Answer: Sounds like volunteer trees and if you're planning to kill them off, you can use a full strength non-selective herbicide such as Round-Up. Simply cut the suckers down to ground level and then paint Round-Up on the fresh cut. It is systemic and will be transported to the roots, effectively killing them. Don't use this method if the suckers are coming from roots of a tree you want to keep. Suckers are attached to the main root system of the tree and systemic herbicides may kill the suckers, but they also can injure the tree.
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