The good news first. Your dahlia tubers do not have the dreaded dahlia gall disease; instead, it looks like a fungal growth due to dampness around the dug tubers. You can use a dry paper towel to wipe off as much of the white as you can. Next, let the tubers dry out in a cool, dark spot so they can cure or harden up a bit before storage. After a few days, dust the tubers with sulfur dust or ground cinnamon. Both have anti-fungal properties.  Next, store the tubers in an open paper bag with just a bit of slightly damp peat moss or wood chips. You can also store them in wooden crates, but be sure they are not kept damp and have some air circulation. Winter storage should be cold but not freezing, between 40 and 50 degrees. An unheated garage or basement is often the perfect spot. In the spring, if your tubers are still firm and not shrivelled, go ahead and plant them. Do not sell or share your tubers, just in case the fungus has survived. I predict your tubers will be fine, and you'll enjoy bushels of dahlias this summer. Keep growing, Marianne Binetti