Four studies examined soil-active herbicides for control of hardwoods both as single-stems and in stands. The first study found that comparable control of sweetgum (Liquidambar styraciflua) was achieved both by tree injection using 2,4-D + picloram (Tordon 101R®) and by soil spot applications, using hexazinone (Velpar L®) and picloram (Tordon K®) liquid formulations. Crown reduction for these treatments averaged 30 to 36 percent, which was low due to drought conditions. A placement-spacing study showed that sweetgum control using tebuthiuron pellets (Spike 20P®) was better when applications were placed within 5 ft of the tree boles. Another placement-spacing study found that spot treatments with hexazinone liquid (Velpar L) around 2 yr old loblolly pine seedlings resulted in excessive mortality when soil-spots were placed within 2 ft of the stem. A comparison trial between formulations of hexazinone showed that comparable control of hardwood stands was achieved using either grid-pattern applications of liquid or pelleted formulations.
Miller, James H. 1984. Soil-active herbicides for single-stem and stand hardwood control. In: Proceedings, 31th Annual Meeting Southern Weed Science Society; 1984 January 17-19; Hot Springs, AR. Champaign, IL : Southern Weed Science Society. 173-181.