Invasive Species



Des Moines Parks Initiates Control of Garlic Mustard, a threat to the woodlands at Greenwood and Ashworth Parks.



The Des Moines Park and Recreation Department has begun measures to control garlic mustard, an aggressive biennial plant that is an increasing threat to the aesthetics and ecological integrity of the woodlands in the city’s Greenwood and Ashworth Parks, located from 45th to 49th Streets, between Grand Avenue and the Raccoon River. Initial eradication efforts will involve herbicide application when the temperature is above freezing this fall through early spring; native plants will be dormant, but the garlic mustard plants will remain green and photosynthesizing. Native plants, which emerge later in the spring, will not be affected by the herbicide because the glyphosate herbicide, known on the retail market by such brand names as Roundup, is not residual in the soil. As is typically the case with herbicide applications, people are asked to stay off treated areas for 24 hours following treatment; dated signs along major entries to the park areas indicate when those portions will be again be available for use.

Intensive follow-up efforts using multiple control techniques over the course of the next four to five years are necessary in order to deplete the seed bank of the garlic mustard in the soil. Measures will include spring prescribed burns, further herbicide applications and cutting of plants. Thereafter, continued monitoring and routine maintenance as well as eradication by property owners adjacent to the parks will be necessary to prevent another outbreak of garlic mustard.

A native of Europe, the rapidly spreading plant was introduced in the United States in the mid-1800s for medicinal and herbal purposes and has no native predatory insects or other natural controls to curb its rapid spread in this country. Growing tall and dense within a few years, it crowds out woodland understory plants such as wildflowers, ferns and tree seedlings as well as wildlife habitat. Garlic mustard prefers shaded and semi-shaded areas, and spreads most rapidly in highly-disturbed areas such as along trails, waterways and forest edges. According to Cathy Mabry McMullen, Ph.D, adjunct assistant professor in the Department of Natural Resource Ecology and Management, Iowa State University:


“The species is not subject to its native predators, pathogens or competitors, factors that would hold its population in check. Without control, garlic mustard populations may double every four years. Because it is capable of explosive population growth, once garlic mustard is established in natural woodland, and if it is not controlled, it is capable of displacing the understory flora and of suppressing the natural regeneration of trees. If the regeneration of oaks and other tree species is suppressed, over time the ability of the woods to regenerate will be compromised. As native species are displaced, it is likely that other wildlife species that feed on the plants will be affected. It is widely recognized by the Iowa Department of Natural Resources and most, if not all forest managers as the number one non-woody invasive species.”

Greenwood and Ashworth Parks are among the last intact remnants of native Iowa woodlands and act as an important refuge for native plants, birds and other animals in addition to buffering the water supply from fertilizers, lawn chemicals and other urban runoff. In order to rid these parks of garlic mustard and preserve the native-plant woodland understory, foster tree regeneration and ecological function, Des Moines Parks and Recreation encourages property owners in areas surrounding these two beautiful and valuable adjoining urban parks to likewise begin removal of the plants in their yards. Photos of garlic mustard as well as a map indicating broad areas with high, medium and low infestations in Greenwood and Ashworth Parks can be found on the department’s website at www.dmparks.org. In addition, a full report and plant inventory and ecological assessment of Ashworth Park can be found on the website.

For more information contact Teva Dawson, Horticulture Inspector, (515) 208-0308 or by e-mail, tldawson@dmgov.org.


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City of Des Moines, Iowa
Parks and Recreation