You will have to say what kind of plant the tubers belong to. And upload a photo too if you can. Then I am sure someone will try to help you.

Guest if you have brown spots on your potato tubers then you have a serious problem with blight. You will need to destroy the crop by digging it up and burning or putting in your wheelie bin make sure you get all the very small potatoes. Don't plant potatoes tomatoes or any other vegetable from the solanum family in the area to 7 years.

If it isn't your potatoes then as Jonathan says you will need to tell us what plant it is and put up a photo.