestation develops. Check nearby plants because mites may spread between them.
Trails or Tunnels Appear Inside Leaves
Pale, winding trails within a leaf are usually caused by leaf-mining larvae feeding between its surfaces.
A small amount of leaf-miner damage is mainly cosmetic. Remove badly affected leaves if necessary, but avoid stripping healthy foliage from the plant.
Crushing a larva within the visible tunnel can stop the damage without removing the entire leaf.
The Tomato Plant Is Wilting
Wilting means the leaves and stems have lost their usual firmness. It does not always mean the plant needs water.
Wilting in Dry Soil
A plant wilting in genuinely dry soil probably needs a thorough watering. Apply water slowly enough to reach the full root zone.
Repeated severe wilting can reduce flower and fruit production and increase the likelihood of physiological fruit problems.
Wilting in Moist or Wet Soil
If the soil is already wet, adding more water may make the problem worse.
Possible causes include:
Waterlogged roots
Root rot
Stem or root damage
Vascular disease
Severe heat
A stem-boring pest
During extreme heat, a plant may temporarily wilt because water is leaving the leaves faster than the roots can replace it. If it recovers as temperatures fall and the soil remains adequately moist, heat stress is a likely cause.
One Branch Is Wilting
A single wilting branch may have been:
Cracked
Bent
Damaged by a tight tie
Injured during pruning
Attacked by a stem pest
Affected by a localised infection
Inspect the branch back to the main stem and check for wounds, dark lesions or constriction.
The Whole Plant Suddenly Collapses
Sudden collapse despite suitable soil moisture can indicate serious root, stem or vascular damage. Examine the base of the stem and compare the plant with its neighbours.
A severely affected plant may need to be removed if an infectious wilt disease is suspected.
Tomato Stems Are Purple
Some tomato varieties naturally develop purple colouring, particularly on the stems.
Purple stems or leaf undersides can also be associated with:
Cool temperatures
Temporary difficulty absorbing phosphorus
Strong light
General plant stress
Natural pigmentation
If growth is otherwise healthy, the colour alone is not usually a reason to add fertiliser.
Tomato Stems Have Lumps or Small White Bumps
Small pale bumps on tomato stems are often root initials. Tomatoes can form roots along their stems, particularly in humid conditions or when the plant is under moisture stress.
These bumps are usually harmless. They do not normally require treatment.
Dark, sunken, soft or spreading stem lesions are different and should be investigated as possible injury or disease.
Tomato Flowers Are Falling Off
Flower drop, also called blossom drop, occurs when flowers fail to set fruit and separate from the plant.
Common causes include:
Excessive heat
Cold nights
High humidity
Very dry air
Poor pollen release
Irregular watering
Inadequate light
Excessive nitrogen
Severe plant stress
Tomatoes are self-fertile, but the flowers benefit from movement. Outdoors, wind and insects usually provide this. Under cover, gently tapping the flower trusses or shaking the supports can help release pollen.
When weather is the cause, later flowers often set successfully once conditions improve.
Flowers Develop but No Tomatoes Form
Look closely before assuming pollination has failed. After successful fertilisation, the flower petals fall and a very small green fruit begins to enlarge behind them.
If flowers remain on the plant for a time and then drop without swelling, consider:
Temperature during flowering
Greenhouse ventilation
Humidity
Watering consistency
Light levels
Nitrogen-rich feeding
The overall health of the plant
Adding more fertiliser will not correct poor pollination caused by temperature or humidity.
The Plant Has Lots of Leaves but Few Tomatoes
Large, dark-green plants with thick stems and few flowers may be receiving too much nitrogen.
Other possible causes include:
Inadequate sunlight
Very high temperatures
Poor pollination
Overcrowding
Irregular watering
A late-maturing variety
Excessive shade
Flowers forming too late to produce a crop
Do not respond by removing large quantities of healthy foliage. Leaves are needed to support fruit development and protect tomatoes from intense sunlight.
Correct the growing conditions where possible and assess whether new flower trusses set fruit.
Tomatoes Are Small or Growing Slowly
Fruit size is strongly influenced by variety. Cherry tomatoes are naturally small, while even large-fruited varieties can produce smaller tomatoes under stress.
Possible causes include:
Variety characteristics
Too many fruits for the plant to support
Inadequate light
Heat stress
Irregular watering
Root restriction
Insufficient or imbalanced nutrition
Poor leaf health
Competition between crowded plants
A plant carrying many fruits may produce smaller individual tomatoes. This is not necessarily a problem if the total crop remains good.
Tomatoes Remain Green
Tomatoes need time and suitable temperatures to ripen. Very high temperatures can slow the production of pigments responsible for ripe colour, even when the fruit has reached full size.
Slow ripening may result from:
Extreme heat
Cool conditions
A naturally late variety
Large fruit size
Insufficient light
Dense, overcrowded growth
Heavy fruit load
The normal length of the ripening process
Avoid stripping away large amounts of foliage to expose the fruit. Leaves help feed the tomatoes, and sudden exposure to intense sun can cause sunscald.
Removing a small amount of obstructive foliage may improve airflow, but the plant should retain a healthy canopy.
Tomatoes Have Dark, Sunken Ends
A dark, sunken patch at the blossom end of the fruit is blossom end rot.
The fruit has not received enough calcium while developing, but this does not automatically mean the soil lacks calcium. Irregular moisture, root damage, excessive fertiliser, salinity or restricted roots can interfere with calcium uptake and movement.
The affected part of the fruit will not recover. Improve watering consistency and protect the root zone from rapid drying.
Tomatoes Are Cracking or Splitting
Cracking often occurs when fruit takes up water rapidly after the soil has been dry. The inside of the tomato expands faster than the skin can accommodate.
Contributing factors include:
Heavy rain after drought
Irregular watering
Overripe fruit
Variety susceptibility
Loss of protective foliage
Rapid changes in growing conditions
Harvest fruit promptly and maintain more consistent soil moisture. Cracked tomatoes may still be usable if they are clean and undamaged by decay, but split fruit should be checked carefully.
Tomatoes Have Pale, Bleached Patches
Pale, yellow-white or papery patches on the side of a fruit exposed to strong sunlight are usually sunscald.
It is more likely when:
Too many leaves have been removed
Disease has caused leaf loss
Branches have moved and exposed previously shaded fruit
Temperatures and sunlight are intense
Retain healthy foliage and avoid severe pruning during hot weather. Damaged tissue will not recover.
Tomatoes Are Ripening Unevenly
A tomato may develop yellow, green or hard areas while the rest of the fruit ripens normally.
Possible causes include:
High temperatures
Nutrient imbalance
Variety susceptibility
Root stress
Inadequate healthy foliage
Certain pests or diseases
Examine both the plant and the fruit. Uneven ripening affecting several otherwise healthy plants during extreme heat is more likely to be physiological than infectious.
Tomatoes Have Small Dark Spots
Small spots on fruit can have several causes, including:
Insect feeding
Bacterial infection
Fungal infection
Physical damage
Hail
Abrasion against stems or supports
Look at whether the spots are raised, sunken, soft, firm or surrounded by a pale halo. Check the leaves and stems for related symptoms.
Fruit spots accompanied by spreading leaf lesions are more concerning than isolated marks on otherwise healthy plants.
Fruit Has Holes or Chewed Areas
Holes in tomatoes may be caused by:
Caterpillars
Beetles
Slugs or snails
Birds
Rodents
Other wildlife
Inspect inside damaged fruit for larvae or droppings. Remove badly damaged fruit before it begins to decay or attract additional pests.
A clean cut or peck differs from a soft, spreading lesion caused by disease. Physical wounds can later become infected, so damaged fruit should be monitored or harvested promptly.
When to Remove Affected Leaves
Remove a leaf when it is:
Clearly diseased
Mostly dead
Touching the soil
Badly damaged
Restricting essential airflow
Do not remove every marked or yellowing leaf at once. Excessive defoliation reduces photosynthesis and exposes fruit to sunscald.
Remove only two or three leaves at a time where possible. Use clean tools for thicker leaf stems and avoid working among wet plants when disease is suspected.
When to Remove the Whole Plant
Removing an entire tomato plant may be necessary when:
It has a serious, rapidly spreading infection
It has completely collapsed and cannot recover
The main stem is irreparably damaged
A likely viral disease is causing severe distortion
The plant is acting as a continuing source of infection or pests
The roots and crown have rotted extensively
Do not compost seriously diseased plants unless the composting system reliably reaches conditions capable of destroying the suspected pathogen.
Before Applying Any Treatment
Do not treat a tomato plant until the likely cause has been identified.
Before using a pesticide, fungicide, fertiliser or homemade spray:
Check the soil moisture.
Review recent weather.
Inspect both sides of the leaves.
Look for insects, eggs, webbing and droppings.
Examine stems and fruit.
Compare the plant with nearby tomatoes.
Consider recent feeding, pruning or transplanting.
Decide whether the problem is spreading.
Many tomato problems improve when watering, ventilation, shade, spacing or feeding is corrected. Spraying an environmentally stressed plant will not address the cause and may create additional leaf damage.
A Simple Tomato Diagnostic Checklist
If the leaves are curled but green
Check for heat, drought, irregular watering, root disturbance or heavy pruning.
If lower leaves are yellow
Check natural ageing, moisture, drainage, nutrition and the presence of leaf spots.
If new growth is twisted
Check for sap-feeding pests, mites, herbicide damage and viral symptoms.
If leaves have holes
Look for caterpillars, beetles, slugs, snails or physical damage.
If the plant is wilting
Check the soil before watering. Consider heat, waterlogging, root damage and wilt disease.
If flowers are falling
Check temperature, humidity, watering, light, nitrogen levels and pollen movement.
If the plant is leafy but has little fruit
Check nitrogen, light, heat, pollination and variety maturity.
If fruit has a dark sunken end
Suspect blossom end rot and improve moisture consistency.
If fruit is cracked
Look for rapid water uptake after dry conditions.
If fruit has pale exposed patches
Suspect sunscald and retain more protective foliage.
If spots are spreading across leaves or stems
Investigate a possible infectious disease and act promptly.
Diagnose First and Respond Calmly
A single damaged leaf or imperfect tomato does not necessarily indicate a serious problem. Established plants can tolerate some pest feeding, weather damage and natural loss of older foliage.
Begin with the simplest explanations: recent weather, soil moisture, root conditions and physical damage. Then inspect for pests and signs of infection.
Make one measured change at a time where possible. This makes it easier to see whether the plant responds and avoids creating additional stress through unnecessary watering, feeding, pruning or spraying.
Regular observation remains the most effective diagnostic tool. The earlier a genuine problem is recognised, the more likely it is that the plant and the remaining crop can be protected.
For complete advice on choosing varieties, sowing, planting, supporting and caring for tomato plants, return to How to Grow Tomatoes: Complete Guide.
