Mugwort
Other names
chrysanthemum weed, common artemisia, felon weed, French tobacco, mugweed, wild chrysanthemum, wild wormwood
Latin names
Artemisia vulgaris L.
Weed Type
Perennial Broad-leaved Weeds
Occurrence
An aromatic perennial with a branching rootstock, mugwort is native in waste places, waysides and hedgerows. It is common throughout lowland Britain and is tolerant of a wide range of soil types and pH. In an early survey of Bedfordshire and Norfolk it was distributed on light calcareous soils. It is able to survive in both cool, dry, and in warm, wet conditions. Mugwort is absent from shaded and grazed sites.
Mugwort can grow up to 1.4 m tall and forms dense stands that smother other vegetation. In the vegetative state it has the appearance of a garden chrysanthemum, hence some of the common names. Mugwort is widely used in herbal medicine including use as a diuretic and the treatment of a variety of gynecological problems. The leaves contain a phytotoxic growth and germination inhibitor. Foliar extracts have also been used in the development of insect repellents. The plant is said to be good for deterring moths.
The related field mugwort (field wormwood, A. campestris) is a non-aromatic perennial with a branched creeping woody stock. It is a native plant but is confined to the breckland heaths of East Anglia. It may be locally common but is nevertheless rare in the UK and is a protected plant.
Biology
Mugwort flowers from July to September. Both ray and disc flowers are present in more or less equal numbers. The flowers are primarily wind pollinated but are also visited by insects. Seed is set from August to October. Seed number per flowering stem is 9,000. Seed number per plant ranges from 50,000 to 700,000. However, some biotypes are reported not to produce viable seeds.
The seeds exhibit some dormancy. Light and alternating temperatures are synergistic in increasing germination, chilling helps too. Seed germination is stimulated by soil cultivation. Germination is faster with dry-stored seed. In the field, seeds begin to germinate from early spring. Seedlings emerge from February to November with flushes of emergence following soil disturbance. Rhizomes are initiated when seedlings approach 4 weeks old, lateral branches are produced at 9 weeks. The rhizomes vary in diameter from a few millimetres up to more than 1 cm. The finer rhizomes usually branch at the nodes and form a dense fibrous mass, the thicker rhizomes exhibit minimal branching. Rhizomes can penetrate to a depth of 7-18 cm in soil. The flower stems die in the autumn and leave a number of separate rhizomes that develop new shoots and overwinter as low leaf rosettes.
Several volatile allelochemicals have been identified in fresh leaf tissue. The chemicals appear to act synergistically. The concentration is higher in young leaves, which suggests that the chemicals may help in early establishment and spread in new habitats. Soil amended with mugwort plant material and leachate suppressed red clover seedling growth.
Persistence and Spread
Mugwort seed is thought to have the potential to form a persistent seedbank. Seeds have remained viable in cultivated soil for at least 5 years. Seed recovered during house demolitions and dated at 30 or more years is reported to have germinated.
There is no obvious seed dispersal mechanism. The light seed may be wind dispersed and/or water borne. It has exploited road and rail systems as dispersal routes. In the USA, mugwort is commonly dispersed by floodwater.
Mugwort spreads slowly by short rhizomes. It can propagate from small rhizome fragments. The rhizomes may be spread or transported by cultivation equipment and among the roots of transplanted herbaceous plants infested with the weed. Rhizome fragments can also be transported in topsoil.
Management
Control is by hoeing, spudding and hand pulling , or by frequent cutting when growing at the margins of fields. However, mugwort is said to be somewhat resistant to mowing and to cultivation. The removal of top growth is reported to stimulate rhizome production and mowing may increase shoot numbers. Frequent cultivation fragments the rhizomes some of which will desiccate if exposed at the soil surface under dry conditions.
A number of insects reside upon and feed on mugwort, some of them may be considered as potential biological control agents. There is predation of the seeds by insect larvae that may destroy around 13% of seeds.
Updated November 2007.