Leafy spurge (Euphorbia esula L.) has its origins in eastern Europe and is thought to have been introduced to North America via contaminated seed brought in by early settlers. As the plant has no natural enemies here, leafy spurge has spread quickly across the prairies and today infests about 130,000 acres in Manitoba.
Leafy spurge (Euphorbia esula L.) is a deep-rooted perennial weed which can spread by both seed and underground creeping rootstocks. The plant stands approximately 2 - 2.5 inches (50-60 cm) in height, has yellowish-green flowers, contains milky white latex, and is usually found growing in patches.
Infestations generally occur in pastures and rangelands. The noxious weed often renders them useless for grazing as the milky latex causes detrimental effects to most grazing animals. Sheep and goats, however, appear to be unaffected and will feed on the plant. Nevertheless, losses in beef production in Manitoba, due to lost grazing capacity, have been estimated at over half a million dollars per year.
Leafy spurge is probably the most difficult noxious weed to control in Manitoba. With a well-developed storage system in its roots, the plant is able to withstand a number of different control methods (i.e. chemical, cultural, mechanical). Added to the difficulty, is the plants preferred habitat of wooded areas and rough terrain which make it difficult to access via conventional means. For these reasons, a combination of two or more control methods has proven to be a more effective leafy spurge management strategy over the long term.
It is important to note that no single chemical treatment will kill this weed. Three herbicides are currently registered in Manitoba for containment and management of leafy spurge. Refer to Manitoba Agriculture, Food and Rural Initiatives Guide to Crop Protection and the product label for application details.
Amitrol-T will give season-long control of leafy spurge but regrowth can still be expected the subsequent year. Banvel provides moderate top growth control which can persist throughout most of the growing season under favorable conditions, while 2,4-D amine will give temporary top growth control, requiring at least one repeat application during the season. All these treatments need to be continued for a few years in order to get significant or complete control of the weed. Annual treatment should persist until at least 90 percent control is achieved or the leafy spurge will rapidly regain control.
Unfortunately, control with herbicides is often not very cost-effective or the weed grows in areas which cannot be reached with spray equipment. Also, required rates of the herbicides recommended for control of leafy spurge are higher than the suggested rates for use on field crops. However, chemicals are useful as a method to contain existing patches when used in combination with other control means.
The use of cultivation or competitive crop species is another alternative control method, particularly in arable land. Mowing and burning have also been used but with very limited success.
Tillage alone as a control method needs to be timely and intense, as leafy spurge can recover quite rapidly from cultivation. Root fragments 3/4 inch (two cm) in length can produce new shoots. For this reason, it is recommended that a spurge infested area be cultivated every three weeks throughout the growing season. If a crop is grown, two post-harvest cultivations every year for three or four years has proven to be an effective control measure, although this may be undesirable for minimum tillage programs or where soil erosion may be a concern. Tillage requirements may be reduced and control achieved more quickly when used in combination with a recommended herbicide in the fall. The herbicide should be applied a minimum of one week prior to the tillage operation to allow for translocation of the chemical to the roots of the plant.
Another cultural control option would be to grow forage or a crop species that are highly competitive with leafy spurge. Significant top growth reduction in spurge has been observed with the use of perennial grasses such as brome, wildrye, and wheatgrass. Growing winter crops such as fall rye is a good source of crop competition in the fall after a tillage or a herbicide treatment, and again early in the spring.
Sheep and goats have performed well when using the weed as a forage and using them to graze the weed is an effective alternative or complement to herbicide use. This method of control is especially practical when the spurge is located in areas where other control means are impractical.
Sheep and goats apparently suffer no harmful effects from grazing leafy spurge and the latex does not cause any irritation. In fact, leafy spurge has been found to be very nutritious.
Studies now in progress near Brandon conducted by Agriculture and Agri-Food Canada, with Manitoba Agriculture, Food and Rural Initiatives and the Brandon Soil Management Association, have shown that after two years, the use of sheep resulted in a significant reduction in leafy spurge dry matter. Grazing by sheep provided a greater decrease in leafy spurge dry matter compared to an application of 2,4-D alone. However, the combination of both sheep and an application of 2,4-D provided the largest reduction.
Although grazing in itself does not kill the plants, it will prevent seed production, and if grazed at a sufficient intensity, will lead to a depletion of root reserves and an associated decrease in plant vigor. This will result in a reduced ability of the weed to compete against grass species, as well as withstand effects of herbicides or other control means.
Sheep should be released to pasture relatively early in the spring so as to provide an immediate attack on the spurge seedlings. If possible, animals should first be corralled in heavily infested areas to allow them to acquire a taste for the plant. There may be a two to three week adjustment period before they begin to consume the weed preferentially.
Studies are still in progress regarding stocking rates for certain levels of spurge infestations, but three to five head per acre per month is suggested at this time. Stocking rate will likely have to be reduced as the season progresses to avoid or minimize use of the grass species. It is advisable to contain animals for two or three days if moving them to a leafy spurge-free area in order to prevent any ingested viable seeds from being transported to the next field.
Results of trials to date indicate that leafy spurge would be sufficiently suppressed and the grass species sufficiently reestablished so that cattle or horses may be reintroduced to a once heavily infested pasture. With lighter infestations, these animals can be permitted to graze, perhaps rotationally, along with the sheep.
Biological control or biocontrol, refers to the use of natural predators, most often insects, as a means to control weeds. The biocontrol agents are introduced to a weed population and released so they can reproduce and repress the weed with little or no further input requirements. Before being introduced into Canada, the agents first undergo rigorous testing to ensure that they do not pose any threat to the environment, such as feeding on beneficial plant species in the absence of spurge.
As the leafy spurge plant is not native to Canada, it has no natural predators here. However, several species of insects exist in Europe, its region of origin, which feed on this weed. Since the early 1980s, Manitoba Agriculture, Food and Rural Initiatives has evaluated several of these species in respect to their impact on leafy spurge populations and their adaptability to our climate.
Two of these insects in particular have provided the greatest impact on leafy spurge to date. Both are flea beetles whose adults feed on the leaves of the plant. However, the root-boring larvae are responsible for the greatest damage to the plant. Aphthona nigriscutis, or black dot beetle, has had a significant impact on leafy spurge populations which are situated on lighter soils in open, sunny locations. Aphthona cyparissiae, or brown dot beetle, prefers somewhat heavier soil and can tolerate denser vegetation, but the insect's habitat must have good sun exposure. Since 1983, approximately 900 black dot and 250 brown dot release sites have been established in Manitoba. At some of the earliest release sites, ninety-five percent of the spurge has been removed by these beetles.
Other insects are being evaluated for use in shaded or moister habitats which are not suitable for the above species. One promising insect for containing the spurge in these areas is Lobesia euphorbiana, more commonly known as the leaf tier moth. Here again, the larvae are responsible for the real damage. The adult moth lays eggs on the spurge plants wherever they are found and when the larvae hatch, they "tie up" the leaves around the terminal bud, preventing any seed production.
Despite these successes, bio-control is a long term management strategy and it may take three to five years for insect populations to become well established. In the meantime, an integrated control strategy can be implemented. The leafy spurge patch should be contained by using herbicides or mowing along the perimeter of the patch. However, a buffer zone around the release site or suppression area must be maintained to allow the insects to spread. It may be advisable to fence off this buffer area around the beetles to prevent trampling by livestock or grazing by sheep. Also, insecticides should not be used within a quarter mile of the release site so consideration should be given to what crops, if any, may be grown in the area.
Biological control is an economical, long term solution to leafy spurge control because once the insects are established there should be no recurring annual costs. All that is required is some occasional monitoring of progress and possibly some minor site maintenance.
Before deciding which control measure or combination of measures to be used on leafy spurge affected areas, several points should first be considered:
For more information, contact:
Your local MAFRD GO Office or Municipal Weed Supervisor.