Chemicals should be last resort for invasive plant control

By: Kevin Bunch | C&G Newspapers | Published May 6, 2014

MACOMB COUNTY — Lovely native plants are not the only ones taking this time of year to spread their seeds and roots, as several invasive plants are bouncing back after winter.

A number of nonnative plants have found their way to southeast Michigan over the years — some of them as ornamental plants that simply got loose. Mary Gerstenberger, consumer horticulture coordinator with the Michigan State University Extension, said that getting a handle on those plants depends on the type and where they are located.

“I know the ones we have the most difficult times with and are the biggest spreaders are phragmites,” Gerstenberger said. “You find them growing in ditches or anywhere with much moisture in the soil. They have a really aggressive root system and get into the water, so you can’t just spray them.”

As many phragmites plants like to grow around waterfronts, Gerstenberger said that spraying them with chemicals requires governmental approval. Even then, the type of chemical is important, as it can easily get into the water and begin impacting fish and other wildlife — as well as all the people who rely on that water.

Oakland Township Natural Area Manager Ben Vanderweide said phragmites can be a major environmental problem, too, as it crowds out native plants in wetland areas, destroying habitat for animal life and reducing property values.

Most people in the area do not live along the water, but she said there are other invasive plants that can prove problematic. Creeping charlie, a type of creeping vine, is a nonnative plant that is particularly difficult to root out, Gerstenberger said.

“You pull it out, you break roots, they send up a new shoot, and you end up with more,” Gerstenberger said. “A lot of time is spent by people trying to remove those from their lawns.”

Timing is important in removing any weed, she said. In creeping charlie’s case, the plant likes shady, moist areas, so watering less frequently and opening the area to more sunlight, if possible, can prevent the plant from spreading or establishing itself. Even if the plant is removed, if the growing conditions are still there, it can return, according to the MSU-E website

“Mostly when we have people dealing with any kind of invasive, first see what the growing conditions and environmental conditions are,” Gerstenberger said. “Usually, if you can improve or change those, it’ll discourage the growing conditions. Like moss — people don’t like it, but that’s from shade and moisture. If you get more sunlight, it takes care of itself.”

The University of Wisconsin Extension website also suggests increasing grass density on the lawn, or replacing grass entirely with shade-loving plants like hosta, English ivy and pachysandra.

While there are effective herbicide treatments, Gerstenberger stressed that people need to read the directions carefully and use them at the right times of the year — in the spring before it blooms, or in the fall after the first frost. Even then, chemicals should always be the last resort, she said.

Chemicals can get into the soil or be spread on the wind to neighboring plants. Or, if they hit an impervious surface, they frequently are washed into the water system through a storm drain, Gerstenberger said.

Vanderweide said that while people in his department are licensed by the state to use herbicides, they try to limit the usage to only when it is appropriate and necessary. Depending on the species and how far it spreads, he said they may try pulling it out by hand or doing a prescribed burn — setting a contained fire to eliminate only the problem plants.

“A lot of communities around here used to be dry oak savannahs or barrens and were fire-dependent communities,” Vanderweide said. “So one thing that helped invasives establish here is when people started building towns; they naturally wanted to keep the fire out, and that allows a lot of invasives to establish a foothold.”

While burning out unwanted plants is not a particularly helpful strategy for residential areas, Vanderweide said his department would soon be having volunteer days where people could learn how to control these invasive plants. He suggested calling him at (248) 651-7810, if interested.

Roseville Department of Public Works Director Thomas Aiuto said that his parks staff sprays chemicals to keep some unwanted plants under control, but otherwise, they do not get involved in invasive plant control.

“Besides just the broadleaf protection for the dandelions and such early in the season, there’s nothing really,” Aiuto said.

The most difficult invasive plants to get a handle on are the ones gardeners plant purposefully, which then spread wildly beyond their lawns, she said, such as lily of the valley or garlic mustard. Both plants can spread very easily — lily of the valley under fences and garlic mustard by going to seed.

Gerstenberger suggested not passing around lily of the valley unless the grower is ready to deal with control efforts, while garlic mustard only goes to seed in its second year — the first year it has only a little green rosette on the ground — so beheading the flower before it can spread seeds will take care of the plant.

Vanderweide said garlic mustard could be contained by spraying it early in the year, before other plants have emerged from winter hibernation, or it can be pulled out by hand. It is a dangerous plant to its neighbors, he said.

“A general problem for a lot of these invasives is that they will displace the native species so they can grow,” he said. “For example, the garlic mustard exudes — its roots give off a chemical that inhibits a fungus in the soil a lot of native plants rely on to get nutrients. That way, they hurt the native plants and open the way for more garlic mustard.”

Another invasive plant, pale swallow-wort, has had a detrimental effect on the monarch butterfly population, Vanderweide said, as the insects will lay their eggs on the plant. When the caterpillars emerge, they are unable to get the nutrients they need to survive from the plant, and so the caterpillars die.

Other problem species include buckthorn, autumn olive, and Asian bittersweet, he said. Those shrubs can be dealt with by using herbicides at specific times of the year.

Gerstenberger said biological control methods — using a plant’s natural predators against it — are an option, but it requires a lot of testing to make sure there are no adverse impacts to native species. She said a kind of beetle that only attacks purple loosestrife has been extremely helpful getting that species under control in Michigan.