Digging potatoes in wet soil and downy mildew onions

Most of my potatoes(Orla,Vanessa(early),Romano,Valor(late) have got serious blight and I have cut the tops off and hoping for the best when I come to dig them in a few weeks time.The only ones that seemed to escape are Kestrel and Picasso (maincrop),which I have spraysd with traditional copper.
The problem I have is digging them,since the potatoes come up covered in mud-a bucket full of potatoes turns into half a bucket after washing.Since the potatoes will not grow any bigger with the haulms cut off,does this imply that the mud will stay with the potatoes even if the soil dries out hopefully in the next few weeks.I hope so,since washing every individual potato,then drying them out before storage will be an arduous task.
The other problem in this extremely wet season is my onion crop,which seems to collapsing with downy mildew by the day.Luckily the onion size is quite good so I am taking them up with the tops still green and drying them off in the garage-another task that I could do without.The onion which seems to withstand the mildew best seems to be Sturon.I have not sprayed the onions with Dithane for example,as I tried a control test (half sprayed,half not) some years ago in a wet season and it made no difference.