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Lotsa Garlic By Geoff Peach Spring is the time of year we look forward to our landscape 'greening up'. The trees breaking out in leaf, plants flowering - it's a time of re-growth and rejuvenation. Not to put a damper on your enthusiasm, but our natural areas are being threatened, and it's by a small plant that has been spreading across the landscape. It has the capacity to affect our wooded areas, including the coast of Lake Huron. Garlic mustard (Alliaria petiolata) is considered to be one of the most invasive exotic plants in Canada. It thrives in rich, moist upland forests and wooded streambanks. It is shade tolerant, and readily invades deciduous woodlands, hedgerows, disturbed areas such as roadsides, trail edges and gardens. This plant is one of the most rapidly expanding invasive plants of woodland habitats in eastern Canada. Its ability to form dense monocultures affects native wildflower populations. Once garlic mustard moves into an area, it steals away available light, water and space from plants like wild ginger, bloodroot, toothworts, trilliums, and other native flowers, as well as choking out forest understory growth. Without sufficient understory growth to replace the existing forest, the long term health of the forest is threatened. New research suggests that Garlic Mustard harms native maples, ashes, and other hardwood trees by releasing chemicals harmful to a soil fungus the trees depend on for growth and survival. The tree-stifling alien, first introduced into North America in the 1860s, has since spread into southwestern Ontario. The research has shown that this invasive plant harms native plants by thwarting the biological “friends” upon which they depend for growth. Garlic mustard targets arbuscular mycorrhizal fungi (AMF), which form mutually beneficial relationships with many forest trees. These fungi have long filaments that penetrate the roots of plants, forming an intricate interwoven network that effectively extends the plant’s root system. AMF depend on plants for energy and plants depend on the fungi for nutrients. The chemical released by Garlic Mustard destroys that ecologically vital relationship. Garlic mustard is one of the threats that has placed two species of woodland plants, designated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), at risk. Both the wood poppy (endangered), and the wood aster (threatened) are at stake. But it’s not just flowers – garlic mustard is also toxic to butterflies, which perform important functions in the ecosystem, like plant pollination. The Huron Fringe Forest (the band of forested area that runs parallel to the Lake Huron shoreline) has shown signs of invasion by garlic mustard. Garlic mustard is a biennial herb in the mustard family. Plants can range in height from 15 centimeters to over one meter in height. The first year plants form rosettes of kidney-shaped leaves which winter as an evergreen. In its second year, the plant grows a stem with leaves that are triangular and sharply toothed. Four petalled white flowers form at the end of the stem. Seeds are black, oblong and found in rows within a long narrow capsule called a silique. Seed dispersal is primarily through human activities and other animals. Seed production can exceed 62,000 per square meter. Seeds are dormant at maturity and require a cold period to germinate. Seeds can germinate up to six years after production. Crushed leaves and stems of this plant give off a distinctive garlic odour. Control? Disposal: Sanitation: More information on Garlic Mustard: |
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