I’m a first time veg gardener and was wondering how long I have to keep spraying my potatoes with Dithane? There is some blight in the crop but I’ve been removing those plants as far as possible. Will the healthier plants give me bigger potatoes if I keep spraying? I’ve been getting conflicting advice from people at the allotment some of whom have only sprayed three times over the summer.
Some varieties need no spraying, some less, some more. The longer moisture rests on the leaves the more damage caused. Temperature plays a role too. If the crop was planted early and has most of its growth done, the tops can be taken off.
Sometimes you can get away with 3 or 4 sprays, sometimes it needs to be done every two weeks from first blight warnings, as commercial growers might.
If the crop has reached good size ( lift a plant or pull back soil from a couple) and they have enough dry matter, (starch in the juice of the tuber), you can stop spraying and take off the tops to prevent the disease spores getting down to the tubers.
If they were planted reasonalby early, you can stop spraying earlier, but if not, you must keep it up.