× Expand Matthew Hamilton attaches one of his inventions to buckthorn shoots. The bag will starve the invasive tree, killing it.

There’s not a lot to like about the stout, spiked branches of the aggressively invasive buckthorn tree. “Buckthorn is spreading actively across the landscape, facilitated by birds eating the berries and spreading seeds,” says Mark Renz, assistant professor of agronomy at UW-Madison and a UW-Extension weed specialist. “The way it is changing the forest understory is really an epidemic in the upper Midwest.”

Buckthorn was imported from Europe over a century ago as an ornamental hedge. But it began to crowd out native plants in woods and natural areas, and nurseries stopped selling it in the 1930s for the most part. A century later, environmentalists and homeowners are still battling it. Now they have a new weapon — Buckthorn Baggies.

Matthew Hamilton, a UW-Madison senior majoring in mechanical engineering, and the Buckthorn Baggie creator, entered the fray when his dad assigned him backyard buckthorn duty at age 12. “He would have me cut them down every year, and they would just grow back even stronger,” Hamilton says. “By my senior year in high school we were trying to kill them with gasoline and other potent chemicals, which was not good.”

Because buckthorn sends up multiple shoots from each cut stump, foresters have recommended cutting in the fall and treating the stumps immediately with glyphosate, the chemical name for Monsanto’s popular Roundup weed killer. Glyphosate is the most widely used herbicide in the world, but last year, the World Health Organization announced that it is a probable human carcinogen. It is restricted or banned in some countries.

In high school, Hamilton began looking for a nonchemical way to kill buckthorn. He tried attaching bags of different materials, colors, sizes and thicknesses to cut stumps. “We had 30 prototypes that we left on for times ranging from a week to a year, and ultimately, we came up with the Buckthorn Baggie. It has the right properties to completely kill a buckthorn stump when you leave it on for a year.”

The Baggie, covering the stump and held in place with a cable tie, cuts off enough light to prevent the vigorous re-sprouts from growing, starving the tree’s roots and leaving behind one dead buckthorn.

One of the many places in Madison where buckthorns have been doing serious damage is Picnic Point on the UW-Madison campus. Buckthorns quickly grow to 40 feet. They leaf out early and lose their leaves late. Native trees leaf out later, and that used to allow spring wildflowers to thrive on the forest floor. But buckthorn shades out that early spring light.

The leaves buckthorns eventually drop in late fall are very high in nitrogen and decompose much more quickly than the leaves of native trees. That encourages critters in the soil that can take up nitrogen quickly and reproduce rapidly, such as destructive non-native earthworms.

Birds gobble up the blue buckthorn berries, but it doesn’t do them any favors. They give the birds diarrhea, which can weaken them. “Birds lose not only nutrients from the fruit, but also any proteins from insects they may have eaten recently,” says Susan Foote-Martin of the Madison Audubon Society.

Autumn Sabo, who manages the UW Forest Ecology Laboratory, says the understory at Picnic Point is primarily buckthorn now. “We found the Buckthorn Baggies online and ordered some. Then we saw that they were made by Matt, who is a UW student. He agreed to come out and demonstrate the Baggie for us.”

Sabo bought 200 bags, and Hamilton donated another 200.

Buckthorn Baggies are a family enterprise, with Hamilton’s mother and sister helping to pack and ship about 20,000 Baggies to date. “The spring of 2015 was our breakout year,” Hamilton says. “It took a little time, but our name is out there, and in the last three years we have never had anyone say it didn’t work or request a refund.”

After graduation, Hamilton will be working for a company that makes commercial heating and cooling equipment. But he plans to keep searching for potential environmental problem-solving products like the Buckthorn Baggie. Says Hamilton: “I’ve always respected nature and tried to take care of it.”