Leafy Spurge (Euphorbia esula)

DESCRIPTION: Leafy spurge is a member of the euphorbiaceae family, and ranges 6 to 36 inches in height. Erect stems support linear, alternate, and apetiolate leaves of a bluish-green hue. The species exhibits yellow-green inflorescence on an umbel near the top of the stem. The yellow-green bracts are the most colorful and conspicuous part of the plant. A milky white sap (latex) is present in all parts of the plant, and aids in identification.

Leafy spurge is considered a noxious weed under Wisconsin law, which requires landowners to attempt eradication of the species.

DISTRIBUTION AND HABITAT: Leafy spurge is a deep-rooted, Eurasian perennial that is adapted to a wide range of conditions. The species was first recorded in the U.S. in 1827, and was probably introduced accidentally in a mix of agricultural seed stock, or intentionally for its attractive, yellow, heart-shaped bracts. The plant is not palatable to cattle. This species is considered a serious pest in the grasslands of the Great Plains. The plant occurs primarily in non-cropland habitats, including roadsides, prairies, savannas, and woodlands. It is tolerant of a wide range of habitats, from damp to very dry soils. In Wisconsin it is usually found in lighter, dry soils. Leafy spurge prefers sunny conditions, but can also grow in savanna habitats. The related cypress spurge (Euphorbia cyparissias) has also invaded some dry grasslands in western Wisconsin. Little is known about control techniques.

LIFE HISTORY AND EFFECTS OF INVASION: Leafy spurge appears to be allelopathic and spreads rapidly, crowding out desirable species. There are a number of spurges that hybridize with leafy spurge. Often these hybrids are collectively referred to as "leafy spurge." The plant can reach densities of up to 1,800 stems per square yard. Its deep root system makes eradication of the species extremely difficult. Roots are woody, tough, and can reach depths up to 15 feet, and lateral spread of up to 35 feet. Vegetative reproduction from both crown and root buds contribute to the weeds= persistence. Even if the foliage of the plant is destroyed, the roots will regenerate new shoots.

The plant's extraordinary seed dispersal mechanisms also contributes to the plant's success. Leafy spurge reproduces readily from seed dispersed by explosive ejection from the seed capsule. The plant can expel its seeds to distances of 15 feet, and has a high germination rate. Once established, the plant reproduces and spreads rapidly via vegetative reproduction. Shoots emerge in late March. Leafy spurge is most easily recognized by its yellow-green bracts that exist from May to the end of July. Seed development continues for up to six weeks. This species usually ceases to grow during the hottest and driest weeks of July and August.

Leafy Spurge

Leafy spurge can be catastrophic to grasslands for both economic and ecological reasons. It is estimated that the plant reduces the productivity of grazing land by 50 to 75 percent. It currently inhabits about three million acres of rangeland in the U.S. The species outcompetes other vegetation by shading competitors and dominating available moisture and nutrients. In natural areas, leafy spurge reduces species diversity and habitat for wildlife, and has the ability to displace native grasses and forbs in the course of only a few years.

CONTROLLING LEAFY SPURGE
Mechanical Control: In the great plains, much effort has been channeled towards finding a control method for leafy spurge. Most agree that control depends on destruction of the root system. No mechanical methods have been found to work effectively. Fire, cultivation, obscuring sunlight, and mowing have not been successful. Hand-pulling, digging, and tilling are only successful if the entire root system can be excavated, and may increase the number of plants if any remnants remain in the soil.

Biological Control: Several biological control agents are being investigated (flies, beetles, fungus, etc.). The USDA has experimentally released six insects: five beetles and one midge. Together, these insects feed on the leaves, shoot tips, stems, root crowns, and secondary roots of leafy spurge. Tests in Montana showed up to 90% reduction in spurge population. Experimental releases in a few sites in Wisconsin since 1995 have shown good insect reproduction, and some impact on spurge is becoming evident.

The Forest Service is beginning to pasture goats in areas infested with leafy spurge. The goats, which show a strong preference for spurge, are less costly than chemical control measures. It has also been observed that the allelopathic effects of black walnut inhibits plant growth.

Chemical Control: Until a proven biological control is approved, herbicides appear to be a temporary solution. Land managers who find small infestations of this plant are advised to take immediate action to control it through the application of chemicals.

Leafy Spurge
(c) Barry A. Rice/The Nature Conservancy

Picloram is the most effective chemical control for this species, but should not be used on high quality natural areas. This chemical may seriously affect woody species, and extreme care should be taken in its application. Picloram moves through the soil and is absorbed by the roots of adjacent plants up to 30 feet away. The recommended application rate for scattered patches is 2 lbs/acre in late spring followed by 2 lbs/acre in early fall; the result is 85-90% shoot control for 3-4 years. For large infestations that are accessible and easily treatable, annual applications in late spring using picloram at 0.5 lbs/acre achieves up to 70% control. This must be followed by 0.5 lbs/acre once a year.

Quinclorac at 5.7 lb/acre plus picloram at 2.8 lb/acre was found to provide 85 percent control of leafy spurge nine months after treatment. Quinclorac has been shown to successfully control leafy spurge in the greenhouse environment when applied either to the foliage or the soil. If plant shoot tops are cut at time of treatment, 0.12 lb/acre of quinclorac should be used. Otherwise, 2-4 lb/acre of soil-applied quinclorac should be used.

A 90% reduction of leafy spurge has been achieved at the University of Wisconsin Arboretum. A 3% active ingredient solution of fosamine was applied to blooming plants in June and July. Fosamine is a bud inhibitor which targets woody species and does not appear to affect herbaceous plants. Control was achieved after one year of chemical application, but follow-up was necessary for three to four years to inhibit germinants from the soil seedbank.

Glyphosate may be used to treat small patches, but requires repeated application. Dicamba has also been cited for selective broadleaf weed control.

The Spurge Society has been formed to fight the spread of leafy spurge, and publishes a newsletter. The editor of the Leafy Spurge News is:

Russell Lorenze
1924 North Grandview Lane
Bismarck, ND 58501.

More Information on the Web (links exit DNR)
Leafy Spurge - Wisconsin State Herbarium
Leafy Spurge - Invasives on the Web

Last Revised: September 3, 2004