another good way to apply the herbicid of your choice is to mix in a bucket and get a chemical safe rubber glove. take a wash cloth and dip it in the herbicide mixture then wipe the the willow from the trunk up getting leaves and all. Do it when the temp is right and no chance of rain. Then after willow dies back completely remove from bank. Problem with cutting first it may stimulate the sucker developement causing new sapling to emerge from roots.