Field test of foliar-spray herbicides to control mountain laurel in mature mixed-oak forests in western MarylandThis article is part of a larger document. View the larger document here.
Successful oak (Quercus spp.) regeneration requires the presence of competitive sources of oak reproduction before parent oaks are harvested. Mountain laurel (Kalmia latifolia) in the understory of many Appalachian forests prevents new oak seedlings from receiving adequate sunlight to survive and grow into competitive size classes. This study examined the efficacy of three herbicides (triclopyr, glyphosate, or imazapyr) applied as a foliar spray on mountain laurel in a mature mixed-oak forest. Each herbicide was applied at three rates, expressed as quarts per acre. The herbicides were mixed in water with a surfactant added to achieve application rates within U.S. Environmental Protection Agency label limits. The nine herbicide/rate combinations were applied once each in four different months (April, June, August, or October). Efficacy was quantified by the percentage of mountain laurel foliage controlled 12 months after treatment on 200 randomly assigned 0.005-acre plots. Triclopyr applied at 4.8 quarts per acre provided > 85 percent foliage control in all four months. Glyphosate applied at 4.8 quarts per acre also provided > 85 percent foliage control in April, June, and August. Imazapyr provided significantly less foliage control, and some hardwood trees were damaged adjacent to plots treated with imazapyr. Study results for all 36 herbicide/rate/month combinations are provided.