Question
Will round kill a tree, I spray my yard ever year first week of February, the guy next door said that the round up I spray the run off from the rain kill his tree, but the flowers at the base of the tree didn't die.

Answer
NO Roundup will not kill the tree unless you spray it on the green foliage or cut into the bark and spray the cambium layer of cells that are just under the bark. Roundup is used by landscaper to spray weeds  around shrubs. It will kill the flowers IF the spry gets on them. Roundup is not soil active but a contact herbicide and will not move through the soil to adjacent plants. Your neighbor is not correct.