Tomato Blight: Identification and Control

Tomato blight is one of the most destructive problems tomato growers face, especially in cool, wet conditions. It can wipe out plants quickly if not identified early and controlled correctly. Understanding how to recognise blight, what causes it, and how to limit its spread is essential for protecting your crop.

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What Is Tomato Blight?

Tomato blight is a fungal-like disease that thrives in damp, cool weather. It spreads rapidly through moisture on leaves and can affect leaves, stems, and fruit.

There are two main types:

• Early blight – slower-spreading, usually less severe
• Late blight – fast-spreading and highly destructive

Both require prompt action.

How to Identify Tomato Blight

Signs of Early Blight

Early blight usually appears first on lower leaves.

Symptoms include:

• Brown or black spots on leaves
• Yellowing around the spots
• Leaves gradually dying and dropping
• Slow upward spread

Plants often continue producing fruit if controlled early.

Signs of Late Blight

Late blight is far more aggressive.

Symptoms include:

• Dark brown or black patches on leaves and stems
• Oily or water-soaked appearance
• Rapid wilting and collapse of foliage
• Firm, dark patches on fruit

Late blight can destroy plants in days under the right conditions.

Conditions That Cause Tomato Blight

Blight thrives when:

• Temperatures are cool (10–20°C)
• Humidity is high
• Leaves remain wet for long periods
• Airflow is poor

In the UK, prolonged rain and mild summers create ideal blight conditions.

How Blight Spreads

Tomato blight spreads through:

• Wind-blown spores
• Rain splash
• Wet foliage touching infected plants
• Tools and hands

Once present, it spreads rapidly if conditions remain favourable.

What to Do If You Spot Blight

Act Immediately

At the first signs:

• Remove affected leaves straight away
• Dispose of them in household waste
• Do not compost infected material

Early removal can slow the spread significantly.

If Late Blight Is Confirmed

If plants show rapid collapse:

• Harvest all usable fruit immediately
• Remove the entire plant
• Dispose of it away from the garden

Leaving infected plants in place risks spreading blight to nearby crops.

Can You Save Tomatoes Once Blight Appears?

• Early blight: Often manageable if caught early
• Late blight: Rarely salvageable once established

Green tomatoes can usually be harvested and ripened indoors if picked early enough.

How to Prevent Tomato Blight

Improve Airflow

• Space plants generously
• Remove lower leaves touching the soil
• Vent greenhouses daily

Good airflow helps foliage dry quickly.

Keep Leaves Dry

• Water at the base only
• Avoid overhead watering
• Shelter outdoor plants from rain where possible

Dry leaves dramatically reduce infection risk.

Grow Under Cover

• Greenhouses and polytunnels reduce blight risk
• Protection from rain is especially effective

Under cover, blight is far less common.

Use Resistant Varieties

• Choose blight-resistant or tolerant varieties
• Especially important for outdoor growing

These varieties won’t be immune, but they last longer in poor conditions.

Practice Good Hygiene

• Clean tools regularly
• Wash hands between plants
• Remove all plant debris at the end of the season

Blight spores can overwinter on plant material.

Feeding and Watering During Blight Risk

• Avoid excess nitrogen (encourages soft growth)
• Keep watering consistent but not excessive
• Do not stress plants with drought

Balanced care helps plants resist infection longer.

Common Mistakes That Make Blight Worse

• Ignoring early symptoms
• Leaving infected plants in place
• Composting diseased material
• Overcrowding plants
• Allowing foliage to stay wet

Blight control depends on speed and cleanliness.

Can Blight Stay in the Soil?

Blight does not survive long in bare soil, but:

• It can survive on infected plant debris
• Volunteer plants can carry it over

Removing all debris greatly reduces next year’s risk.

Final Thoughts

Tomato blight is a serious problem, but early identification and fast action can protect much of your harvest. Improving airflow, keeping foliage dry, and acting immediately at the first signs are the most effective controls.

In blight-prone areas, prevention is far more reliable than cure. With good hygiene and sensible growing practices, even UK gardeners can successfully manage tomato blight and enjoy productive crops.