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Leafy spurge [DRAFT] (Euphorbia esula)
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Leafy spurge, an introduced perennial forb with an expansive root system and milky sap, is a weed of grasslands, riparian areas, and dry meadows. Though tolerant of a range of soil types, it grows best in coarsely textured soils.
Leafy spurge is native to Eurasia, where its range extends from Southern Europe to Eastern Siberia. It was likely introduced to North America multiple times over the 19th century as a contaminant in grass and cereal seed and in dumped ship ballast. It was first collected in the United States in Massachusetts in 1827. By 1900 it had spread throughout New England and was present throughout the midwestern and central United States.
Leafy spurge is upright, clump-forming, and grows up to 1 meter in height. Mature stems are somewhat woody and generally unbranched. All parts of the plant exude a milky sap when injured. Leaves on the stem are alternate, lanceolate, and sessile and have with smooth or somewhat wavy margins. Near the inflorescence the leaves are whorled and heart-shaped. The flowers grow in threes and are reduced, without petals or sepals—what appear to be yellow-green petals are actually a pair leafy bracts beneath the floral structures. The root system is robust and extensive, spreading up to 1.1 m horizontally and reaching beyond 3 m in depth. Upper roots are woody and up to 1.3 cm in diameter.
Leafy spurge is a perennial, and shoots and seedlings begin to emerge as early as mid-April. Flowering begins in mid-May and continues throughout the season and, occasionally, into mid-Autumn. Seed production occurs from late June and, like flowering, is continuous. Leafy spurge flowers are unisexual and plants are usually monoecious. Though self-pollination is possible, the flowers produce sticky pollen and generally insect pollinated. Each stem produces up to several hundred seeds which, under low humidity and high temperatures, can be ejected up to 4 m from the plant. Most seeds germinate within 2 years, though they can survive for over 4 years in soil. Leafy spurge roots produce buds prolifically, and plants can expand vegetatively by several feet per year. Root fragments as small as 1.3 cm can produce new plants.
Leafy spurge is an aggressive competitor and is capable of invading established plant communities. It is unpalatable to cattle, and large infestations can diminish land value substantially. In natural areas, leafy spurge can displace native plants and decrease diversity. It is a particular threat to rangelands and native grasslands. It spreads rapidly, forms dense stands, and produces thick litter which can smother and shade smaller plants.
Its capacity for vegetative regeneration can make leafy spurge difficult to control. Mowing, clipping or other methods of mechanical control may reduce seed production, but will not likely prevent populations from spreading. The sticky sap of leafy spurge may accumulate in mechanical equipment, slowing control efforts. Though cattle will not feed on leafy spurge, sheep and goats will, and heavy browsing can reduce abundance, though this risks spreading seed should it pass through their digestive systems. Repeated applications of glyphosate combined with 2,4-D (.45 kg/ha and 7 kg/ha respectively) over several seasons can substantially reduce leafy spurge density (Lym 2000).
A number of insects have been released to control leafy spurge, the most successful of which have been 5 flea beetles in the genus Apthona. Though they will not eradicate leafy spurge, they can reduce the density and productivity of leafy spurge infestations (Cline et al 2008).
Lym, R. G. 2000. Leafy spurge (Euphorbia esula) control with glyphosate plus 2, 4-D. Journal of Range Management, 68-72.
Cline, D., Juricek, C., Lym, R. G., & Kirby, D. R. 2008. Leafy spurge (Euphorbia esula) control with Aphthona spp. affects seedbank composition and native grass reestablishment. Invasive Plant Science and Management, 1(2), 120-132.