Euphorbia esula (leafy spurge)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- Biology and Ecology
- Natural enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Impact Summary
- Environmental Impact
- Impact: Biodiversity
- Threatened Species
- Social Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Euphorbia esula Linnaeus
Preferred Common Name
- leafy spurge
Other Scientific Names
- Euphorbia gmelinii Steudel
- Euphorbia intercedens Podp. ex Harrington
- Euphorbia poderae Croizat
- Euphorbia pseudovirgata (Schur) Soó
- Euphorbia x pseudovirgata (Schur) Soó
- Euphorbia zhigulienis Prokh.
- Galarhoeus esula (L.) Rydb.
- Tithymalus esula (L.) Hill
International Common Names
- English: Hungarian spurge; wolf's milk
- French: Euphorbe esule
Local Common Names
- Germany: Esels- Wolfsmilch; Scharfe Wolfsmilch
- Netherlands: Heksenmelk
- Sweden: vargtoerel
- USA: faitours-grass
- EPHES (Euphorbia esula)
- EPHPV (Euphorbia x pseudovirgata)
Summary of InvasivenessTop of page
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Euphorbiales
- Family: Euphorbiaceae
- Genus: Euphorbia
- Species: Euphorbia esula
Notes on Taxonomy and NomenclatureTop of page
DescriptionTop of page
Plant TypeTop of page
DistributionTop of page
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.Last updated: 30 Jun 2021
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|-Inner Mongolia||Present||Original citation: Hou TianJue et al., 1984|
|Federal Republic of Yugoslavia||Present||Native|
|Germany||Absent, Formerly present|
|-Russian Far East||Present|
|-Ontario||Present, Few occurrences||Introduced||Invasive|
|United States||Present, Widespread||Introduced||Invasive|
|-Nebraska||Present, Few occurrences||Introduced||Invasive|
|Argentina||Absent, Invalid presence record(s)|
History of Introduction and SpreadTop of page
Historical events related to leafy spurge origins, introduction and control:
1000 designated wolf's milk, still known by this name in some European locations (Bakke, 1936)
1753 Euphorbia esula L. named by Linnaeus (Bakke, 1936)
1827 Leafy spurge documented in Newbury, Massachusetts (Hanson and Rudd, 1933; Bakke, 1936; Dunn, 1985; Anderson et al., 2003)
1842 Leafy spurge found in Missouri (Dunn, 1979)
1876 Identified in New York as 'rare plant' (Anderson et al., 2003)
1881 Leafy spurge found in Michigan (Anerson et al., 2003)
1890 Leafy spurge probably introduced into Minnesota by contaminated oats from southern Russia (Hanson and Rudd, 1933; Bakke, 1936)
1899 Leafy spurge collected in Mount Pleasant, Iowa (Bakke, 1936)
1899 Leafy spurge found in province of Ontario (Dunn, 1985)
1902 Leafy spurge collected in Brookings, South Dakota (Bakke, 1936)
1915 Leafy spurge collected in Fargo, North Dakota (Bakke, 1936)
1927 Leafy spurge collected in Cambridge, Wisconsin (Bakke, 1936)
1930 Oats harvested at Hawarden, Iowa, had up to 200 leafy spurge seeds per bushel (Bakke, 1936)
1933 Leafy spurge found in at least 21 states and several Canadian provinces (Hanson and Rudd, 1933; Bakke, 1936)
1950 Leafy spurge found in all Canadian provinces except Newfoundland (Anderson et al., 2003)
1964 Hawkmoth released as biological control agent (Anderson et al., 2003)
1970 Leafy spurge found in 26 states (Anderson et al., 2003)
1975 Leafy spurge found in 30 states (Watson, 1985)
1985 Aphthona flea beetle (A. flava) released as biocontrol agent (Anderson et al., 2003)
1989 Aphthona flea beetle (A. nigriscutis) released as biocontrol agent (Anderson et al., 2003)
1990 Leafy spurge infestations determined to be doubling every 10 years, possibly every 5 years (Anderson et al., 2003)
1993 Aphthona flea beetle (A. lacertosa) released as biocontrol agent (Anderson et al., 2003)
1994 650,000 hectares of leafy spurge infested land estimated in North and South Dakota, Montana and Wyoming (Anderson et al., 2003)
1997 Leafy spurge found in 35 states and six Canadian provinces (Quimby and Wendel, 1997; Anderson et al., 2003)
1996 USDA/ARS initiates a 5-year TEAM Leafy Spurge Program (The Ecological Area-wide Management) (Anderson et al., 2003)
1998 2 million hectares of leafy spurge infested land estimated in USA (Anderson et al., 2003)
2001 ARS scientists initiates genomics-based programme to study leafy spurge (Anderson and Horvath, 2001)
2003 15 biological control agents for leafy spurge approved for use in USA between 1964-1998 (Anderson et al., 2003)
HabitatTop of page
Habitat ListTop of page
|Terrestrial||Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed forests, plantations and orchards||Present, no further details|
|Terrestrial||Managed||Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural forests||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Riverbanks||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Wetlands||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Deserts||Present, no further details||Harmful (pest or invasive)|
|Littoral||Coastal areas||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
Host Plants and Other Plants AffectedTop of page
|Anemone canadensis (Canada anemone)||Ranunculaceae||Wild host|
|Platanthera praeclara (western prairie fringed orchid)||Orchidaceae||Wild host|
|Rosa arkansana (prairie wild rose)||Rosaceae||Wild host|
Growth StagesTop of page
Biology and EcologyTop of page
The genetics of leafy spurge is complicated and a high degree of genetic variability among North American leafy spurge populations has been reported (Rowe et al., 1997). Leafy spurge has been studied by cytotaxonomic (or cytogenetic: study of shape, ploidy and chromosome number) and genotypic (study of variation at the genomic DNA level) approaches. Cytotaxonomic approaches have been used to determine Euphorbia species; however, since introgressive hybridization (intercross and backcross) occurs frequently among Euphorbia species (i.e., E. pseudovirgata, E. cyparissias and E. virgata), cytotaxonomic approaches are limited for species determination. At present, three basic chromosome numbers (x = 8, 9, 10) of leafy spurge have been reported in the literature, and the chromosome number of 2n = 60, a hexaploid, is most prevalent in nature (Schulz-Schaeffer and Gerhardt, 1987; Stahevitch et al., 1988). On the basis of cytotaxonomic analysis, the chromosome of leafy spurge has revealed a high degree of instability (mosaicism); chromosome number varies from 2n = 48 to 2n = 60 (Schulz-Schaeffer and Gerhardt, 1987). Composite idiograms of E. esula (2n = 6x = 60) imply the occurrence of segmental allopolyploidy (composed of partially homologous chromosome sets from closely related species) (Schulz-Schaeffer and Gerhardt, 1989). Both results reflect that introgressive hybridization is a common phenomenon among Euphorbia species.
A genotypic approach is used to identify genotypes among Euphorbia species. The identification of plant genotypes is important for biological control because the establishment of biological control agents is often linked to plant genotype. It is known that variability in the establishment of biological control agents is associated with differences in the genotypes of host species (Lym and Carlson, 2002). Two methods, chloroplast DNA restriction fragment length polymorphisms (cpDNA RFLP) and random amplified polymorphic DNA (RAPD), are commonly used for genotypic identification of leafy spurge (Nissen et al., 1995; Rowe et al., 1997). Genotypic analysis has found that North American leafy spurge has a high degree of genetic variability, suggesting possible multiple introductions or high levels of variation in the native range (Rowe et al., 1997).
Physiology and Phenology
Leafy spurge reproduces by seeds and underground adventitious buds (root and crown buds). Population expansion was thought to occur mostly from underground vegetative buds. However, recent analysis suggests that a high degree of genetic variability exists in isolated stands or patches of leafy spurge indicating that seed reproduction may be a significant mechanism for expansion (D Horvath, USDA/ARS, Fargo, ND, USA, personal communication, 2003). Under normal growing conditions, root buds develop but are maintained in a quiescent state by the aerial portion of the plant. These buds develop into new shoots when the shoot is killed or separated from the roots. Two types of inhibition were observed during bud dormancy in leafy spurge: innate and correlative inhibition. Innate inhibition is normally associated with post-senescence and flowering. JV Anderson (USDA/ARS, Fargo, ND, USA, personal communication, 2003) has observed that in the late autumn or early winter, both root and crown buds enlarge and develop deep innate dormancy. Chilling breaks this inhibition status (Nissen and Foley, 1987a; Harvey and Nowierski, 1988; Chao et al., 2001). Correlative inhibition, on the other hand, occurs mostly during the growing season, where inhibition is under the control of signals produced by the aerial portion of the plant. Two separate signals, one from the mature leaves and one from the meristems (apical or axillary buds), result in correlative inhibition. Horvath (1999) demonstrated that the presence of either leaves or growing axillary buds was sufficient to inhibit root bud growth. However, the leaf-derived signal required photosynthesis for its production or transport, whereas no photosynthesis was required for the signal from growing axillary buds. Current results suggest that the leaf-derived signal acts through gibberellic acid (GA) and is responsible for inhibiting the G1/S-phase transition, and the meristem-derived signal is responsible for the inhibition of cell division post S-phase (Chao et al., 2001; Horvath et al., 2002; Horvath and Anderson, 2002).
Other factors such as nutrients, water status, light, temperature, phytohormones and carbohydrates affect leafy spurge development and/or survival (Selleck et al., 1962; McIntyre, 1972, 1979; McIntyre and Raju, 1967; Morrow, 1979; Nissen and Foley, 1987a, b; Harvey and Nowierski, 1988; Cyr and Bewley, 1989, 1990; Chao et al., 2001). Nitrogen appears to be important in the development and growth of leafy spurge. The number of root buds increased at high nitrogen levels (105 p.p.m.). Under deficient nitrogen levels (2.1 p.p.m.), the outgrowth of lateral buds was completely suppressed (McIntyre and Raju, 1967). Carbohydrate and nitrogen reserves stored in the roots appear to provide a source for long-term survival. Total sugars, total readily available carbohydrates, and total nitrate decline sharply in roots from late April through early May (Cyr and Bewley, 1989). The total available carbohydrates reached the lowest level in mid-May when plants began to bloom, followed by a short period of rapid storage and finally, a moderate rate of build-up until the end of the growing season. As the temperature dropped in the autumn, the percentage of true starch declined and sugars (mainly sucrose) increased in the roots (Cyr and Bewley, 1989). Total organic nitrogen in the roots declined from early spring to August then increased. Free amino acids and soluble proteins are also reported to show an increased accumulation in roots of leafy spurge during the onset of autumn and winter (Cyr and Bewley, 1989, 1990). However, unlike starch and soluble carbohydrates, soluble protein, free amino acids and nitrate reserves in the roots of leafy spurge were reduced in decapitated or defoliated plants (Cyr and Bewley, 1990). Higher internal water levels enhance root bud growth. McIntyre (1979) showed that the water content of the root buds increased by 25% within 24 hours of shoot removal, promoting the growth of root buds. Increasing the humidity from 50 to 95% increased the rate of emergence and elongation of root buds after stem removal (McIntyre, 1979). Different phytohormones act differently on root bud growth. GA can promote root bud growth and reverse the status of correlative inhibition in leafy spurge root buds. In contrast, abscisic acid, auxin, cytokinin and sugar (glucose and sucrose) can inhibit root bud growth. Sugar and GA were functionally antagonistic since GA has been shown to overcome the inhibitory effect imposed by glucose and sucrose (Chao et al., 2001). The importance of light and temperature has also been documented. For example, the percentage of flowering shoots decreases under limiting light (Selleck et al., 1962) and plant height increases progressively upon increasing soil temperature (Morrow, 1979).
Leafy spurge is one of the first plants to emerge in the spring. It emerges during March in Iowa and Wisconsin, in late March to early April in North Dakota, and late April in Saskatchewan (Hanson and Rudd, 1933; Bakke, 1936; Selleck et al., 1962; Anderson, 1999). Shoots originate from crown tissue around the soil surface and from intermittent buds along the root system. Bud sprouting declines in mid-summer during pollen production (Best et al., 1980; Messersmith, 1983; Lym, 1991). The plant usually ceases growing during the hot and dry summer months. Stems from seedlings or small root segments generally do not flower in the first year.
Flowering occurs primarily in May but continues through autumn. Bracts are seen about 2 weeks before the emergence of flowers and give leafy spurge the appearance of blooming (Lym, 1998). Each flowering shoot produces more than 150 to 200 seeds. The seeds can be propelled 4.6 or more metres when the mature capsule dehisces. The seeds germinate in spring and continuously throughout the growing season; however, the peak period of germination is late May and early June. Normally, 99% of the seeds will germinate within 2 years, but some are viable for up to 8 years in soil (Bowes and Thomas, 1978; Cole, 1991). The optimal temperature for germination fluctuates between 20 and 30°C. Seedling emergence is optimal at depths of 1.5-5 cm. Young seedlings develop an extensive root system in a short time. All seedlings become perennial by the time they reach the 10-leaf stage, but on some occasions they are able to reproduce vegetatively from buds within 7 days of germinating (Selleck et al., 1962; Lym, 1991).
Leafy spurge has vigorous, rhizome-like, long horizontal roots, short horizontal feeder roots, and short and long vertical roots. The vertical roots can grow as deep as 4.6 m (Bakke, 1936). The roots serve as a nutrient reserve capable of sustaining the plant for years. Vegetative buds are formed on the crown or anywhere along the length of the root. These buds produce shoots in the spring and form new roots for the lateral spread of an infestation. Root fragments are also capable of regenerating new shoots. Partial injury to root systems, stems or foliage induces bud growth and spread of the plant (Selleck et al., 1962; Messersmith, 1983; Wolters et al., 1994).
Reproduction occurs by both vegetative re-growth from underground adventitious buds located on the crowns and spreading roots and by the production of large quantities of seeds. For seed reproduction, insects usually carry out flower pollination. The pollen is most viable approximately 24 hours after emergence of the male flower (Selleck et al., 1962). The female is most receptive to pollen when the stigma opens while the pistil has not inverted. As female flowers develop before male flowers, leafy spurge has a preference for cross-pollination. The fruit develops from a three-celled ovary. Seeds grow inside a three-valved capsule and ripen from early July till late autumn. When ripe, the capsule dehisces, shooting seeds up to 4.6 m for distribution. Fresh seed is generally 60 to 80% viable. Temperature is an important environmental factor affecting seed germination. Alternating temperatures of 20 to 30°C produces the highest germination rate (84%) (Hanson and Rudd, 1933). Light and water are other environmental factors affecting leafy spurge seed germination. Light impedes germination whereas water contributes to rapid germination (Messersmith et al., 1985). The testa (seed coat) of germinable seeds breaks between 12 and 24 hours after imbibition and the radicle can emerge as early as 12 hours (Selleck et al., 1962). Root hairs develop 12-24 hours after the radicle has reached 1 cm. The hypocotyl arises within 12 hours after the appearance of the root hairs. Vegetative buds are visible 10-12 days after seedling emergence from the soil surface (Messersmith et al., 1985). Seedlings do not usually flower in the first year (Selleck et al., 1962; Morrow, 1979).
Vegetative reproduction of leafy spurge occurs from underground adventitious buds on the crown and root tissue (crown and root buds). These buds develop into new shoots when the aerial portion of the plant is removed. Visible buds are present all year around. However, during flowering, new buds are emerging while old buds are deteriorating; the underground vegetative buds are tiny but discernible. Throughout the growing season, new buds enlarge and elongate (see Pictures). Some buds can become many centimetres long during the autumn but fail to develop/differentiate into new shoots due to correlative inhibition and cold temperatures (Selleck et al., 1962; Messersmith et al., 1985; Raju, 1985).
Leafy spurge grows in diverse environments from dry to sub-humid and from subtropic to subartic, but most commonly under conditions of a well-balanced water supply (Lym, 1998). It establishes more readily in disturbed soil, and is primarily found in untilled, non-cropland habitats such as abandoned cropland, pastures, rangeland, woodland, roadsides and waste areas. It can also establish in an undisturbed, pristine plant community (Derscheid et al., 1985; Dunn, 1985; Watson, 1985). Although leafy spurge grows most commonly on coarse-textured soils (Selleck et al., 1962), it tolerates a wide range of soils including a coarse-textured group of light loam to sand, the intermediate group of loam to clay loam, and the clay to heavy clay soils. However, seed germination and seedling establishment appears to be more suited to fine-textured soils (Messersmith et al., 1985). Generally, leafy spurge requires a cold acclimation period to break autumn-induced (post-senescent) innate dormancy in vegetative buds (Harvey and Nowierski, 1988) and to assist in flowering.
Many insects are identified as natural enemies of leafy spurge; for further information, see section on Biological Control.
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Aphthona abdominalis||Herbivore||Plants|Leaves; Plants|Roots|
|Aphthona cyparissiae||Herbivore||Plants|Leaves; Plants|Roots||North Dakota|
|Aphthona czwalinae||Herbivore||Plants|Leaves; Plants|Roots||North Dakota|
|Aphthona flava||Herbivore||Plants|Leaves; Plants|Roots||Idaho; Montana; North Dakota|
|Aphthona lacertosa||Herbivore||Plants|Leaves; Plants|Roots|
|Aphthona nigriscutis||Herbivore||Plants|Leaves; Plants|Roots||North Dakota; Ontario|
|Chamaesphecia crassicornis||Herbivore||Plants|Roots; Plants|Stems|
|Chamaesphecia hungarica||Herbivore||Plants|Roots; Plants|Stems|
|Chamaesphecia tenthrediniformis||Herbivore||Plants|Roots; Plants|Stems|
|Dasineura capitigena||Herbivore||Montana; North Dakota|
|Dasineura sp. near capsulae||Herbivore|
|Oberea erythrocephala||Herbivore||Plants|Roots; Plants|Stems||Montana|
|Spurgia esulae||Herbivore||Plants|Inflorescence||Montana; North Dakota|
Means of Movement and DispersalTop of page
Numerous natural mechanisms of dispersal exist including seed dispersal when the capsule dehisces, water (rivers and streams), wind-blown seeds, and frost breakage of roots with adventitious root buds (Messersmith et al., 1985).
Vector Transmission (biotic)
Biotic transmission of seeds of leafy spurge is attributed to spread by animals (birds, humans, insects and other wildlife) (Watson, 1985).
Although tilling helps to disperse seed and root fragments, which allows for increased spread and reduced competition from other native species (Messersmith et al., 1985), minimum till or no till systems (including range and pasture land) have better establishment of leafy spurge than other types of cropping ecosystems that incorporate regular ploughing. Sowing of seeds contaminated with leafy spurge seed is also a serious source of infestations.
E. esula can be spread by casual contact and dispersed by human activity; soils contaminated by leafy spurge seeds may adhere to shoes, cars and farming equipment. Other forms of accidental introduction include the planned movement of soils containing seeds and roots from infested to non-infested areas.
No intentional introductions have been documented.
Pathway VectorsTop of page
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Growing medium accompanying plants||roots; seeds|
|True seeds (inc. grain)||seeds|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Stems (above ground)/Shoots/Trunks/Branches|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page
Environmental ImpactTop of page
Impact: BiodiversityTop of page
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Astragalus anserinus (Goose Creek milkvetch)||NatureServe; USA ESA candidate species||Idaho; Nevada; Utah||Competition (unspecified); Ecosystem change / habitat alteration||US Fish and Wildlife Service (2014)|
|Gaura neomexicana subsp. coloradensis (Colorado butterfly plant)||NatureServe; USA ESA listing as threatened species||Colorado; Nebraska; Wyoming||Competition - monopolizing resources||US Fish and Wildlife Service (2012)|
|Silene spaldingii (Spalding's catchfly)||USA ESA listing as threatened species||Idaho; Montana; Oregon; Washington||Competition - monopolizing resources; Competition - smothering||US Fish and Wildlife Service (2007)|
Social ImpactTop of page
Risk and Impact FactorsTop of page
- Proved invasive outside its native range
- Highly adaptable to different environments
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Highly mobile locally
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Negatively impacts agriculture
- Negatively impacts human health
- Negatively impacts animal health
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Competition - monopolizing resources
- Competition - smothering
- Competition (unspecified)
- Highly likely to be transported internationally accidentally
- Difficult to identify/detect as a commodity contaminant
- Difficult/costly to control
UsesTop of page
Uses ListTop of page
- Poisonous to mammals
Similarities to Other Species/ConditionsTop of page
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.Cultural Control
Cultural control, including planting of competitive grasses, burning, hand-pulling, grubbing of seedlings, deep mulching and grazing by goats and sheep, can be effective in reducing the spread of leafy spurge. Smooth brome (Bromus inermis) and western- (Agropyron smithii), slender- (A. trachycaulum) or pubescent- (A. intermedium) wheatgrass are the competitive grasses of choice (Lym, 1998). In the clay and sandy loam soils of North Dakota, USA, these grasses have provided up to 85% control of leafy spurge over 3 years. The grasses also provided high yields and nutritive value for grazing (Lym, 1998). Burning is an effective means for reducing top growth of leafy spurge (Bjugstad, 1986; Wolters et al., 1994; Masters and Nissen, 1998). However, burning alone is an ineffective way to reduce leafy spurge infestation, and can actually stimulate sprouting and increase plant density. Controlled burning should be used in combination with other control techniques. Hand pulling can be effective for very small patches of leafy spurge and pulling needs to be repeated every 2 to 3 weeks, since hand pulling will generate growth of new underground adventitious buds. Grubbing of seedlings can be effective if done within the first 7 days after germination (Selleck et al.,1962). Deep mulching can reduce leafy spurge but will also reduce all other vegetation in the treatment area (Bowes and Thomas, 1978).
Grazing by goats and sheep has been used for reducing the top growth of leafy spurge since at least the 1930s (Helgeson and Longwell, 1942). Grazing reduces foliar cover, stresses the root system, and opens up areas for native grasses to establish and grow. Grazing also removes the flowering portion of leafy spurge and, over time, helps to reduce the number of seeds deposited into the soil bank. Studies have shown that 8 years of grazing will reduce viable seed density from an average of 325 to 1.4 seeds/ft² and after 13 years of continuous sheep grazing, infestations of leafy spurge could be reduced to 5% of the ranch area (Bowes and Thomas, 1978; Lacey et al., 1984). The disadvantages are that fencing increases expense, requires care, and that leafy spurge will return when the sheep or goats are removed (Bangsund et al., 2001; IPMPA, 2003).
Cultivation and mowing are the most effective mechanical control methods used (Lym and Zollinger, 1995). Cultivation twice each autumn for 3 consecutive years completely controlled leafy spurge in North Dakota (Lym and Messersmith, 1993). In other habitats, heavy cultivation every 2 weeks during the growing season and every 3 weeks during the late summer and autumn for 2 or more years will also reduce regenerating buds, top growth, and eventually stress the root system. Mowing is less effective at controlling leafy spurge infestation but will prevent seed production and reduce top growth. Mowing also allows for an even regrowth that can increase the effectiveness of herbicide applications (IPMPA, 2003).
Herbicides are one of the most commonly used management tools for controlling leafy spurge infestations. They reduce top growth and, with persistence over time, can gradually reduce the underground root system. However, in some instances, the root system can exude herbicides into the surrounding soil, usually in the top 46 cm, resulting in protection of the lower root system (Lamoureux and Rusness, 1995; IPMPA, 2003). All herbicides presently labelled for leafy spurge control were selected from chemicals labelled for use on rangelands and grasslands (see Herbicide Control of Leafy spurge, USDA-ARS, 2003b). Herbicides that have been used for the chemical control of leafy spurge include picloram + 2,4-D, dicamba, glyphosate + 2,4-D, dichlobenil, fosamine, sulfometuron, glyphosate, imazapic and quinclorac (Lym and Zollinger, 1995; USDA-ARS, 2003b). The most effective chemical control results from the combination of either picloram + 2,4-D or glyphosate + 2,4-D at mid- to late June, or in early to mid-September. Picloram is somewhat cost prohibitive over large areas but does work well as a spot treatment (Lym, 2000). Picloram is also restricted from use in environmentally sensitive habitats containing high water tables, wetlands or flood plains and cannot be used near trees or other desirable broadleaf vegetation. The most effective use of picloram is accomplished by spraying with a mixture of 2,4-D (picloram + 2,4-D) during the true-flowering stage (Lym and Messersmith, 1990). Autumn application of glyphosate provides 80-90% control of leafy spurge after 1 year (Lym and Messersmith, 1985) but has the disadvantage of being non-selective and not applicable to most range and cropping systems. As with picloram, glyphosate can work well as a spot application. However, the application of glyphosate + 2,4-D resulted in a 67% control of leafy spurge 3 months post-treatment compared to the application of glyphosate alone (Lym, 2000). A 3 year application alone, or in rotation with dicamba (another cost-prohibitive herbicide) or picloram + 2,4-D, resulted in 80-90% leafy spurge control, but had the advantage of a 30-65% savings in cost compared to picloram + 2,4-D applications, which result in similar levels of control (Lym, 2000). The use of sub-lethal concentration of glyphosate is thought to induce the breaking of dormancy in leafy spurge roots; possibly allowing for increased translocation of 2,4-D to the root system/buds. Other herbicides registered for leafy spurge such as imazapic are safe to use under many shrubs and trees and quinclorac is safe for use around trees, shrubs and grasses. Imazapic and quinclorac appear to work best during autumn applications prior to the killing frost. Imazapic applied in the autumn can cause temporary injury to grasses; however, the grasses recover herbage production the following year (Markle and Lym, 2001). Fosamine applied during the true-flowering stage can safely be used near water to control leafy spurge. 2,4-D specifically labelled for use near water can also be used annually to prevent seed set or emerging seedlings when applied from June to mid-July.
The most effective methods of controlling leafy spurge have been achieved by screening for biological control agents in Europe. Of the nearly 40 European insect species identified as potential biological control agents of leafy spurge (Gassmann and Schroeder, 1995), 15 have currently been approved for release in North America: Aphthona abdominalis (1993), A. cyparissiae (1986), A. czwalinae (1987), A. flava (1985), A. lacertosa (1993), A. nigriscutis (1989), Chamaesphecia crassicornis (1996), C. hungarica (1993), C. tenthrediniformis (1975), Dasineura sp. nr. capsulae (1991), Hyles euphorbiae (1964), Oberea erythrocephala (1980), Spurgia capitigena (1998) and Spurgia esulae (1985). Aphthona spp. have been the most successful at reducing leafy spurge cover, density and yield, and allowing for increased yields of desirable grass species (Kirby et al., 2000). Aphthona flea beetle adults feed exclusively on the foliage of leafy spurge during the summer. In mid- to late summer the females lay eggs near the base of leafy spurge plants and the hatching larvae feed on roots near the surface until the autumn when they overwinter in the surrounding soil. In the spring, the larvae continue to feed on the roots before pupating and emerging as adults. Among the Aphthona spp., A. nigriscutis and A. lacertosa currently show the most promise for controlling leafy spurge. Other approved biocontrol agents include the gall midge (Spurgia esula) which are tiny midges that lay eggs in leafy spurge flowers resulting in a gall that interferes with flowering/seed production. In the case of gall midge, leafy spurge genotype appears to play a role in egg and larval survival (Lym et al., 1996). In addition, Oberea erythrocephala and Chamaesphecia spp. are stem-miners that lay eggs in stems and the resulting larvae weaken the stem as they burrow down into the root crown where they cause additional damage by feeding (USDA-ARS, 2003b). To date, reduction of leafy spurge with biological control agents has not reduced the overall leafy spurge infestations as fast as the spread of this weed. However, the most effective biocontrol agents (A. lacertosa and A. nigriscutis) were only approved in the last 10 years and the final success rate is still to be realised (Anderson et al., 2003). Many bio-control agents can take 5 to 10 years to establish and increase in numbers sufficient to reduce the density of leafy spurge. It is also important to note that leafy spurge genotype has an influence on the establishment and reproduction of Aphthona spp. (Lym and Carlson, 2002).
To date, no single control method will eradicate leafy spurge. An integrated pest management system consisting of biological control, herbicides, grazing, and species plant competition has been the most effective approach to reduce leafy spurge. This is due to the continued reduction in top growth, reducing the plant's ability to produce new seed, and to supply the root system with nutrient reserves that are important for survival during stressful periods.
Several aspects should be kept in mind when formulating an integrated management programme for a particular habitat. When using biological control, such as flea beetles, herbicides should be limited to autumn application because spring and summer application would reduce top growth and interfere with the adult life-cycle (Lym and Nelson, 2002; USDA-ARS, 2003b). For example, autumn application of picloram + 2,4-D had minimal effects on the establishment and reproduction of flea beetles; therefore, leafy spurge densities were reduced more rapidly by using autumn-applied herbicide in combination with flea beetles than by using either flea beetles or herbicides alone (Lym and Nelson, 2002; Nelson and Lym, 2003). However, herbicide should still be used year round to control small infestations of leafy spurge that may emerge in previously controlled areas. The incorporation of grazing and biological control are also effective. Sheep and goat grazing reduces leafy spurge densities allowing for better flea beetle establishment. Autumn application of herbicides, after grazing, can be incorporated into the integrated management programme. Burning can be incorporated most effectively in the spring or autumn. This practice reduces ground litter and leafy spurge densities and can make herbicide applications more effective. Spring and autumn burning also allows for new top growth of leafy spurge and should be a consideration for integrated management programmes utilizing grazing and biological control. Reseeding can also be part of an integrated management practice that allows for desirable grass species to establish and compete for space, water and nutrients. Effective grass establishment in several North Dakota locations was greatest in areas autumn-treated with imazapic and glyphosate (Masters et al., 2001). Mowing and tilling are other practices that can also be effectively incorporated into an integrated management programme. However, leafy spurge covers a vast area of North America with many different ecosystems and no one integrated management programme is universally standard. Integrated management programmes generally work best by developing a programme that is most cost effective for the habitat under management.
ReferencesTop of page
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