Borden is correct.Borden811 said:Fall will work best, as it will kill the entire root system. Spraying( orhack/squirt) now will kill the tree and most of the roots. You might have to sparay again for a couple of years to get all the root sprouts if you don't kill them all the first year or two. If you can get some Garlon 4, and mix it 25%-75%(one quart to a gallon) with basal oil(or diesel fuel),it will kill the heck out of them. All you have to do is spray or paint it on the bark from the soil line to about 2 feet high, and it will absorb through the bark, and kill the tree. The roundup will work too, but as stated, it will work much better if you cut or drill into the tree. You don't have to cut or drill in very far though. The only part of the tree that will take up the herbicide is the cambium layer, directly inder the bark. The rest of the trunk is just dead wood. The roundup will take longer however, and might not be as effective at getting the entire root system the first application.