Weed Busters: Students Tackle the Purple Menace

By Eve Pranis

"When my third graders asked a local naturalist to help them identify wild plants growing on our school grounds, we never imagined their query would lead to a long-term environmental action project," reports Minneapolis, MN, teacher Sherri Rogers.

The lovely magenta plant gracing the cattail marsh on the school campus turned out to be purple loosestrife, an invasive, non-native plant that chokes out other vegetation needed by wildlife. After dissecting the plants and estimating the number of tiny seeds they produced (millions!), Sherri's students began to appreciate that this plant is well adapted for survival. When they then learned about the plant's impact on their wetland wildlife habitat, students wondered what they could do to make a difference.

Beetle Battles

The school's naturalist partner suggested contacting a local scientist who was researching ways to eradicate loosestrife. After examining the school grounds and discussing the plant's life cycle and the risks it poses, the scientist helped students set up a controlled investigation that mirrored his own research. They released loosestrife-eating beetles in experimental plots of loosestrife, and left others alone as a control. "The kids eagerly checked their plots through the summer and fall, and noticed that the beetles were indeed taking a toll on the plants in the experimental plot," says Sherri. Once it was clear the beetles were keeping the loosestrife in check, the class brainstormed with their partner ways they could grow loosestrife in the classroom GrowLab through the fall and winter. Their goal was to investigate which conditions promote and which hinder loosestrife growth and to rear loosestrife-eating beetles that could eventually squelch the weeds in the schoolyard.

With support from the naturalist, students collected loosestrife seeds and dug up the plants' crowns to try to propagate them in GrowLab indoor gardens. Pairs of students tested different germination conditions for the seeds or tried growing some plants from roots, then observed and recorded plant growth. When plants were 12 inches high, students generated ideas about ways to damage or kill the plants besides introducing beetles. They experimented by using environmentally benign substances, such as salt and sugar solutions. "When students discovered that salt water killed the plants, I shared that the 'real' science they had done was on target," explains Sherri. Saltwater marshes are not plagued with loosestrife.

Return of the Natives

Later in the year, the class brought beetles they'd raised on plants in a plastic wading pool into the experimental plots. "We have begun to notice that as the beetles take care of the loosestrife, the cattails and other plants and animals are starting to return," says Sherri. But the class isn't assuming the problem is solved. They continue to experiment with other methods of eradicating the weed, she reports. In one section they've tried cutting plants back to the roots; in another, they've removed all of the seed heads. Students observe and keep track of the growth of loosestrife and other plants in each area. Their beetle rearing was so successful that this year's class merely collects them, rather than raising them, to move to selected areas of the school grounds.

"The project and opportunity to work with real scientists has provided some tangible lessons about plant adaptations, habitat needs, and more," says Sherri. "Just as important, students have a growing confidence that they can make a difference and help protect the environment by controlling this habitat-destroying weed in the state," she adds. In fact, they've become local experts of sorts. They've published their research in an environmental journal, other schools have tapped into their growing expertise, and they plan to tout their successes on a school Web site.

Sherri invites educators interested in learning more about this biological control project to contact her at Breck School, 123 Ottawa Ave. North, Minneapolis, MN 55427 or via e-mail sherri.rogers@breckschool.org.

Editor's Note: Twenty-six states now have loosestrife control projects. To learn more about what's happening in your area with this or other invasive weeds, contact your state Agency of Natural Resources or Fish and Wildlife Service.

Are Natives Friendlier?

Sherri's students discovered that plants brought into a foreign country (in the case of loose-strife, probably in the ballast of 19th-century ships from Europe) can become so aggressive that they crowd out native vegetation and threaten wildlife. Loosestrife, for example, has amazing reproductive abilities, and lacks natural predators in its "adopted" country. (A single stalk may produce as many as 300,000 seeds, and the plant can also reproduce quickly from stem or root segments!)

A plant that is considered native to an area has evolved in a region over time and developed complex, interdependent relationships with other organisms. Some plants are dependent on nutrients made available by certain types of local soil fungus. Some butterflies depend for survival on toxic substances produced by local plants for protection.

Native plants will rarely overtake an area, since they're kept in check by their relationships with other populations. And not all introduced plants wreak havoc with the existing ecosystem. Many plants that are not native to an area make fine garden or landscape plants. While tomatoes may have originated in South America, for instance, they've been bred to be so dependent on human care that they are not likely to get out of control. But some non-native plants, like purple loosestrife, become invasive and destructive because they compete well and are not kept in check by natural predators.

One way of preserving habitat health in schoolyard projects is to try to plant or maintain as many native plants as possible. They are better designed to meet regional wildlife needs and, because they have adapted to local climatic conditions and soils, they should be easier to maintain. Always try to obtain native plants from local or regional sources, or start your own from collected seeds of plants that are plentiful. Never dig up wild plants unless you're rescuing them from a site under construction.

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