Leafy Spurge
(Euphorbia esula) Spurge Family
By Thomas J. Elpel with additions by Pamela G. Sherman
About Leafy Spurge: If you have seen a Poinsettia at Christmas time then you have met a close relative of leafy spurge. The colorful bracts are common in the spurge family and may be mistaken for sepals or petals; there are actually no sepals or petals. World-wide there are about 1600 species of Euphorbia.
Leafy Spurge (Euphorbia esula) was first introduced into eastern North America from Russia in the early 1800s. Other introductions were made in the midwest later in the century, probably as contaminants in seed grain. Some researchers believe our leafy spurge is a hybrid of two or more Old World species. Today the plant covers more than 1.1 million hectares (about 2.7 million acres), mostly in Montana, North Dakota, South Dakota, Nebraska and Wyoming . Leafy spurge can reduce grass production by 75% in infested fields. The perennial plant spreads by seeds and roots. Triggered by high temperature and low humidity, the seed head capsules explode to project the seeds up to 15 feet. The deep and extensive root system makes the plant resistant to grazing, cultivation, and herbicides.
Deer do not like leafy spurge, but evidently they do ingest it. In northeastern Montana and western North Dakota, 1 leafy spurge seed was found intact in deer scat and it germinated. "During feeding trials...the total viability of leafy spurge seeds passed by white-tailed deer ranged from 10.5% to 20.4%. Seeds were passed for 4 days, and viability was greatest for seeds passed 2 days after ingestion." [U.S. Forest Service]
Pulling or plowing the plant may stimulate the roots to spread even more. A root fragment as small as 1/2" can grow into a new plant, and new shoots will sprout up from almost any depth. Although the majority of shoots come from leafy spurge roots within the top 1 foot (0.3 m) of soil, excavation experiments revealed that regeneration is possible from deeply buried roots and from root fragments collected from great depths. On a leafy spurge plant excavated from a field in Iowa, a shoot was found growing from a root bud 10 feet (3 m) deep. [U.S. Forest Service]
"[S]oil texture and fertility can affect growth and distribution of leafy spurge roots... In fine soils, leafy spurge roots were thick in the top 6 inches (15 cm) of soil. In coarse soils, roots were thick at soil depths below 30 inches (76 cm). Root weight in undisturbed native grasslands was about twice that of recently cultivated areas...
In a greenhouse experiment, leafy spurge roots grew downward about twice as fast in sandy soil as in clay soil. Roots in clay soil had greater branching than those in sandy soil... Controlled outdoor experiments showed that high levels of soil nitrogen can reduce the biomass of leafy spurge roots and lead to greater root concentrations near the top of the soil profile..." [U.S. Forest Service]
196 insect species have been observed on leafy spurge by researchers in Jameson, SaskatchewaN... Little damage to leafy spurge plants was noted, suggesting that most insects were profiting from leafy spurge pollen and nectar sources (Maw unpublished data cited in...)... Ants, bees, flies, and mosquitoes were all seen feeding on leafy spurge nectar in Saskatchewan.Selleck... [U.S. Forest Service]
Although leafy spurge is most common and problematic in semi-arid continental climates, it also occurs in xeric to subhumid and subtropical and subarctic climates... [U.S. Forest Service]
Medicine: The spurges (all species of Euphorbia) contain an acrid latex sap which may cause a rash when the sap on the skin is exposed to sunlight. The eyes should never be rubbed until after the hands are thoroughly washed. The sap is considered carcinogenic if it is handled a lot. The whole plant contains the latex, but it is most concentrated in the roots. The acrid sap is useful externally on warts, or internally to irritate and open up the body-functioning as an emetic, anthelmintic, vasodilator, and potentially violent purgative. A European species is considered to toxic for medicinal use. Large doses have a depressant effect on the heart and can be fatal to people.
Prevention: Ahead of the front lines of a leafy spurge invasion it may be beneficial to cultivate soil-building legumes like alfalfa, sweet clover, or possibly some of our native clovers. Spurge seedlings do not compete well with these nitrogen-fixers. On the other hand, legumes do not fair as well in established spurge patches, and they will not survive either herbicides or extensive sheep grazing. Leafy spurge has been eliminated from crop fields in two years by plowing and close-drilling sorghum or soybean plants for forage. But on spurge-infested rangelands, legume seeding may be most successful if used together with biological controls.
Mechanical Controls: Intensive cultivation of spurge infested plots at two to three week intervals will reduce leafy spurge stands by 90% in the first year and give complete control in two years. Rather than leaving the fields up-turned all season long, repeated cultivation in the spring can be combined with later plantings of competitive crops such as legumes or buckwheat.
Mowing prior to spraying may reduce the amount of herbicide required to control the plants, but multiple treatments are still necessary.
Fire: Controlled burning of leafy spurge has been experimented with in North Dakota and Wyoming. Burning has little effect on established plants with deep root systems but it is effective in reducing seed and seedling viability. Burning against the wind results in more complete combustion and hotter fires. But keep in mind that consuming the organic matter and exposing the soil surface may promote more weeds, especially if used repeatedly.
Biological Controls: Real success has been made in controlling leafy spurge infestations with the aid of spurge-specific insects imported from the Old World. The best results have been obtained with several species of flea beetle (Apthona cyparissiae, A. czwalinae, A. flava, A. lacertosa, and A. nigriscutis. ), plus one species of stem-boring beetle (Oberea erythrocephala). The flea beetle larvae feed on the roots in the spring, while the adult beetles feed through late summer on the foilage and sometimes the flowers. (Scroll down the page to see an amazing photo sequence of leafy spurge flea beetle work.) The stem-boring beetle larvae feed on the stems and the root crowns, killing the above-ground plants. Each of these insects has specific habitat requirements, so you must obtain the right ones for your location. Flea beetles have eliminated up to 85% of some leafy spurge infestations within five years of their release.
Several other insects have been released to control leafy spurge, including the spurge hawk moth (Hyles euphorbiae). Hawk moth caterpillars (as shown here) defoliate the plants, but do not kill them. A spurge-specific aphid (Acrythosiphum neerlandicum) was released in Canada. It has been effective at killing the plants. The shoot-tip gall midge (Spurgia esulae) has also been released. It forms galls over the branch tips that slow growth, stunt the plant, and prevent blossoming.
Grazing: Leafy spurge causes scours and weakness in cattle, and they rarely eat it unless it is given to them in dry, weedy hay or when better forage is not available. Excessive consumption can be fatal.
Sheep and goats favor leafy spurge, and sheep gain weight faster on the weed than on grass. The effects on the spurge population are varied. Continuous grazing throughout eight summers in Saskatchewan reduced the seedbank from 3,500 seeds to 15 seeds per square meter of ground. Another study found that continuos sheep grazing over a four-year period reduced leafy spurge populations by more than 90%. Keep in mind that continuous grazing can have strongly negative effects on other desirable plant species.
More recent tests with a rotational grazing cycle reduced seed production, but had little effect on the mature plants. The tests were conducted in mid-summer to minimize impact to cool-season grasses. Grazing increased the density of Idaho fescue, but with shorter leaf and stem heights. Grazing reduced the density of bluebunch wheatgrass, but increased the density of Kentucky bluegrass, Sandberg blue grass, annual brome grasses (like cheat grass), plus sedges and dandelions.
Because leafy spurge has such a vigorous root system, many years of grazing may be required to significantly weaken the plants. In the Saskatchewan study, stem densities remained steady for the first three years, then dropped dramatically.
Sheep readily eat the seed heads of leafy spurge, and a significant number of those seeds pass through the digestive tract intact. Seeds also cling to the wool, although it is believed that virtually all of the seeds remain in the wool until shearing. It is recommended that sheep from spurge infested pastures be confined for at least five days before moving to weed free pastures. Sheep grazing can be combined with herbicides along the front-line of existing patches for optimal control.
Chemical Controls: Herbicides applied prior to flowering will burn-down the top growth but do not give lasting control of well-established plants. Without a long-term strategy, herbicides often lead to greater problems in the future because of their effect on other plant species, the development of resistance, and the inability to completely eliminate weed populations. If you use herbicides then you must be prepared to come back and finish the job through subsequent years.
2,4-D is minimally effective on leafy spurge during the growing season. It is more effective if used in combination with glyphosate (Roundup®) in the fall while grasses are dormant. Dicamba (Banvel®-spring/early summer) or picloram (Tordon® 22K-any time during growing season) are also effective, but any chemical treatment must be followed up in successive years to get the plants that regrow from the roots. Leafy spurge often grows near the water or where the water table is shallow. There are special formulations of 2,4-D and glyphosate (Rodeo®-late summer) for use near water. Avoid spray drift on the foilage or green bark of trees.
Important: Most "weed problems" are really "people problems" from poor land management and a lack of ecological insight. It is easy to reach for a tool like fire, mowing, or herbicides to attack an out-of-control weed, but often those tools do little to get to the root cause of the weed infestation, and sometimes make the problems worse. Please read more about range ecology, desertification, and invasive weeds on this website before applying any tool of weed control. Go to: Desertification and Invasive Weeds.
Notes
- Thomas J. Elpel. Botany in a Day. HOPS Press: Pony, MT. January 2000.
- Jim Story. Biological Control of Knapweed and Spurge: Principles and Status. Weeds as Teachers: Proceedings of AERO's 1995 Weed Management Alternatives Conference. AERO: Helena, Montana. 1997.
- Sherry Lajeunesse, Roger Sheley, Rodney Lym, Diana Cooksey, Celestine Duncan, John Lacey, Norman Rees, Mark Ferrell. "Leafy Spurge: Biology, Ecology, and Management." MSU Extension Service Circular EB 134. Reprinted June 1997.
- Allan Savory. Time & Overgrazing. Holistic Resource Management Quarterly. Albuquerque, NM. Fall 1992. Pgs. 5-6. (Holistic Thought and Management. 1997 Study Guide. PSES 421, Cliff Montagne, MSU.)
- Roger L. Sheley and Jack Stivers. "Whitetop". MSU Extension Service Publication #EB 138. 1996, 1998.
- Jane Krueger. "St. Johnswort's Drawback." The Montana Pioneer. No date available.
- Bret E. Olson and John R. Lacey. "Sheep: A Method For Controlling Rangeland Weeds." Sheep Research Journal. Special Issue: 1994. Pages 105-112.
- _____. 1997-1998 Montana - Utah - Wyoming Weed Management Handbook. Extension Services: MSU, USU, UW. Pages 258-259.
- Bret E. Olson and Roseann T. Wallander. "Effect of sheep grazing on a leafy spurge-infested Idaho fescue community." Journal of Range Management. Volume 51, #2. March 1998. Pages 245-250.
- Bret E. Olson and John R. Lacey. "Sheep: A Method For Controlling Rangeland Weeds." Sheep Research Journal. Special Issue: 1994. Pages 105-112.
- Bret E. Olson and Roseann T. Wallander. "Effect of sheep grazing on a leafy spurge-infested Idaho fescue community." Journal of Range Management. Volume 51, #2. March 1998. Pages 245-250.
- Bret E. Olson, Roseann T. Wallander, and Rodney W. Kott. "Recover of leafy spurge seed from sheep." Journal of Range Management. Volume 50, # 1. January 1997. Pages 10-15.
- _____. 1997-1998 Montana - Utah - Wyoming Weed Management Handbook. Extension Services: MSU, USU, UW. Pages 247-248.
- Sherry Lajeunesse, Roger Sheley, Rodney Lym, Diana Cooksey, Celestine Duncan, John Lacey, Norman Rees, Mark Ferrell. "Leafy Spurge: Biology and Management." MSU Extension Service Publication EB 134. July 1995.
- l U.S. Forest Service: https://www.fs.fed.us/database/feis/plants/forb/eupesu/all.html#176
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