Tomato blight
Learn how to recognise and tackle tomato blight, in this expert guide.
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This article has been checked for horticultural accuracy by Oliver Parsons.
Tomato blight, a fungus-like infection called Phytophthora infestans, spreads by wind and water-splash. It attacks tomatoes and potatoes and is triggered by wet conditions, making outdoor tomatoes more susceptible than those in a greenhouse. The crop is quickly ruined and even if you pick the tomatoes at the first sign of infection, you can't stop them rotting.
How to identify tomato blight
Spread by airborne spores that can be carried over 30 miles on the wind, tomato blight is most prevalent when conditions are warm and wet. Outdoor tomatoes are more susceptible to blight than those growing in a greenhouse, mostly because they are exposed to rainfall on their leaves, whereas greenhouse plants can be watered right into the roots. Greenhouse crops are also slightly less likely to be exposed to the air-borne spores from other plants nearby.
When affected by blight, ripening tomatoes develop brown sunken spots, which spread to the leaves and stems.
In this video, Monty Don explains what to do if blight affects your tomatoes, and explains whether you can still eat the tomatoes growing on blight-infected plants:
How to prevent tomato blight
Keep tomatoes dry
Grow tomatoes in a greenhouse or polytunnel if possible, as this will keep the leaves dry and the warmer environment will help fruits ripen sooner than those grown outside.
Use short stakes with bush types to keep their leaves away from the soil.
Take care to water only the soil or compost, keeping the leaves dry.
Provide good ventilation
Pick a sunny, sheltered but well-ventilated spot for growing tomatoes outdoors. Leave enough space between plants for air to circulate – don't be tempted to plant closer than the seed pack recommends.
Perform regular sideshooting on cordon-type tomatoes, or they will grow bushy and be more susceptible to blight.
On cordon types, remove lower leaves where fruits have already formed, to increase air circulation, let in light and speed up ripening. Vigorous bush varieties will tend to produce more leaves than they need, and benefit from drastic pruning to thin the foliage and encourage good ventilation.
Once tomatoes start to flower, use only fertilisers that are high in potassium, such as dedicated tomato feeds. A high-nitrogen fertiliser will boost leaf production, making blight more likely.
Keep greenhouses or polytunnels well ventilated to stop them becoming too humid and to increase air flow.
Avoid planting tomatoes near potatoes
Don't plant tomatoes near potato plants, as these are also susceptible to blight and their proximity will make it easier for the blight to spread between crops.
Check plants regularly for blight, from summer onwards, and dispose safely of badly diseased plants.
When the weather conditions are optimum for blight, remember to check your tomatoes and potatoes more frequently.
Grow early tomatoes
Cherry tomatoes tend to be less likely to catch blight than larger ones such as beefsteaks, because they ripen more quickly and are often harvested before blight hits.
Practice good hygiene
Once blight hits, remove and destroy the affected foliage to reduce chances of further infection.
New blight strains in the UK may be able to produce resting spores that remain on plant material through winter and could reinfect next year's crop. Burn the waste, bury it underground in a deep hole or add the material to your green bin.
Don’t leave potato tubers in the ground at harvest as they, too, could harbour blight.
Blight resistant tomatoes to grow
Some tomatoes have been bred with a degree of blight tolerance – they may still catch the disease but are able to survive and yield some healthy fruit. Here, Monty Don picks the fruit of blight-resistant tomato variety 'Losetto':
We've picked our favourite blight-resistant tomatoes to grow, below.
Tomato 'Berry'
This unusual cordon tomato produces strawberry-shaped cherry tomatoes which have a super-sweet flavour. It’s early to ripen, and shows some resistance to blight.
Tomato 'Fandango'
A blight-tolerant cordon tomato that's reliable and resistant to verticillium wilt. It produces a heavy crop of medium-sized, deep-red fruit with an excellent flavour.
Tomato 'Fantasio' F1
A superbly flavoured cordon tomato, bearing a prolific crop of medium-sized fruit. Blight tolerant and resistant to fusarium and verticillium wilt, it's best grown under glass.
Tomato 'Ferline' F1
This cordon variety has some blight tolerance, and resistance to fusarium and verticillium wilt. 'Ferline' bears heavy crops of tasty, medium-sized fruit.
Tomato 'Latah'
Bush variety 'Latah' produces large cherry tomatoes with excellent flavour, and usually crops early enough to avoid blight.
Tomato 'Legend'
Bush variety 'Legend' holds the RHS Award of Garden Merit and has some blight tolerance. A salad type with heavy crops, it produces almost seedless fruit with superb flavour.
Tomato 'Lizzano' F1
A vigorous semi-determinate variety with lots of sweet, round cherry fruits and a trailing habit, 'Lizzano' is perfect for pots and hanging baskets. It also has good blight tolerance.
Tomato 'Losetto' F1
This very blight-tolerant semi-determinate variety produces masses of bright red, sweet cherry tomatoes. 'Losetto' is ideal for growing in pots.
Tomato 'Red Alert'
Bush tomato 'Red Alert' bears a lot of small, sweet cherry tomatoes. Its sparse leaves reduce humidity and fruits ripen very early, so are often harvested before blight strikes.
Frequently Asked Questions
What does blight look like in tomatoes?
There are a few signs to look out for when trying to spot blight on your tomato plants. It will cause leaves to shrivel and turn brown. It also causes brown lesions on the leaf stalks, and the plant stems. Blight symptoms on fruit will appear as sunken areas which turn brown. Mature fruit will rot more quickly if infected.
Can tomato plants recover from blight?
You may still get edible fruit from a plant that has blight, just make sure any fruit you eat has no signs of the disease. However, an infected plant will not fully recover. The best thing to do is to remove the most obviously infected leaves and dispose of them in council compost bins, where material is composted at a much higher temperature. Do not re-use the soil for future tomato or potato crops for at least four years.
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