Invasive plants can be controlled with other living organisms. Specimens, usually arthropods or pathogens are collected from the invasive plant’s native land, bred in a lab, tested to ensure safety, then released into a site where the invasive plant is present.
While the concept is straightforward, early biological control experiments sometimes had unintended consequences. Newly-introduced herbivores eat the target weed, then turn to other sources of nutrition (such as related or unrelated native plants). sometimes the introduced predators eat everything in sight, disturbing the ecosystem in unanticipated ways.
For example, triploid grass carp have been used to control hydrilla populations in Florida lakes. Stocked at 2 to 25 fish per acre, the herbivorous fish effectively removed populations of the submerged aquatic plant. But grass carp are indiscriminate herbivores, and will eat all submerged vegetation, stirring up bottom sediments in the process to the detriment of the aquatic ecosystem. Once introduced, grass carp are extremely difficult to remove from a waterbody.
More recent and rigorous research has found biocontrol agents that function as intended to suppress invasive plant populations. Cornell University’s College of Agriculture and Life Sciences provides an excellent overview of biological control research and application.
Much like mowing, grazing cannot completely eradicate a population of invasive plants, however in areas where herbicides cannot be applied, or are too expensive, grazing can effectively control invasive plants. A balance must be reached because any overgrazing will disturb the soil, native plants, or even promote the growth of new invasive pants.
Goats, cows, sheep, geese, and even buffalo have been used to manage weeds in various situations, each option presenting selected drawbacks. Goats have been preferred in many situations for their draw to aggressive invasive shrubs and for their ease of management.