L.

leafy spurge, wolf’s milk

Tithymalus esula, Galarrhoeus esula

25

10

CalEPPC List A-2,CDFA A

Butch Kreps

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.)

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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.

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).

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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).

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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).

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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.

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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).åÊ

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)

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.

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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‰Ûªs 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).

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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.

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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.

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