So, talking about Blightwatch as we were, supposing there is a blight warning? What can you do?
The Potato Council offers a pdf of Leisure Growers’ Advice on how to avoid blight, which includes photographs to aid identification. In their words, “The most effective control for the spread of infection is warm, dry and sunny weather.”
But, in the absence of that, they suggest repeated applications of copper-containing fungicides, such as Dithane 945 and Bordeaux Mixture.
How to control Potato Blight is one of the Top Ten subjects that come up again and again on Gardeners’ Question Time.
Matthew Biggs suggests various tactics, most of which you should have implemented before the dreaded warning. These include avoiding sheltered sites (presumably because it reduces the possibility of a hot and humid patch with its very own Smith periods), planting wider apart, and looking for early signs on neighbours’ crops and spraying with Bordeaux mixture before the blight reaches yours.
And, of course, Bob Flowerdew has his own solution, which he described in Kitchen Garden Magazine back in February 2003.
As we know, free water on leaves allows the blight to flourish, so Bob erects a sort of lop-sided tent to keep rain off the plants. A clear plastic sheet is put over a support, forming a wall at the back and pulled out and down at the front. Tomatoes are planted at the back of the structure, and trained to grow forward at an angle. Their roots receive water dripping off the back wall of plastic, but the front keeps the rain off the plants, while the open structure means that they get plenty of air and light which, according to Bob, makes tomatoes much tastier.
It’s taken a bit of working out to understand exactly what he meant, but, having grasped it, I’ve come up with a sketch above (feel free to laugh at my drawing).