Help please - Potatoes now a problem

[vegnovice10]

Just checked potato plants in front garden where grass was taken up. They seem to be going the same way as the courgette plant I have. Is it serious? Worried it might spread to tomatoes which are in greenhouse in back garden.

It only seems to be some of the bottom leaves as the tops still look fine - it was only when I was weeding the gravel that I noticed it.

thanks.