Which method is NOT commonly associated with controlling invasive wetland plants?

The method that is not commonly associated with controlling invasive wetland plants is encouraging their natural spread. This approach runs counter to the goal of managing invasive species. Invasive wetland plants can outcompete native vegetation, leading to decreased biodiversity and disruption of the ecosystem. By encouraging their spread, the problem would likely worsen rather than be controlled.

In contrast, mechanical removal involves physically removing invasive plants from the environment, which can be effective but often requires repeated efforts to manage regrowth. Herbicide application utilizes chemicals specifically designed to target and eliminate invasive species, allowing for more controlled and efficient management of these plants. Biological control methods involve introducing natural predators or diseases that can help keep invasive plant populations in check, providing an ecological means of managing their growth. These three methods are all aimed at reducing the impact of invasive species, while encouraging their spread directly undermines the efforts to control them.