The sooner you can treat it the better. Might want to add a little food coloring if you have a lot of stumps in one area...this will help you see which one you have treated easily and or at a distance. I use tordon mostly and it's already a purple/blue type color. I have heard stories of tordon leaching in the soil however and killing other things... I have not had that issue personally. I have also used straight gly before. Just put some in a container and brush it on or put in a squirt type bottle and cover the entire stump face. I have also used a cordless drill to put a cavity in the stump as well... Lots of ways to do it.