Saving the Aquaculture Industry from a Damaging Invasive Plant

Researchers at the USDA's Agricultural Research Service (ARS) are helping the U.S. aquaculture industry by developing a natural method to control flowering rush, a costly aquatic invasive species in the U.S.

Flowering rush is a perennial aquatic plant introduced from Europe that is spreading throughout the U.S., particularly along the Columbia River Basin. It poses problems in aquaculture, recreation and water management, and farming—agricultural irrigation systems. 

One significant challenge in managing flowering rush is its submerged underground stems called rhizomes, which facilitate easy spreading and establishment of new infestations, making the plant difficult to remove effectively. 

In the Columbia Basin, the flowering rush is quickly spreading through the movement of floating rhizomes fragments. Managers use manual removal, machinery, and chemical treatments to combat it. However, these methods are not entirely effective in preventing regrowth and require many years of repeated labor-intensive and costly applications.

Driven by this challenge, regional stakeholders and experts throughout the Columbia River Basin developed a regional strategy under the Columbia Basin Cooperative Weed Management Area to address the flowering rush problem.  A key part of this multi-state, multi-agency management plan includes developing and implementing a biological control program to provide those who rely on the Columbia River Basin with an effective, economically and ecologically favorable, management tool.  

Research Ecologist Natalie West and Research Entomologist Joshua Campbell from the ARS Pest Management Research Unit, Sidney, MT, along with research partners, are leading efforts to introduce the first biological control agent released for flowering rush in the U.S.: a tiny swimming weevil (a plant-eating insect from Europe) that feeds only on flowering rush.

This bug does not harm other plants or animals. In fact, early tests showed a substantial decrease in the plant’s underwater rhizomes and buds and significantly fewer flowers when weevils were introduced. These reductions are crucial to successful control of this weed’s abundance and spread in the area.

West explained that ARS plays a critical role in the implementation phase of the management plan initiated by regional stakeholders. Working with state partners in Montana and Washington, ARS researchers are establishing field nurseries to serve as the initial release sites for the weevils and a source for state-wide distributions. The insect will soon be introduced in both states to help naturally control the plant.

Meanwhile, the researchers are also studying how the introduction of these weevils will interact with local invertebrate communities, such as pollinators and aquatic insects, to examine the overall impact on the existing ecosystem.

 “The permitting of this agent is the result of a collaborative effort involving many individuals and organizations,” said West.  “This initiative was driven by stakeholder needs, leading to partnerships in which ARS played a key role in the introduction of the weevil, ensuring its implementation is both safe and effective.”– By Maribel Alonso, Office of Communications.