Herbicide Use in the US and Canada
In commercial forestry, herbicides are used to control competing vegetation and improve timber productivity. Herbicides may also be applied in forest ecosystems to control invasive plants, create special features important to wildlife (e.g., dead trees), help restore native ecosystems (e.g., native pine- grasslands ecosystems), and manage early successional and savanna habitat conditions favored by high- priority species.
Before herbicides can be applied, they must be approved and registered by the Environmental Protection Agency (EPA) in the United States and by the Pest Management Regulatory Agency (PMRA) of Health Canada in Canada. The approval process includes extensive study and review of data on chemical composition, mode of action, environmental fate, and toxicity to a range of plant and animal species. Based on these data, a label is developed that specifies, among other things, the approved uses, application concentrations and methods for those uses, and mitigation measures that must be used to protect applicators and bystanders. Herbicides must be applied according to the label directions and when those directions are followed, there is no potential for significant adverse effects on humans or the environment.
In Canada, there are five herbicide active ingredients registered for use in forestry: glyphosate, triclopyr, hexazinone, 2,4-D, and simazine. However, historically, glyphosate has seen nearly exclusive use. According to Canada’s National Forestry Database, in 2014, 95% of forest land treated with herbicides was treated with glyphosate-based herbicides and the remainder with “other herbicides,” which were not individually identified aside from hexazinone being shown with zero hectares treated. In Canada, glyphosate-based herbicides are sold under several different product names, including Vision, VisionMax, Forza and Vantage.
In the United States, in a survey conducted by NCASI (2015), forest landowners and managers reported using 12 different herbicides on managed forest land in 2011. Imazapyr was, by far, the most commonly applied.
Under its Forestry Program, NCASI provides technical support on the use of silvicultural chemicals for forest vegetation management, and is working to quantify herbicide movement into streams following operational herbicide applications.