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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.
Help your community protect local resources by preventing and managing
invasive plants. Invasive plants vary greatly in western Canada's diverse climates.
To find out more about invasive plants in your area or to seek alternative plants,
visit www.invasiveplantcouncilbc.ca or phone (250) 392-1400 or 1-888-WEEDSBC.