Defending Mother Nature

Nowhere is the push to minimize the environmental impact of herbicides stronger than among those who battle invasive plant species.

Plants introduced from one region of the globe to another, purposefully or by accident, can lead to headaches for federal and state environmental officials. A few of the faster growing species can crowd out native understory plants and choke trees if they escape into forests and wetlands. They can also overwhelm native submerged aquatic plants in lakes and streams and deplete dissolved oxygen, killing fish and other aquatic organisms.

Using herbicides to manage these plant pests is necessary to maintain forests and waterways for recreation, for functional uses such as fishing and irrigation, and for aesthetic purposes. What the public doesn't know is that invasive plant management "has always been green," says William T. Haller, acting director of the Center for Aquatic & Invasive Plants at the University of Florida. "Why try to save a wetland from an invasive fern if you are going to kill all the plants in the wetland with a herbicide?"

Scientists have discovered effective herbicides and their optimal formulations that result in high selectivity for the invasive plants and short half-lives of the chemicals in the environment-and have stuck with them, Haller says. In fact, little has changed during the past 20 years, he notes. "We still use mostly the same compounds, those few that are registered and labeled for invasive plants."

In Florida, the old-world climbing fern that takes over forests and wetlands and the fernlike aquatic plant hydrilla that has hard-to-destroy rhizomes top the list of troublemakers. Common herbicides used against these species include glyphosate, diquat, imazapyr, and fluridone, Haller says. Chelated copper ethanolamine compounds are being used to replace copper sulfate-an old standard-because copper and sulfate ions can be problematic in aquatic settings, he adds. These herbicides are used infrequently at low rates to spot-treat invasive plants, often in conjunction with cutting and removing vegetation for effective control.

Environmentally friendlier biopesticides based on natural-product chemistry have not made significant progress on the herbicide front, Haller says, so none is being used on invasives for now. But given the growing emphasis on identifying and developing biopesticides, it is just a matter of time before an effective and even greener herbicide option for invasive species hits the market.