More blight

I ventured out into the pouring rain this afternoon to have a look in the garden. I had a good look at the potaotoes and tomatoes which I planted in a portion of my neighbours' garden, and noticed some blight on both lots of plants which i hadn't seen before. I think it may be too far along to do anything, but I found this site:-
http://web.ukonline.co.uk/suttonelms/
which has a strange array of information including advice on treating blight on poatoes and tomatoes.
Pete says he has treated tomatoes with copper sprays. Has anyone else treated blight, if so at what stage and with what results, or do you think it is better generally to chuck everything at the first signs?
Finally I have been reading about virus transfer and wonder whether people think the spread of diseases is mainly due to the weather, or if good husbandry has a big part to play.