How can I protect tomatoes from blight?
Q
Is there a fail-safe way of avoiding tomato blight? Paul Ashworth, via email
A
The fungus that causes blight is encouraged by warm wet weather and its spores are spread by air currents and water splash.
A film of moisture covering the leaves is necessary for the spores to take hold and infect the plant, so anything that can be done to prevent moisture sitting on the foliage will help, such as watering the ground directly and keeping air moving around the plants.
For greenhouse plants, keep doors and vents open as much as possible to encourage air movement to reduce the production of condensation.
If you grow tomatoes in the greenhouse every year, it is worth disinfecting the structure and glass during the winter to be sure of dealing with any spores. Jeyes Fluid is a very effective way of doing so.
Use fresh growbags or compost each year, or sterilise the soil if planted in beds. Greenhouse tomatoes are less vulnerable to blight as they are in an enclosed environment, but they are not entirely safe from infection.
Unfortunately, there is little you can do to prevent the fungal spores being released (they can travel quite some distance on air currents), so it is worth considering preventative spraying early on.
This should be done as soon as the first tomatoes have set, and then repeated according to the manufacturer’s instructions. Fungicides are widely available.
There is little you can do once the disease has appeared, but it might be possible to slow the spread by removing infected leaves as soon as you see signs of the disease.
However, it is a fine balance and if too many leaves are removed the plant has no means of photosynthesising or drawing water up and therefore no means of providing nutrients or water to stems or developing fruits. This will effectively, and unfortunately, mean the death of the plant anyway.