Soil spot herbicides for single-stem hardwood control
Soil spot treatments of undiluted Velpar® L and a concentrated mixture of Spike® 80W were applied aorund test trees of five hardwood species. The test rates were 2, 4, and 6 ml of herbicidelin, of dbh applied to the soil within 3ft of each tree. Hardwood topkill was assessed after two growing seasons. The 4-ml rate of Velpar L was required to achieve 80% or greater average topkill of sweetgum (Liquidambar styraciflua) and water oak (Quercus nigra) on loamy soils, while a 6.ml rate was needed to exceed 80% topkill of dogwood (Cornus florida). Spike 80W gave about 80% topkill of both water oak and dogwood at the 2-ml rate but was ineffective on sweetgum. Only Spike 80W at the 6-ml rate yielded greater than 70% average topkill of of boxelder (Acer negundo) and hophornbeam (Ostrya virginiana). Nearby hardwood of susceptible species within 3 ft of treated teres were also killed, extending the cost-effectivenss of these hardwood control treatments.