History & Introduction

Slender leafy spurge is a species of spurge native to Europe and Asia but is considered invasive in the United States. The plant was introduced in several different ways throughout the 1800s via oat bushels, seed introduction, and ballast dumps. Since then it has spread rapidly across the United States, colonizing the states of Oregon, Idaho, Montana, Wyoming, Colorado, North Dakota, South Dakota, Nebraska, Minnesota, and Wisconsin. As of 2005, slender leafy spurge occupied an estimated 4.6 million acres in the United States, of which about half or more was rangeland in the northern Great Plains.

The plant is often found in grasslands, prairies, meadows, woodlands, riparian areas, shrublands, and savannahs. In the United States, it’s known to invade almost every conceivable habitat, excluding boreal forests. The plant grows in full sun to part sun, in a wide range of soil conditions, from very dry to very moist. In LIISMA, there are six known research-grade infestations of slender leafy spurge in Suffolk and Richmond counties, some of which are larger in magnitude than others. LIISMA’s goal is to contain slender leafy spurge on Long Island and keep it from invading nearby surrounding areas. 

Identification & Biology

Slender leafy spurge is an erect, perennial forb that grows 8 to 35 inches in height, growing in thick, dense clumps. Mature stems can be woody, resulting in an almost shrubby appearance. Its leaves are blueish-gray, simple, and oppositely arranged on the stem. The leaves can grow up to 6 inches and are about 4 to 8 times as long as they are wide. Leaves associated with the inflorescences are heart-shaped. Leaves associated with the stem bases are greatly reduced. 

Each inflorescence consists of a single pistil and 12 to 25 staminate flowers. The flowers are greatly reduced and lack both sepals and petals. The plant produces small, three-chambered capsules that forcibly eject seeds up to 15 feet from the parent plant. The seeds are durable and can last in the seed bank for up to ten years. If stems or leaves are cut, a white, milky sap exudes. This sap is a known poison and irritant to humans and can be extremely poisonous to livestock and other animals if consumed. Belowground, slender leafy spurge produces a prolific, massive root system that is rhizomatous and known to bud to produce new shoots. For this reason, and its means of seed dispersal the plant easily invades wherever it is growing. 

Damage and Concern

Slender leafy spurge grows in a variety of climate environments.  It displaces native vegetation in prairie habitats and fields through shading and by usurping available water and nutrients and through plant toxins that prevent the growth of other plants underneath it. It is an aggressive invader and, once present, can completely overtake large areas of open land to form monocultures in only a few short years. It is known to form dense clumps that quickly colonize large areas and outcompete with other native species. Native forbs and grasses can become entirely displaced. Due to the plant’s extensive root system, ability to resprout from fragments, and seed dispersal ejection up to 15 feet from the parent plant, the plant serves as a serious threat to other existing vegetation in its ability to quickly reproduce and displace other plants. The plant can disperse by wildlife, wind, water, vehicles, contaminated soil, and hay. Disturbances such as road construction create opportunities for leafy spurge to spread along roadways and into agricultural and natural areas. The plant is also heavily toxic to animals and people. Hay that is contaminated with spurge infestations cannot be cut, sold, transported, or bought, resulting in increased economic loss for farmers. 

Reproduction Threats

From California Invasive Plant Council

“Although a successful seed producer, leafy spurge spreads primarily through its extensive lateral root system. Vegetative reproduction occurs from both crown and root buds. Most plants in the center of a patch are the result of crown buds, while plants growing on the edge of a patch are primarily from lateral root buds. Crown buds are the first to form, developing seven to ten days after seedling emergence. Lateral roots and buds begin to develop as plants mature. Roots may be either long or short. Long roots can produce shoots and may reach nearly seventeen feet (5 m) laterally and about 15 feet (4.6 meters) in depth. Up to 300 buds have been counted on a single long root. Because of the large numbers of buds, any tillage technique may quickly spread the plant.”

Management & Control

Early detection and eradication of populations soon after they are discovered are extremely important for leafy spurge control. Due to copious seed production and a widespread underground root system, spurge populations established over large areas are extremely difficult to eradicate; therefore, continuous aggressive management measures are needed to keep populations under control

Manual: Hand cutting or repeated mowing in localized situations can reduce leafy spurge’s seed production and its competitive ability with desirable grasses and forbs (flowering plants), but these methods will only suppress growth. Plants should be clipped within 4 inches of the ground just before the seed set and then repeated throughout the growing season. Flower material should be bagged or burned since the seed will continue to mature if left onsite. 

Biological: At least thirteen USDA-approved biological agents have been released to control slender leafy spurge in North America. Insects that have shown the most promise to date include several species of flea beetles: Aphthona nigriscutis, A. czwalinae, A. lacertosa, A. flava, and A. cyparissiae. The larvae of these beetles feed on leafy spurge roots, which may explain why they have been successful in controlling some infestations that herbicides failed to kill.

Chemical: A systemic foliar-applied herbicide is the most effective treatment to control leafy spurge populations. Herbicides are most effective if applied in mid to late June, as flowers and seeds are developing, with reapplication by mid-September when regrowth occurs. In management studies, picloram provided the best control. However, it is often used in combination with 2,4-D for large infestations as a more economical alternative with reduced impact on non-target species. 

Herbicide spraying will reduce leafy spurge populations, but follow-up spot spraying should always be anticipated for a minimum of several years to attain long-term control success. Herbicide treatments are more effective when made in the fall than in spring because the chemical is more easily transported to the root system after flowering. Picloram has long been used for leafy spurge control because the herbicide provides selective weed control while allowing native grasses to return naturally. However, picloram is a restricted-use pesticide and should not be used near waterways or wherever the water table is near the surface. Other herbicides, including imazapic, are also effective and should be considered for spurge treatment on permeable soils, around trees, or near-surface water. Always check state and local regulations before applying herbicide to be sure the herbicide is approved in your location and for any particular species.

Monitoring & Reporting

LIISMA is currently monitoring slender leafy spurge as part of our Early Detection and Rapid Response program. As reports of the species are collected, LIISMA is dedicated to delineating and managing any early emerging infestations of the species before they become widespread. Slender leafy spurge is currently a Tier 3 species on Long Island, prioritized for early detection and containment. 

Your reports matter to us– report the species to iMapinvasives as soon as you detect it. 

Citations 

California Invasive Plant Council. (n.d.). Euphorbia virgata. California Invasive Plant Council. https://www.cal-ipc.org/resources/library/publications/ipcw/report49/

Minnesota Department of Agriculture. (n.d.). Leafy spurge. Minnesota Department of Agriculture. https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/noxiouslist/leafyspurge

Missouri Department of Conservation. (2012, April). Leafy Spurge. https://mdc.mo.gov/sites/default/files/2020-04/leafyspurge.pdf

USDA Forest Service . (2014, September). Field guide for managing leafy spurge in the southwest – US forest service. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5410117.pdf

Western NY PRISM. (2022, June 7). Leafy spurge. Western New York PRISM. https://www.wnyprism.org/invasive_species/leafy-spurge