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Species
Euphorbia esula Linnaeus)
IUCN
NCBI
EOL Text
Global Range: Euphorbia esula and its closely related taxa are native to central and eastern Europe with extensions into western Europe and temperate Asia. It is now found worldwide with the exception of Australia. It was most likely introduced into North America via Minnesota with shiploads of oats (Batho 1932).
Euphorbia esula is presently a major economic concern in the northwestern and north-central states of the United States and in the adjacent prairie regions of the provinces of Canada. States with the greatest infestations include Colorado, Idaho, Minnesota, Montana, Nebraska, North Dakota, Oregon, South Dakota, Wisconsin, and Wyoming.
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Phenology: Euphorbia esula is one of the first plants to emerge in the spring. It emerges in early April in North Dakota, during March in Iowa and Wisconsin, and late April in Saskatchewan (Hanson and Rudd 1933, Bakke 1936, Selleck et al. 1962). Stem elongation is very rapid as daily temperatures increase from May through June. Seedlings may emerge when temperatures are near freezing (Biesboer, personal observation). Seedlings appear deep red or purplish because of anothcyanin production in the hypocotyl. As the growing season progresses some seedlings will appear to dry up and die but their underground parts will persist and produce adventitious buds especially near the hypocotylar end of the shoot (Raju 1975). The main seedling shoot usually does not survive and flower because of the rapid development of adventitious organs. It is replaced by an adventitious shoot that will mature into the flowering shoot.
Infloresences form on the main axis from May to the end of July with flowering and seed development again occurring for a short time in the fall, usually from axillary branches. Seed development and maturation continue for 4-6 weeks after the appearance of the last flowers with seed dispersal occurring into early August. The plant usually ceases to grow during the hottest and driest weeks of July and August. Stems from seedling or root buds generally do not flower the first year. During senescence in the fall, the plants turn a pleasant golden-yellow or reddish-yellow before the leaves fall from the plant. The naked stem axis is woody enough to persist from summer to summer and remnants of it can be seen at the base of newly emerged shoot. As light becomes limiting, plants fail to flower, decrease in density, and increase in height. As patches develop, density reaches over 200 shoots/sq m in light soils, and up to 2000/sq m in heavy soils. On heavy soils about 60% of the shoots are produced from seed, whereas on light soils density is maintained and increased mainly by vegetative reproduction (Selleck 1958).
Maintenance: Leafy spurge, once established, will spread very rapidly, crowding out and shading desireable species. It emerges earlier in spring than most other species and also shows allelopathy toward associated species as evidenced by bare ground and lack of other forbs in dense patches of leafy spurge (Steenhagen and Zindahl 1979).
Pests: Although many pests of leafy spurge have been identified, none has been shown to effect much control on this weedy species (Harris et al. 1985).
Reproduction/Sexual: Flowers of leafy spurge are insect pollinated. The flowers produce copious amounts of pollen and nectar. A survey in Saskatchewan showed 8 orders, 39 families, and 60 species of insects on the flowers of leafy spurge (Best et al. 1980).
Fruits ripen and seeds are dispersed from mid- to late-July in the United States. The number of seeds produced per stalk varies from 252 seeds in habitats where spurge competes with native grasses to ca. 200 seeds where spurge competes with annual weeds and crested wheatgrass (Selleck et al. 1962). Seed yield can be very high. In Saskatchewan, leafy spurge patches were calculated to produce 24 to 3400 lbs of seed per acre (Selleck et al. 1962).
Seeds of leafy spurge have a rather high germination rate of 60-80% (Bakke 1936, Bowes and Thomas 1978, Hanson and Rudd 1933). Seed may remain dormant for ca. 5 to 8 years following maturity, but 99% of the germination occurs within the first two years (Selleck 1958). The optimal temperature for germination is 30-32 C. Alternate freezing and thawing, wet and dry periods, and prolonged dark periods promote germination; scarification does not (Selleck 1958). The peak period for germination is late May to early June, but given adequate moisture seeds will germinate throughout the growing season.
Seed dispersal is initially affected by explosive dehiscence of the seed capsule. The seed may be ejected up to 4.6 m from the parent and distributed fairly uniformly from 0.3 to 4.0 m from the plant (Hanson and Rudd 1933). The seeds can also float and initial infestations often occur along stream or river banks where seeds have floated into appropriate habitat (Biesboer, personal observation). Birds have been implicated in spreading seed but documentation is limited except for sharptail grouse (Noble 1980).
Reproduction/Asexual: One of the most important aspects of leafy spurge biology (in addition to production of large amounts of seed) is its ability to reproduce and spread rapidly via vegetative reproduction. Vegetative reproduction occurs from both crown buds and root buds that overwinter and produce new shoots in the spring. The crown of leafy spurge develops just under the surface of the soil and produces a large number of buds that annually produce new stems. The crown region of the plant can also produce new roots that contribute to the spread and persistence of the plant. Leafy spurge crowns can live for many years but the number of years is unknown (Bowes and Thomas 1978).
Seedlings have a remarkable capacity for vegetative reproduction, and can develop buds within 7-10 days after emergence. Buds will form on the proximal portion of the hypocotyl of the seedling. The number of buds produced on the hypocotyl is limited, unlike the roots where up to six times as many buds will form. Bud formation will limit the growth of the seedling. All hypocotylar buds and root buds have the potential to produce a new shoot axis.
Once control practices have been initiated, it is the root system that ensures that leafy spurge spreads and persists in the soil. The root system, consisting of long roots and short roots, can give rise to shoot buds almost anywhere along its length. The long shoots give rise to most of the buds and have been excavated to a depth of 4.8 m (Best et al. 1980). The upper portion of the plant can be killed by herbicides or tillage but living roots below the treatment zone or detached roots will regenerate new shoots. Cultivation or other shallow removal of leafy spurge plants can actually cause a net increase in the number of stems in an infestation. This was demonstrated by Selleck et al., (1962) who showed that regrowth of leafy spurge after rototilling averaged 316 shoots/sq m in comparison to 134 shoots/sq m in undisturbed control. Shoots can emerge from 90 cm of overlying soil for 5 successive years after removal of the major portion of the root system by excavation (Coupland et al. 1955).
The scientific name of leafy spurge is Euphorbia esula subg. Esula L.
(Euphorbiaceae) [42,58,89,155].
Kartesz [89] recognizes 3 leafy spurge varieties: leafy spurge
(Euphorbia esula var. esula), Oriental leafy spurge (E. esula var. orientalis), and Russian leafy spurge (E. esula var. uralensis). Plants Database [221] recognizes only 2 varieties: leafy spurge and Russian leafy spurge. However, after analyzing 26 morphological characters for 600 Euphorbia species within the Esula subgenus,
Crompton and others [42] concluded that in North America, leafy spurge is a
single, variable species and has hybridized only with cypress spurge (E. cyparissias).
Considerable taxonomic confusion surrounds leafy spurge varieties, subspecies,
and hybrids (see the Synonyms section below). Likely multiple introductions of leafy spurge into
North America resulted in a complex of variable genotypes [114].
Hybrids: Only the tetraploid cypress spurge type is known to hybridize with leafy spurge [147,167], resulting in the hybrid, Euphorbia × pseudoesula Schur. [42,146,147,174]. In Canada, Euphorbia × pseudoesula has been collected from British Columbia, Saskatchewan, and Ontario [207], but hybrids are possible anywhere leafy spurge and the tetraploid cypress spurge type occur together.
More info for the term: nonnative species
Leafy spurge is native to Eurasia but occurs as a nonnative species nearly throughout western North America and the central two-thirds of eastern North America [58,221]. At the edges of this range, leafy spurge is less common. In western Canada, leafy spurge is known as far north as Yukon. Leafy spurge is rare along the Pacific Northwest Coast [166] and is generally restricted to the northern regions of California, Nevada, Arizona, and New Mexico [20,77,90,130,165]. In the Great Plains, leafy spurge is much more common in the northern 75% than the southern 25% [60], and it is rare along the Atlantic Coast [48].
Leafy spurge is most widespread and invasive in the US states of Oregon, Idaho, Montana, Wyoming, Colorado, North Dakota, South Dakota, Nebraska, Minnesota, and Wisconsin [16,117]. By 1975, leafy spurge populations were largest and most extensive in the Great Plains region and occurred in 80 counties in Minnesota, 54 in Montana, 54 in Nebraska, 52 in North Dakota, and 49 in South Dakota [49]. As of 1979, leafy spurge occupied 2.5 million acres (1 million ha) in North America, including 800,000 acres (320,000 ha) in Minnesota, 600,000 acres (240,000 ha) in North Dakota, and 543,000 acres (220,000 ha) in Montana [153]. By 2000, 1.2 million acres (490,000 ha) of rangelands in North Dakota were infested by leafy spurge (Lym and others 2000 cited in [45]). As of 2005, leafy spurge occupied an estimated 4.6 million acres (1.9 million ha) in the United States, of which about half or more was rangeland in the northern Great Plains [45,117].
The Russian leafy spurge variety that is recognized by some [89,221] is found in scattered locations from Saskatchewan to Colorado and Kansas and from Michigan to Pennsylvania and Connecticut. However, only the typical variety is reported in the Northeast by Magee and Ahles [128]. Leafy spurge and Russian leafy spurge distributions are available from the Plants Database website.
Introduction to North America: There were likely many separate introductions of leafy spurge to North America [51,200]. In a review, Dunn [50] suggests at least 4 possible early introductions of leafy spurge in North America. The first US leafy spurge collection was made in 1827 from Newbury, Massachusetts, where leafy spurge was thought to originate from a ballast dump. The first Canadian leafy spurge collection was made in 1899 from Huron County, Ontario; the species was likely brought by Russian immigrants in contaminated spelt from Germany [18,50]. Early spread of leafy spurge in North America was attributed to the planting and cultivation of contaminated smooth brome (Bromus inermis) and cereal seed from within and outside North America [5,50,200]. Royer and Dickinson [191] suggest that leafy spurge in Massachusetts came from the Caucasus region of western Asia, and leafy spurge found in Minnesota in 1890 came from Russia. When researchers compared the DNA from leafy spurge plants collected from Nebraska, Montana, Russia, Italy, and Austria, they found the DNA in plants from Nebraska, Montana, and Russia to be most similar [152]. In another DNA study, researchers found a high degree of genetic variability among 123 leafy spurge plants collected from Colorado, North Dakota, South Dakota, and Nebraska, which suggested multiple North American introductions or a high degree of variability for leafy spurge in its native range [190].
Perhaps because of multiple introductions and the cultivation of contaminated crops, leafy spurge was widespread in the northern United States and southern Canada by the early 1900s. Leafy spurge occurred in Ontario by 1889 [191] and in Iowa by 1899 [5]. As of 1900, it was described as "naturalized" in parts of the northeastern United States [155]. Leafy spurge was also reported in Oregon and Washington by 1900 and in Idaho in the early 1900s [33]. Although leafy spurge was found in 2 Michigan counties before 1900, the majority of collections occurred after 1930 [226]. Leafy spurge was quite common throughout New York by 1924 [150], and occurred in Nova Scotia by 1928 [189] and in British Columbia by 1939 [191]. In Arizona, however, leafy spurge was first collected from Coconino County in 1970 [165].
Local distribution changes: Several studies report dense populations as well as rapid spread of leafy spurge in North America. Populations with densities of 1,000 stems/yard² are not uncommon [20]. By 1962 in Canada, 35,000 to 40,000 acres (14,000-16,000 ha) were occupied by leafy spurge. In a Saskatchewan municipality, the acreage infested with leafy spurge more than doubled in 3 years despite control efforts [199]. In North Dakota, the number of acres with leafy spurge doubled in the 9-year period from 1973 to 1982 [16]. The annual spread rate for leafy spurge from 1909 to 2002 in North Dakota was about 16% [117]. In Montana's Lolo National Forest, the estimated 10-year spread rate was reported as 100% in an Environmental Impact Statement draft published in 1989 [219]. A 2005 Weed Science Society of America publication reported that the "historic" annual spread rate of leafy spurge in the United States ranged from 12% to 16%. The time frame used to estimate this rate was not reported [47].
More info for the terms: capsule, density, fire frequency, fire severity, fire suppression, forbs, frequency, fuel, litter, prescribed fire, restoration, severity
Potential for postfire establishment and spread: Although some leafy spurge seed mortality is likely on burned sites, there is high potential for postfire establishment from on- and off-site seed sources and vegetative spread into open sites. Leafy spurge produces abundant seed in most years, adds a small portion of seed to the soil seed bank, and disperses seed by ejection from the capsule, water transport, and animal movements. Open sites and soil disturbances are associated with increased leafy spurge seedling establishment, growth, and survival (see the discussion on Disturbances and seedling establishment).
Preventing postfire establishment and spread: Preventing invasive plants from establishing in weed-free burned areas is the most effective and least costly management method. This may be accomplished through early detection and eradication, careful monitoring and follow-up, and limiting dispersal of leafy spurge propagules into burned areas. General recommendations for preventing postfire establishment and spread of invasive plants include:
- Incorporate cost of weed prevention and management into fire rehabilitation plans
- Acquire restoration funding
- Include weed prevention education in fire training
- Minimize soil disturbance and vegetation removal during fire suppression and rehabilitation activities
- Minimize the use of retardants that may alter soil nutrient availability, such as those containing nitrogen and phosphorus
- Avoid areas dominated by high priority invasive plants when locating firelines, monitoring camps, staging areas, and helibases
- Clean equipment and vehicles prior to entering burned areas
- Regulate or prevent human and livestock entry into burned areas until desirable site vegetation has recovered sufficiently to resist invasion by undesirable vegetation
- Monitor burned areas and areas of significant disturbance or traffic from management activity
- Detect weeds early and eradicate before vegetative spread and/or seed dispersal
- Eradicate small patches and contain or control large infestations within or adjacent to the burned area
- Reestablish vegetation on bare ground as soon as possible
- Avoid use of fertilizers in postfire rehabilitation and restoration
- Use only certified weed-free seed mixes when revegetation is necessary
For more detailed information on these topics, see the following publications: [4,24,59,220].
Use of prescribed fire as a control agent: Prescribed fire alone is not used to control leafy spurge, but fire in conjunction with herbicides has provided some control, and fire may improve the effectiveness of flea beetle biocontrols.
Fire and herbicides: Eliminating woody or dead stems and ground litter with prescribed fire can be useful in increasing the visibility of small leafy spurge plants and seedlings and improving herbicide coverage [125]. In a tallgrass prairie restoration handbook, Solecki [205] suggests that leafy spurge can be controlled with repeated fall herbicide treatments followed by spring burning. Two to 3 herbicide and burning treatments were necessary for control, but the duration of control was not reported. Smith (personal communication 1987 cited in [16]) reported "excellent" control of leafy spurge after 5 to 6 years of biennial burning and herbicide treatments. Fire timing was not critical to control, but herbicide treatments needed to occur 3 to 4 weeks after burning.
Fire did not improve herbicide control of leafy spurge in 2 studies in North Dakota. In a mixed-grass prairie site at Gilbert C Grafton South Military Reservation, leafy spurge density was not significantly different on plots treated with herbicide only and plots treated with herbicide and burning (P>0.05) [170]. When unburned, burned, and combination (herbicide treated, then burned) treatments were compared in the Little Missouri National Grassland, leafy spurge density was lowest on combination plots, but combination treatments did not reduce stem density significantly more than herbicide treatments alone. However, leafy spurge germination was lower in soils collected from burned-only and combination plots than in soils collected from unburned or herbicide-only plots. Germination was lower on spring-burned than on fall-burned plots, regardless of herbicide treatments [240]. Leafy spurge abundance was still low and native grasses and forbs were reestablishing on plots 2 years after combination treatments (Bjugstad 1987 personal communication cited in [16]).
Fire and flea beetles (Aphthona spp.): Researchers found that fall or spring burning prior to the release of A. nigriscutis improved its colonization of leafy spurge-infested grasslands in south-central and southeastern North Dakota. Fires occurred in mid-October or early May, and beetles were released in late June of the following growing season. Within a year of the release, there were significantly more flea beetles on burned than unburned plots (P<0.01). Flea beetle colonization success was positively associated with percentage of bare ground and negatively associated with increasing litter depths. In this study, most beetle populations failed to persist past the first generation [53]. In another study, burning before releasing a large number of flea beetles showed immediate leafy spurge control benefits. Within a year of beetle release in plots burned in June, the average leafy spurge-free radius extended 37 inches (93 cm) from the release sites in burned plots and 14 inches (36 cm) in unburned plots. In burned plots, there was a zone of reduced stem density 10 to 13 feet (3-4 m) beyond the major defoliation area. Unburned plots lacked this additional reduction zone (Fellows unpublished data cited in [53]).
Some researchers report that fires from mid-May to mid-August could interfere with the life cycle of adult flea beetles in leafy spurge-infested areas [142]. However, the study conducted in North Dakota indicates that appropriately timed prescribed burning programs can occur without disrupting established flea beetle populations. When grassland sites with established A. nigriscutis populations were burned in the spring (mid-May) or fall (mid-October), there were no significant differences in flea beetle numbers within a year of burning. Researchers suggested that spring fires should occur early enough to allow for leafy spurge regrowth prior to beetle emergence. In southeastern North Dakota, emergence occurred around 25 May in most years but could be as early as 15 May in a dry year. Because the flea beetles have typically laid their eggs by early September, fall fires after this time should not harm flea beetle populations [53].
Altered fuel characteristics: The effects of dense leafy spurge stands on fire frequency or fire severity were not described in any detail in the reviewed literature (as of 2010). For a short discussion on this topic, see the Fuels and FIRE REGIMES sections.
Leafy spurge reproduces readily by seeds that have a high germination rate and may remain viable in the soil for at least seven years, enhancing its chances of recovery over time. Its seed capsules open explosively, dispersing seed up to 15 feet from the parent plant and may be carried further by water and wildlife. Leafy spurge also spreads vegetatively at a rate of several feet per year. The root system is complex, can reach 15 or more feet into the ground, and may have numerous buds.
for Euphorbia esula var. esula:
Euphorbia intercedens Podp. [41,89,221]
Euphorbia podperae Croizat [221]
Euphorbia × pseudovirgata (Schur) Soó [51,60]
Galarhoeus esula (L.) Rydb. [89,221]
Tithymalus esula (L.) Hill or Scopoli [89,221,232,233]
for Euphorbia esula var. uralensis:
Euphorbia esula var. orientalis Boiss. [221]
Euphorbia esula ssp. tommasiniana (Bertol.) Kuzmanov [41,174]
Euphorbia uralensis Fisch. ex Link [41,174]
Euphorbia virgata Waldst. & Kit., non Desf. [41,51,60,89,221]
Tithymalus uralensis (Fisch. ex Link) Prokhanov [89,221,232,233]
Leafy spurge occurs across much of the northern U.S., with the most extensive infestations reported for Montana, North Dakota, Nebraska, South Dakota, and Wyoming. It has been identified as a serious pest on a number of national parks and on preserves of The Nature Conservancy in eleven northern states.
More info for the terms: fire exclusion, fire frequency, fire regime, fire severity, frequency, severity
Fuels: According to Bjugstad (personal communication 1987, cited in [16]), the high oil content of leafy spurge foliage allows for "good" fire spread, and an herbicide treatment prior to burning may improve flammability and/or fire spread. Senescing plants may support better fire spread than green plants.
FIRE REGIMES: The effects of dense leafy spurge stands on fire frequency or fire severity were not described in any detail in the reviewed literature (as of 2010). Some have speculated that leafy spurge infestations can alter fire frequency [28], but the ways in which fire frequency was changed were not reported, and the studies or observations that support this assertion were not described. Some suggest that leafy spurge expanded its range rapidly with fire exclusion from grasslands in the northern Great Plains [23]. However, because leafy spurge introductions were occurring at about the same time as fire exclusion began (see discussion on North American introductions), the cause and effect relationships suggested by Brockway and others [23] may be purely coincidental. See the Fire Regime Table for additional information on the FIRE REGIMES in those habitat types or vegetation communities where leafy spurge may be abundant.