Invasive aquatic weed creeps across U.S.

MINNEAPOLIS (LOG NEWS SERVICE) — A fast growing aquatic weed that is hard to kill is creeping across the Great Lakes region.

The first North American sighting of “starry stonewort,” which forms dense surface mats in lakes, turned up in New York State’s St. Lawrence River in 1978. Researchers think it arrived in ballast water from ships entering the Great Lakes.

It wasn’t a big concern for about 30 years, but then it took off. Now it’s widespread on Michigan’s Lower Peninsula, where it has infested more than 200 lakes, and parts of western New York. It was found in Wisconsin in 2014 and in Minnesota in 2015. It also reached some lakes in Indiana, Pennsylvania, Vermont and portions of Canada.

The name starry stonewort comes from a tiny, white six-pointed-star-shaped “bulbil” on its stems. The plant is considered beneficial and even endangered in its native Europe and Asia. But for some reason it turned aggressive here in American waters.

It’s difficult to kill with herbicides because it doesn’t have a vascular system to carry the poison to the entire plant, said University of Minnesota invasive species specialist Dan Larkin. Herbicide treatments often result in a “haircut effect” that burns off the top of the plant, but leaves the rest alive to re-grow.

The weed mats can be a nuisance to boaters and anglers. Scientists are also concerned about the potential harm to native plants and fish habitats.

Researchers are just starting to understand the conditions in which the plant thrives, and modeling suggests that large swaths of the U.S. could be highly suitable, including much of the West, Larkin said.

It reproduces when plant fragments and bulbils break off, and they can hitchhike on boats and trailers. Recent discoveries have often been concentrated near public accesses such as boat ramps.

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