Connecticut plant scientists and volunteers who work on invasive issues are gravely concerned that mugwort (Artemisia vulgaris) is spreading rapidly throughout our road network. Minute seeds are blown across the winter landscape and carried in road dirt, in tire treads, on undercarriages, and by snow plows.  The seeds germinate well in bare spots,  and new mugwort patches spread from roadsides into adjacent meadow and forested habitats. A two- meter-tall plant yields up to 200,000 seeds!

We urge a time-sensitive measure: please mow the mugwort on your own land and encourage roadside mugwort mowing on municipal, DOT & commercial land preferably before the end of September when the tiny seeds ripen. Leave the larger patches of native roadside wild flowers, e.g.  yellow goldenrod, fluffy -seeded milkweed, and purple  Vernonia & Joe Pye. This recommendation emerged from a germination study by Jeffrey Ward, a plant scientist at the CT Agricultural Station (CAES), which showed that immature mugwort seeds germinated poorly or not at all; hence cutting in early fall spreads few seeds, and saves the expense of picking up the cuttings. 

Mugwort was repeatedly transported from Europe to New England several centuries ago  in ship ballast. Ignored for centuries as a tough, clonal weed of vacant land, it has begun to spread by seed, as well as by rhizome bits – found even in screened commercial topsoil. Each established patch has a large network of vigorous rhizomes (underground stems), like Japanese knotweed, also shown in bloom in the background of photo at left, which depicts a stand of mugwort in bloom, relatively low because it was mowed in early summer. Note that  most  Japanese knotwood clones have non-viable seeds, but seed germination has been detected in a few studies, an urgent research need, as Japanese Knotweed is, like mugwort, a “supercompetitor”.

Mugwort grows in sun or shade, and in droughty or soggy soil. Dense mugwort colonies crowd out even the hardiest native goldenrods, grasses, and asters, but mugwort has far less ecological value. The seeds are too small for birds to eat. In September, mugwort plants form plumes with tiny, dull white flowers  which yield no nectar, though the abundant wind- dispersed pollen causes hay fever. The finely dissected, gray-green leaves have a strong medicinal smell, and are eaten by few herbivores;  because it repels fleas and vermin, mugwort has been  used as bedding for  livestock. Mugwort often reaches over 5 feet in height, though early summer mowing, shade,  or very infertile soil may reduce its mature height to 1-2  feet.  Artemisia vulgaris threatens Connecticut’s biodiversity, agriculture, public health, and natural scenery.  Simple mowing can much slow down its advance. Other control measures include double layers oif landscape fabric or other mulch.  Herbicidal treatment with herbicides is tricky, due to the deep, dense rhizomes.

Unfortunately, it has begun to colonize some of Connecticut’s most special, beautiful places where uncommon and rare plants can still be found, such as rocky summits, sand plains, and river floodplains, termed “Critical Habitats” by the Wildlife Division of the Connecticut Department of Environmental Protection (CTDEEP).  On a CBS botany field trip in North Haven, last summer, we noticed that mugwort is now abundant in the beautiful pin oak forest east of the Quinnipiac Marsh and in a silver maple floodplain forest along the Still River, in a Weantinoge Land Trust preserve in New Milford.

In a botanically diverse state park or preserve, careful pulling of young plants may prevent establishment of new colonies, but only if done before rhizome formation. Research is needed to find out at what stage  this takes place, and also how long rhizome fragments remain viable. Snow plows & street sweepers likely disperse seed & rhizome bits.Would additional mowing during the summer be helpful?

The photo of a mugwort seeedling  (or rhIzome sprout) was taken in about 2015 at the edge of a gravel tracking pad in Meriden, at the Platt High School  construction site (where I was an erosion & sediment control monitor). Nearby, I noticed that along the Sodom Brook  linear trail the city practice of  trailside mowing in early summer was allowing mugwort to coexist with native goldenrods and small white asters, over a two-year period – but for how long?   Frequent mowing will help control a mugwort colony, but will result in a mugwort-dominated lawn, NOT a scenic meadow, with perennial grasses & flowers like chickory, goldenrods, Joe Pye, ox-eye daisies, asters, and Vernonia.

Members of the Right-of-Way Sub-committee of the CBS Ecology & Conservation Committee are concerned that Eversource’s new wide gravel roads and gravel pads along powerlines, will in all likelihood become new mega-seed sources, and spread into remaining ROW habitats, which are especially rich in biodiversity, including rare Lespedeza bush clovers, shrubland birds, Eastern box turtles, and the New England cottontail, our only rare rabbit species.

Although mugwort seeds are known to remain viable for several years, protracted sprouting from the seed bank may not be an issue, after a nearby seed source is controlled.  Kathleen Nelson, a CIPWG volunteer scientist, made a welcome discovery: mugwort seedlings entirely  stopped sprouting on her land,  the first year after a neighboring mugwort stand was mowed  in early October of 2015 & 2016.

The Connecticut Botanical Society suggests you call an official you know at your town hall, and explain why it is wise to mow down mugwort colonies in early fall; mention that prompt stabilization of  bare soil will help eliminate seed beds for mugwort patches, as well as protect water quality.  You could e-mail the link to this on-line article . The photo below shows mugwort and Japanese knotweed colonies on a  former soil pile.  Eversource officials and/or the CT Siting Council also need to understand that even thick gravel pads are readily colonized by mugwort, and become a significant seed source, statewide.  

About sigrungadwa

Consulting Ecologist and Registered Soil Scientist. My firm, Carya Ecological Services, LLC conducts inventories of vegetation, wetlands, and habitat; wetland delineations; and ecological assessments - for open space grants, application reviews, and applications for open space/cluster developments. We work either as the lead firm or as a subconsultant. I have a Masters Degree from UCONN-Storrs, Dept of Ecology & Evolutionary Biology (1997) & a Bachelors from Brown U. in Biology.
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  1. sigrungadwa says:

    This article is one of three prepared for a CBS press packet. Thanks for input from several friends (also plant scientists) from CIPWG, the CT Botanical Society and the Cheshire Land Trust. We really hope that towns and roadside property owners coordinate mugwort mowing in early to mid Sepember, so that the state is not subjected to yet another deluge of mugwort seeds. This formerly clonal species now, unfortunetely, has altogether viable seeds in Southern New England. This occurred some time in the last two decades. Perhaps fertility had been genetically suppressed by inbreeding depression during the past three and a half centuries, if most of the ballast transported by colonial sailing ships originated from just a few port-side mugwort clones in Europe.

  2. Geoffrey Wiswell says:

    I am available. Thank you for bringing this article to the public’s attention. I am a Vegetation Management company, Beech Hill Vegetation, who specializes in mowing on slope, mounds, catch basins, reservoir dam faces, retention ponds and clearing land of invasive bushes, shrubs, weeds and trees. We are licensed and insured.
    Please give us a call we are available to be dispatched to helping eradicate the Mugwort.
    We can be reached by phone: 860-608-5533 or via email
    Geoff Wiswell

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