The tree appears dead and was planted near a drainage ditch

Never plant the weeping willow near drainage ditches, or sewage lines. The roots of this tree grow deep and can break these lines, causing damage for the area and itself in the process. However, if you observe your tree shedding its leaves and looking almost dead, and know that it was planted near a drainage ditch, try this. Scrap off a little piece of the bark and check if it is green. Keep scraping the bark at a distance of 6 inches in the branches, if you find green, that means it is alive. If you find it brown, it means that the tree is dead. If the tree is alive, replant it elsewhere, if the tree is dead, get rid of it.

hmm'kay
I'm going out now to see if the evil willows are alive and kicking and just about to strangle my precious sewer lines to death, wish me luck, it's really cold outside but a man's gotta do whut a man's gotta do eh?!

I was rather hoping this Trolls post would just die without response. This is a Bonsai forum smallfish. We don't plant willow for long enough for them to do any of the damage you rightly ascribe to them.

This advice also applies to many other trees and is a matter of common sense, so it should really go without saying!