We had a large sumac in our front garden which for various reasons, has had to be cut down. But now, not only is the stump sprouting new leaves, but mini sumacs are now sprouting all over the front garden lawn, up to 30 feet away from the main tree. I am assuming the tree has sent suckers out all over the place, but how do I get rid of them and kill the tree once and for all? I've been obsessively pulling the sproutlets up, but they spring back up as quickly as I pull them out. I have already used a woody plant/tree stump killer on the stump, but wonder if it's not working because the sap is still rising?