Garlic Mustard (Alliaria petiolata)
Invasive Plants
Imported as an edible green by European settlers, this biennial shade-tolerant species dominates the groundcover of deciduous forests and disturbed areas such as flood plains, stream banks and roadsides. Since its introduction to a few locations in North America in the 1800s garlic mustard spread gradually, but has recently undergone a series of population explosions over the past 20 to 30 years. It is now widespread across north-eastern North America south of the Canadian Shield, and has also been found to the west in Vancouver and California. Garlic mustard is found in many forests and disturbed sites throughout the Credit River Watershed.
In its first year garlic mustard is often easily-overlooked, growing as a relatively small basal rosette of leaves that may be mistaken for native species such as violets. It can be easily distinguished by the garlic odour it gives off when crushed. By its second year garlic mustard grows a flowering stalk up to 1 metre in height, bearing clusters of 4-petaled white flowers in early spring. Each plant is capable of producing hundreds of seeds which remain viable in the soil for up to 5 years. Seeds can be dispersed by flowing water as well as by birds, animals, and people.
Invasion of forests usually begins along the forest edge, and spreads along watercourses and trails. An aggressive competitor, garlic mustard is able to alter soil chemistry, making it unfavourable for many native plants, and its early spring growth crowds out species such as trilliums, violets, wild ginger, and many tree seedlings. Consequently, it comes to dominate the understory, often forming dense single-species stands in invaded sites.
Garlic mustard invasions may lead to reduced biodiversity and loss of forest productivity and growth. They may also deprive insects and other wildlife of suitable food or habitat by reducing or eliminating the required native plant cover. Some fauna may disappear from an area after garlic mustard has become established, and it has the potential to dramatically alter the long-term composition and structure of forests and natural areas. Once garlic mustard has become established at a site, control methods need to be repeated every year until the existing seed bank is exhausted or the population may re-establish itself and spread. Early detection and removal of garlic mustard before the first generation of seeds is produced is therefore the best way to prevent its establishment.
