Published: April 30, 2013 by the Central Office
MADISON -- This year's late spring is giving people plenty of time to plan for controlling invasive plants like garlic mustard. However, with the recent warm up, state invasive species specialists say those fast growing plants may quickly bolt and start to flower. Landowners, land managers and volunteers who work in parks and other natural areas should be prepared to get outside and start their control efforts soon.
Most people are familiar with garlic mustard (Alliaria petiolata), a biennial plant that overwinters as a rosette of small green leaves and in the spring sends up one to many flower stalks with triangular leaves and small, four-petaled white flowers.
"Anyone uncertain about the identification can crush the rapidly growing leaves" says Kelly Kearns, invasive plant specialist with Department of Natural Resources Bureau of Endangered Resources "If it smells like garlic, you probably found garlic mustard."
This rapidly growing biennial spreads through forests, eliminating native wildflowers, limiting tree seedlings from developing and even slowing the growth of mature trees.
Landowners wanting to keep this weed from overtaking their woods must prevent any of the plants from producing seed each year. For smaller populations this usually involves hand-pulling. Kearns says people can save themselves extra work if they pull before the plants start to flower. At that time the plants can be thrown onto the shrubs or scattered to dry them out.
"Avoid leaving them in piles as that will allow them to stay moist and continue to grow and flower. If the plants have started to flower, they need to be removed from the sites and disposed of to prevent seeds from developing," Kearns says.
Although state law bans yard waste from landfills, any plants that are regulated as "restricted invasive plants" by Wisconsin's Invasive Species Rule can be sent to landfills to keep their seeds and roots out of municipal and county compost facilities. They should be bagged, with the bags marked "Invasive Plants" so the landfill operator knows they are exempt from the yard waste ban. The list of regulated invasive species and photos and fact sheets for most of the invasive plants can be found on the DNR's website and type in keyword "invasives."
In addition to garlic mustard there are a number of other herbaceous plants that can invade forests and spread quickly. In southern counties hedge parsley (Torilis japonica) is quickly expanding its range.
"Don't be fooled by the delicate look of the fern like leaves and small umbrella shaped clusters of tiny white flowers," Kearns says. "These plants produce seeds with burrs that stick to clothes and fur and hitchhike to new areas."
Dame's rocket (Hesperis matronalis) is related to garlic mustard and spreads in similar ways. Its flowers range from white to pink to lavender. Its flowers have only four petals, whereas the look-alike phlox has five petals.
Homeowners, and especially landowners, should be vigilant in watching for any plants that seem to be spreading and "taking over." Even some native species can become aggressive and more abundant than is desired. The key to keeping any invasive plants from completely overtaking an area is to keep them from reproducing.
"Diligent efforts to prevent the plants from producing seed can keep woodlands free of the weed and protect the habitat for an array of wildflowers and native trees," Kearns says.
To keep any weedy plant under control, landowners will need to use some combination of pulling, cutting, burning or using an herbicide before the plants flower to keep them from developing seeds. Some plants also spread by creeping stems or roots, so additional effort may be needed to stop their spread.
If herbicides are used for these herbaceous forest invasives, it must be done early and carefully to prevent killing wildflowers and other desirable plants. There is information about controlling these plants on the Web and in publications from the DNR and University of Wisconsin-Extension.