Reining in Loosestrife

Professor of Biology George Ellmore and biology research student Lauren Griffen inspect roadside loosestrife.

Photographers, tourists and hikers may sing the praises of the purple loosestrife, a tall, vivid weed frequently seen along roadsides and wetlands. But wildlife experts know it as an invading menace.

Brought to this country from Europe in ship ballast, probably in the late 1700s, the plant has pushed out natural plants whose seeds provide food for fish and wildlife and whose foliage makes nesting places. Not only is the plant tenacious--a woody pillow at the base makes it extremely difficult to uproot--but each one is capable of producing nearly three million seeds a year, seeds that can still sprout several years hence and are easily spread by water.

Now George Ellmore, associate professor of biology, and biology research student Lauren Griffen, a senior, have devised a way they believe can help drastically slow the growth of purple loosestrife. Working at the Hummingbird Cay Field Station in the Bahamas, Griffen and other students have used the extended growing season to study seed germination. Visiting Hummingbird Cay each March, Ellmore and his students are able to test seeds at soil temperatures that won't be reached in New England until mid-summer.

"We asked, how might warm temperatures be used to restrict germination of loose-strife?" Ellmore explained. "In the lab, we found that constant temperatures above about 130 degrees Fahrenheit were lethal, even when experienced for as little as three hours per day."

The next question was whether that temperature could be achieved outside to actually kill the seeds by heating them up. The team used the sun to overheat the soil, a process called solarization. They put clear plastic over the wetland soil and kept a continuous record of the temperature, using data loggers supplied by J. Michael Reed, assistant professor of biology. The plastic acted as a greenhouse and elevated the temperature for about eight hours a day.

The result: The seeds died. Heat-retentive plastics are used in agriculture in certain parts of the world, Ellmore said, so the process is not a new one. Plastic can be set down over a quarter acre of land at a time.

But, said Ellmore, the Tufts study is the first evidence that loosestrife seeds can be killed while still in wetland soil. One approach with solarization could be to have wetlands managers draw down the wetlands to mud, cover the soil with plastic for a week, then restore the water. Another would be to put plastic down over the plants themselves before they sprout.

"We're not suggesting this as a way to stop an established population of loosestrife," Ellmore said. "Instead, solarization can prevent a new population from getting established, or can be used to make older populations more vulnerable to plant-removal programs by depleting seed banks."







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