Source: California Invasive Plant Council


URL of this page: http://www.cal-ipc.org/ip/management/ipcw/pages/detailreport.cfm@usernumber=49&surveynumber=182.php

Invasive Plants of California's Wildland

Euphorbia esula
Scientific name   Euphorbia esula
Additional name information: L.
Common name leafy spurge, wolf's milk
Synonymous scientific names Tithymalus esula, Galarrhoeus esula
Closely related California natives 25
Closely related California non-natives: 10
Listed CalEPPC List A-2,CDFA A
By: Butch Kreps
Distribution
euphorbia-map

HOW DO I RECOGNIZE IT?
Distinctive features:

Leafy spurge (Euphorbia esula) is a perennial, rhizomatous, erect herb to three feet tall with distinctive bluish green leaves. It reproduces vegetatively from vigorous rootstocks and by seed. The entire plant contains a milky sap and has forked branching. Leaves are alternate, narrow, and long. Many stems may arise from a single rootstock and often appear clustered. The flowers are yellow-green, inconspicuous, and arranged in numerous small clusters, each cluster enclosed by paired, heart-shaped, yellow-green bracts. The massed flower clusters and accompanying bracts of dense infestations are conspicuous from a distance. The roots are brown and bear numerous pink buds, which may produce new shoots or roots. Seeds are oblong, grayish to yellow-brown, contained in a three-celled capsule, each cell containing a single seed (Whitson et al. 1991.)

 

Description:
Euphorbiaceae. Perennial herb. Plant has milky sap throughout and extensive rootstocks. Roots may extend to depths of 15 ft (4.6 m) or more, spreading and most abundant in the upper foot of soil, woody, brown with many pink buds that can produce new shoots if upper portion destroyed. Stems erect, glabrous, branched at the top, to 3 ft (0.9 m) tall. Leaves sessile (no petiole), alternate, broadly linear to narrowly oblong-lanceolate or inverted lanceolate, 1-3 in (2-8 cm) long, bluish green.
euphorbia-illus

Flowers borne in distinctive clusters (cyathia), generally with 1 female flower at the center surrounded by 11-21 male flowers, clusters surrounded by 5 bracts fused into a bell-shaped involucre 1.5-2.5 cm, topped by crescent-shaped, 2-horned, bright yellow-green glands, 1.5-2 mm. Flowers small, male flowers stalked, with 5 small sepals, no petals; female flowers stalked, style divided half the length, ovary exserted from involucre bearing large 3-lobed pistil that matures into a capsule containing up to 3 seeds if pollinated. Seeds elliptic-oval, about 0.08 in (2 mm), oblong, smooth, light gray to yellow-brown, with yellow (or white) emarginate caruncle (description after Whitson et al.1991, Hickman 1993).

 

WHERE WOULD I FIND IT?

Leafy spurge may be found at scattered locations in northern California, particularly in the far northern portion of the state. Over 500 acres were infested in Siskiyou County in the late 1960s, but, after twenty years of eradication efforts, only ten to twenty acres remain infested. Small infestations were found and eradicated in Lassen and Modoc counties. Populations have been found in Sonoma County and as far south as Los Angeles County. Leafy spurge is widespread in the western United States and extremely troublesome in prairies, pastures, rangelands, and other grasslands from western Minnesota and the Dakotas to northern Idaho and northeastern Oregon and south to Colorado. It also invades pine savannahs, riparian areas, cultivated fields (grains, alfalfa), and roadsides throughout the northern plains and northern Rockies. It is usually found in patches or large infestations rather than as single plants. Patches and infestations are easiest to spot when spurge is in full bloom, generally for several weeks between late May and late July.

Leafy spurge grows in a wide range of habitats. It is most aggressive in semi-arid areas, but it can be found in xeric to subhumid and subtropic to subarctic habitats. It will tolerate flooding for more than four months. It is only slightly limited by shade. Leafy spurge occurs most commonly on untilled, non-crop areas such as pastureland, rangeland, woodland, prairies, roadsides, stream and ditch banks, and waste sites. It grows on all kinds of soils, but it is most abundant on coarse-textured soils and least abundant on clay soils. Root growth and vegetative reproduction are highest on coarse-textured soils. Sexual reproduction, germination, and seedling establishment are highest on clay soils (Butterfield and Stubbendieck 1999).

 

WHERE DID IT COME FROM AND HOW IS IT SPREAD?

Leafy spurge is native to Eurasia, where it is known from Spain, Italy, and Germany to central Russia. It was first recorded in North America in Massachusetts in 1827 and was probably introduced to the United States repeatedly in contaminated grain, particularly in the northern plains. It was established in California after 1900, being found in Modoc and Siskiyou counties by 1917 (Robbins 1940). The invasive leafy spurge found in North America may be a hybrid or series of hybrids of two or even three Euphorbia species (including E. virgata) that were native to Eurasia and had the chance to interbreed following introduction here.

Leafy spurge spreads by seed, by vegetative growth, and by root fragments, which may be cut up by plowing and carried on road maintenance or farm machinery. Pieces of root as small as 0.5 inches (1.3 cm) long and 0.125 inches (0.3 cm) in diameter can produce shoots that grow rapidly. Animals, birds, insects, equipment, seed, hay, grain, and the natural dehiscence of the capsule all assist in the dispersal of leafy spurge (Butterfield and Stubbendieck 1999).

 

WHAT PROBLEMS DOES IT CAUSE?

Leafy spurge can invade and dominate a variety of vegetation types, including prairies, grasslands, and pine savannahs, crowding out native plant species. At present it infests nearly 2.5 million acres in North America. Stem densities of 1,000 plants per square yard are not uncommon in infested areas. This results in almost complete exclusion of native forbs and grasses and other desirable vegetation. Exclusion of other plants may result in part from the allelopathic chemicals that have been found in leafy spurge (Butterfield and Stubbendieck 1999).

Leafy spurge is unpalatable and often toxic to most native ungulates, including deer, elk, and antelope, as well as to cattle and horses. It has been reported to cause severe irritation to the mouth and digestive tract in cattle and can result in death (Whitson et al. 1991). Sheep and goats can be induced to feed on spurge, and in some cases will acquire a taste for it and help to reduce its cover. Leafy spurge has an extensive root system with nutrient reserves that, once plants are established, make it extremely difficult to remove and control.

 

HOW DOES IT GROW AND REPRODUCE?

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. An experiment showed that rototilling increased the density of leafy spurge to 316 shoots/m2 compared with 134 shoots/m2 in an untilled area. Root fragments only 0.66 inches (1.5 cm) in length produced new shoots (Butterfield and Stubbendieck 1999).

Leafy spurge is one of the earliest plants to emerge in spring, usually in mid-March to late April. Once the stem emerges, elongation occurs rapidly. Initiation of the inflorescence occurs within one to two weeks of stem emergence. Yellowish bracts form in May, making leafy spurge conspicuous from late May through June. Flowering in the terminal inflorescence generally ends in late June to mid-July. If conditions are favorable, leafy spurge may continue flowering throughout summer and into fall. Plants may produce seed until frost. Pollination of leafy spurge is entirely by insects. Over sixty species of insects have been found on leafy spurge flowers (Butterfield and Stubbendieck 1999).

Seeds mature about thirty days after pollination. Each plant produces from ten to fifty capsules, with a seed yield range of 200 to 250 seeds per plant. Seeds can be propelled up to fifteen feet (4.5 m) from parent plants. Sixty to 80 percent of fresh seeds are viable. Seeds can remain viable in the soil for five to eight years. However, annual viability in the soil decreases by about 13 percent each year. Ninety-nine percent of viable seeds will germinate in the first two years. Temperature is the most important requirement for germination. Temperatures between 68 and 85 degrees F (20-30 degrees C) are optimal. Alternating freezing and thawing, wet and dry periods, and shortened photoperiod promote germination. Peak germination is from late May to early June. If adequate moisture is present, germination can occur throughout the growing season (Butterfield and Stubbendieck 1999). 

euphorbia-large2

Much early seedling growth is devoted to establishing a root system rather than shoot elongation (Robbins 1970). Leafy spurge emerges from the soil from root buds or from germinating seeds after soil begins to warm in early spring. Shoots from root buds grow rapidly, reaching maximum height between late May and mid-July when they flower. Shoots set seed three to six weeks after flowering. Leafy spurge shoots remain green until the first heavy frost in fall when foliage dies.

(click on photos to view larger image)

euphorbia-small2

HOW CAN I GET RID OF IT?

Leafy spurge is extremely difficult to control, and the best approach is to detect and eliminate or contain new infestations as quickly as possible. An integrated management approach using chemical, biological, cultural, and grazing control methods will usually yield the best results with established populations. Regardless of the method of control used, all formerly infested areas should be monitored for new spurge plants for at least ten years. Leafy spurge seeds may remain dormant in the soil for several years before germinating and reestablishing an infestation. Spurge roots may also lie dormant for more than five years before producing new shoots, particularly after they have been treated with herbicides. Mapping infested areas will make reinfestations easier to detect, and this will make eradication or containment more efficient.

 

Physical control:

Manual/mechanical methods: Opinions differ on the effectiveness of mechanical control methods. Butterfield and Stubbendieck (1999) do not generally recommend cultivation for leafy spurge control, because of the plant’s ability to sprout from buds. Other researchers report that properly timed cultivation and/or planting of competitive species can be effective. Cropped areas infested with leafy spurge must be cultivated twice in fall or every two weeks during the entire growing season to ensure reasonable control. Cultivation should be continued for three growing seasons to prevent reinfestation. Mowing can reduce above-ground stands, but it stimulates underground shoot development (Butterfield and Stubbendieck 1999).

Prescribed burning: Burning is not effective in controlling leafy spurge (Butterfield and Stubbendieck 1999).

 

Biological control:

Insects: At least thirteen USDA approved biological agents have been released to control 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. Different species of insects are known to be more effective in various climates or soil types or against different populations of spurge, but it is still difficult to explain why this is so. Thus far few, if any, of these beetles have been released in California, since leafy spurge infestations here are currently small. They have been released in southern Oregon, however, where there are also scattered leafy spurge infestations, and they may help prevent these populations from spreading southward (Lym and Zollinger1995).

When a new release is made, leafy spurge outside the release site is sometimes treated with herbicides to prevent the infestation from increasing during the time it will take for the insect population to grow. As the insects become established, herbicide applications are reduced. A gall midge, Spurgea esulae, and a stem-boring beetle, Oberea erythocephala, were also released for leafy spurge control, but they have had little or no success in controlling spurge populations (Lym and Zollinger1995).

Grazing: Sheep and goats have been useful in reducing stands of leafy spurge. Goats have been most effective because they tend to graze spurge regardless of plant density, while sheep consume less spurge as its density in the vegetation declines. Sheep also may take two to three weeks before beginning to feed on spurge, while goats begin immediately. Goats, however, are harder to manage and less profitable (Lym and Zollinger 1995). Unfortunately, both sheep and goats can pass viable leafy spurge seeds through their digestive systems, so animals that have been feeding in areas with flowering or fruiting leafy spurge should be confined for four to five days before being allowed into spurge-free areas.

Plant competition: Few, if any, smother crops can eliminate this plant. However, sowing perennial grasses after tilling can reduce leafy spurge populations as much as 80 percent. Local university or government sources can advise on the best choice of competitive grasses in the area. Good management of existing vegetative cover can often reduce the likelihood of a new invasion.

 

Chemical control:

Picloram or picloram + 2,4-D are the most widely used herbicides for leafy spurge control, but picloram is not currently registered for use in California. Compounds registered for use in California, including 2,4-D alone, glyphosate, and triclopyr, have not been as effective for leafy spurge control in experiments and field trials.

Applying 2,4-D in spring and summer and glyphosate in fall have been the most commonly used and effective methods for eliminating leafy spurge in California. Costs can be minimized by ensuring that herbicide rates and times of application control against leafy spurge while leaving surrounding vegetation to compete with spurge regrowth.

Sometimes chemical treatments should not be used because of local environmental factors. A well timed combination of cultivation, planting competitive grasses, and the use of herbicides is probably the most effective method for controlling leafy spurge.