Gather Background Information
The first step in an IVM program is to gather information on the life cycle and habits of the noxious weed.
Leafy spurge is a deep-rooted perennial weed of the family Euphorbiaceae. Because certain structural characters of the weed are very variable, there has been some confusion about how to classify it taxonomically. In North America it is commonly referred to as Euphorbia esula (Watson 1985).
Leafy spurge grows as clusters of upright stems one to three feet tall. The stems are erect, tough and woody, and frequently have many non-flowering branches. The plant emerges in early spring, producing bright yellow bracts which appear from early to late May, with the true flower emerging in mid-June. The bracts surround a cluster of 11-20 small, stalked yellow-green flowers. Leaves are dark blue-green, hairless, narrow, and alternate on the stem. Maturing stems change color from pale green in early summer to yellow or red in the fall. Leafy spurge can be distinguished from other plants by the white sap that will ooze from all parts of the plant when cut or broken open (Lajeunesse et al. 1995; Lym 1991).
Leafy spurge is an aggressive weed that tends to displace all other vegetation in pastures and rangelands. The latex in leafy spurge is a skin irritant that can cause severe dermatitis in humans and grazing animals, and is unpalatable and toxic to cattle and horses. Cattle and horses generally avoid leafy spurge, but if ingested it causes scours and weakness that may result in the death of the animals. Sheep and goats are not affected by the toxin and can eat young leafy spurge plants (Muller et al. 1990).
The presence of leafy spurge in pastures can reduce the livestock carrying capacity 50 to 75%. In North Dakota, South Dakota, Montana, and Wyoming, the economic damage done by this weed has been conservatively estimated at over $110 million per year due to losses of forage production and beef cattle production, plus the costs of herbicides and herbicide applications. There is an additional loss of over $11 million annually in North Dakota alone due to reduced wildlife habitat and associated recreational activities. Native prairie species, such as the western prairie fringed orchid, Plantathera praeclara, in Sheyenne National Grassland of North Dakota, show serious decline in association with leafy spurge infestations. It is also eliminating the vegetation that is the required habitat for the threatened northern prairie skink, Eumeces septentrionalis septentrionalis (Lym & Kirby 1987; Lym & Messersmith 1990; Bangsund & Leistritz 1991; Thompson et al. 1990; Wallace et al. 1992; Van Driesch & Bellows 1996).
Originally of European or Eurasian origin, leafy spurge is widespread in Europe as far south as central Spain, Italy, and the Balkans, extending eastward through central Russia into Siberia. It was first reported in the United States in Massachusetts in 1827, and currently infests over 2.7 million acres in the Northern Great Plains of the U.S. and Prairie Provinces of Canada. North and South Dakota, Montana, Idaho, and Wyoming have the highest numbers of infested acres (Lym 1991; Noble et al. 1979; Dunn 1979).
Leafy spurge grows in diverse environments from dry to sub-humid and from subtropic to subartic. It establishes more readily in disturbed soil, and is primarily found in untilled, non-cropland habitats such as abandoned cropland, pastures, rangeland, woodland, roadsides and waste areas. It can also establish in an undisturbed, pristine plant community (Meyers et al. 1964; Derscheid et al. 1985; Watson 1985; Coombs 1996; Dunn 1985).
Leafy spurge reproduces from seed and from vegetative buds on the extensive root system. Most seeds germinate in the spring, but some may germinate at any time during the growing season from spring to fall. Some seedlings may become perennial and reproduce vegetatively from buds within 7 days of germinating. All seedlings are perennial by the time they reach the 10-leaf stage (Lym 1991; Selleck et al. 1962).
In areas subject to frost, seedlings and shoots from overwintering plants first emerge in early spring, often the first plant to emerge in a plant community following winter dormancy. At this time the seedlings may be a deep red or purplish in color. The primary stem is replaced by rapid growth of adventitious stems sprouting from either crown buds or root buds. Bracts may appear within two weeks of emergence and precede flowers by two to three weeks. The ability of buds to sprout declines in midsummer during pollen production (Messersmith 1983; Lym 1991; Best et al. 1980).
Established plants may also produce flowers within a month of breaking dormancy. Each flowering shoot normally produces from 10 to 50 fruits and each fruit usually contains 3 seeds. Four to six weeks after flowering, each stalk can disperse more than 150 to 200 seeds, with a 60-80% germination rate. Because the seeds lack any appendages such as plumes, spines, or air bladders, they are mainly dispersed only a short distance by dehiscence of the seed capsule, which can propel seeds up to 15 feet away from the plant. Leafy spurge is also dispersed larger distances by birds, waterways, and to a great extent, people. Seeds can germinate and emerge from up to six inches depth. Some remain dormant for up to eight years, but 99% will germinate within two years (Cole 1991, Bowes and Thomas 1978).
Leafy spurge has a very extensive root system, with vertical roots reaching depths of 30 feet. New stems can sprout from the root crown or anywhere along the length of a horizontal root, and viable plants can regenerate from root fragments. Root systems of well-established older plants can regenerate from fragments even if roots are removed to a depth of three feet (Lacey et al. 1984; Messersmith 1983; Selleck et al. 1962; Lym 1998).
Leafy spurge can spread by seed and horizontally growing roots, which send up shoots beyond the perimeter of the leafy spurge patch. Even if the foliage of the plant is removed or destroyed, the living root tissue will regenerate new shoots, and the new shoots can emerge from buds located anywhere along the length of the root. Buried seeds can remain viable for years, with viability of remaining seeds declining by 13% annually. Since typical infestations may have seedbanks of 350 to 1,000 seeds per square foot, even a decade of repeated control efforts may leave enough seeds for the population to re-establish. Partial injury to root systems, stems, or foliage encourages bud production, and can aid the growth and spread of the plant. In agricultural fields, tillage aids leafy spurge by disturbing soil, distributing root fragments, and bringing buried seeds to the surface. Hand cutting, mowing, burning or digging is usually not effective because the entire root system must be excavated for complete control (Bowes and Thomas 1978; Wolters et al. 1994; Selleck et al. 1962).
Neither short-term nor long-term control with chemicals alone is effective. Herbicides will only kill roots to a depth of 18 inches, allowing well-established plants (3 years old or older) to regenerate within three years (Lacey et al. 1984, Senft and Cooke 1994). However, long-term control can be obtained through repeated treatments in an integrated management program.
Some questions, such as those below, can only be answered on site.
Set Realistic Goals
for Your IVM Program
The answers to the following questions can help you set realistic objectives and goals.
Containment - keeping an established population of the weed from spreading to non-infested areas. This strategy is especially useful when time and money are in short supply or when the infestation is very large. For example, a barrier strip between infested and non-infested areas can be maintained and monitored so that adjacent lands remain weed free. In addition, measures that stop seed production will help prevent further spread of the weed.
Reduction - reducing the area covered by leafy spurge, or reducing its dominance. This strategy can also be used against new or established weeds, but it requires more resources and more time than containment.
The "Bradley Method" (see Appendix 2), developed in Australia, is a simple yet innovative strategy for natural areas that combines containment and reduction.
Eradication - completely eliminating the weed from the management area. This strategy usually consumes the greatest amount of time and resources and is applicable mainly to newly-invading weeds that are confined to a limited number of small areas.
Establish Monitoring Programs
When planning a monitoring program, keep in mind the context of your target weed: is it invading or has it already invaded?
Locate and record leafy spurge infestations on a map. (Chapter 2 of the University of Northern Iowa IVRM Technical Manual contains a detailed discussion on how to map and inventory vegetation - see Bibliography). Note particularly sensitive areas on the map, such as critical habitat for threatened or endangered species, agricultural production areas, or areas subject to frequent disturbance and thus prone to invasion. Update maps at regular intervals.
Focus monitoring efforts on sites where leafy spurge problems are most likely to occur (see Distribution). Encourage public sighting and reporting through an education or incentive program (see Educate Vegetation Management Personnel and the Public).
Prioritize the sites you will work on. Make a realistic assessment of your weed management resources, keeping in mind the goals of your project and the cost of a follow-up program after any treatments. Without follow-up, your control efforts will be wasted. It is better to thoroughly control a weed at one or two sites than to use up resources to incompletely control the weed at many sites. If the weed is very widespread, try to determine where it poses the most serious economic, social, or environmental problem and concentrate on those areas.
Plan monitoring and treatment efforts to coincide with critical life stages of the weed. To use your resources efficiently, try to include monitoring with other planned activities in the area.
Maintain records of your monitoring activities. Creating standardized forms will make data collection easier and help remind you to gather all the information you need. Forms work best if they include labeled blanks for all pertinent information and allow the user to check or circle rather than having to write words or numbers (See Appendix 3 for some examples of forms).
Include information such as the name(s) of the person(s) collecting the data, the location, and date of monitoring; a qualitative description of the vegetation, such as the names of the plants or types of plants (native vegetation, annual/perennial weeds, trees, etc.) and stage of growth (germinating, flowering, setting seed, etc.); a quantitative description, such as percent cover, plant density, size of the patch, or if possible, the number of plants.
Note special conditions such as unusual weather events and record treatment history, including information on treatment applications (who, when, where, how, cost, difficulties, and successes). This will allow you to evaluate and fine-tune treatments.
Set Treatment Thresholds
Setting treatment thresholds includes prioritizing and balancing treatments with resources. Weeds will be treated when populations increase beyond a predetermined level. This level will largely depend on the characteristics of the site and weed. In some cases the level may be no weeds at all, and in other cases the number of weeds you can tolerate may be much greater.
What is the size of the weed population? The opportunity for control is related to the infested area. Small patches can be more easily controlled than large infestations.
What is the level of the threat? Is the leafy spurge population changing? Is it in an area where soils are frequently disturbed? Does it threaten agriculture, pastures, or rangeland? Is it encroaching on critical habitat for a rare, threatened, or endangered species? Is it displacing the best examples of native communities?
What resources are available? Do you have the resources required for carrying out your goal?
With the advent of herbicides, prevention as a weed management technique has often been neglected; however, it is a practical, cost-effective, and extremely important part of noxious weed control.
General Weed Prevention Measures
(Adapted from Fay et al. 1995).
Revegetation - Follow-up Weed Prevention
Establishing dense, competitive vegetation can help permanently replace weeds. Revegetation is critical in preventing weed infestations in areas where the soil has been disturbed or the vegetation removed. In some situations you may be able to encourage desirable vegetation that is already in place; but because of the aggressive nature of leafy spurge, it is more likely that you will need to thickly sow seeds of desirable, competitive plants.
Apply Management Methods
No individual method will control leafy spurge in a single treatment; diligence and persistence will be required over a number of years to subdue this weed. The treatment methods described in this section will help you to design an integrated program that will suit the circumstances of your particular situation.
Biological control does not aim to eradicate weeds, but to keep them at low, manageable levels. After their introduction, biocontrol agents can take 5 to 10 years to become established and increase to numbers large enough to reduce the density of the target weed. Once established, effective biological controls provide an inexpensive, long-term, and non-toxic means to control weed populations. Since insects have specific requirements for growing and thriving, it is important to match the insect to the weed management site. Understanding these requirements will help you integrate the insects into other weed control efforts. When you release biocontrols, continue using other control methods on the perimeter of the release site, but avoid using them where they might adversely impact the insect population.
The information provided below is only a summary. For more information consult Biological Control of Weeds in the West (see Bibliography) or contact commercial weed biocontrol insectaries (see Insectaries).
Five species of flea beetles in the genus Aphthona (Chrysomelidae) that have been imported into North America have shown varying degrees of success as control agents of leafy spurge. Root feeding by larvae is the primary source of control, but adults contribute by feeding on foliage and flowers. Control is most successful in open areas with well-drained soils, but less so in mesic- and wet-spring, shaded and cool-summer sites.Aphthona species generally establish on warm, sunny, south-facing slopes with medium density of leafy spurge. Aphthona species have the same life cycle. Adults lay eggs on leafy spurge stems near the soil line every 3 to 5 days after emergence in the spring or summer. Larvae hatch within weeks and feed on the roots, overwintering there. In early spring, larvae pupate in the soil, emerging as adults in early to midsummer (CAB International 1995).
Adults of all five species of these flea beetles can be collected with a sweep net in the summer (late June to mid July). About 500 beetles will be needed to establish a new site. Following their release, they should be protected from heavy disturbance (insecticides, soil cultivation, burning, grazing or destruction of leafy spurge) for several years to enhance establishment of the insects (Lajeunesse et al. 1995; Cole et al. 1991).
Researchers have found an area in Lewis and Clark National Forest, Montana, where leafy spurge is declining naturally. A native basidiomycete fungus produces a compound that inhibits leafy spurge root growth and makes the plants more susceptible to pathogenic organisms in the soil. An established colony of the fungus will expand four inches a year, more in moist years. So far this fungus has proven easy to produce in quantity and persistent in the soil. Recent tests combining the fungus with Aphthona spp. beetles suggest that the combined effect of both is greater than the sum of the effects of each. The researchers hope to isolate the active agent produced by the fungus and develop techniques for producing and releasing the agent (Caesar 1996, Senft and Cooke 1994).
Permits are required to transport biocontrol insects or pathogens across state borders. Such permits are obtained from either the state Department of Agriculture or from the USDA Animal and Plant Health Inspection Service (APHIS). However, a given control agent may already exist in nearby established sites and you may be able to transport them to your area. Consult with your extension agent for help in determining if a biocontrol agent is present near your site and what control strategies will be detrimental to the agent.
Grazing with sheep or goats can be a very effective tool for controlling leafy spurge populations —even more effective than herbicides if long-term grazing is used (greater than five years). Grazing can also generate an economic return from land that other livestock won’t graze. Leafy spurge is not toxic, and in fact, very nutritious for these animals, providing good forage for lambs, kids, and lactating ewes and nannies. The crude protein content is greater than 27% in the early season, declining to less than 20% after maturity (Sedivec et al. 1995).
Goats and sheep should be forced to graze leafy spurge in the spring by fencing them off in a heavily infested area with temporary corrals or woven fence. This will help them quickly adapt leafy spurge as their dominant food source. In general, grazing should begin when leafy spurge plants are 4-6 inches tall in the mid- to late spring, and repeated in the late summer if regrowth shows signs of flowering. It should be grazed in the spring until the plant is completely defoliated. Then rotate the animals to the next infested pasture and repeat the process.
Sedivec (1995) defined four classes of grazing management plans: 1) seed removal— in which leafy spurge is grazed during the spring to remove the yellow bracts and flowers, and perhaps again in late summer. This type of grazing prevents seed-set but does little to reduce the root system; 2) multiple pasture rotational system—in which a properly timed rotational grazing system continuously defoliates the leafy spurge throughout the growing season. This eliminates seed production and causes limited stress on the root system, and is often recommended when large infestations occur over many acres; 3) intensive rotational grazing—in which the plant is grazed in the spring until it is completely defoliated, and then the animals are rotated to the next pasture. In late summer each pasture is grazed a second time. This method achieves optimum stress on the plant, decreasing plant vigor and carbohydrate reserves; and 4) continuous grazing—in which about four months of continuous grazing allows goats or sheep to graze throughout the growing season, thus preventing a leafy spurge recovery period and maximizing stress on the root system and its reserves.
Generally, managers use continuous rather than short duration or rotational grazing throughout the growing season. However, if desirable shrub and forb species are present, continuous grazing can damage them, and rotational grazing is recommended.
In one 4-year experiment in North Dakota, leafy spurge control by angora goats tended to be more rapid with continuous rather than rotational grazing. This is in agreement with Bowes and Thomas (1978), who found that annual intensive, continuous grazing by sheep was necessary to reduce leafy spurge density in Saskatchewan. However, according Olson and Lacey (1994), short duration and rotational grazing may be more effective practices because they allow for more regrowth of the plants between defoliations, and insure multiple defoliations of each plant annually, putting maximum stress on the leafy spurge plants (Lym et al. 1997).
Avoid grazing leafy spurge with mature seed (brown to gray in color), as leafy spurge seeds may be get caught in animal hooves or hair, or will be carried in feces and deposited in non-infested pastures when the animals are moved. Animals that have grazed on leafy spurge seed should be held on the pasture for at least five days to allow all seed to pass from their systems before moving them (Hansen 1996; Lacey et al. 1992).
There are some limitations in the use of sheep to control leafy spurge. It is not cost effective to move large numbers of sheep a significant distance to graze an infested area. It may not be possible to graze the entire area of very large infestations before seed production occurs. In most cases where sheep are used, the landowner has purchased the animals and incorporated them into the production system, or a neighbor has sheep and is willing to graze them on non-infested pasture. Sheep are more susceptible to predators than cattle, and losses sustained while grazing a neighbor’s pastures may be unacceptable. Electric or other fencing plus guard donkeys or special guard dogs can help protect sheep.
Despite these limitations, sheep grazing remains a very
popular and effective means of leafy spurge control in many places. Because
of the value of leafy spurge control, federal agencies may not charge a
fee for grazing leafy spurge infested federal land, and private land owners
may lower rental fees for infested pastures (Olson and Lacey 1994).
An average stocking rate of three to four goats/acre of leafy spurge over a four-month grazing season is required to maintain acceptable control. For one month, the goat stocking rate would be 12 to 16 goats per infested acre (Sedivec et al. 1995).
Currently, it is uncommon for range managers to keep goats, and it may be difficult to locate a herd for grazing leafy spurge. Like sheep, goats are more vulnerable to predators, such as coyotes, than are cattle. Goats are also more difficult to contain than sheep, particularly when their hair gets long enough to reduce the impact of a shock from electric fencing. Goats often pull up fencing with their horns; therefore, the fence needs to be anchored to the ground. One way of doing this is to stake it down by bending one end of a piece of rebar into a hook, hook it onto the bottom of the fence, then pound it about 1 1/2 feet into the ground. Escaped goats can result in crop damage to neighboring fields, as well as aggravation and loss of time spent chasing them. Also, where it is desirable to preserve woody vegetation, sheep might be better than goats, which can seriously damage young trees and shrubs unless they are protected by fencing.
An electric shock collar linked to a single wire system has been used successfully to contain goats. The collar emits a warning sound, then a shock when the animal gets close to the wire. The wire carries a small current, producing a magnetic field that the collar responds to. The animals are easily trained to the collar, and the single wire needed may be quickly set up or removed from difficult terrain.
Costs for commercial units are high, but researchers are working on developing an inexpensive version that could be used for livestock management (Fay 1991).
Any type of domestic farm animal, including sheep, goats, pigs, and chickens, can be induced to trample an area of leafy spurge. Feeding or salt lick stations can be established inside leafy spurge-infested areas. Animals will concentrate there, trampling the plants and destroying stems and foliage. A leafy spurge area can also be fenced off and used as a corridor to move animals through. If this is done twice a year, once in midsummer when seeds are maturing and once in the fall when regrowth is observed, control can be achieved over a period of years as seeds and root systems are exhausted. This control method must be used repeatedly until seeds and root systems are exhausted, or leafy spurge will flourish in the disturbed, fertile soil created by the animals (Selleck et al. 1962).
When beginning a hand-removal project, flag the treated areas so they can be identified for follow-up treatments. It is easiest to work in relatively small areas of infestation. When faced with dense and/or extensive stands of leafy spurge, it is best to divide them into grids (with flags, stakes, etc.) so that workers can thoroughly weed smaller areas before moving onto the next grid. The grid system also facilitates dividing work activities between those pulling and those removing the debris.
Hand pulling and grubbing is only effective where there are a few plants in their first year of growth. Leafy spurge plants are relatively easy to pull by hand, but pulling usually results in breaking off the root system a few inches below ground. It is best to pull or grub out seedlings within 7 days of germinating, and sprouts from buds should be pulled before they get more than 2 inches tall. Expect to repeatedly pull regenerating leafy spurge plants every 3 weeks or so from early spring until winter for several years. This approach will eventually exhaust the root systems. Plants should be removed when soil is moist to maximize how much root material is removed and to minimize disturbance (Selleck et al. 1962).
Mowing alone is ineffective for reducing leafy spurge infestations, but can be used to prevent seed production and to weaken underground parts. To prevent seed production, mowing should be done before viable seeds are formed (before they turn from brown to grey). To weaken root reserves, repeated cutting may be needed for 1 to 3 years. The best time to start mowing is usually when the underground root reserves are at a low ebb, between full leaf development and the time that flowers appear during late spring (Derscheid et al. 1985).
Mowing is also used to increase the effectiveness of herbicide applications by providing uniform regrowth. For best control, allow at least five weeks of regrowth before herbicide application in early summer (at flowering) and midsummer (after seed set), cutting to a height of three to four inches. Mowing in the fall decreases effectiveness of herbicide treatments (Lajeunesse et al. 1995; Lym and Messersmith 1986).
Although light cultivation will encourage leafy spurge, repeated heavy cultivation can be used as a control technique. In agricultural fields, leafy spurge should be cultivated with a duckfoot cultivator to a depth of 4 to 5 inches. The sweeps or blades should overlap 3 to 4 inches, be kept sharp, and adjusted so they are flat when in the soil. Cultivation should be repeated every two weeks during good growing conditions (May, June, and July) and three weeks during dry, hot conditions (August, September, and October) from early spring (two to four weeks after leafy spurge emerges) until the first killing frost. Two or more years of this regime will be required. Do not interrupt the schedule or regenerating shoots will begin storing food and the control clock will be set back.
In cropland, 2 cultivations in the fall, after crop harvest, for 3 years has successfully eradicated leafy spurge. Care must be taken not to transport root pieces on machinery into other areas (Derscheid et al. 1985; Lajeunesse et al. 1995; Lym 1998).
Controlled burns should only be used in combination with other control techniques such as grazing or herbicide treatments. Burning alone is ineffective for reducing leafy spurge infestations, and stimulates sprouting of established plants, increasing plant density. However, both spring and fall burns can reduce leafy spurge seed viability, but spring burns tend to be more effective. Burning can also increase visibility of the plants and eliminate old stems and ground litter, thus improving herbicide spray coverage. Burning may also be used to control regrowth (Lajeunesse et al. 1995; Wolters et al. 1994).
Deep mulching (12 inches or more) with straw was used as a control method prior to the widespread availability of herbicides. Unless the patch is surrounded by dense, competitive vegetation or a hostile environment, mulch should extend 15 ft or more beyond the perimeter of the leafy spurge patch to prevent roots or recently dispersed seeds from sprouting. The mulch layer should be maintained for at least three years to kill the root systems of the plants. Deep mulching will eliminate leafy spurge along with all other vegetation in the treatment area (Bowes and Thomas 1978).
In IVM programs, herbicides are considered transition tools that enable the manager to suppress weeds and replace them with desirable, competitive vegetation. Thus, it is important to select the least-toxic, low-residual herbicide that is effective against the target weed, and to apply them in a judicious manner.
The following links discuss the primary considerations
when using herbicides: Use
Herbicides Properly, Herbicide
Information Resources, Criteria
for Selecting an Herbicide, and Application
Applying herbicide to plants when leafy spurge is most susceptible (preferably before seeds are produced) is crucial to the effectiveness of the treatment. Most herbicides effective on leafy spurge should be applied when true flowers are in bloom and seeds are forming. The plants will have green leaves along the entire stems and swollen seed capsules at this time. The yellow bracts, which are modified leaves rather than true flowers, should not be confused with the flowers. If herbicides are applied when the bracts have reached full color but the flowers have not matured, seed production will be prevented, but little herbicide will be translocated. Fall herbicide treatments should be applied after leafy spurge regrowth is noticeable but before a killing frost. Timing will be different when herbicides are used in combination with other control techniques (see above). Only young leafy spurge plants, seedlings or adults less than three years old can be killed by a single herbicide treatment (Lym and Whitson 1991).
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Bowes, G.G. and A.G. Thomas. 1978. Longevity of leafy spurge seeds in the soil following various control programs. Journal of Range Management 31(2):137-140.
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Caeser, Anthony J. 1996. Pers. Comm. Res. Plant Pathologist, USDA-ARS. P.O. Box 1109, 1500 North Central, Sidney, MT 59270.
Carlson, R.B. and D. Mundal. 1990. Introduction of insects for the biological control of leafy spurge in North Dakota. North Dakota Farm Research 47(6):7-8.
Cole, D.E., A.S. McCay, and C.J. Richardson. 1991. Control of leafy spurge with spurge beetles. Agri-fax pamphlet, Agdex 643-3, Print Media Branch, Alberta Agriculture, Edmonton.
Cole, M.A.R. 1991. Vegetation management guideline: leafy spurge (Euphorbia esula). Natural Areas Journal 11(3):171-172.
Coombs, Eric M. 1996. Pers. Comm. Biological Control Entomologist, Oregon Dept. of Ag. 635 Capitol St. NE, Salem, Oregon, 97310.
Coombs, E.M. 1995. Biological control of weeds project summaries. Oregon Dept of Ag. Commodity Inspection Div.Nox.Weed Control Prog. Tech. Bulletin 96-1.
Derscheid, L.A., L.J. Wrage, and W.E.Arnold. 1985. Cultural control of leafy spurge. In: Watson, ed., Leafy Spurge. No. 3 of the Monograph Series of the Weed Sci. Soc. of America, Champaign, IL.
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Ferrell, M.A., T.D. Whitson, D.W. Koch, and A.E. Gade. 1992. The control of leafy spurge (Euphorbia esula L.) by the interaction of herbicides and perennial grasses. Western Society of Weed Science Research Progress Report 1992:I-54.
Fuller, TC., and GD. Barbe. 1985. The Bradley method of eliminating exotic plants from natural reserves. Fremontia. 13(2):24-25
Hansen, Richard. 1996. Pers. Comm. Entomologist, USDA Forest Tree Sciences Laboratory. P.O. Box 170278, Montana State University, Bozeman, MT 59717-0278.
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Hein, D.G. 1988. Single and repetitive picloram treatments on leafy spurge (Euphorbia esula L.) and resulting changes in shoot density, canopy cover, forage production and utilization by cattle. Ph.D. Thesis, University of Wyoming [cited in Lym and Messersmith 1990].
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