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Leafy Spurge--Euphorbia escula
Spurge Family
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. World-wide there are about 1600 species of Euphorbia.
Leafy Spurge (Euphorbia escula) 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. The deep and extensive root system makes the plant resistant to grazing, cultivation, and herbicides.
Pulling or plowing the plant may stimulate the roots to spread even more. A root fragments as small as 1/2" can grow into a new plant. Herbicides will kill the vegetation and roots near the soil surface, but they do not translocate to the deeper roots. The roots can extend thirty feet down into the soil, and new shoots will sprout up from almost any depth. Several repeat chemical applications may be required to kill the entire plant and root system.
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. Check out this amazing photo sequence! 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 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, but 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. You must read the range ecology sections of this website before applying any tool of weed control. Return to the Wildflowers & Weeds Home Page for articles on Desertification and Noxious Weeds.
Leafy spurge flea beetles can be purchased through the N-Bar Ranch.
Notes
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