Read up on basal injection of trees, or just tree injection. Pay attention to the chemicals used, and be very careful when applied to keep pond water contamination to a minimum. Tordon RTU and Pathway are a few that are used for injection purposes.

http://www.forestry.state.al.us/PDFs/ResourceSheets/Herbicides/Individual_Tree_Injection.pdf

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).