I bought the mix for Bluestone, which is what is in the off the shelf spray Bordeaux mixture which is a recommended organic remedy.
Ravenscourt garden centre supplies the ingredients ( Washing crystals & the blue Copper sulphate) and the mix ratio, it suited me as we only have a small amount of potatoes and of them only the Pink Fir Apple are not Blight resistant. The rain stopped on fri evening and I thought I would go out and spray as the weather had turned humid and misty, ideal blight conditions.
I was stopped in my tracks as soon as I reached the plot as the leaves on the Sarpo Axona were discoloured and seemed to be getting worse as I was looking at them! The worst affected were at the right hand side of the potato patch, a few were affected on the other rows and the Pink Fir Apple seemed relatively unaffected?!
I had dissolved the washing crystals in hot water and allowed to cool at home, I added the bluestone and sprayed the whole plot of potatoes.
We were out early on sat morning and I was amazed to find they did not look any worse than they did the previous night, I thought they would be wiped out!
A couple of others arrived with the same intention of spraying, all plots had some slight damage but none as bad as our Sarpo Axona?I was told by someone who always grows the blight resistant varieties that their foliage may get damaged but they grow new leaves and the tubers remain unaffected!
The rain on fri was absolutely torrential and quite cold for this time of year and may have caused the blackening but then is it blight on the spuds or not?!
The weather has continued changeable and wet but summer is supposed to begin on wed!