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IDENTIFY, PREVENT, TREAT TOMATO BLIGHT


Tomato Blight initially appears on the leaves of tomato plants but then goes on to affect the stems and the fruit. It is more of a problem with tomato plants grown outdoors compared to greenhouse plants. The disease is commonly called Late Blight.
It is caused by the same virus which causes potato blight and like it or not, the spores which cause it are present in almost every single allotment in the UK. It's not a matter of "are the spores there?", it's more a matter of "will they infect my tomato plants?".

There are two broad types of blight, late and early, with late blight being the main disease as far tomato plants are concerned. Distinguishing between early and late blight is a bit irrelevant for the amateur gardener, both will render your crop useless and there is no treatment when plants have been infected.

As at August 2015 there is only one tomato variety in the UK which is claimed to be resistant to tomato blight. It is called Crimson Crush and a full review of this variety can be found here.

SYMPTOMS OF TOMATO BLIGHT


The likely symptoms are listed below in the order in which they normally occur:
  1. Small brown marks appear on the leaves which enlarge as the blight takes hold.
     
  2. Leaves on the lower part of the plant may well have light coloured patches of fungal infection on the undersides.
     
  3. Brown spots will then appear on the stems and branches, quickly turning to deep brown black. These marks will expand and at this stage the general health of the plants will begin to fail, the stems and branches will begin to turn to mush and possibly collapse. It will be clear that your tomato plants are suffering badly.
     
  4. Finally the fruits, both green and ripe, will show brown marks on them. The affected leaves will dry up, shrivel and fall off.

leaves affected by Tomato blight
Tomato Blight

HOW TO TREAT TOMATO BLIGHT


If your tomato plants are suffering from tomato blight there is no cure, even farmers who have access to strong pesticides are helpless once the disease has hit. There are however measures you can take next year to greatly reduce the likelihood of the disease occurring again. Plants affected with blight in any form should be dug up and burnt, under no circumstances put them on the compost heap. 

There are several things you can do to prevent tomato blight and these are listed below:

  1. Practice good hygiene throughout the entire growing season. Remove decaying leaves from the plant and the surrounding soil.
     
  2. Practice crop rotation every year. Tomatoes should never be grown in the same soil two years running. Blight, especially, stays in the soil over winter and will re-infect tomato plants grown in the same soil two years running.
     
  3. Burn all parts of infected plants, never put them on the compost heap and do not dig them into the soil.
     
  4. Remove lower leaves and side stems so that none are toughing the ground and preferably are at least 5cm / 2in above the ground. This will go a long way to preventing infection which often occurs when rain splashes on the soil and transfers soil to the lower leaves.
     
  5. Space plants correctly. This will allow good air circulation to dry off leaves and stems and reduce the risk of fungal infections. Follow seed packet instructions but as a general rule 45cm to 60cm (18in to 24in) between plants should be sufficient.
     
  6. Water the soil and not the leaves. Damp conditions amongst the foliage provides ideal conditions for tomato blight.
     
  7. Grow blight resistant tomatoes. There is currently only one tomato variety which shows exceptional resistance to tomato blight, it's called Crimson Crush and was first made available to the public in 2014 / 15. Read our full review of this variety here.

    Other varieties of tomato such as Ferline claim to have resistance to blight but in reality it is only minimal. At the moment, Crimson Crush is the only variety with significant resistance.
     
  8. Sprays for Tomato Blight. There are no effective sprays or chemical treatments available to amateur gardeners in the UK to treat tomato blight. Copper based sprays were believed to have helped but these were withdrawn in 2014.

    Many articles (online and in books) mention copper sprays (including Bordeaux Mixture) but they are simply out of date now.

LIFECYCLE OF TOMATO BLIGHT


It may help in preventing tomato blight if you understand the lifecycle of this disease. 

Movement of the spores (called Phytophthora infestans) cause blight. Their movement and infection rate is highly dependant on a combination damp wet weather and specific temperatures. When it is damp and warm the danger of infection is high. The spores are released into the atmosphere from late spring to late summer and they travel on wind and / or rain drops.

It's very difficult for the amateur gardener to predict when danger periods occur however the website Fight Against Blight offers a blight prediction service which is well worth signing up to if you plan to spray your tomatoes (see below), It's run by the Potato Council but what works for potato blight also works for Tomato Blight. The service is free and you can receive email or text warnings for free.

Other common pests and diseases which affect tomato leaves include:

  1. Tomato Blight
     
  2. Tobacco Mosaic Virus
     
  3. Nutrient Problems
     
  4. MAIN INDEX TOMATO PESTS AND DISEASES

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