Grand Canyon National Park to Apply Herbicide Along Colorado River Corridor

Grand Canyon, AZ - From April 15 to 30, 2019 the Grand Canyon National Park Division of Science and Resource Management (SRM) will be applying cut-stump and occasional spot spray treatments of herbicide to invasive plants along the banks of the Colorado River to aid in the control of several invasive plant species for which mechanical removal is ineffective.

In spring of 2009, an Environmental Assessment (EA) was prepared for implementation of Grand Canyon National Park's Exotic Plant Management Plan which identifies the need to use an integrated approach to exotic plant management including the use of herbicides. The EA was conducted in accordance with the National Environmental Policy Act (NEPA) and generated a Finding of No Significant Impact (FONSI). The FONSI, signed by the Regional Director in July of 2009, states that expansion of chemical pest control in the park was a reasonable alternative to no action and would have no significant negative impact on the park's ecology.

SRM staff will be targeting Russian knapweed (Acroptilon repens), camelthorn (Alhagi maurorum), pampas grass (Cortaderia selloana and C. jubata), and perennial pepperweed (Lepidium latifolium) at numerous locations along the river corridor. These non-native invasive plants have been determined by park facilitators to be a major threat to native vegetation. Some species, such as camelthorn, also have a negative effect on visitation to the inner canyon due to its needle-like spines and potential to form dense populations.

SRM staff will be using an imazapyr-based herbicide which is approved for use in and around recreational water by the Department of the Interior's Pesticide Use Proposal System. Though approved for aquatic use, no herbicide will be applied directly to water. When reasonable, SRM staff will use a cut-stump method of application to further limit the amount of herbicide in the immediate environment of each treatment. This method involves clipping the main stem of an invasive plant and applying a small drop of herbicide to the cut. Application of herbicide for control of invasive plants has occurred occasionally along the banks of the Colorado River for the last ten years.