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Leafy spurge (Euphorbia esula L.) is a persistent perennial weed that was introduced to Canada from Eastern Europe in the late 19th century. It spreads by creeping underground rootstocks as well as by seed. Leafy spurge is widespread through central and southern Alberta, covering approximately 15,000 acres of public and private pasture, rangeland, right of ways, abandoned farmland and other uncultivated land.
Cattle do not eat leafy spurge and will avoid grazing areas where it is present. Leafy spurge also competes with pasture and rangeland grasses, further reducing the livestock carrying capacity of infested land. It is a difficult and costly weed to control for an extended period of time with herbicides.
Biological control involves the use of an insect or disease to control leafy spurge. It is an alternative to the use of herbicides and may be the only option where the use of herbicides is limited, such as by water bodies. Biological control can provide on-going control of leafy spurge.
Finding a biological control agent
Leafy spurge is not considered a serious weed problem in Europe. There it grows in small, scattered patches because it is attacked by a wide range of insects and diseases. Several survey studies were conducted in Europe to identify natural insect predators of leafy spurge. These insects were extensively screened to ensure that they would feed only on leafy spurge and not harm native or cultivated plants in Canada. They were then released at a few closely monitored sites in Western Canada to determine their adaptability and effectiveness in their new environment.
The spurge beetle
The biological control agents that are having the greatest effect on leafy spurge in Western Canada are the spurge beetles. Several European spurge beetles have been screened and released in Alberta, with two of them available for larger scale redistribution.
The black dot spurge beetle (Aphthona nigriscutis) was introduced into Alberta from Hungary in 1983. It has increased in numbers at the original release site to over 400 spurge beetles per square metre and has spread a distance over 500 metres from the initial release point. An accompanying decline in the amount of leafy spurge and an increase in the amount of grass and other vegetation has occurred at the release site.
Although the copper spurge beetle (Aphthona flava) was introduced into Alberta from Italy at the same time, it has not increased in numbers as quickly as the black dot spurge beetle.
Adult spurge beetles of both species emerge between early June and mid-July, depending on the warmth of the soil, and begin feeding on the leafy spurge leaves. They mate and the females lay eggs in the soil beside the leafy spurge roots.
The females continue to lay eggs all summer and into fall, producing up to 450 eggs per season. The adult beetles die in the fall.
The eggs hatch about three weeks after being laid and the larvae feed on leafy spurge roots. It is this feeding on the roots that has the greatest effect on the leafy spurge plant. The larvae continue to feed into the late fall when they build Overwintering cells in the soil and become dormant. The larvae pupate in the soil in the spring and emerge as adults about three weeks later.
What makes a good release site
Selecting a good leafy spurge release site is critical for the establishment of the spurge beetle and the success of control.
The release site should be in an area that will not be cultivated, mowed, sprayed, burned or otherwise disturbed for several years following the release of beetles to allow the spurge beetles to build up in numbers and become established on the infestation. Heavy grazing with the accompanying trampling should also be avoided.
The black dot spurge beetle will be more effective on higher, drier and more exposed leafy spurge patches where the soil is coarser and contains less organic matter. Thin stands on a knoll or south facing slope with sandy soil are ideal for black dot spurge beetle establishment.
The copper spurge beetle prefer a moister, less exposed leafy spurge infestation on sandy soil. Good sites are often low lying spots near trees, bushes or water bodies.
Since it takes several years for the spurge beetle population to build up to an effective level, small isolated leafy spurge patches may be more effectively controlled by chemical or mechanical means to prevent further spread of the leafy spurge.
How to obtain spurge beetles
Arrangements to obtain spurge beetles can be made through the local agricultural field man or district agriculturist or by contacting the Soil and Crop Management Branch, Alberta Agriculture or, when public lands are involved, the range management section of Public Lands Division, Alberta Forestry, Lands and Wildlife.
Collecting and transporting spurge beetles
Spurge beetles are collected as adults, usually just after they start to emerge in larger numbers in early July. They are easier to collect on a warm, sunny day when they tend to be up on the top of the leafy spurge plants. A sweep net is used to gather the approximately 500 spurge beetles needed for one release site. These spurge beetles are carefully transferred into a separate container with a few leafy spurge stems for food. A large plastic pail, cloth bag or plastic bag can be used for a container. Since the spurge beetles are only 3-4 mm in length (about twice the size of an alfalfa seed) and can climb, hop and fly, the container must be tightly sealed and secured for transport. The spurge beetles should be protected from overheating in transport by placing the separate release containers in a cooler with ice or cold packs at the bottom. Do not place the containers directly on the ice.
Releasing spurge beetles
Spurge beetles should be released from their containers within 48 hours of collection. They should be released on the plants at one spot in the centre of a suitable leafy spurge patch rather than scattered over a wide area. The release point should be well marked with a painted or flagged wooden stake for future monitoring of the release. A larger stake, pounded well into the ground, is required where cattle are grazing. Landmarks may be noted on a sketched map to assist in relocating the release site. Photographs taken at the time of release and subsequent years provide a measurement of the effect of the spurge beetles on the leafy spurge.
Checking for establishment of spurge beetles
One year after the spurge beetle release, a successful establishment will have the following characteristics:
The spurge beetle can be found by close scrutiny at and around the point of release, or there is evidence of adult feeding on the leaves. Adult feeding is indicated by small notches cut out of the edge of the leaf often towards the top of the stem. The spurge beetle is easier to find on the leafy spurge plant in mid to late July on a warm, sunny day. Limited use of a sweep net can aid in locating the adults to verify their establishment.
· A reduction will have occurred in the number of flowering leafy spurge shoots, usually in a 1 to 5 metre radius around the release point.
· The amount of grass and/or other vegetation growth may have increased in response to the reduction in leafy source Growth.
What to expect
The spread of established spurge beetles is slow in the first few years. When a dense population builds up they will start to spread over a larger area. On suitable sites, spurge beetles can reduce the leafy spurge population to below 5 per cent cover within 3 years. At this level of infestation, leafy spurge does not seriously affect the carrying capacity of grazing land. Spurge beetles will not totally eradicate leafy spurge. As well, they will not move onto native or cultivated plants to harm them.
Redistributing spurge beetles
Redistribution of spurge beetles to new leafy spurge patches accelerates the dispersal of the beetles and thus their effectiveness, because natural spread is slow. It is the intention of the spurge beetle release program that release sites be used for subsequent harvesting and redistribution of the spurge beetle when the colony becomes mature. Normally spurge beetles should not be harvested from suitable release sites for at least three years to ensure their establishment and a build up in population. In the first year of redistribution only enough spurge beetles should be harvested to release at a few new leafy spurge infestations. This may be in the same field or other locations.
Spurge beetles take several years to start having a significant impact on leafy spurge, but they are a viable alternative for the control of leafy spurge in pastures, rangeland and other suitable non-crop land areas. Once established on a leafy spurge infestation, spurge beetles provide continuing control without additional expense.
Information for this publication was developed through co-operative projects of:
D.E. Cole, Soil and Crop Management Branch, Alberta Agriculture, A.S. McClay, Alberta Environmental Centre, and C.J. Richardson, Range Management Public Lands.
Copyright © 1991 Alberta Agriculture
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