I have a polytunnel, and have just discovered that my early potatoes look like they have been hit by what looks like blight – there are also some spots on my tomato plants – is this possible in early may – how do i get rid of it – can I plant new tomato plants in the tunnel – if so – do I need to just grow bags – will I have to change the soil in the borders for next year. I have now sprayed with dithane and cut off the bad foliage off the tubers – potatoes are the size of golf balls and marbles !! – can you please advise?