I've clipped and stumped sprayed over much of the yr except spring. Fall and winter seem to be when I do it the most and no problems with that time frame. Tordon mix kills most everything (the only problem I have is root suckering with Locust). This is kind of my first real attempt at doing much with just a basal spray. This first batch was an experiment which will lead to doing it in mass this winter. Maybe someone else can give you a better answer but I don't think it matters much when you do it.