Blight is recognized by brown withered blotches on potatoes and other members of the Solanaceae family, such as tomatoes, peppers and aubergines. If the plants are left in the ground the whole plant withers and falls, with the spores dropping into the soil where they find their way into the tubers, rotting them.
Firstly,it is useful to recognize the conditions in which blight occurs. It is prevalent later in the season about July and is more likely in cool, damp summers. This is because the oospores that transmit it are water borne, so they prefer rainy conditions. Generally farmers spray their crops with a copper based fungicide, though the traditional Bordeaux mixture is now banned in the EU because of its effect on soil life. Copper sulphate can be used.
Prevention also means eliminating scutch potatoes, which are potatoes left in the ground from the previous crop, overlooked probably, and which grow the subsequent year. These can be reservoirs of the fungal spores, so it is important that they are pulled up when they arise.
Growing blight resistant varieties is highly desirable. First and second early varieties are not usually prone to blight, though main crop are. But there are main crop varieties that are not susceptible to this fungus.Sarpo Mira is a highly resistant variety, but there are others, which can be purchased through reputable suppliers.
In greenhouse crops susceptible to blight avoid watering the leaves, so as to obviate the conditions in which blight grows on them. Water the soil. This is the safest way to water any plant.
When blight is noticed, you can spray to hold it back, but some growers pull up the potato haulms and dispose of them. They do not do so on the compost heap, as on a normal garden heap the temperature is too low to guarantee that the spores are killed, so they dispose of them in facility where there is a hot composting system. I take infected plants to the council's green waste facility.
It is also important to rotate your crops, as this gives the fungal spores in the soil time to die off. Growing potatoes in fresh soil is also useful. Next year to avoid blight I am growing in containers.
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