Most, but not all, trees resprout after cutting. Cutting those that don't resprout is an effective control method. For example, eastern redcedar is a very common species that will not resprout after cutting. Trees that do resprout include Siberian elm, hackberry, Osage orange (hedgeball), oak, ash, aspen, cottonwood, maple, sycamore, willow and many more. These trees will either need to be dug out or the cut stump treated with herbicide after cutting.
Note that when we say volunteer trees, we mean those that come from seed rather than suckers that originate from the roots of an existing tree. The recommendations given in the remainder of this article are designed to kill these volunteer trees. Using herbicides on suckers will damage and very possibly kill the original tree. Trees that commonly produce suckers include tree of heaven, honeylocust, black locust, hackberry, western soapberry, cottonwood, aspen, poplar, willow and boxelder.
It is also possible for larger trees of the same species to be root-grafted. Even though root-grafted trees are not suckers, they do share materials between the individual root systems and therefore herbicides used to treat one tree can be passed to its neighbor. Let's say we have a tree we want to control that is a volunteer and there are no other trees of the same species close enough to be root-grafted that we do not wish to harm. What do we do? If the tree is any size, you probably do not want to dig it out. That leaves using a herbicide on the cut stump. Basal treatments are also possible but that is beyond the scope of this article. First decide what herbicide to use.
Triclopyr and glyphosate are the herbicides most commonly available to homeowners. Triclopyr is found in many brush killers and glyphosate is found in Roundup as well as numerous other products. Read the label before purchasing to make sure that a cut stump treatment is listed. Most often the undiluted product is applied to the stump immediately after cutting. A paint brush is often used for the application though some people will dip their pruning shears in the products immediately before cutting. Regardless, it is important that the stump is treated immediately or at least within 5 minutes. Note that a paint brush with foam rather than bristles is less likely to drip. If there are a large number of small trees to treat, you may want to invest in an applicator such as the Buckthorn Buster. See https://landscape-restoration.com/ .
Trees do not need to be actively growing to be controlled. Actually this time of year is a very good time to treat as long as applications are made when the temperature is above freezing. (Ward Upham)