Have your tomatoes gone brown? It could be blight…
We look at this common problem for tomato growers and what you can do about it
Tomato blight is among the most frustrating diseases for gardeners.
You spend months growing and nurturing these beauties when that telltale brown stalk appears, spreading like wildfire to decimate the fruits of your labour and, before you know it, you’ve lost the lot.
I always consider late blight to be the most brutal of diseases, just when all your tomatoes are starting to ripen and you have already harvested quite a few, which is what has happened to me this year.
So, is there anything you can do to prevent the late summer scourge decimating your tomato crop?
What causes tomato blight?
Generally, it is warm, humid weather from mid-summer onwards, when temperatures are above 10C (50F) and your crops don’t have adequate ventilation. Spores are spread by wind and rain – and can be carried up to 30 miles – needing only a minute film of moisture on the foliage to cause damage. Late blight (Phytophthora infestans) is fatal to the plant.
What are the symptoms?
Initially dark spots or brown patches appear on the leaves, which curl up and wither, followed by fast-spreading brown patches on the stems as the disease makes its way rapidly to infect the fruits, which turn brown, leaving them inedible.
The tomatoes will develop a brown discoloration and may appear to shrink inwards, quickly dropping off the diseased stems.
Potatoes may also be attacked, although they succumb slightly earlier than tomatoes.
How do you deal with it?
You could spray every two weeks with Bordeaux Mixture – a combination of copper sulphate, lime and water – available from garden centres.
As the main ingredient is copper, it’s not off limits for organic gardeners. It’s likely to be effective only if you spray early as a preventative measure, not once the blight has taken hold.
This may be particularly relevant if there are other potato or tomato crops nearby, and in a wet summer, do it as soon as the first tomatoes have set.
Cut off affected foliage and stems to prevent spores spreading further along the plant and harvest the tomatoes early, even if they are still green. You will find, however, that some tomatoes will still suffer blight symptoms when they have been picked.
Look out for blight-resistant varieties including ‘Crimson Crush’, ‘Early Cascade’, ‘Latah, ‘Ferline’ and ‘Legend’, although no tomato plant can be said to be totally blight-immune. Newer F1 (hybrid) varieties which claim to have some resistance include ‘Summerlast’, a dwarf patio variety, and ‘Crimson Blush’, a beefsteak type.
Can you prevent it?
Good plant hygiene and making sure the plants are as strong as they can be early on can help. Do this by keeping the plants well ventilated both in the greenhouse and outside, prevent large fluctuations in temperature, particularly at night, in early summer.
Try to keep the leaves dry, watering only at the base of the plant, and stake plants to keep the leaves off the soil. Keep the plants sheltered from heavy rainfall and feed them with tomato feeds high in potassium, not nitrogen-rich mixes which will just boost leafy growth.
Improve air circulation by cutting off leaves at the top and the bottom of the plants, which will also allow more sunshine to ripen the fruits.
If you grow your tomatoes in a greenhouse, blight is likely to be less of a problem, as the spores have to find their way in through vents and doors, according to the RHS. However, once they’ve infected plants in a glasshouse, the blight is likely to spread rapidly, because of the high humidity.
What should you do with infected plants?
Remove and destroy all affected parts as soon as you see them. And don’t plant tomatoes or potatoes in that soil the following year.
The Press Association
Latest posts by The Press Association (see all)
- Camilla warns older generation facing ‘blight of loneliness’ - September 29, 2020
- 8 surprising things you didn’t know about your skin - September 29, 2020
- 10 easy ways to get rid of pet hair in your home - September 29, 2020
- 5 areas of your house you probably forget to clean – but really should - September 28, 2020
- 8 subtle signs of heart disease you might not know about - September 28, 2020
Leave a Comment!
Community Terms & Conditions
These content standards apply to any and all material which you contribute to our site (contributions), and to any interactive services associated with it.
You must comply with the spirit of the following standards as well as the letter. The standards apply to each part of any contribution as well as to its whole.
be accurate (where they state facts); be genuinely held (where they state opinions); and comply with applicable law in the UK and in any country from which they are posted.
Contributions must not:
contain any material which is defamatory of any person; or contain any material which is obscene, offensive, hateful or inflammatory; or promote sexually explicit material; or promote violence; promote discrimination based on race, sex, religion, nationality, disability, sexual orientation or age; or infringe any copyright, database right or trade mark of any other person; or be likely to deceive any person; or be made in breach of any legal duty owed to a third party, such as a contractual duty or a duty of confidence; or promote any illegal activity; or be threatening, abuse or invade another’s privacy, or cause annoyance, inconvenience or needless anxiety; or be likely to harass, upset, embarrass, alarm or annoy any other person; or be used to impersonate any person, or to misrepresent your identity or affiliation with any person; or give the impression that they emanate from us, if this is not the case; or advocate, promote or assist any unlawful act such as (by way of example only) copyright infringement or computer misuse.
Nurturing a safe environment
Our Silversurfers community is designed to foster friendships, based on trust, honesty, integrity and loyalty and is underpinned by these values.
We don't tolerate swearing, and reserve the right to remove any posts which we feel may offend others... let's keep it friendly!