Weed of the Week: Leafy Spurge
Plants like to grow, and gardeners love to grow them; however, some plants are invasive, including leafy spurge (Euphorbia esula).
Leafy spurge has a highly competitive growing ability that causes a drastic, irreversible shift in the ecology of surrounding habitats; as native plants are displaced, biodiversity declines.
Leafy spurge is considered among the most ‘unwanted’ invasive plants in British Columbia (BC), and rated provincially noxious under the BC Weed Control Act. It was first identified in Canada in 1889, and has grown to be a large problem, economically, socially, and ecologically. Leafy spurge now occurs extensively in the southern prairie provinces and southern Ontario. In Manitoba, leafy spurge infests 140,000 hectares of land, costing an estimated $19 million per year in protection of grazing land, public land, and right-of-ways, says the Canadian Food Inspection Agency.
Leafy spurge is a uniquely competitive invasive plant because it produces a compound that actively inhibits the growth of other plants nearby. Affecting surrounding soil, leafy spurge then spreads quickly with an extensive root system, which can exceed five metres horizontally and nine metres vertically. Up to 300 new buds can form on the roots of a single plant and seed production also contributes to new growth. Seed capsules open explosively, dispersing seed up to five metres from the parent plant, with seeds further dispersed by people, water, and wildlife.
Because of its persistent nature and ability to regenerate from small pieces of root, leafy spurge is extremely difficult to control. Multiple treatments are necessary every year for several years, making leafy spurge control an extremely expensive undertaking. If left uncontrolled for a single year, this aggressive invader can re-infest rapidly.
Leafy spurge has clusters of petite, yellowish-green flowers supported by distinctive heart-shaped leaves just below flowers. It is a bushy plant with narrow leaves that spiral around the stem, and grows up to a metre tall.
Also known as “wolf’s milk,” the entire plant contains white, milky latex that can irritate skin of livestock and people, resulting in blisters and swelling. The North Dakota State University reports that its toxin has produced inflammation and loss of hair on the feet of horses from freshly mowed stubble during haying, and has caused mortality of sheep that grazed leafy spurge exclusively. However, sheep and goats may graze leafy spurge as a portion of their diet without suffering health problems.
Animals will eat dried plants in hay, but many livestock, particularly cattle, avoid grazing this plant all together. Consequently, rangeland suffers a loss of productivity. North Dakota State University research indicates that in that state, there are 5 million hectares of untilled land on farms such as pastures, range, woodlands, and roads. Since leafy spurge is found primarily on untilled land, the present infestation covers approximately six percent of the state’s farmland.
In Washington, the State Noxious Weed Control Board reports that leafy spurge reduces pasture and rangeland carrying capacity for livestock by 20 to 50 percent, causing an estimated $35-45 million loss per year in United States beef and hay production, in addition to the millions of dollars spent for control. Another Washington study reports that the invasion of leafy spurge in four northern US states has resulted in annual economic losses of US $129 million, equivalent to approximately 1,433 jobs.
Native to Europe and temperate Asia, leafy spurge is found throughout the world with the exception of Australia. It was probably introduced into the United States as a contaminant in imported grain. In BC, isolated pockets occur in the Cariboo, Boundary, East Kootenay, Nechako, and North Okanagan areas. It is a major concern in the Kootenay, Okanagan, Thompson, Cariboo, and Omineca regions.
In total, leafy spurge infests just over two million hectares of land in the U.S. and western Canada. It reduces plant diversity and rangeland productivity, and degrades wildlife habitat, requiring aggressive management to prevent further spread.
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