Tomato Diseases: How to Recognise Blight, Leaf Spot and Other Infections
Tomato diseases can affect leaves, stems, roots and fruit. Some develop gradually, while others can spread through a planting in only a few days when weather conditions are favourable.
Not every marked or yellow leaf is diseased. Heat, irregular watering, nutrient stress, sunscorch, chemical injury and natural ageing can produce similar symptoms.
Accurate diagnosis begins with the pattern of damage, the parts of the plant affected and the conditions in which the problem developed.
Disease or Environmental Stress?
Environmental stress often appears after an identifiable event such as:
Extreme heat
Cold weather
Drought
Waterlogging
Strong wind
Hail
Transplanting
Fertiliser application
Spray exposure
Heavy pruning
Several plants may develop similar symptoms at the same time because they experienced the same conditions.
Disease becomes more likely when:
Spots increase in number
Lesions continue expanding
Symptoms move from lower to upper leaves
Dark marks develop on stems
Fruit develops related lesions
One plant becomes affected before its neighbours
Leaves die rapidly during wet or humid weather
The plant wilts despite suitable soil moisture
Symptoms continue worsening after environmental conditions improve
More than one problem can occur at once. A heat-stressed or waterlogged plant may also become more vulnerable to infection.
How Tomato Diseases Spread
Different pathogens spread in different ways.
Possible routes include:
Rain splashing contaminated soil onto lower leaves
Water moving between plants
Wind-blown spores
Infected seed or young plants
Contaminated hands and tools
Diseased plant debris
Insects carrying viruses
Infected weeds or volunteer tomatoes
Soil-borne pathogens entering roots
Reusing contaminated pots or supports
Warmth and moisture favour many leaf-spot diseases, while late blight often develops rapidly during cooler, wet conditions.
Early Blight
Early blight is a common tomato disease caused by species within the genus Alternaria.
Despite its name, it does not necessarily appear early in the season. It often becomes more noticeable as plants begin carrying fruit or experience stress.
Early Blight Symptoms
Look for:
Brown spots on older, lower leaves
Concentric rings within the spots
A target-like appearance
Yellowing around the lesions
Spots enlarging and joining together
Lower leaves dying and falling
Dark, sunken stem lesions
Dark fruit lesions, often near the stalk
The disease commonly begins on lower foliage and progresses upwards.
A plant that loses a large proportion of its leaves may produce smaller fruit and become more vulnerable to sunscald.
Managing Early Blight
Take the following steps:
Remove badly affected lower leaves
Keep diseased foliage away from healthy plants
Avoid touching plants while they are wet
Water at soil level
Mulch to reduce soil splash
Improve spacing and airflow
Support plants so foliage remains off the ground
Remove infected crop debris at the end of the season
Rotate tomatoes and related crops where practical
Do not strip the plant of all marked foliage at once. Retain as much healthy leaf area as possible.
Where early blight is repeatedly severe, resistant or tolerant varieties may reduce losses, although resistance is not always complete.
Septoria Leaf Spot
Septoria leaf spot is another common fungal disease. It primarily affects tomato foliage rather than the fruit.
Septoria Leaf Spot Symptoms
Typical symptoms include:
Numerous small, round leaf spots
Pale, grey or tan centres
Darker brown borders
Tiny black dots within mature spots
Yellowing around heavily affected areas
Symptoms beginning on lower leaves
Progressive loss of foliage
The tiny black dots are fruiting structures produced by the fungus, although they may require close inspection to see.
Septoria spots are generally smaller and more numerous than early blight lesions. They usually do not contain the same obvious concentric rings.
Managing Septoria Leaf Spot
Management includes:
Removing badly affected leaves
Watering at the base
Reducing soil splash
Mulching
Improving airflow
Avoiding overcrowding
Removing infected debris
Cleaning reusable supports and tools
Rotating susceptible crops where practical
Because Septoria can cause extensive leaf loss, early recognition is important.
Late Blight
Late blight is caused by the fungus-like organism Phytophthora infestans. It affects tomatoes and potatoes and can destroy plants rapidly under favourable conditions.
This disease requires prompt attention.
Conditions Favouring Late Blight
Late blight is associated particularly with:
Cool or mild weather
High humidity
Frequent rain
Prolonged leaf wetness
Poor airflow
Infected tomato or potato material nearby
Disease development may slow during hot, dry weather, but infected tissue does not recover.
Late Blight Symptoms
Look for:
Irregular, water-soaked areas on leaves
Grey-green patches becoming brown or black
Rapidly expanding lesions
Darkened leaf stalks
Brown or black stem lesions
Leaves and stems shrivelling
White growth around lesions in humid conditions
Firm, brown or olive-coloured fruit lesions
Rapid collapse of large parts of the plant
Symptoms can progress far more quickly than early blight or Septoria leaf spot.
What to Do About Late Blight
If late blight is strongly suspected:
Inspect all tomato and potato plants.
Avoid handling healthy plants after touching affected foliage.
Remove heavily infected plants promptly.
Contain infected material while moving it through the garden.
Do not leave infected plants exposed nearby.
Clean tools, footwear and reusable equipment.
Follow local guidance for disposing of infected material.
Monitor surrounding crops closely.
Do not place suspected late-blight material into a composting system that may not destroy the pathogen.
Because several problems can resemble late blight, seek local diagnostic advice where possible if identification is uncertain.
Early Blight or Late Blight?
The names can be confusing.
Early Blight
Usually:
Begins on older, lower leaves
Produces brown spots with concentric rings
Progresses more gradually
Is favoured by warmth and moisture
Causes progressive defoliation
Late Blight
Usually:
Produces irregular, water-soaked lesions
Affects leaves, stems and fruit
Can spread extremely rapidly
Is strongly associated with wet, humid conditions
May produce white growth around lesions
Can collapse entire plants
Do not rely on the time of year alone. “Early” and “late” are disease names, not reliable descriptions of when symptoms must appear.
Bacterial Spot and Bacterial Speck
Bacterial spot and bacterial speck can affect leaves, stems and fruit. Their leaf symptoms may be difficult to distinguish without close examination or laboratory testing.
Leaf Symptoms
Possible signs include:
Small, dark leaf spots
Yellow halos around spots
Spots joining into larger dead areas
Damaged leaf margins
Progressive yellowing and leaf loss
Fruit Symptoms
Bacterial speck tends to produce very small, dark, slightly raised spots on the fruit.
Bacterial spot usually creates larger, rough or corky lesions. These may become sunken as the fruit grows.
Warm, wet weather and splashing water can encourage bacterial spot. Bacterial speck may be more active in somewhat cooler conditions, although symptoms and conditions overlap.
Managing Bacterial Spot and Speck
Useful measures include:
Starting with healthy seed and plants
Removing affected plant material
Avoiding overhead watering
Keeping foliage dry where possible
Improving airflow
Avoiding handling wet plants
Cleaning tools and supports
Controlling volunteer tomatoes and related weeds
Rotating crops
Not saving seed from infected plants
Bacterial diseases cannot be corrected with fertiliser.
Bacterial Canker
Bacterial canker can affect the plant’s water-conducting tissues as well as its leaves, stems and fruit.
Bacterial Canker Symptoms
Possible signs include:
Wilting of individual leaves or branches
Browning along leaf edges
One-sided plant decline
Light-coloured streaks on stems
Stem cracking or cankers
Vascular browning inside stems
Small pale fruit spots with darker centres
General plant collapse
The distinctive fruit marks are sometimes described as bird’s-eye spots.
Symptoms vary, and laboratory diagnosis may be needed.
Managing Bacterial Canker
Heavily affected plants should normally be removed.
Also:
Avoid saving seed from affected plants
Clean tools between plants
Avoid working among wet foliage
Remove infected debris
Clean pots, stakes and greenhouse equipment
Use healthy transplants
Rotate away from tomatoes and related crops where practical
Fusarium Wilt
Fusarium wilt is a soil-borne fungal disease that enters through the roots and interferes with water movement through the plant.
Fusarium Wilt Symptoms
Look for:
Yellowing beginning on lower leaves
Wilting during the day
Temporary early recovery at night
Symptoms affecting one side of a leaf or plant
Progressive permanent wilting
Brown discolouration inside the lower stem
The soil may contain adequate moisture, but the plant cannot move water normally through its infected tissues.
Managing Fusarium Wilt
There is no treatment that removes Fusarium from an infected plant.
Management includes:
Removing affected plants
Choosing resistant varieties
Avoiding movement of contaminated soil
Cleaning tools and equipment
Improving general root health
Rotating crops, while recognising that the pathogen may persist for years
Resistance codes on tomato seed packets or plant labels may indicate protection against particular Fusarium races.
Verticillium Wilt
Verticillium wilt is another soil-borne fungal disease that affects the plant’s vascular system.
Verticillium Wilt Symptoms
Possible signs include:
Yellowing of lower leaves
V-shaped yellow or brown areas
Wilting, sometimes affecting one side first
Gradual decline
Brown discolouration inside the lower stem
Reduced growth and yield
Verticillium symptoms can resemble Fusarium wilt, root damage or water stress.
Managing Verticillium Wilt
Remove seriously affected plants and avoid moving contaminated soil.
Resistant varieties can be helpful where Verticillium is known to be present. Rotation may reduce disease pressure but may not eliminate a long-lived soil-borne pathogen.
Southern Blight and Other Crown Rots
In warm conditions, certain soil-borne diseases can attack the stem at soil level.
Possible symptoms include:
Sudden wilting
Dark or rotting tissue at the stem base
White fungal growth around the crown
Small round fungal structures near the soil
Rapid plant collapse
Remove badly affected plants with the surrounding infected material and follow locally appropriate disposal guidance.
Avoid allowing mulch to remain tightly packed and constantly wet against tomato stems.
Root and Crown Rot
Tomato roots can decay when drainage is poor or when soil-borne pathogens attack weakened plants.
Possible signs include:
Wilting despite wet soil
Yellow leaves
Slow growth
Darkened roots
Soft or decaying stem tissue at soil level
Plant collapse
An unpleasant smell from saturated container compost
Improving drainage can prevent further root stress, but badly rotted roots will not recover fully.
Do not keep adding water to a wilted plant without checking the soil.
Grey Mould
Grey mould, caused by Botrytis, is favoured by humid conditions and dying plant tissue.
Grey Mould Symptoms
Look for:
Grey-brown fuzzy growth
Dead flowers becoming mouldy
Soft stem lesions
Leaf spots spreading from damaged tissue
Fruit decay
Infection beginning at wounds or old flower parts
Covered tomatoes are particularly vulnerable when ventilation is poor and humidity remains high.
Managing Grey Mould
Remove infected tissue promptly
Improve ventilation
Reduce prolonged humidity
Avoid wetting foliage unnecessarily
Remove dead flowers and damaged material
Space plants adequately
Avoid injuring stems during pruning
Contain mouldy material while removing it so spores are not scattered through the growing area.
Powdery Mildew
Powdery mildew on tomatoes appears as pale or white powdery patches on leaves.
Affected foliage may:
Develop white surface growth
Turn yellow
Become brown and dry
Curl
Die prematurely
Unlike many fungal diseases, powdery mildew does not require water sitting on the leaf surface to develop, although humidity and poor airflow can favour it.
Improve airflow, remove badly affected leaves and avoid overcrowding.
Anthracnose Fruit Rot
Anthracnose commonly affects ripe or overripe tomatoes.
Anthracnose Symptoms
Look for:
Small, round, sunken fruit spots
Lesions enlarging as fruit ripens
Dark structures developing within the spots
Softening and secondary decay
Fruit may have been infected while green but show obvious symptoms only as it ripens.
Reducing Anthracnose
Harvest ripe fruit promptly
Avoid allowing fruit to rest on the soil
Water at the base
Mulch against soil splash
Remove infected fruit
Rotate crops
Clean up affected plant material
Do not store diseased fruit with healthy tomatoes.
Buckeye Rot and Soil-Contact Fruit Rots
Fruit touching or hanging close to wet soil may develop large brown lesions.
Buckeye rot can produce broad, smooth lesions with visible rings. It is favoured by warm, wet soil and splashing water.
Reduce the risk by:
Supporting plants and fruit
Applying mulch
Improving drainage
Avoiding overhead watering
Removing affected fruit
Preventing fruit from resting on wet ground
Viral Diseases
Several viruses can infect tomatoes, including mosaic viruses and tomato spotted wilt virus.
Different viruses can produce similar symptoms, and visual diagnosis alone may not identify the particular virus.
Possible Viral Symptoms
Look for combinations of:
Light and dark green mottling
Yellow mosaic patterns
Distorted leaves
Narrow or thread-like foliage
Curling
Stunted growth
Shortened spaces between leaves
Rings or unusual patterns on fruit
Uneven ripening
Reduced fruit number and size
One plant remaining stunted while its neighbours grow normally
Heat, herbicide injury, mites and nutrient stress can mimic some viral symptoms.
Can a Tomato Virus Be Treated?
There is no treatment that removes a virus from an infected plant.
Where a virus is strongly suspected:
Remove severely affected plants
Control relevant insect vectors
Clean tools and hands
Remove nearby host weeds
Do not propagate from affected plants
Use healthy seed and transplants
Seek laboratory confirmation where necessary
Do not automatically remove a plant for one curled leaf. Look for persistent distortion, mottling, stunting and abnormal new growth.
Herbicide Damage or Disease?
Tomatoes are sensitive to certain weedkillers. Exposure can occur through spray drift or contaminated manure, compost, straw and grass clippings.
Herbicide injury may cause:
Twisted growing tips
Cupped leaves
Narrow, strap-like foliage
Thickened veins
Abnormal stem growth
Damage concentrated on one side
Similar distortion in several broad-leaved plants
Disease may be more likely when symptoms spread gradually from plant to plant or include characteristic spots and lesions.
Severe herbicide injury can resemble viral disease. Laboratory testing or knowledgeable local diagnosis may be required.
Nutrient Problem or Disease?
Nutrient stress tends to produce a more consistent pattern across leaves of a similar age.
Disease more often causes:
Irregular spots
Expanding lesions
Dead tissue
Water-soaked areas
Stem damage
Progressive spread
Symptoms affecting individual plants before others
However, root disease may create general yellowing that resembles a nutrient shortage.
Before feeding, check:
Soil moisture
Drainage
Root condition
Soil pH
Recent fertiliser use
Whether the symptoms include distinct lesions
Adding fertiliser cannot cure an infection and may further stress damaged roots.
Should Diseased Leaves Be Removed?
Remove leaves that are:
Clearly infected
Mostly dead
Touching the soil
Acting as a source of spreading lesions
Remove foliage gradually where possible. Severe defoliation reduces photosynthesis and exposes fruit to sunscald.
Use clean tools and avoid working among wet plants. Clean cutting tools before moving to another plant, especially when bacterial or viral disease is suspected.
Should a Diseased Tomato Plant Be Removed?
Removal may be necessary when:
Late blight is strongly suspected
The plant has a serious vascular wilt
A likely virus is causing severe systemic symptoms
The main stem or crown is extensively infected
The plant is collapsing
Infection is progressing rapidly
The plant is unlikely to produce a usable crop
It presents a continuing risk to nearby plants
A plant with a few lower leaf spots may not need to be removed. Early sanitation and improved growing conditions may slow some leaf diseases enough to preserve the crop.
What to Do With Diseased Plant Material
Disposal should reflect the suspected disease and the composting method available.
Avoid putting seriously diseased material into a composting system that does not become hot enough to destroy plant pathogens.
Options may include:
Disposal through an appropriate local waste system
Hot composting where the process is reliably managed
Burying material where locally recommended
Other methods permitted in the area
Do not leave infected plants beside the growing area.
Never burn plant material where burning is unsafe or prohibited.
Cleaning Tools and Supports
After working with diseased plants:
Remove visible soil and plant sap from tools
Clean cutting blades
Disinfect equipment with a suitable horticultural disinfectant
Wash hands before handling healthy plants
Clean stakes, cages, strings and reusable containers
Replace heavily contaminated porous materials where necessary
Cleaning is particularly important when bacterial or viral disease is suspected.
Preventing Tomato Diseases
No method prevents every infection, but disease pressure can be reduced.
Start With Healthy Plants
Use healthy seed and inspect purchased plants for spots, distortion and wilting.
Provide Suitable Spacing
Air should be able to move between plants. Crowded foliage remains wet for longer and is harder to inspect.
Keep Foliage Off the Soil
Support plants and remove selected lower leaves that touch the ground.
Water at the Base
Apply water to the root zone rather than routinely wetting the foliage.
Use Mulch
Mulch reduces soil splash and helps maintain consistent moisture.
Ventilate Covered Spaces
Open greenhouses and polytunnels to reduce heat, condensation and prolonged humidity.
Remove Diseased Material
Do not allow heavily infected leaves and fruit to accumulate around the plants.
Rotate Crops
Avoid repeatedly growing tomatoes, potatoes, peppers and aubergines in the same soil where practical.
Rotation is helpful but cannot eliminate pathogens that survive for many years or arrive through wind, plants and insects.
Choose Resistant Varieties
Resistance codes may indicate protection against particular strains of:
Fusarium wilt
Verticillium wilt
Tomato mosaic virus
Certain other diseases
Resistance reduces risk; it does not guarantee that a plant will remain completely disease-free.
Inspect Plants Regularly
Check lower leaves, stems, growing tips and fruit. Early detection makes it easier to remove localised infections before extensive damage occurs.
Should an Organic Fungicide Be Used?
A fungicide approved for organic growing may help protect healthy plant tissue from certain fungal or fungus-like diseases, but it will not restore damaged leaves.
It will not treat:
Bacterial disease unless specifically labelled
Viral disease
Herbicide injury
Heat stress
Watering problems
Nutrient disorders
Product approvals and permitted uses differ between countries and may change. Use only a product approved for organic growing and legally authorised for tomatoes and the identified disease in the location where it will be applied.
Follow the label exactly, including:
Application rate
Protective equipment
Maximum number of applications
Harvest interval
Environmental precautions
Organic status does not mean that a product can be used without care.
A Quick Tomato-Disease Checklist
Brown lower-leaf spots with concentric rings
Suspect early blight.
Numerous small spots with pale centres
Suspect Septoria leaf spot.
Rapidly spreading water-soaked lesions during wet weather
Treat late blight as a serious possibility.
Tiny dark spots on leaves and fruit
Consider bacterial speck or bacterial spot.
One-sided wilting with internal stem browning
Investigate Fusarium or Verticillium wilt.
Grey fuzzy growth on dying tissue
Suspect grey mould.
White powdery patches
Suspect powdery mildew.
Sunken spots developing on ripe fruit
Consider anthracnose.
Mottled, distorted and stunted growth
Investigate a possible virus while also considering herbicide injury and pests.
Wilting in saturated soil
Check for root or crown rot rather than adding more water.
Diagnose Before Treating
Tomato diseases are easier to manage when they are recognised early, but symptoms are not always distinctive.
Before acting:
Examine the entire plant.
Check both surfaces of affected leaves.
Look for stem and fruit symptoms.
Review recent weather.
Check soil moisture and drainage.
Compare nearby plants.
Consider pests and chemical exposure.
Photograph symptoms as they develop.
Seek local diagnostic help when the problem is serious or uncertain.
Avoid treating every spot as blight or every curled leaf as a virus. Correct diagnosis prevents unnecessary spraying, feeding and foliage removal.
Some diseases can be slowed enough to preserve the crop. Others require prompt plant removal. Careful observation, sanitation, healthy growing conditions and rapid action when serious symptoms appear provide the best protection for the remaining tomatoes.
For complete advice on growing healthy tomato plants from sowing through to harvest, return to How to Grow Tomatoes: Complete Guide.
