Sustainable and profitable control of invasive plant species by small ruminants

Final Report for LS05-175

Project Type: Research and Education
Funds awarded in 2005: $178,000.00
Projected End Date: 12/31/2009
Region: Southern
State: Texas
Principal Investigator:
Dr. James Muir
Texas A&M AgriLife Research
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Project Information


Overgrazed rangeland and invasion of aggressive vegetation in disturbed land are environmental concerns in the southeastern USA, St. Croix, and Puerto Rico. This project addressed plant:animal interface concerns that contribute to resolving both issues by expanding the use of small-scale commercial flocks (goats and sheep) to control invasive weeds. How this is done effectively, on what species and at what cost was addressed in five representative locations throughout the southern SARE region: Puerto Rico, St. Croix, Florida, Georgia and Texas. Defining and refining intensive, short-duration goat/sheep browsing (ISDGB) techniques for controlling weeds was the goal. The experiments, presentations, field days, demonstrations, and publications produced should encourage the commercialization of ISDGB by small ruminant farmers and managers of land with invading vegetation.

Puerto Rico

In Puerto Rico, invasive weed species reduce forage availability in tropically grazed pastures by over 50%. On alkaline and dry sites, Leucaena (Leucaena leucocephala Lam. De Wit) form thickets and limits grass growth. Invasive legume weed species on wet sites include White acacia (Albizia procera), climbing mimosa (Mimosa casta) and catclaw (M. pellita; formerly M. pigra). Mature trees of albizia can be eradicated with ISDGB in a one-year-period. Catclaw will require mechanical cutting as very little is consumed by goats. Younger resprouts can be maintained at acceptable levels in pastures with ISDGB. Climbing mimosa can be eradicated with ISDGB, but the short dry period in these areas will pose a challenge. Minimizing leucaena in thick stands will require mechanical maintenance (1 cut per year), followed by intensive stocking with goats. In conclusion, ISDGB is an alternative to chemical control of invasive species in the Caribbean basin.


In Georgia and much of the southeastern United States, kudzu (Pueraria lobata), a drought-tolerant, perennial warm-season vine, was once considered an important forage plant for grazing animals, but is now classified as a weed species, often choking out other vegetation with its climbing growth habit and large leaves. Both goats and sheep readily consume kudzu forage, and its leaves maintain high levels of crude protein (>20%) throughout the grazing season, suggesting its use as a source of feed. Its growth can be controlled through ISDGB in areas where it is not wanted, although the length of time needed to achieve total eradication is still to be determined.


Perennial peanut, a nitrogen-fixing legume, is planted under fruit trees in Florida orchards. However, invasive weeds are difficult to control in this herbaceous, mat-forming species. The use of sheep in ISDGB systems was tested with mixed results. When rainfall is good, weed growth outpaces ISDGB suppression whereas when rainfall is low, sheep tend to eat too much of the perennial peanut. Further refinement of the system is needed.


Greenbriar (Smilax spp.) suppression was targeted in wooded areas using goats in ISDGB. Results indicate that eradication is not permanent with this deep-rooted perennial vine although better results occur when vines are initially cut below the browse line to make regrowth accessible and when higher stocking rates are used. Mesquite (Prosopis juliflora var. glandulosa) eradication is not achievable using ISDBG because goats do not browse it sufficiently, even when it is mechanically cut at ground level to bring regrowth within browse reach.

St. Croix

Throughout the Caribbean Basin, the ornamental exotic, coral vine (Antigonon leptopus), has become an invasive weed. ISDGB on-farm and on-station indicate that St. Croix sheep will consume both leaves and vines of this deep-rooted perennial and suppression (but not permanent control) is possible, providing access to land that was densely invaded that no other agricultural use was possible.

Project Objectives:

1) Develop ISDGB trials that address flock owner/landowner questions and serve as local demonstrations of this method for environmentally sustainable invasive plant control.

2) Research specific plant:animal interface issues that will develop into the techniques that effectively control of permanently eradicate invasive plants in each environment and for each species, including stocking rates, seasonal vulnerability, browsing duration, and negative effects on both native vegetation and flock performance.

3) Develop farmer-to-farmer contacts, demonstrations, brochures, popular press articles, web pages, and refereed articles to foment greater commercial application of ISDBG in the region.

4) Assist both landowners and goat/sheep flock mangers in determining equitable cost sharing for the commercial application of ISDGB.


The invasion of fallow cropland, pasture and woodland by native and non-native weeds is a common problem throughout the southern USA, Puerto Rico and the U.S. Virgin Islands (USVI). In Florida alone, 29% of non-cultivated plants are classified as non-native (Langland and Stocker, 2001). Native mesquite (Prosopis glandulosa), cedar (Juniperus spp.), and greenbrier (Smilax spp.) are examples of widespread southeastern USA invasive plants resulting from overgrazing by cattle and its disruption the natural balance in plant communities (Welch and Hyden, 1996; Racher and Britton, 1997; Taylor and Fuhlendorf, 2003). Kudzu (Pueraria lobata), coral vine (Antigonon leptopus) cogongrass (Imperata cylindrica), Japanese climbing fern (Lygopodium japonicum), and leucaena (Leucaena leucocephala) are well-documented examples of non-natives that have become widespread invasive species in the region (Miller, 1988; Engle et al., 1994; Langland and Stocker, 2001; Terrill et al., 2003). Most of the non-native species have proved very difficult to eradicate once established. For example, current guidelines for kudzu control warn that repeat applications of herbicide may be necessary for 5 to 10 years after initial treatment (Demers and Long, 2002).

For this reason, it is not hard to understand why both public and private landowners are often overwhelmed by the logistics and cost of controlling invasives. Dade County Florida Parks and Recreation Department spent $2.3 million for the removal of invasive plants from 500 acres of upland area from 2002 to 1993 (Langland, 2003). In one year alone, the State of Florida budgeted $12 million for control of wetland species alone (Langland, 2003). The environmental repercussions of widely applied and indiscriminate chemical and mechanical control are poorly understood, however. This is particularly true in natural areas where special care is needed to minimize damage to non-target vegetation, soil and fauna that depend on them (Langland and Stocker, 2001).

Non-chemical methods exist for controlling invasive weeds. Non-grass weedy invaders can sometimes be suppressed using grass-fueled fires (Briggs et al, 2002) but this rarely results in 100% eradication and is sometimes a socially or environmentally unacceptable means of brush management. Other methods commonly used include grubbing, root-plowing, removal by hand, chaining, and herbicides (Taylor, 1992; Hart, 2001), all of which have environmental and economic downsides. Biological control of regrowth following mechanical or chemical brush control has proven more effective than single-control approaches (Magee, 1957; Green and Newell, 1982). The use of small ruminants for biological control may be more socially acceptable (Ball, 2004) and their forage predilections (Huston, 1978) and specialized digestive tracts (Huston et al., 1986; Hofman, 1989) make them better brush control tools than other larger ruminants. In addition, goat and sheep feed preferences are determined by a complex mixture of genetics, learned behavior, and feed availability (Malechek and Provenza, 1983) that can be manipulated to produce specific modifications in plant communities.

In a review of studies involving grazing animals for weed control, Popay and Field (1996) indicated two important limitations to effective weed control with livestock: 1) the low availability of animals and, 2) no means to control grazing pressure. They felt that one of the reasons this practice is not more widespread in the United States is because a high percentage of the farms have no livestock. Thus, small ruminant producers have greater opportunity in this country to sell the use of their animals for weed control than, for example, in New Zealand and Australia where mixed farming and grazing operations are more common (Popay and Field, 1996), or in the western United States where small ruminants have historically been more numerous.

The use of intensive, short duration goat/sheep browsing (ISDGB) may be an efficacious, remunerative, and ecologically mild form of manipulating vegetation (Muir et al., 1997; Briggs et al., 2002). The use of small ruminants for brush control is not completely unknown in the southern USA (Bull, 2000) and has been supported by SARE grants (LS01-119) in the past. The commercial application of this practice, namely contracting herds specifically to suppress invasive vegetation (Ball, 2004), is not, however, widespread in the southeastern USA or its Caribbean territories but has been successful elsewhere (Green and Newell, 1982). At the same time, market demand for goat and sheep meat is strong (, indirectly encouraging over-stocking on ecologically sensitive rangelands where most small ruminants have traditionally been raised (Malechek and Leinweber, 1972) and in the eastern United States where most producers have limited land areas to utilize. The growing invasive plant problems, in conjunction with a strong small ruminant market, provide a fortuitous opportunity to combine profitable animal husbandry with biological control of weeds. The details for this union of circumstances, however, have not been developed.

Both stocking rates and rotations have proven important in reducing perennial brush using small ruminants in regions outside the southeastern USA, Puerto Rico and the U.S. Virgin Islands (Muir et al., 1997; Torrano et al., 1999; Tsiouvaras et al., 1999; Mellado et al., 2003). But the key word is “reduction” and not “eradication”. Even when heavy stocking rates force intensive browsing, goats and sheep cannot always completely destroy target species (Muir et al., 1997; Torrando et al., 1999) and these can still make a comeback in subsequent years from rootstocks or soil seed banks (Torrando et al., 1999). Heavy browsing can even stimulate some browse production (Provenza et al., 1983) while season of vegetation removal can also affect regrowth vigor (Hardesty et al., 1988). Timing for ISDGB or combinations of different weed control methods that include ISDBG may have to be developed to ensure long-term eradication.

While clear-cutting brush will often increase forage immediately available to small ruminants (Pfister and Malechek, 1986; Kirmse et al., 1987; Schacht and Malechek, 1990), subsequent flock management can have a strong effect on the plant-animal interface. Continuous grazing tends to produce superior control (Lym et al., 1997) but often at a cost to animal production. Heavy stocking can reduce the quality of browse available to goats and sheep (Malechek and Leinweber, 1972) which can be detrimental to flocks. Desirable species (a strong movement by landowners in the region favors natives) may also be vulnerable to eradication if stocking rates or grazing duration exceeds their tolerance level (Green & Newell, 1982), mostly determined by their place on the palatability scale of the particular flock being used (Allan and Holst, 1996).

A review of the literature on the use of small ruminants for the biological control of brush makes one thing clear: successful vegetation suppression, with or without the use of small ruminants, is governed by a complex set of factors. The commercial application of ISDGB requires greater knowledge including effects of prior vegetation manipulation, season of application, stocking rates, duration of exposure, and growing conditions which all combine to affect the degree of successful weed control.

Southern-SARE Planning Grant LS03-150 funded a series of forums in which small-scale landowners, limited-resource goat/sheep farmers, extension personnel and researchers determined 1) whether ISDGB was already being widely employed in the southeastern USA, Puerto Rico and the U.S. Virgin Islands, 2) what farmer/landowner perceptions of ISDGB are, and 3) what limitations exist to its wider commercial application. At all locations (south-central Georgia, north-central Texas, St. Croix and Puerto Rico) the answers were uniformly 1) only one successful commercial application was found (Ball, 2004), 2) landowners were interested in the concept but goat/sheep farmers were in doubt how to apply ISDGB and, 3) questions arose as to the efficacy of ISDGB and the plant:animal interface tools needed to apply it commercially. In addition, both landowners and goat-owners were in doubt as to the economics of such contracts, a problem identified in other regions (Hart, 2001).


Click linked name(s) to expand
  • Sam Coleman
  • Tom Terrill
  • Elide Valencia
  • Stuart Weiss


Materials and methods:

Objective 1: ISDBG trials. A series of trials, doubling as demonstrations, at each of the five primary locations, tested ISDGB feasibility and efficacy in realistic, commercial situations.


The local research team, including both landowners and goat owners, determined that efforts would focus on using goats to control greenbrier (Smilax spp.) and mesquite (Prosopis glandulosa). An on-farm location at the Harp grazing lease in Erath County was used. Due to the business failure of the Harp lease, the trial focusing on greenbriar was moved to the Stephenville AgriLife Research Center. Treatments at both locations used Boer/Spanish cross meat goats in oak upland forest heavily infested with greenbriar to achieve suppression with the following treatments:

1. Control, no brush control
2. ISDGB alone
3. 100% mechanical brush removal
4. 100% mechanical removal/ISDGB
5. 100% mechanical removal/ISDGB/spot herbicide
6. 100% herbicide/ISDGB
7. 100% herbicide/ISDGB/spot herbicide

Replicated, 3-yr trial on 40 X 25 m fenced paddocks commenced after the last danger of frost was over in the spring of 2005 to allow vegetation baseline data collection. Mechanical control of woody/viney vegetation was imposed manually. Herbicide application followed “Chemical Weed and Brush Control” (McGinty et al., 1995) on greenbrier involve basal/stump application of a 15% Remedy and 85% diesel mixture. The greenbriar trial had an additional stocking rate treatment which targeted 0, 5 and 10 animals/ha which were removed after 95% of the greenbriar leaf material was browsed.

Baseline data in the greenbriar trial included herbaceous vs. invasive plant species frequency, height, biomass ( 2 m) and, in the case of the mesquite trial, diameter at base before treatments are applied. This data was collected again every 12 months along diagonal transects in the greenbriar trial and once at the end of 3 years for the mesquite trial. Representative forage samples were analyzed for nutritive value, including fiber and major mineral analyses (Gallaher et al, 1975; Van Soest and Robertson, 1980). Young wethers (20-25 kg) were used on the greenbriar trial. Weight changes were monitored in the greenbriar trial.

St. Croix

Coral vine (Antigonon leptopus), was determined to be the primary invasive specie targeted by ISDGB. In St. Croix, coral vine can completely dominate ground understory and tree canopy overstory. Coral vine produces copious seed that stay viable in topsoil seed banks for years until germination is triggered by sunlight. The removal of coral vine vegetation allows sunlight to reach seed bank reserves, thus triggering coral vine germination. In addition, coral vine produces a starchy root tuber (up to 7 kg) which provides abundant regrowth reserves for rapid vegetative regeneration if not mechanically removed, chemically killed, or crowded out by alternative plants impede coral vine regeneration.

In St. Croix there are few large commercial goat flocks which could be utilized in an ISDGB system to control invasive plant species. However, there are larger commercial St. Croix White Hair (SCWH) sheep flocks which could be suitable for ISDGB application. Therefore, it was determined that this portion of the research would focus on the utilization of tropical hair sheep for the control of coral vine instead of goats in an ISDSB (sheep). ISDSB was tested on-farm at two locations. Prior to the initiation of the on-farm trials, test sheep were screened for coral vine acceptance and palatability. After several introductory feeding trials of mature SCWH ewes vs. 7 month old SCWH lambs, it was determined that there was a lower level of coral vine palatability and consumption in mature ewes vs. 7 month old lambs. Furthermore, it was determined that consumption and palatability levels could be increased for the diets of younger lambs in a confinement feed lot environment when fed fresh-cut coral vine opposed to mature ewes whose diet was pre-established and palatability and consumption levels were lower than diet-conditioned 7 month SCWH lambs. Therefore, prior to on farm application, ISDSB lambs were preconditioned to a fresh cut coral vine diet for 6 weeks to increase coral vine palatability and consumption. At the end of the preconditioning period, Bob Scribner’s 2 acre pasture was stocked with 32 yearling SCWH sheep for a period of 8 weeks. Baseline data in the on-farm coral vine trial included herbaceous vs. invasive plant species frequency, height, and biomass. This data was collected at the beginning of the trial and again at the end of the 2 month ISDSG period along diagonal transects. Representative forage samples were analyzed for nutritive value, including fiber and major mineral analyses (Gallaher et al, 1975; Van Soest and Robertson, 1980). Young lambs (20-25 kg) were used on the coral vine trial. Weight changes were monitored every 14 days

Results indicate that ISDSG was effective in reducing and partially eliminating coral vine. It quickly became apparent, however, that it will be necessary to provide follow-up management of coral vine infested lands to suppress regeneration of coral vine from soil seed banks and from tuber reserves. This can be accomplished by repeated periodic ISDSG as well as the application of herbicides to regrowth. The most effective result of ISDSG on Bob Scribner’s land was to open up coral vine dominated areas that allowed the establishment of a more desirable forage resource directly after grazing was completed.

Puerto Rico

In the scheme of forage testing, exotic plants are introduced for evaluation for different purposes (e.g., ruminant grazing and erosion control). Leucaena (Leucaena leucocephala Lam. de Wit) is an excellent legume for cut-carry or grazing systems for dry sites on Caribbean Islands, but it seeds profusely and invades abandoned fields, right-of-ways, open residential lots, and form thickets that limit grass growth. Albizia procera introduced for erosion control in Puerto Rico is adapted to high rainfall areas. It also seeds profusely and invades open pastures and limits grass growth. In the genus Mimosa, M.pigra and M. casta are native of the Caribbean and are found mainly on river beds, both invasive in pasture lands and wetlands. Invasive weeds reduce pasture grass growth, increase the costs of road maintenance and result in the increased use of herbicide, which is not environmentally friendly.

A series of studies were conducted in the area of Gurabo, Puerto Rico (1800 mm annual rainfall) from April to December, 2006, and 2007 in replicated paddocks (23 x 23-m; Table 1) of A. procera mixed with guineagrass (Panicum maximum Jacq.) and Venezuela grass (Paspalum virgatum L.). Paddocks were stocked with 6 mature goats and moved every 7 days (or until forage on offer was reduced to approximately 1,200 kg/ha; visual observations).

The same goats were moved to another study to allow rest periods for the Albizia and were stocked similarly on catclaw (M. pigra) and climbing mimosa (M. casta) mixed with guineagrass and Venezuela grass. Based on results of this first study, a larger study was designed from 2007 to 2008 to target climbing mimosa. Replicated studies were conducted on 3-acre areas containing 25-40% climbing mimosa in the pasture. Goats were stocked until all the leaves and twigs of the mimosa were consumed.

In the Lajas Valley of Puerto Rico, ISDGB targeted leucanea (Leucaena leucocephala Lam. De Wit). Six paddocks (25 x 25-m) were fenced. Existing 15 yr-old trees of leucaena (>50%)-mixed with guineagrass were cut to ground level and leucaena allowed to sprout back to 100-cm and intensively stocked with 12 mature ewes for a 6-mo period. Animals were removed after all the leaves and twigs were consumed. Leucaena re-sprouts were counted on 10 marked areas 2-wks after ewes were removed. A follow-up study used mature goats and rotationally stocked on young regrowths of leucaena.


Weed control with goats and/or sheep in perennial peanut (Arachis glabrata) hayfields was tested at USDA-ARS STARS, Brooksville FL, in 2005 and 2006 using replicates of 1-acre paddocks. Animals were weighed every 28 days and body conditions scores determined. Impact of grazing on perennial peanut was determined by the difference in the weed, grass, and perennial peanut content in the sward vs. permanent exclosures in each paddock. Initial stocking rates were adjusted as necessary to minimize impact of grazing on the perennial peanut component of the sward. In addition to the livestock, control paddocks were treated with currently recommended herbicides and efficacy monitored by determining botanical composition and herbage yields. Grazing treatments were repeated in 2006, but only a portion of the herbicide-treated areas were treated in 2006 to determine carry-over effects.

Objective 2: Research plant:animal interface. Questions raised by both land and animal owners were addressed through field, pen and laboratory trials. The difference between control versus complete eradication of invasives, vis-à-vis the long term effect on native or desirable (in the case of planted pastures) plant ecology, is of particular interest. For example, the complete eradication of weeds comes at too high a price if desirable native plant communities are sacrificed.


A study on the Turkey Creek Ranch in Brown County examined season of ISDGB on mesquite (Prosopis glandulosa) control. Materials and methods were similar to the Texas Objective 1 trial except that mesquite was the target species and stocking rates were not used as a treatment. All treatments were imposed on new plots every 3 months over a 24 month period to determine if season had any effect on brush control. Mesquite survival was measured on all plots in the spring of 2009 36 months after the first treatments were imposed. Herbaceous forage production was not measured and the entire reproductive flock was used as ISDGB during the spring of each year for the mesquite trial.

Brush control treatments:
1. Animals only
2. Animals & Mechanical (with and without herbicide)
3. Animals & Herbicide (with and without mechanical)

1. Spring (April)
2. Summer (July)
3. Autumn (October)
4. Winter (January)

In addition, the question of how much condensed tannin exists in rangeland plants and how this may explain whether they are not readily consumed by goats was studied through a series of in sacco disappearance (ISD) trials using rumen-fistulated wethers (Lowrey, 1969). These were collected in many private ranches with the laboratory analyses taking place at the Stephenville Research Center. These variously included nutritive value (in rumen disappearance, nitrogen and fiber concentration) and anti-quality factors (lignins and condensed tannins; Terrill et al., 1997) based on ISD in goats (Conklin, 1994 for in vitro) versus fistulated steers and how they relate to degree of ISDGB control of invasive weeds and escape of native plants.


A kudzu trial in Georgia was carried out at the Fort Valley State University Agricultural Research Station, Fort Valley, Georgia. A 9-acre block of kudzu was divided into nine 1-acre paddocks to provide 3 pasture replicates of 3 grazing treatments: 1) Continuously grazed, 2) Once-grazed, and 3) No grazing control. During the study, each grazing paddock (approximately 1 acre) was mob-grazed by a combination of sheep (n=192) and goats (n=45) until all vegetation was consumed. Grazing treatments were initiated on June 24 and terminated on October 31, 2007. Grazing treatments were repeated in 2008, but fencing problems led to excessive grazing of the control and once-grazed paddocks, which compromised the grazing data from the second year of the trial. All animals were provided free-choice mineral and water throughout the trial.

Leaf and stem samples were collected on June 22 (pre-grazing) and November 7, 2007 (post-grazing), and June 17, 2008 (pre-grazing) from each paddock. Four 3.28 x 3.28 ft areas per paddock were randomly selected for herbage collection. Herbage was collected by hand clipping all the leaf and stem (vine) material within the selected space. Leaves were picked off the vines by hand, counted, and measured for leaf area, with leaf area index (LAI) calculated as in2 leaf area per in2 ground area. Leaves and vines were dried, weighed, and ground for crude protein (CP) analysis.

St. Croix

A coral vine confinement feeding trial was carried out from June 6 through July 26, 2006 and was repeated Febuary 4 through April 13, 2009 to determine the palatability and consumption of coral vine in SCWH lambs. Feeding trials examined animal intake, palatability, and resistance to anti-quality factors. Results will provide information on grazing behavior, consumption patterns, and anti-quality tolerance in weanling lambs through pen feeding trials.

Nine feed pens were designed to encompass 3 feeding treatments replicated 3 times with all treatment groups (n=36) receiving a forage and a concentrate ration. The forage ration comprised of either fresh cut coral vine (FCCV) or guinea grass hay (Panicum maximum, GG) and the concentrate ration was a pelleted total mixed ration (TMR) with 16% crude protein. Treatment 1 served as the control treatment with the TMR fed at 4% of body weight and GG hay fed at 1% of body weight, treatment 2 comprised of 4% TMR and 1% FCCV, and treatment 3 comprised of 3 % TMR and 2% FCCV. All forage feed rates were fed on a dry matter basis and feed values were calculated from live weights taken every 14 days. Animal performance was determined by live weight measured every 14 days to determine average daily gain. Daily feed refusals were measured to determine feed intake and feed efficiency. Guinea grass and coral vine leaves and vines of both FCCV and coral vine refusals were dried, weighed, and ground for crude protein (CP), nutrient, and fiber analysis.

Objective 3: Farmer-to-farmer contacts, brochures, popular press articles, and web pages. About half the trials took place on private land using farmer flocks under farmer management. Word-of-mouth and direct contact, both spontaneous and orchestrated by project participants, was an important means of information dissemination. A concerted effort at each location provide results to the public in extension publications, newspaper and magazine articles, and a web site. Each location contributed to its own web page focused on regionally important invasives, how to use ISDGB, and local associations or individuals who can be contacted for assistance; these pages were placed on-line at the Stephenville AgriLife Research web site (

St. Croix:
Information regarding the use of preconditioning SCWH lambs to coral vine to increase palatability and consumption for ISDSB management systems was disseminated through 3 seminars taking place in 2007 and 2008 to local farmers. In addition, this material was incorporated into the small ruminant section of a 7 day livestock short course provided to local farmers in June 2006 which was hosted by the University of the Virgin Islands Cooperative Extension Service and the Agriculture Experiment Station. Participation in this event totaled 43 local farmers. Other direct farmer interactions occurred where ISDSB concepts were presented. This occurred on a one on one basis on individual farms, through presentations made to the St. Croix Farmers Cooperative, and through the displays at the annual Agriculture and Food Fair which takes place in Febuary.

Objective 4. Economics of ISDGB. Small ruminant producers and landowners need to devise an equitable division of cost when implementing ISDGB on a commercial basis. How feasible such operations are, how much of the cost can be covered by animal production and how much by the enhanced value of the land was estimated for each region. In particular, the relative cost of vegetation control versus species eradication (the latter will likely take a heavier toll on small ruminant production and reproduction) needs to be assessed, in light of research results from objective 3.

Research results and discussion:


Objective 1. Greenbriar control.

1. The number of goats per paddock significantly decreases the number of days to 95% clear in the paddocks (P=0.005). On average, 5 goats/acre took 46 days to clear a 1-acre paddock while 10 goats/acre took only 30 days to clear a 1-acre paddock.
2. The number of goats and the year of study (rainfall) also showed significant differences between paddocks (P=0.009).
3. Percent of Smilax spp. plants/paddock did not show a decline over the three year study period as affected by stocking rate (P>0.05). However, the greenbriar biomass of the unbrowsed plots was greater than the browsed paddocks after the first year.
4. Percent grass in the browsed paddocks did not show a significant change over the three year study period (P<0.05). Paddock 5 and paddock 10 were both control paddocks and showed a decrease (P<0.05) in percent grass over the three year period. One of the driest years on record was recorded during the 2006 study and one of the wettest summers on record was recorded during the 2007 study.

Objective 2. Mesquite control.

Our results indicate that:
1. Mechanical pre-cut was the only means of giving goats access to mesquite in the form of regrowth.
2. Herbicide application was not 100% effective in killing either mechanically pre-cut mesquite or uncut trees.
3. Goat browsing was effective for suppressing mechanically pre-cut tree regrowth and suppressing new seedlings in herbicide-applied plots but was not effective when pre-ISDGB applications were not used.
Objective 2. Condensed tannin concentrations in native vegetation.

Results showed that CT concentrations vary from none to 17% in native forage and browse. Herbacous forbs as a whole had greater concentrations than taller browse species and vines.


Results: There were no differences in leaf, stem, and DM production, leaf number, and LAI across the 9 paddocks prior to initiation of grazing in June, 2007. At the end of the grazing season, all plant material had disappeared from the paddocks subjected to repeated grazing. The remaining leaf, stem (vine) and total DM in the single-grazed paddocks were 32.3, 47.5, and 40.4% lower (P < 0.05), respectively, than in the ungrazed paddocks. The leaf number and LAI were the same between ungrazed and once-grazed paddocks at the end of the grazing season. Leaf CP was also the same between ungrazed and once-grazed paddocks at the end of the season (21.8 and 20.7%, respectively).

The leaf, stem, and total DM production were higher in the ungrazed paddocks in June, 2008 than they were in June 2007, possibly due to an extremely dry spring in 2007. Compared with the ungrazed control paddocks, the repeatedly-grazed paddocks had lower (P<0.05) leaf, stem, and total DM, leaf number, and LAI in 2008, while the once-grazed paddocks were lower (P<0.05) in stem and total DM, leaf number, and LAI. There was no difference between the once-grazed and continuously-grazed paddocks for any of these parameters at the 2008 initial sampling date.

Discussion: This study shows that sheep and goats can be used as a biological control tool to suppress growth of kudzu where this plant is not wanted. Although it would likely take several years to completely eradicate kudzu using chemical herbicide or grazing animals, major subsequent (following year) reduction in growth can be accomplished in a single growing season using small ruminants. High kudzu leaf CP suggests that this plant also has potential as low-input high-quality forage for small ruminant production.


A trial to control invasive broad leaf forbs in perennial peanuts was started in 2005 and was conducted through 2008. Six one hectare plots were established and 25 whether goats were purchased. Several stocking rates and rotations were compared to mowing and wicking with roundup.

The goats were very good at controlling the undesirable forbs during the winter and early spring months. Although when the goats were left in the plots too long they would begin pulling or digging up the perennial peanut rhizomes. As rain fall and temperatures in the summer began to increase and the perennial peanut began to grow the goats switch from eating forbs to eating peanuts.

St. Croix

ISDSB provided alternative control measures for coral vine management. Coral vine can be consumed and adequately because St Croix sheep (SCWH) tolerated it as the primary forage source in both confinement feeding environments and under field browsing conditions dominated by invasive coral vine. Sheep can be habituated to browsing behavior similar to that expressed by goats and preconditioned to select and consume large quantities of coral vine with minimal to no negative physiological effects on animal performance and health. Therefore, SCWH sheep can be utilized to control and manage coral vine similar to the use of goats to control other invasive vegetative species.

Puerto Rico

There was a 28% reduction in A. procera trees 8-mo after the initiation of the study, with an extensive damage observed on the bark of the trees (Table 1). All of the trees that had extensive bark damage died by year 2. Young seedlings recruitments did not recover and were completely killed.

During the same period mature goats were rotationally stocked on catclaw mimosa and climbing mimosa. Goats consume basal leaves of catclaw but did not little damage to the branches or stems. There was however 90% reduction on climbing mimosa. Grazed plants did not recover, but new plants originated from existing seeds in the pasture.

Table. 1. Number of plants, mean diameter and percentage dead and regrowth of Albizia procera at Gurabo, Puerto Rico.

A. procera Mean trunk diameter Dead Regrowth
No. of trees cm % %
Paddock A 88 0.89 26 30

Paddock B 50 1.41 30 70

Leucaena was not affected by intensive stocking with sheep, but guineagrass was greatly reduced. In this study, ewes were observed to graze the grass component first and then were forced to consume the leucaena.

In the follow up study, using goats, paddock having less than 50% leucaena shrubs were killed as observed from the a reduction in the re-sprouts from the permanently marked areas. In paddocks with >50% leucaena plants, there were still new seedlings recovering after two years of ISDGB. Minimizing leucaena in thick stands will require mechanical maintenance (1 cut per year), followed by intensive stocking with goats.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Our project SARE web site has been updated as information came in from all sites and can be viewed at:

Our project was summarized in oral and poster presentations at the 2007 Caribbean Food Crops Society annual meeting held in San Juan, Puerto Rico, the 2008 Southern SARE annual conference, and the 2007 National Weed Science meetings:

Boggs, L., J.P. Muir and J.W. Dunn. 2007. Got weeds? Get Goats. National Weed Science Society meetings. Poster.

Muir, J.P., E. Valencia, S. Weiss, and T. Terrill. 2007. Small ruminants for biological control of invasive vegetation. Proceedings XXIV Caribbean Food Crops Society Meeting. July 9-14, San Juan Puerto Rico.

Boggs, L., J.P. Muir and J.W. Dunn. 2008. Got weeds? Get Goats. Southern SARE annual conference poster.


The 2006 video of the ISDBG, created by the Texas AgriLife Extension can still be viewed at:

Additional publications, presentations and posters arising from research in Texas include:

Acero, A., J.P. Muir, and R.M. Wolfe. Nutritional composition and condensed tannin concentration changes as leaves become litter in nine trees and vines. Anim. Feed Sci. Tech. (submitted)

Muir, J.P., J.R. Bow, and L. Boggs. Response of perennial herbaceous Texas legumes to shade. Native Plants Journal (at press)

Packard, C.E., J.P. Muir, R.D. Wittie, and R.M. Harp. 2007. Peanut stover and bermudagrass hay for wethers on summer hardwood range in north central Texas. Sheep & Goat Research Journal 22:7-14.

Acero, R.A., J.P. Muir, and R.M. Wolfe. 2008. Nutritional composition and condensed tannin concentration of leaves and litter of nine Texas trees and vines. ASA-CSSA-SSSA International Meetings, Houston, TX, Oct. 5-9. Agronomy Abstracts (on CD).


Outreach: A fieldday presentation at the American Sheep Industry Association on February 24, 2009 at Watkinsville, GA was held to demonstrate biological control of unwanted weed species.

Terrill, T.H, W.R. Getz, S.L. Dzimianski, W.F. Whitehead, B. Singh, and J.P. Muir. 2009. Effect of repeated or one-time grazing of kudzu by sheep and goats in central Georgia. Vol. 18 on CD. AFGC.

St. Croix

Muir, J.P., E. Valencia, S. Weiss, and T. Terrill. 2006. Small ruminants for biological control of invasive weeds. P. 77. Caribbean Food Crops Society 42nd Annual Meeting, San Juan Puerto Rico. FOR 2P.

Muir, J.P., E. Valencia, and S. Weiss. 2006. Harnessing the potential in native herbaceous legume germplasm. P. 26. Caribbean Food Crops Society 42nd Annual Meeting, San Juan Puerto Rico. ANR 5.

Puerto Rico

Outreach: Field day in the Gurabo Area on 25th October, 2008. Twenty farmers form the North eastern of Puerto Rico attended. Another field day was held on the Lajas Valley on the 14th March, 2009 to discuss results of two-grazing of leucaena with goats.

Recently, the TSTAR program funded a grant entitled “Biological control of invasive weed species in Puerto Rico” to continue research in the area targeting invasive plants in wetlands and in crop lands.


Valencia, E., M. de L. Lugo Torres and J. Muir. 2007. Browsing goat effects on control of invasive tropical weed species in Puerto Rico. p. 218. In: Lugo, W.I., and W. Colon. (eds.). Proc. of the 43rd Caribbean Food Crops SocietyAnnual Meetings, San Jose, Costa Rica. September 16 – 22nd 2007.

Valencia, E., J. Muir, M. de L. Lugo Torres y L. Amodovar. 2008. Ramoneo intensivo de corta duración para el control de plantas invasoras. p.347. En: Resumen del Programa Cooperativo Centroamericano para el Mejoramiento de Cultivos y Animales. 14 al 18 de abril, San Jose, Costa Rico.

Project Outcomes

Project outcomes:

Our economic analyses, undertaken primarily by land and flock owners, indicates that ISDGB will be more expensive and not as biologically effective as traditional herbicide and mechanical treatments. However, the benefits to the environment and to society are difficult to quantify monetarily and this is where ISDGB has the advantage over traditional herbicide methods. Land areas such as urban parks, green zones, forest reserves where herbicides are specifically prohibited by inhabitants or public health issues are of particular interest. The flock owner must take into account the expenses involved in temporary fencing, transport, protection (from theft, predators or loss) above and beyond what a conventional mowing/herbicide system would cost. These are specific to each location and must be negotiated on a case-by-case basis. Our project participants also identified another recurring theme: ISDGB is not a one-time, permanent solution; it must be repeated periodically, adding additional cost. Despite the added expense, interest is widespread and we fully expect ISDGB to increase income for flock owners in the southeast as our research results are disseminated by the publications, demonstrations and web sites we have generated at our five locations.

Economic Analysis

Our economic analyses, undertaken primarily by land and flock owners, indicates that ISDGB will be more expensive and not as biologically effective as traditional herbicide and mechanical treatments. However, the benefits to the environment and to society are difficult to quantify monetarily and this is where ISDGB has the advantage over traditional herbicide methods. Land areas such as urban parks, green zones, forest reserves where herbicides are specifically prohibited by inhabitants or public health issues are of particular interest. The flock owner must take into account the expenses involved in temporary fencing, transport, protection (from theft, predators or loss) above and beyond what a conventional mowing/herbicide system would cost. These are specific to each location and must be negotiated on a case-by-case basis. Our project participants also identified another recurring theme: ISDGB is not a one-time, permanent solution; it must be repeated periodically, adding additional cost. Despite the added expense, interest is widespread and we fully expect ISDGB to increase income for flock owners in the southeast as our research results are disseminated by the publications, demonstrations and web sites we have generated at our five locations.

Farmer Adoption

Landowner interest in using ISDGB for controlling invasives grew during the project throughout the southeastern USA, St. Croix and Puerto Rico. Web site hits, phone calls and e-mails are on the increase at all five locations. For example, based on the 2006 results on control of Albizia, biological control using goats has increased in Puerto Rico. What we need to do as a group is to assist land-managers and small-flock owners as they seek commercial ways of incorporating this as an additional income-generating activity off-farm.


Areas needing additional study


Although our results indicate that ISDGB does not necessarily destroy greenbriar completely, it does show that this invasive vine can be suppressed using goats. However, the contract details need to be worked out between flock owners and landowners over time and experience. Our next challenge is to foster greater herder/landowner communication so that this additional income can become available to farmers in Texas. Use of this system in urban settings is of educational value as well, with municipalities perhaps willing to include animal production education for their residents along with the ISDGB.


Long-term studies with kudzu grazing are needed to determine if total eradication of this species can be accomplished using small ruminants.


The use of sheep to control weeds under fruit trees has great promise. Combining this with an herbaceous legume that provides nutrients to both sheep and the tree will also be useful. Because perennial peanut is also palatable to sheep, the details on how to manage weed infestation under fruit trees still needs further work.

St. Croix

St. Croix is an interesting place to work with ISDGB control of corral vine and other invasive plants because landowners are rich and of North American culture while goat & sheep owners are generally subsistence and of Caribbean culture. The ISDGB partnership on St. Croix is potential of great benefit to both groups but the socio-cultural divide is great. Now that we know sheep will readily consume and suppress corral vine, our next challenge will be to work out the logistics of how to get flocks onto private land.

Puerto Rico

The potential role of ISDGB in controlling invasive plants needs to expand beyond leucaena, albizia and guineagrass. The afore-mentioned species can be suppressed with small ruminants but how permanent this control is also needs to be studied. The financial interaction between herders and landowners also needs to be further studied in order to assist with contract rates.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.