Can anybody help please. I have a poly tunnel with raised wooden beds made from sleepers. I have had the beds for two years & this year a white fungus is spreading from the sides of the beds into the soil. I can actually peel the fungus from the inside of the beds & when I dig down the side I have removed what looks like white roots, though these don't belong to any fruit or veg. Some of the fungus has spread to my turnips & made them 'mushy'. Does anyone know what this is and what I should do.