By Steven Apfelbaum
Dame’s rocket has escaped from gardens and is rapidly invading the surrounding landscapes. Left unchecked, this beautiful, yet lethal plant will wreak havoc on the natural environment, threatening the survival of native plants and degrading habitat and water quality.
Dame’s rocket (Hesperis matronalis) is a tall, short-lived perennial, which produces white, pink or purple flowers in the spring. Known for its colorful and fragrant blooms, the plant has been a traditional garden favorite. However, in recent years, Dame’s rocket has gone rogue, moving from yards and garden plantings into the adjoining landscapes.
An abundant seed producer, Dame’s rocket is dispersed with the aid of mammals. When the seed-bearing pods ripen, they pepper seed onto the coats of a wide variety of wildlife, allowing for extensive seed spreading. As a result, the plant is rapidly infiltrating waterways, wetland margins, farm fence rows and tree lines, and even colonizing natural areas of prairie, savanna, stream course and many types of wetland margins.
Dame’s rocket seems to be following explosive growth patterns similar to its close relatives in the mustard family, garlic mustard, yellow rocket, hedge mustard and wild radish, all highly invasive species that have infested agricultural lands and native woodlands, savannas and grasslands across the country. In the U.S., the annual damage costs from invasive species are estimated to be more than $200 billion a year, which doesn’t take into account the costs associated with impacted ecological systems, such as loss of biodiversity. Allowing Dame’s rocket to continue its current expansion will cause similarly costly impacts to the environment and economy.
Very high-quality landscapes, including state natural areas, are not immune from the invasion, nor are agricultural lands. Evidence of the compelling risk this plant represents have been personally observed by the author in many settings in Wisconsin and Northern Illinois, including Stone Prairie Farm, located in southern Wisconsin.
At Stone Prairie Farm, Dame’s rocket was first found along the perimeter roadways and the stream bisecting the farm. Multiple methods have been employed to eradicate the plant. These include mowing of open non-forested locations, hand pulling in the fence rows and forested locations and direct Roundup (herbicide) application on the plant in hard-to-reach areas containing desirable native vegetation.
Surprisingly, Dame’s rocket was also found widely dispersed over a several hundred- acre cornfield, coming up from between the stalks of the corn stubble from the previous year. Closer observation suggested the field had been no-till planted with corn the previous year. Because no-till planting is usually preceded by an herbicide application, this may suggest that Dame’s rocket has herbicide tolerance (unless the farmer did not treat his field with herbicide).
Dame’s rocket appears to have allelopathic tendencies (the ability to produce chemicals that prevent or reduce the growth of other plants) similar to garlic mustard. Observations in floodplain forests have shown nearly continuous development of Dame’s rocket along with an equally dense growth of garlic mustard—both plants are able to quickly form dense monocultures within a few years of colonization.
Controlling Dame’s rocket is not easy. In moist soils, simply pulling the plant removes it from the ground, roots and all. In slightly drier conditions, pulling the plant will cause the flowering stems to break off above ground level, leaving roots to re-grow. Mowing curtails seed development, but some plants have been observed to re-flower and produce seed after mowing. Mowed materials dry quickly, and mowing should be conducted before pods are fully mature. As a precaution, any hand-pulled plants should be properly removed, bagged and disposed until more data is available about whether seed pods can ripen after plants are mowed or pulled.
Dame’s rocket is not a protected native wildflower, but, in most locations, it is not classified as a noxious weed. Due to its widespread encroachment on native landscapes and species, it is imperative to educate the public about the risks of Dame’s rocket and encourage states to list the plant as an invasive species. Further actions must also be taken to develop plans addressing containment and removal of Dame’s rocket. Any plan must also be mindful of desirable native plant species and habitat conditions in a targeted location that may be vulnerable to herbicide uses and mowing.