research article the use of domestic goats and vinegar … · and vinegar as municipal weed control...

RESEARCH ARTICLE

The Use of Domestic Goatsand Vinegar as MunicipalWeed Control Alternatives

Annie L. Booth, Norman W. Skelton

This article presents the results of a two year pilot case

study of alternative weed control in a northern Canadian

community. Investigators tested the efficacy of acetic acid

(vinegar) and a domestic herbivore (goats) as invasive weed

control alternatives to the use of commercial herbicides in

a north central British Columbian municipal setting. Results

were positive for using an 8% concentration of vinegar as

a control for Canada thistle (Cirsium arvense (L.) scop.),

although these results were significant only in the second

year of applications. Domestic goats demonstrated signifi-

cant interest in thistle, as well as hawkweed, (Hieracium

spp.), two species of horsetail (Equisetum arvense and Equi-

setum pratense), oxeye daisies (Leucanthemum vulgare),

and the common dandelion (Taraxacum officinale). Cost

estimates suggest that over a five year period, both methods

are as cost effective as single application herbicides, while

posing fewer concerns over impacts on human and ecosys-

tem health. Both are simple solutions easily implemented,

with some planning, even by small municipalities and

communities.

Environmental Practice 11:3–16 (2009)

T he last decade has witnessed a change in govern-ments’ and the public’s comfort level regarding the

usage of herbicides to control weeds. This manifests in anumber of ways, ranging from an interest in organics togovernment bans on the cosmetic use of herbicides andpesticides. For example, in 2008, France passed a country-wide ban on the use of certain herbicides and pesticides~Environmental News Network, 2008!, while Canadian prov-inces are considering similar actions ~Block, 2006; The

Canadian Press, 2008!. Concerns are growing over the im-pacts of chemical herbicides and pesticides on the health ofhumans, non-humans, and ecosystems; however, agenciesalso need to control unsightly or noxious invasive weeds.Although conventional herbicides have a role to play inweed control, alternative control mechanisms are needed.This article presents the results of a two year case study ofalternative controls in a northern Canadian community.

In 2005, the City of Prince George, British Columbia, andthe University of Northern British Columbia developedthe Prince George Northern Sustainable Landscape Initia-tive ~SLI!, with the goal of exploring sustainable landscap-ing within the municipality, including alternative weedcontrol options. Prince George, British Columbia, is a north-ern, resource-dependent community with a population ofapproximately 80,000. Located 500 miles north of Vancou-ver, British Columbia, it sits within Canada’s boreal forestand in Growing Zone 3. Its northern location gives it cold~2358 C! winters, mild summers ~228 C!, and a relativelyshort growing season of 12 weeks. Snow accumulation av-erages two meters annually; however, climate change isaffecting Prince George, creating both warmer winters andsummers, leading to a rise in invasive weed species ~Reb-man, 2007!. Further, Prince George faces the same chal-lenges as most municipalities, including restricted budgetsand a changing legal context around herbicide use, whichhas resulted in several Canadian municipalities passingherbicide bans. Thus, city employees were seeking moreenvironmentally benign, socially acceptable, and cost ef-fective weed control alternatives, particularly for Canadathistle ~Cirsium arvense (L.) scop.! and dandelions ~Tarax-acum officinale!. Municipal staff members were interestedin the use of acetic acid ~commonly known as vinegar! andlivestock.

Affiliation of authors: Annie L. Booth, Ecosystem Science and Man-agement Program, University of Northern British Columbia, Prince George,British Columbia, Canada; Norman W. Skelton, Prince George NorthernSustainable Landscape Initiative, University of Northern British Colum-bia, Prince George, British Columbia, Canada

Address correspondence to: Annie L. Booth, Associate Professor, Eco-system Science and Management Program, University of Northern BritishColumbia, 3333 University Way, Prince George, British Columbia V2N4Z9, Canada; ~fax! 250-960-5538; ~email! [email protected].

© 2009 National Association of Environmental Professionals

doi:10.10170S1466046609090012 Goats and Vinegar as Weed Control Alternatives 3

Review of the Literature

The control of Canada thistle ~Figure 1! is a research pri-ority. An extremely invasive plant species, it is capable ofcrowding out native species and other plants ~Sullivan,2004!. It has spread rapidly throughout the Prince Georgearea ~North West Invasive Plant Council, 2008!. Althoughthe annual application of conventional herbicides controls,but rarely eradicates, thistle, there are concerns about suchherbicide use. Studies by the Canadian Association of Phy-sicians for the Environment ~CAPE! and others suggestthat pesticides/herbicides are a leading cause of acute poi-sonings in Canada and can also cause chronic health ef-fects, both as sequelae of acute poisonings and from chronicexposure ~Canadian Association of Physicians for the En-vironment, 2008; Union of Concerned Scientists, 2008; seealso Daniels, Olshan, and Savitz, 1997; Ecojustice Canada,2008; Infante-Rivard and Weichenthal, 2007; Rudant et al.,2007!.

Research has suggested that vinegar is effective in control-ling or eradicating thistle ~Daniels, 2003; Sullivan, 2004;Webber, 2005; Webber and Shrefler, 2006a; Webber andShrefler, 2006b; Webber et al., 2005!, but this type of re-search has examined vinegar use in either an agricultural

or range setting. We were interested in its utility in amunicipal setting, where public expectations might be verydifferent; we were interested in impacts on adjacent veg-etation, the use of readily available concentrations of vin-egar, and impacts of vinegar in a short growing andapplication season.

We also wished to experiment with livestock and weedcontrol. Research suggests that three domestic livestockspecies control thistle: donkeys, sheep, and goats ~Launch-baugh, 2006!. We chose to examine goats for experimentalpurposes.

There is a very modest literature on the use of goats forcontrol of weeds, largely focused on leafy spurge ~Euphor-bia esula! ~Dovel, Todd, and Richman, 2005; Hanson andKirby, 1993; Lacey, Wallander, and Olson-Rutz, 1992; Lym,Sedivec, and Kirby, 1997; Prosser, Sedivec, and Barker, 1997;Sedivec, Barker, and Messmer, 1994; Sedivec, Hanson, andHeiser, 1995; Sedivec and Maine, 1993! and spotted knap-weed ~Centaurea biebersteinii ! ~Frost and Launchbaugh,2003; Williams and Prather, 2006!. The United States De-partment of Agriculture does cite the use of goats as apotential controller of thistle species ~Sullivan, 2004; Web-ber, 2005!. For well over 100 years, goats have been used to

Figure 1. Canada thistle. ~Photograph: Adam Humphrey!

4 Environmental Practice 11 (1) March 2009

manage unwanted vegetation in the United States, includ-ing by the Army Corps of Engineers ~Webber, 2005!. Goatscan also assist in increasing the biodiversity of grasslands,as well as help heal gullies and washes ~Frost and Launch-baugh, 2003!, reducing water runoff and active erosion~Launchbaugh, 2006!. They do not pollute natural watersources with their waste ~Tartowski, 2005! and reduce theproduction of seeds by consuming seeding stems, which donot survive passage through the digestive tract. Throughdigestion, goats release plant nutrients tied up in unwantedvegetation ~Clements and Young, 2005; Peterson BuffaloRanch, 2006; Popay and Field, 1996!. A final benefit ofusing goats to control vegetation is that while these ani-mals consume undesirable plants they are producing asaleable product ~milk, cheese, meat, and hides! ~PetersonBuffalo Ranch, 2006!. For our research, we were interestedin the full range of weeds goats would consume, althoughthistle was of key interest. Further, we were interested inhow well goats would adapt to a municipal setting. In2007, the city of Seattle, Washington, began using goats forweed control on city grounds ~Harrell, 2007; McDonald,2007; Siderius, 2007!; San Francisco and Los Angeles, Cal-ifornia, also use goats, but no research exists confirmingtheir effectiveness in a municipal setting.

Project Methods

Vinegar Trials

We conducted three years of experimentation with the useof vinegar at Moore’s Meadow, a city park with extensivethistle infestation. The City does not employ herbicides inthis park, as it is an off-leash dog park. A kettle moraine,the park is an elongated bowl with wooded sides and agrassy bottom, which is a mix of weeds, Phelum prantense~timothy grass! and Bromus inermis ~brome!. The Citymows the bottom periodically. The bottom is sunny andmoist.

The site was an open area divided on the long axis by atrail. Thistle was abundant. In 2006, we established our testsite, consisting of two sections, one on each side of thetrail. Each section consisted of six 18-meter 3 6-meterplots, with two inventory quadrants of 1 meter 3 1 meterat each end of each plot.

Our key concern was whether vinegar application could bereadily adopted by a cash- and time-strapped municipal-ity; therefore, we based our trials on requirements city staff

estimated they might manage. After reviewing existing re-search, we chose two different concentrations of vinegar,5% and 8%. Both concentrations were less than the morecommonly tested concentrations, which required extensivesafety precautions ~possibly limiting municipal adoption!.Based on estimates by city personnel, we chose two timingvariables, every two weeks and every four weeks. We es-tablished five treatments: control plots ~no treatment!, treat-ment every two weeks with 5% vinegar, treatment everytwo weeks with 8% vinegar, treatment every four weekswith 5% vinegar, and treatment every four weeks with 8%vinegar. To avoid mixing, one side of the trail was ran-domly assigned to 5% and the other to 8%. Plots on eitherside were randomly assigned as control, two week, or fourweek plots. Vinegar was applied by hand, using backpacksprayers at a constant rate and with an even application of12.5 liters per section from a one meter height. Due toinitial funding issues, applications began very late in June,well after the thistle was established.

For the 2007 trials, we modified our trials. We did notutilize control plots. Vinegar was applied as an 8% solutiononly. One section of plots was sprayed at two week inter-vals, randomly assigned, and a second set at three weekintervals. We therefore had a series of test plots, as follows:

• 2006 no treatment/2007 application of 8% vinegar atthree week intervals;

• 2006 application of 5% vinegar at two week intervals/2007 application of 8% vinegar at three week intervals;

• 2006 application of 5% vinegar at four week intervals/2007 application of 8% vinegar at three week intervals;

• 2006 application of 8% vinegar at two week intervals/2007 application of 8% vinegar at two week intervals;and

• 2006 application of 8% vinegar at four week intervals/2007 application of 8% vinegar at two week intervals.

In 2008, we wished to limit vinegar applications to deter-mine thistle recovery rates, as well as to see whether a“maintenance” schedule was viable. Therefore, we sprayedall plots with 8% vinegar once in mid-May and once at thebeginning of June, as plants were beginning their growthseason.

Each year, assistants counted and recorded all plants withinthe inventory quadrants. All weed species were countedindividually. In 2006, we conducted inventories in July andAugust. In 2007 and 2008, inventories occurred monthly,from mid-May to early September.

Goats and Vinegar as Weed Control Alternatives 5

Livestock Trials

In 2006, test plots were established at three city sewagelagoons. Sewage lagoons were selected for two reasons:herbicides could not be used in these areas and the siteswere already partially fenced. One site subsequently wasabandoned due to dog depredation on the goats. We wereleft with two sites, the Danson site ~21,673.60 square me-ters, or 233,293 square feet! and the CN site ~7,238.44 squaremeters, or 77,914 square feet!. Both sites are located in anindustrial zone adjacent to the Fraser River. Both sitesnormally were mowed once a year. Gravelly soil createdpoor growing conditions, although vegetation around theedges of the ponds was quite lush. Invasive weeds, partic-ularly Canada thistle, were well established in several sec-tions of the site, particularly within one-and-a-half-meterzones around the ponds. Other invasive species were presentin extensive numbers, including Taraxacum officinale ~dan-delion!, native species of Hieracium ~hawkweed!, Leucan-themum vulgare ~oxeye daisies!, and Equisetum arvense andEquisetum pratense ~horsetail!.

In 2007, the original plots were reorganized to more com-prehensively capture the vegetative diversity at each site. At

Danson, we established four original plots and addedan additional two. At the CN site, we started with fourplots and added a fifth. All plots were 1 meter3 1 meter insize and were scattered across sites, both adjacent to theponds and at a distance. Plant inventories were conductedat both sites—once in July 2006—as a baseline. In 2007and 2008, inventories were conducted once in May, June,August, and early September. All plants within the testplots were individually counted and recorded. In addition,all plants were visually surveyed for evidence of grazing.Due to terrain difficulties, no safely accessible control plotsoutside the sites could be established.

Our livestock grazing trials began in 2007, using four do-mestic Boer goats ~Figure 2!. We intended to place them atthe first green-up of the vegetation and rotate them be-tween the two sites on at least a monthly basis, givenestimation of available browse. Instead, the four goats didnot start until early June. The Canada thistle was wellestablished, aged, and not as palatable to the goats. Thegoats did not arrive at the CN site until mid-July, where asimilar situation prevailed. We maintained continuous graz-ing of the Danson site until mid-September, adding anadditional four goats from mid-August to mid-September;

Figure 2. A goat grazes a test plot of weeds in Prince George, British Columbia. ~Photograph: Adam Humphrey!


however, the CN site received a single month of grazing byfour goats.

We had one further challenge at the Danson site. Due to amiscommunication with city personnel, approximately 75%of this site was mowed in early August, including several ofour test plots. Although disrupting our data, it did dem-onstrate that the new growth of thistle that occurred withintwo weeks of mowing caused the goats to focus their graz-ing on thistle.

In 2008, we placed goats back on site in mid-May. Weinitially placed six goats at Danson and four at CN. In earlyAugust, the City mowed again at Danson, because theyounger goats were not comfortable eating at the edge ofthe pond and had left a half-meter border of thistle at thepond edge ~conversely, the mature, experienced goats atthe CN site grazed right down to the water’s edge!. The sixgoats were relocated to CN and within three weeks, allgraze was eliminated. We then transferred all ten goatsback to Danson for two further weeks. The goats werepermanently removed in mid-September.

Results

Vinegar Trials

During the first year of vinegar treatment, it appeared thatvinegar was unsuccessful in controlling thistle. We saw nosignificant impact with our use of 5% vinegar, either at twoor at four week application schedules. Indeed, thistle num-bers actually increased, sometimes significantly so. The twomost heavily infested sites saw plant numbers increase by33% and 64%, respectively.

Our May 2007 inventory, however, demonstrated that insix out of eight plots treated with vinegar, thistle sufferedsignificant over-winter mortality. Thistle numbers were re-duced by anywhere from .08% to 88%, with two plotsshowing either a constant number or a modest rise ~thosesites received 5% vinegar applications during the first year!.By the time of our June inventory, thistle survival wasalmost zero for all plots treated with vinegar. This heldconstant into September for the plots that received 8% atfour weeks ~2006! and 8% at two weeks ~2007!. Those thathad received 8% at two weeks for both years showed verymodest rebound. Our third year, with two spring vinegarapplications, demonstrated some rebound in net thistlenumbers. Rebound was greatest in plots receiving one year

of treatment, reaching almost 50% of original plant num-bers. Plots that had received two years of vinegar applica-tions showed much more modest rebound, ranging from.01% to 27%, on average. Figures 3 and 4 present results forthistle on all plots treated for two years with vinegar. ~Duelletter/number combinations for plot identification, as seenin the figure legends, are a result of plots being re-labeledfrom 2006 to 2007; i.e., each plot had two sets of numbersassigned to it for tracking purposes.!

The results for one of our former control plots confirmthat 8% vinegar applied at three week intervals on a “new”site also resulted in a significant reduction of thistle by thespring of the second year, from 66% to 100% reductions,with only one year of application. Figure 5 presents theresults for thistle treated for one year with 8% vinegar.

We also examined impacts on other weed species. Resultsfor dandelion ~Taraxacum officinale) were complex. Sitesthat received 5% and 8% vinegar treatments during thefirst year suffered substantial mortality. Dandelion num-bers were reduced by 50% by the end of the first year andclose to 0% by the end of the second year; however, re-bound was significant in the third year ~with its minimalvinegar applications!. Rebound was greatest ~almost 100%of original numbers! in plots treated with 8% vinegar overtwo years. Plots that originally were treated with 5% vin-egar and the 8% in the second year experienced only a 50%rebound in numbers. Figure 6 presents the results of an 8%vinegar treatment on dandelions for two years. Plots re-ceiving only one year of treatment with 8% vinegar showeda similar 100% mortality after the first year, followed by100% recovery in numbers in the second year. Figure 7shows the results for dandelions treated with vinegar forone year.

Vinegar does appear to affect other invasive weeds. In2006, we documented limited occurrences of Hieraciumaurantiacum ~orange hawkweed!, Leucanthemum vulgare~oxeye daisy!, and Galeopsis tetrahit ~hemp nettle!. Theseplants had completely disappeared within a month aftertreatment with two applications of 8% vinegar and did notreoccur in 2006, 2007, or 2008. Although the numbers ofthese plants were small enough that other factors mighthave played a part in their failure to reoccur, results aresuggestive.

Livestock Trials

During the first year at the Danson site ~2007!, which hadconsistent grazing, the numbers of thistle plants in our test


Figure 3. Vinegar control of Cirsium arvense 2006–2008; two years of treatment with 5% and 8% vinegar ~each plothad two sets of numbers assigned to it for tracking purposes!.

Figure 4. Vinegar control of Cirsium arvense 2006–2008; two years of treatment with 8% vinegar ~each plot hadtwo sets of numbers assigned to it for tracking purposes!.


Figure 5. Vinegar control of Cirsium arvense 2006–2008; one year of treatment with 8% vinegar ~each plot had twosets of numbers assigned to it for tracking purposes!.

Figure 6. Vinegar control of Taraxacum officinale 2006–2008; two years of treatment with 8% vinegar ~each plothad two sets of numbers assigned to it for tracking purposes!.


plots experienced significant reductions, ranging from 35%to 100%, in the month after the introduction of thegoats. By September, after mowing, the thistle had recov-ered 100% of their spring numbers. We speculate thatmowing induced these plants to spread or to re-sproutmore quickly than after grazing. The first inventory in2008 demonstrated significant over-winter mortality. Plantnumbers were reduced from 70% to 100% in our testplots. By mid-summer, all plots experienced a modestrebound to 50% of the previous year’s numbers ~one plotincreased by 20% over the previous year!, but by August,plant numbers again were declining by 20% to 30%.Plants numbers did not rebound to match pre-grazedlevels of 2006, showing a significant overall reduction intotal plant numbers. We are unclear, however, as to whatimpacted the thistle—grazing, mowing, or the combina-tion of both.

The CN site presents mixed results. Thistle numbers rosesignificantly after a brief period of grazing by goats inmid-summer, only to decline precipitously in all but oneplot over the winter ~100% mortality!. The singular excep-tion ~the most physically inaccessible plot, because it sitson the edge of a steep slope! showed a modest decline in

numbers after regular grazing in the second year. Figure 8presents the findings regarding goat browsing on thistle forplots at both sites over two years.

Although we measured “success” in thistle control by thephysical numbers of plants remaining within a test plot,we observed that there was significant evidence of browseof new thistle growth, reducing plant height by averagesof .3 to .6 meters. The browse line against unreachablethistle was clearly visible and almost unbroken within thethistle patches. Further, the goats showed an obsessiveinterest in thistle flowers, which were removed promptlyupon appearance. By our rough estimate, 90% of thistleflowers at both sites were consumed before seeding out~Figure 9!.

Goats also affected two species of horsetail, Equisetum ar-vense and Equisetum pratense. At Danson, E. arvense expe-rienced 100% mortality by the August 2007 inventory andshowed 0% recovery during 2008. E. pratense also demon-strated an 80% to 100% mortality by September 2007, butin the spring of 2008 demonstrated not only a recovery tooriginal numbers but, in three plots, increases of 20% to30%. The plants again showed 100% mortality by early

Figure 7. Vinegar control of Taraxacum officinale 2006–2008; one year of treatment with 8% vinegar ~each plot hadtwo sets of numbers assigned to it for tracking purposes!.


September, however. The CN site held only E. pratense,which demonstrated a modest 30% drop after a few weeksof grazing in 2007, followed by a substantial increase thefollowing spring. As at Danson, constant grazing droppednumbers steadily over the course of the next summer,reaching 100% mortality by September 2008. Figure 10presents the results of goat browsing on Equisetum spp. atboth sites over two years.

The goats did consume a native Hieracium species ~hawk-weed!. At CN, numbers began dropping around the timeof goat introduction—between 60% to 100%—followed bya rebound in the second spring. Constant grazing in thesecond year again reduced numbers to zero by June, butnumbers increased again through to September. The Dan-son site presents another complex picture, with four plotsdemonstrating significant declines, while two show in-creases. Although the plants experienced a spring reboundin the second year, after a second summer of steady graz-ing, all but one plot had been reduced by almost 100%,while the exception demonstrated over a 50% decline inplant numbers. Although the species present was not Hi-eracium aurantiacum ~the species of interest for the PrinceGeorge region!, samples of H. aurantiacum were picked atother sites and offered to the goats on two separate occa-

sions; at both times, the goats very promptly consumedthis species.

There is also evidence that goats eat Leucanthemum vulgare~oxeye daisies!. At CN, although numbers in the plotsdropped after the introduction of the goats in the first year,they rebounded dramatically after their removal. By thesecond year, however, spring numbers were down 70% to80% and the plant was almost completely eradicated by thetime of the goats’ removal. At Danson, the Leucanthemumexperienced 90% mortality by the June 2008 inventory and100% by September. Figure 11 presents the results for goatsbrowsing on oxeye daisies at both sites over two years.

Finally, goats do consume Taraxacum officinale, the com-mon dandelion, particularly early on in the season, but thegoats were less interested as the leaves aged and becamebitter. They specialized in eating flowers, which did preventthe plant from seeding the site. Results are more significantat the CN site, where four plots showed 90% mortality~one plot increased from zero to 30 plants!. The Dansonsite demonstrated 100% mortality after the second year inthree plots, while two plots doubled or tripled their num-bers ~one plot held no dandelions!, suggesting that thedandelions are not always a preferred browse.

Figure 8. Goat control of Cirsium arvense 2006–2008. D 5 plots at the Danson site; CN 5 plots at the CN site.


Discussion

Vinegar

It appears that an 8% vinegar solution controls Canadathistle, with most mortality showing up in the second year.We theorize that the three week applications were mosteffective, because they gave the thistle a chance to try tore-grow repeatedly, thereby depleting resources necessaryfor successful over-wintering. Two week intervals did notpermit regrowth and resources were simply stored untilthe next growing season. After two years of application,mortality remained significant, but there was rebound inthe third year, with limited treatment; however, the num-bers of thistle recovering in the third year were substan-tially lower than pre-treatment, by up to 88%. These findingssuggest that vinegar cannot eradicate thistle, which canre-seed or re-colonize by rhizome spread from adjacentsites, but it can reduce the individual plant’s ability tosurvive. Intermittent treatment will likely always be re-

quired. Further research is needed to determine whichintervals, after an initial treatment, would create lowerthistle numbers.

Vinegar also offered some control against the ordinarydandelion over the short term, but less over the long term.Significant mortality occurred after a first year of vinegarapplication, but the plants proved more resistant duringthe second. This might be due to other environmentalfactors, differences in application techniques, or the pos-sibility that a third year of treatment is required becausethe plant easily re-seeds. Dandelions are a plant of signif-icant concern for municipalities. In Prince George, almostthree-quarters of the public complaints logged over citygrounds are regarding dandelions and almost half of theherbicides used are for the control of dandelions ~Kadla,2007!. The ability of vinegar to partially control dandelionsis therefore of interest to our municipal partner, althoughit appears more research will be required to determine ifvinegar can fully control dandelions.

One caveat on the use of vinegar is that it is an effectivecontrol on more desirable vegetation. By the end of oursecond year, most vegetation in our trial plots also sufferedsignificant mortality. Phelum prantense ~timothy grass! andBromus inermis ~brome! suffered significant mortality inthe first year. The timothy grass did persist and began togrow again by the second year. It was substantially re-colonizing by the third year. In our third year, we re-seededusing red clover ~Trifolium pratense!, an acid tolerant spe-cies. The clover re-colonized most plots successfully.

Vinegar offers economic savings over other herbicides. In2007, Prince George paid $13,452.55 to treat 4.26 hectareswith conventional herbicides. Using 8% vinegar would costapproximately $8,387 for the materials and our labor costswere minimal, because we used existing research person-nel. A municipality might have to budget for an additionalsummer staff person, depending upon the area requiringtreatment; however, because vinegar requires minimal safetyprecautions and no special training or licensing for appli-cation, this role might easily be filled with summer studentlabor rather than full-time municipal employees. Althoughvinegar use would require more frequent treatments thanconventional herbicides, it offers compensatory benefits.Vinegar offers no known health risks. Some precautionsare needed during application, but after it dries, it has littleimpact on skin or lungs. Animals that utilize a treated siteare unlikely to ingest any toxics as a consequence; this isnot the case with conventional herbicides.

Figure 9. An example of goat-browsed thistle in PrinceGeorge, British Columbia. ~Photograph: Adam Humphrey!


Figure 10. Goat control of Equistem spp. 2006–2008; D 5 plots at the Danson site; CN 5 plots at the CN site.

Figure 11. Goat control of Leucanthemum vulgare 2006–2008; D 5 plots at the Danson site; CN 5 plots at theCN site.


Environmentally, we are still assessing impacts. We do notknow vinegar’s potential impact if large quantities were toenter a water body. Although any quantity of acid willcause disruptions, we do not know disbursement and flush-ing rates required to limit significant acidification.

Livestock Trials

The results for the use of goats are mixed, but suggestive.Delays in getting the goats on site during the first year oftrial likely limited the effectiveness of grazing for control-ling thistle. By the second year of grazing, thistle numberswere significantly reduced, but not completely eradicated.Visual inspection revealed that outside the fence line, this-tle continued to look healthy and was spreading, suggest-ing that it was not a change in environmental factors thatcaused reduction in thistle numbers. We were able to doc-ument that goats prefer new growth on thistle and offeredsubstantial control on seed proliferation through flowerconsumption. We believe it might take additional years ofgrazing to completely eradicate thistle and, given thistle’sability to move in from other sites, would likely requireyearly grazing to maintain control. The results for oxeyedaisies are very clear and goats appear to be a highlyeffective control, because this plant was eradicated fromour test plots. Hawkweeds and horsetails also showed sig-nificant depredations by goats, which seem to be a reason-ably effective control on these species.

Two years of grazing, however, is likely insufficient to pro-vide very high levels of control of particularly perniciousplants such as thistles. Unlike vinegar or herbicides, goatsdo pick and choose what they consume and have clearrank order preferences in feeding, preferring younger growthfor tough plants like Canada thistle. Other species, such ashorsetails, are consumed regardless of their stage of growth.

Further, during both trial years, the mowing at the Dansonsite affected our findings. Mowing does stimulate an even-aged regrowth of new foliage in thistle. We are unclear,however, as to how this might have affected the impact ofgrazing overall. Further research, utilizing either pure graz-ing or more controlled mowing/grazing trials, is required.

The number of goats is also important. Four goats wereinadequate for the Danson site, but were adequate at theCN site, which is approximately one-third the size of theDanson site, when given a full four months to graze. Sixgoats however, provided substantial, although not com-plete, control at the Danson site during a full summer. Weproject that an area the size of Danson ~21,673.60 square

meters, or 233,293 square feet! might require eight to tengoats for full control.

One further note on the use of goats: they proved to be asocial success as well. The goats proved highly manageableby relatively unskilled individuals. The greatest difficultywas in ensuring that the gate and fencing were sufficient toprevent escape, which required early monitoring and none-theless resulted in a few impromptu roundups ~althoughthe amount of graze available must be regularly moni-tored, hungry goats are highly motivated and competent atfinding previously ignored exits!. Care of the goats wasminimal, involving daily checks to ensure fresh water wasavailable, monitoring of health, and hoof trimming everyfew months. Transportation between sites was accom-plished using only an SUV. Further, the goats proved pop-ular with city staff needing to enter the sites, who perceivedthe goats to be friendly, non-threatening, and even inter-esting. Such acceptance on the part of municipal workersis essential for any new alternative to work. The City iscurrently planning to lease goats and place them back atthe sewage ponds in 2009.

The goats were also popular with the public. Municipalitiesface public concerns over the use of alternative landscapingmethods and weed control, which can limit the widespreadadoption of alternatives. Given the social acceptance of thegoats in Prince George, we believe that the City would notface extensive social resistance if they utilize goats on aregular basis.

Goats also proved to be very cost effective over the longerterm, in comparison with conventional herbicide applica-tion. Costs for the goats involve one-time startup costs andongoing maintenance costs. Startup costs were $14,130. On-going costs were $6,056, for a total of $20,186 for one yearof grazing approximately 2.891 hectares of land. In com-parison to the City’s cost for spraying a similarly sized area~$9,129.42!, goats do not seem cost effective; however, thelargest proportion of costs was for fencing. Sites that arealready fenced would not incur this cost. Mobile corralsthat can be taken from site to site or the use of a goatherder would result in fewer startup costs. Ongoing costswere considerably less expensive, reducing to $1,656 in thesecond year ~mostly for winter boarding!. Given depreci-ation over time, the cost of using goats equals the cost ofconventional herbicides within four years and, by year five,would result in cost savings. One cost-saving alternative formunicipalities is to rent a herd from an owner, as didSeattle and San Francisco. Many ranchers are looking tofinancially justify their herds and this limits a municipality’s


expense in terms of over-wintering costs and provision ofdaily monitoring and care.

We could determine no risks to human health from goats.Goat feces do not appear to be a source of pathogens ofconcern. Although quantities were left behind, they de-composed over the winter, adding soil nutrients. In termsof environmental costs, the goats did not graze the grass,focusing instead on weeds and tree saplings. Their use nearflower beds, tree plantations, and ornamental plantings isnot advisable, given their wide range in taste.

Another significant limitation on the use of goats is theirvulnerability to domestic dogs. Solutions do exist, includ-ing the deployment of livestock guardian dogs or humanguardians during the day, while securing the herd in adog-proof enclosure at night. Within a municipal setting,wild predatory animals may or may not be a consideration.Interested municipalities would need to make a survey ofknown or potential threats to goats and plan accordingly.

The biggest drawback we can identify to the use of goats isthat appropriate containment might restrict the types ofareas in which they can be utilized. Portable corrals or theuse of goatherds would expand their utility; however, areasthat are close to hazards, such as roadsides or residentdogs, might never be suitable. Goats will likely work mosteffectively in larger areas such as sewage lagoons, larger cityparks and open spaces ~with adequate guards!, or institu-tions with large grounds ~such as business parks oruniversities!.

Conclusions

Although both are longer-term investments in noxiousweed control, vinegar and domestic goats each show con-siderable promise as alternative weed control mechanisms.They pose fewer risks to human health than do conven-tional herbicides, can be relatively cost effective ~particu-larly over the long term! in comparison with conventionalherbicides, and attract less social disapprobation than doconventional herbicides. Further, both appear to affect abroader range of noxious weeds than has been previouslydocumented, suggesting the ability to utilize both for broadranging weed control. Although additional research—particularly if it takes a more sophisticated approach tostatistical or economic analysis over a longer time frame—will be useful in fully determining long term effectiveness,we believe this research supports such further investigation

into implementation of these mechanisms in municipalsettings.

Acknowledgments

This research was funded by grants from the North West Invasive PlantCouncil and the Federation of Canadian Municipalities’ Green MunicipalFund. The authors gratefully acknowledge the in-kind contributions andsupport of the City of Prince George ~which provided the land base forthe research! and of Deanna Boomhower of Prince George, who providedconsiderable assistance with the goats. Research assistance was providedby Cari Edger, Anna Gradowski, and Ian Parker, all Research Assistants onthe Prince George Northern Sustainable Landscape Initiative.

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Submitted April 11, 2008; revised November 27, 2008; accepted December3, 2008.


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