We have an apparently healthy weeping willow. About 6 years old. Grows well, leaves and branches look healthy. On the main trunk, 24-30 inches from ground, is a large growth with a volcanic like shape--with a center going back into the trunk. Really ugly and deformed bark around it. Any ideas?

Robert-sounds like the tree is trying to heal over an old wound, from a canker or something mechanical. Take some photos, and see if you can email or bring them in to your local office: http://www.mastergardener.umd.edu/local/Talbot/index.cfm . They will be able to help!