What species are you trying to kill? Unless it is sweetgum, you could accomplish the same thing with a herbicide that doesn’t have the soil activity imazapyr does. If you spray imazapyr in the root zone of desirable trees, such as oaks, imazapyr can definitely hurt their feelings.

If you do the things you need to do when you need to do them then someday you can do the things you want to do when you want to do them.