Montana Field Guide

PLANTS: Glabrous, perennial forb with spreading roots and branched stems that are 30–80 cm tall. Plants produce vegetative and flowering stems that when cut exude a white, milky latex. Stems are pale green to blue-green. Sources: Jacobs 2007; Lesica et al. 2012

LEAVES: Stem leaves are alternately arranged and sessile or with very short petioles. Leaf blades are green to blue-green, linear-oblanceolate in shape, 2–6 cm long, and have entire (smooth) margins. When cut leaves cut exude a white, milky latex. Sources: Jacobs 2007; Lesica et al. 2012

INFLORESCENCE: A terminal umbel of yellow-green, ovate bracts containing inconspicuous flowers that lack petals and sepals. The bracts are 8-16 mm long. Above the bracts, the true flowers are green and occur within a cup-like involucre called a cyathium (plural is cyathia). Each cyathium contains one seed (female) flower, 3 (male) pollen flowers, are 2–3 mm long, and have 4 yellowish glands with a lunate appendage. Fruits are a capsule, about 4 mm long, lobed and nearly smooth. Sources: Jacobs 2007; Stein 2011; Lesica et al. 2012

Flowering and fruiting in spring through fall (FNA 2016).

Leafy Spurge - Euphorbia virgata, exotic and Noxious
* A rhizomatous perennial.
* Stems are blue-green to pale green.
* Stem leaves are alternate below the inflorescence. Leaf blades are linear, linear-oblanceolate, or linear-oblong, 6-15 times longer than wide, margins are (almost) parallel at the middle, leaf apex is acute, and leaf base is truncate to abruptly attenuate.
* Leaf margins smooth (entire).

David's Spurge - Euphorbia davidii, invasive exotic
* Annual with a taproot; not rhizomatous.
* Stem leaves all opposite.
* Capsules and seeds are larger. Seeds are essential for identification.
* Leaves are more elliptic and thicker with toothed margins.
* Hairs are shorter and stiffer.

Yellow Toadflax - Linaria vulgaris, exotic and Noxious.
* Non-flowering plants are similar. Leaves are glabrous, long, and narrow.
* Flowers are snapdragon-like, yellow, and lack leafy bracts.

TAXONOMY & NOMENCLATURE
Leafy Spurge is part of a taxonomically complex group of species native to Europe and Asia (Berry et al. in Flora of North America (FNA) 2016).

The true Euphorbia esula Linnaeus is restricted to certain parts of Europe where it shows little tendency to weediness (Berry et al. in FNA 2016). It is distinguished from Euphorbia virgata Waldstein & Kitaibel by leaf shape. Euphorbia esula Linnaeus has leaves that are oblanceolate to obovate-elliptic in shape, margins that are not parallel at the mid-leaf, an apex that is rounded to subacute, a base that is gradually attenuate to cuneate, and general size that is 3-8(-10) times longer than wide (Berry et al. in FNA 2016). Herbarium specimens of Euphorbia esula Linnaeus indicate plants were present in North America, but apparently have not persisted, and are assumed absent (Berry et al. in FNA 2016).

Euphorbia virgata Waldstein & Kitaibel is widespread across Europe and temperate Asia, where it shows the same weedy characteristics found in North America (Berry et al. in FNA 2016). Euphorbia virgata Waldstein & Kitaibel retains the common name of "Leafy Spurge" (Berry et al. in FNA 2016).

Grasslands, meadows, woodlands, and riparian forests in the plains and valleys of Montana (Lesica et al. 2012).

Presumably due to it high genetic variability it easily adapts to local growing conditions. It is often found in pastures, rangelands, roadsides, waste areas, abandoned fields, and bottomlands. It is less frequent on upper slopes, summits, and shoulder slopes.

Leafy Spurge can avoid direct competition with other plants by growing at the very early and late portions of the growing season. Its deep and extensive root system makes it a strong competitor.

Plants reproduce by seed and by adventitious buds on the root crown and on the spreading rootstock.

LIFE CYCLE [Adapted from Lajeunesse et al. in Sheley and Petroff 1999; Jacobs 2007.]
Shoots that grow from adventitious buds on the roots often emerge in April. Seeds typically germinate in the spring with peak emergence occurring from May to early June. Shortly after emergence seedlings grow roots with vegetative buds. If injured the buds break their dormancy to re-generate new shoots. Plants develop a root crown and produce both vegetative and flowering stems.

Plants that flower are usually two years old. In May to early June plants develop bracts, followed about 2 weeks later (mid-June) by flowers. It is the appearance of bracts that gives an appearance of blooming. By mid-July flowering is done. About 20-30 days later capsules have matured. Upon drying, capsules burst open to disperse the many seeds. This action can disperse seeds up to 15 feet. Each capsule produces 1-3 seeds.

Plants can also separate from its roots which breaks bud dormancy and stimulates shoot development. In later summer as soil moisture declines, the stems dry, appearing as light-brown to tan canes, and can become dormant. In the fall growth can resume. Plants are killed by a hard frost.

It is estimated that a plant can produce 30 to 130 seeds. Seeds buried 2 to 4 inches below the surface can germinate. In the soil seeds have been shown to retain viability for at least 8 years. Typically seeds germinate within two years after maturing. Seed dormancy is easily broken and germination can occur in a wide range of temperatures.

Seeds are dispersed by many methods: mechanical action of the drying capsule; floating in water; in mud that adheres to boots, vehicles and other equipment, animal hooves; cling to animal hair or clothing; through ingested and deposition in feces; and a contaminant in seed and haying.

FLOWERS
In the Cited Literature section consult Stein 2011 to learn about Euphorbia 'flowers', cyanthia.

ROOTS [Adapted from Lajeunesse et al. in Sheley and Petroff 1999; Jacobs 2007.]
Vertical roots can grow to 10 feet deep. Lateral roots can extend outwards from the parent plant by 15 feet per year. Roots are covered with thick, corky bark which allows them to better withstand drought, grazing pressures, or herbicide application. The roots sometimes exude translocated herbicides into the soil. The extensive root system can store large reserves of carbohydrates, which helps the plant sustain itself for years and be able to provide energy for re-growth. The extensive root system grows rapidly and extensively, making the plant difficult to manage (Lajeunesse et al. in Sheley and Petroff 1999). In 4 months and in the absence of competition, seedling roots grow to 3 feet deep and spread to 40 inches.

An integrated vegetative management approach provides the best long-term control for Leafy Spurge. It requires that land-use objectives and a desired plant community be identified (Shelly et al. in Sheley and Petroff 1999). Once identified the integrated weed management strategy can promote a weed-resistant plant community that serves other land-use objectives such as livestock forage, wildlife habitat, or recreation (Shelly et al. in Sheley and Petroff1999).

PREVENTION [Adapted from Lajeunesse et al. in Sheley and Petroff 1999]
Preventing the establishment of Leafy Spurge can be accomplished by many practices:
* Learn how to accurately identify Leafy Spurge in order to detect occurrences and know where to implement control methods.
* Prevent vehicles from driving through and animals from grazing within infested areas.
* Thoroughly wash the undercarriage of vehicles and wheels in a designated area before moving to uninfested areas.
* Frequently monitor for new plants, and when found implement effective control methods.
* Maintain proper grazing management that creates resilience to noxious weed invasion.
* Use certified weed-free seeds and hay, including feed for pack animals.
* Before moving animals from infested areas, hold cattle for 6 days and sheep for 11 days in corrals or pastures to allow seed to pass through the digestive tract before moving to uninfested areas. Monitor and treat the holding area for emerging Leafy Spurge.
* Do not pick the flowers or transport plants. Where possible, contribute to or develop educational campaigns to help eradicate or reduce Leafy Spurge populations.

PHYSICAL and CULTURAL CONTROLS [Adapted from Lajeunesse et al. in Sheley and Petroff 1999]

Hand-pulling can be done for small infestations. However, it is considered ineffective because of the deep depth of the root system and its numerous buds.

Mowing may remove flowering stems, but is ineffective for controlling Leafy Spurge because it re-sprouts from buds on the spreading roots.

Tilling can be effective if done intensively throughout the growing season or only during fall. The intensive program would begin in the spring, use a duckfoot cultivator that tills 4 inches deep, and repeats the tilling every 3 weeks until the soil freezes for 1 to 2 growing season. The schedule must not be interrupted because fragmented rootstock will quickly re-sprout. Machinery must be thoroughly cleaned to prevent contaminated the field and other areas. Fall-only cultivation would occur in the autumn when Leafy Spurge is 3-6 inches tall, cultivate 1-2 times after harvest, and for 3 years. Fall-only cultivation allows crops to grow, limits organic matter degradation, and reduces soil erosion. Combining the Fall-only cultivation with other methods could provide better control.

Prescribed burning by itself is ineffective for controlling Leafy Spurge because fire stimulates seed germination and re-sprouting of the buds on the root crown and spreading roots. However, herbicide absorption might be improved when integrated with a burning plan. Burning removes all of the above-ground biomass and provides a uniform surface for re-growth to be seen and for the herbicide to be applied uniformly. After burning about 5 weeks of re-growth should occur before the herbicide is applied. The combination does not control Leafy Spurge any better, but provides a better surface for herbicides to be applied and absorbed into the plant.

BIOLOGICAL CONTROLS [Adapted from Jacobs 2007]
14 insects have been approved for introduction into the U.S. as biological control for leafy spurge by the U.S. Department of Agriculture.

Of all the biocontrol insects for Leafy Spurge Aphthona Flea Beetles are widespread and have reduced Leafy Spurge the most in Montana. The exception is Minute Spurge Flea Beetle (Aphthona abdominalis) which is reported as not established in Montana and not available in the U.S. The Leafy Spurge Flea Beetles are capable of surviving cold, sub-freezing winter temperatures. Larvae of Aphthona Flea Beetles develop in the soil, and cool soil temperatures can delay development and establishment. Herbicide applications, grazing, or mowing that reduces the density of Leafy Spurge has been observed to improve flea beetle establishment. Ants are predators on these insects and releases should not occur where there are ant mounds.
Some bio-control companies sell or provide mixed releases to boost success since release sites vary in soil type, canopy cover, and moisture.

* Brown Dot Leafy Spurge Flea Beetle (Aphthona cyparissiae): Best where soils are 40 to 60 % sand and Leafy Spurge stems are taller than 21 inches and 50-121 stems per square yard based on research in Canada. Green Needle Grass (Stipa viridula) is an indicator of suitable habitat in Canada.

* Black Leafy Spurge Flea Beetle (Aphthona czwalinae): It not does establish well in clay or acidic soils or in deeply shaded areas.

* Copper Leafy Spurge Flea Beetle (Aphthona flava)

* Brown-legged Leafy Spurge Flea Beetle (Aphthona lacertosa): Best where sites are open, sunny, mesic to moderately dry, but can do well on wet sites too.

* Black Dot Leafy Spurge Flea Beetle (Aphthona nigriscutis): Best suited for dry sites with full solar exposure, well-drained soils with less than 3% organic matter, and Leafy Spurge plants of less than 30 inches tall and fewer than 60 stems per square yard (Jacobs 2007). It has been found to feed on the native Euphorbia brachycera, which is a plant that occurs in Montana.

Clearwing Moth (Chamaesphecia crassicornis): Moth where larvae attack roots and stems.

Hungarian Clearwing Moth (Chamaesphecia hungarica): Moth where larvae attack roots.

Spurge Hawkmoth (Hyles euphorbiae): Best where Leafy Spurge plants are dense within open areas near trees. Larvae consume leaves and can kill the plants. Larvae pass through five growth stages before becoming adults. Larvae have toxins that deter predators; however, their pupae are eaten by birds, ground squirrels, and other small mammals.

Red-headed Leafy Spurge Stem Borer (Oberea erythrocephala): It seems to establish best in riparian areas and mesic sites with trees. When adults lay eggs they girdle and often kill Leafy Spurge stems. Larvae will kill stems when feeding, which reduces the plant’s ability to store energy or produce seeds. They are compatible with Apthona Flea Beetles, causing greater negative impacts to Leafy Spurge.

Leafy Spurge Tip Gall Midges (Spurgia esulae): Best where sites are have cooler areas (partially shaded) with dense Leafy Spurge. The insect forms a gall at the tip of the stem. From the gall larvae attack the growing shoot tips, which prevents flowering but stimulates branching and shoot re-growth. The insect can produce up to three generations each summer which attack the new shoots.

Useful Links:
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage.
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides

Leafy spurge is very competitive, displacing native plants, and it can form monocultures (Lajeunesse et al. in Sheley and Petroff 1999). This causes a loss in plant diversity and a loss of forage and habitat for wildlife species (Lajeunesse et al. in Sheley and Petroff 1999).

Leafy spurge is a strong competitor because mature plants can sprout new stems from buds on the roots in April – before many other plants are growing (Lajeunesse et al. in Sheley and Petroff 1999). Plants may become dormant in late summer as soil moisture declines, but come fall plants can re-grow by take advantage of moisture, light, and nutrient resources (Lajeunesse et al. in Sheley and Petroff 1999).