One of the most persistent and problematic weeds to infest large areas of pasture and prairie in Western Canada is leafy spurge. It is even a larger problem in the northern U.S. — North Dakota, and parts of Montana are badly infested; Wisconsin and Minnesota are also dealing with it.
Leafy spurge is not native to North America. It came here from Europe sometime in the mid- to late-1800s and has spread. “There are different corridors that it seems to spread along, such as railroads, highways, rural roads and waterways. Despite great efforts undertaken to control it, leafy spurge is spreading in Saskatchewan. The current control efforts are not consistent enough to actually make the overall population shrink,” wrote Harvey Anderson, invasive plant management co-ordinator with the Saskatchewan Association of Rural Municipalities (SARM).
This perennial weed spreads quickly and crowds out native vegetation overtaking large areas of open land and reducing land value. Horses and cattle avoid the plant because the stems produce a milky sap, which may cause scours and mouth blistering. Sheep and goats, however, will readily eat the weed without any apparent harmful effects.
Leafy spurge spreads by seed and an extensive root system. Roots are known to go down 26 feet (eight metres) and spread laterally up to 4.5 metres a year. The plant grows to a height of 40 to 90 cm (15 to 36″), is extremely adaptable and thrives in a variety of soil and growing conditions. The roots release a toxin that inhibits other plant growth nearby. The plants’ ripe seedpods explode, scattering seeds up to five meters (six yards) in all directions. Seeds that do not germinate the following year can remain viable for at least eight years.
A noxious weed
Leafy spurge is classified as a noxious weed under Saskatchewan’s Weed Control Act, which states: “Every owner or occupant of land shall contain and control any noxious weeds located on the land.”
Control measures that were initially implemented included annual spraying with 2,4-D. “Later Tordon 22-K was used but some landowners have concerns. The active ingredients in Tordon 22-K do move into the soil, so it’s not recommended around flowing water sources or in sandy soils where it can move into groundwater. New products are being developed that are more environmentally friendly — products that don’t move into the groundwater and move very short distances from where it is sprayed,” says Anderson. Spraying is also expensive, difficult to carry out in rough terrain, and will not totally eradicate established patches of spurge.
Other methods of control include regular mowing, the use of sheep or goats, and the introduction of beetles brought in from Europe.
Mowing, if done before the plants go to seed, helps to curb the spread of the seed. However, like other perennials with lateral roots, mowing encourages the plant to regenerate itself by sending up sprouts from the lateral root system.
Sheep have been used extensively in the U.S., Alberta, Manitoba, and to some extent, in Saskatchewan, to control leafy spurge. Sheep will selectively graze leafy spurge and reduce its density and prevent plants from going to seed. They crop the young plants close to the ground, which, over time, weakens the plants so they become susceptible to disease.
Spurge provides a good source of nutrients to the sheep. There is also the benefit of revenue that can be generated from the sheep; bearing in mind there will be associated costs, such as fencing, water and shelter for the animals. Predatory control is another factor sheep owners need to take into account. “Sustaining a flock takes effort by the producer, but I do encourage the use of sheep. It’s an ecologically sound way to go,” says Anderson.
Beetles as control
The use of beetles is the most cost-effective way to control this weed. Once the insects become established, they are self-sustaining.
According to Anderson, 19 species of leafy spurge beetles were brought into Canada for bio-control purposes, with the first releases over 30 years ago. “Most of these 19 species were released at one site south of Weyburn on six quarters of pasture land covered with leafy spurge. Over the years, some of these species have died off, but we believe we have three species remaining,” he says.
These three species are the brown dot spurge beetle Aphthona cyparrissiae and the black dot spurge beetle Aphthona nigriscutis, both of which require full sun and sandy soil conditions to thrive. The black spurge beetle Aphthona lacertosa prefers clay/loam soils and will tolerate some shade.
The beetles are small — about the size of a match head — and have similar life cycles. The adults emerge from the soil in late June or early July and feed on the uppermost parts of the spurge plants. They mate and the females will lay their eggs beneath the soil surface at the base of the plants. Females, depending on the species, can lay up to 300 eggs in a season. When the larvae hatch, they begin feeding on the small roots and continue on the larger roots. This weakens the plant by impairing its ability to take up moisture and nutrients. Plants become more susceptible to diseases. The larvae become dormant in the soil over winter. In the spring the larvae resume feeding for about three weeks before they pupate and emerge as adults.
“With the use of beetles, we know it takes several years before you see a noticeable reduction of spurge,” notes Anderson. “But over the last five to 10 years of the 30 years since the beetles were first released at the Weyburn site, there is very little spurge left on the six quarters that were once completely covered. In fact the beetle population has dropped down to the point now where we won’t be using it as a bug collection site this year. In its heyday, we could collect 2,500 beetles in 45 minutes. We’ll be collecting them at a site west of Moose Jaw this year.”
Anderson has a contract with SARM to oversee an invasive weed program and provides weed management support and education to rural municipalities. He organizes collection days every year at several sites in Saskatchewan in early July before the females begin laying eggs. Volunteers, private landowners and agencies such as Ducks Unlimited, the city of Regina, the Saskatchewan Parks Department, and First Nations communities collect beetles with sweep nets.
“It takes effort to collect the beetles. We supply people with equipment and teach them how to use it, as well as how to release the beetles. They prefer being released at the edge of a leafy spurge patch, rather than in the middle.”
The beetles will not eliminate leafy spurge completely, Anderson says. Like other programs such as mowing, using sheep, or herbicides, beetles are a means of control rather than total eradication.
“However, the success I’ve seen in the southern portion of the province is encouraging. This is where most of the spurge problem is. The northern half of the agricultural portion of Saskatchewan has had more limited success. We don’t know all the factors involved as to why a beetle population grows and flourishes at one site more than another. Our approach more recently has been to distribute the beetles around over all the province where there is spurge, monitor the areas, and find out where it appears to be naturally successful,” Anderson says.
Co-operative weed management
For the last 10 years Anderson has been promoting co-operative weed management with other municipalities by pooling funds to fight the spread of leafy spurge on a larger, more effective basis. “It’s being accomplished through encouragement and example, and it’s been quite successful,” he notes.
For more information contact Harvey Anderson at [email protected].