A Meta-analysis of Canada Thistle Cirsium 
arvense Management
Authors: Stacy Davis, Jane Mangold, Fabian 
Menalled, Noelle Orloff, Zach Miller, and Erik 
Lehnhoff
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Weed 
Science following peer review. The version of record, see full citation below, is available online at: 
https://dx.doi.org/10.1017/wsc.2018.6.
Davis, Stacy, Jane Mangold, Fabian Menalled, Noelle Orloff, Zach Miller, and Erik Lehnhoff. 
"A Meta-analysis of Canada Thistle Cirsium arvense Management." Weed Science 66, no. 4 
(July 2018): 548-557. DOI:10.1017/wsc.2018.6.
Made available through Montana State University’s ScholarWorks 
scholarworks.montana.edu 
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Short title for running footer: Management of Canada Thistle 
 
A Meta-Analysis of Canada Thistle (Cirsium arvense) Management 
 
Stacy Davis, Jane Mangold, Fabian Menalled, Noelle Orloff, Zach Miller, and Erik Lehnhoff 
 
Although stand-alone and integrated management techniques have been cited as viable 
approaches to managing Canada thistle [Cirsium arvense (L.) Scop.], it continues to impact 
annual cropping and perennial systems world-wide. We conducted meta-analyses assessing 
effectiveness of management techniques and herbicide mechanism of action groups for 
controlling Canada thistle using 55 studies conducted in annual cropping systems and 45 studies 
in perennial systems. Herbicide was the most studied technique in both types of systems and was 
effective at reducing Canada thistle. However, integrated multi-tactic techniques, with or without 
herbicides, were more effective than sole reliance on herbicides for long-term control in both 
annual cropping and perennial systems. A variety of management techniques such as biocontrol, 
crop diversification, mowing, and soil disturbance provided similar control as herbicide. Our 
results suggest that many management techniques aimed at reducing Canada thistle can also 
improve crop yield or abundance of desired plants. This study highlights the need to devote more 
research to non-chemical and integrated management approaches for Canada thistle control. 
                                                          
 First, second, and third authors: Research Associate, Associate Professor, and Professor, Department of Land 
Resources and Environmental Sciences, Montana State University, Bozeman, MT 59717; Fourth author: Associate 
Extension Specialist, Schutter Diagnostic Lab, Montana State University, Bozeman, MT 59717; Fifth author: 
Assistant Professor and Superintendent, Western Agricultural Research Center, Montana State University, 
Corvallis, MT 59828; Sixth author: Assistant Professor, Department of Entomology, Plant Pathology, and Weed 
Science, New Mexico State University, Las Cruces, NM 88003. Corresponding author’s E-mail: 
stacy.davis1@montana.edu 
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Nomenclature: Canada thistle, Cirsium arvense (L.) CIRARV 
Key words: Noxious weeds, invasive plants, herbicide, integrated weed management, perennial 
weeds, herbicide mechanism of action. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 The control of and impacts resulting from perennial, invasive plants are challenging in 
both annual cropping systems and perennial plant communities. For example, a recent review of 
invasive plant control publications found that 16 of the 20 most-studied species were perennials 
(Kettenring and Adams 2011) and 83% of the most commonly listed noxious weeds in the 
United States and Canada were perennials (Skinner et al. 2000). Many perennial species spread 
both by seed and vegetatively, enabling effective dispersal (Hakansson 2003a). Such perennial 
plants also have the ability to store carbohydrate reserves in their extensive root systems. Due to 
these biological characteristics, perennial weeds can be persistent, difficult to manage, and 
tolerant of certain management techniques, such as mechanical disturbance (Hakansson 2003b).   
 Canada thistle (Cirsium arvense L.) is a perennial plant that is particularly difficult to 
control once established in both annual cropping and perennial systems (Tiley 2010). Canada 
thistle was first introduced to North America in the 1600’s from Europe via contaminated grain 
seed, hay, and ship’s ballast (Morishita 1999). It commonly invades croplands, natural areas, 
pastures, rangelands, and roadsides (Tiley 2010). Canada thistle was listed as a noxious weed in 
all but four U.S. states by 1957 (Tiley 2010), and as of 2000 it was the most frequently listed 
noxious weed in the United States and Canada (Skinner et al. 2000). Producers on certified 
organic land in the Pacific Northwest and Great Plains regions recently listed Canada thistle 
among the most problematic weeds (OAEC 2013; Tautges et al. 2016).  
 This invasive plant is an effective competitor, with a tall growth form and efficient 
vegetative spread aiding its rapid colonization ability and suppression of other plants (Tiley 
2010). Yield losses in a variety of annual crops including barley (O'Sullivan et al. 1982), 
rapeseed (O'Sullivan et al. 1985), and spring wheat (Donald and Khan 1996) are associated with 
increased Canada thistle density. In addition, Canada thistle infestations can cause further 
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economic losses due to contamination of seed, grain, or straw, which results in changes in 
product handling, processing, and quality (Tiley 2010). Although Canada thistle is regarded as a 
major weed in perennial systems, there is less information published on yield losses in perennial 
pastures compared to annual crops (Tiley 2010). Grekul and Bork (2004) demonstrated 
significant grass and forb yield losses associated with increasing Canada thistle density in 
perennial pastures in western Canada. Furthermore, Canada’s thistle’s prickly mature foliage can 
reduce pasture productivity by deterring livestock from grazing in infested areas (Tiley 2010).  
 Although stand-alone and integrated management techniques have been cited as viable 
approaches to managing Canada thistle (Donald 1990), it continues to invade and persist in 
temperate regions of the world. Carefully reviewing and systematically summarizing results from 
previous studies may help refine management strategies for Canada thistle. A statistical tool 
useful for achieving this goal is meta-analysis, i.e., the systematic and quantitative review and 
synthesis of previous studies (Koricheva and Gurevitch 2014). For example, through a meta-
analysis of 52 studies, Lutman et al. (2013) determined that mechanical cultivation and time of 
seeding were the most efficient non-chemical approaches to manage blackgrass (Alopecurus 
myosuroides Huds.). Additionally, a meta-analysis on downy brome (Bromus tectorum L.) 
management indicated that a variety of control methods reduced short-term abundance of downy 
brome, but only those that included herbicide or revegetation led to long-term control (Monaco 
et al. 2017). Finally, a recently completed meta-analysis of management of Canada thistle and 
field bindweed (Convolvulus arvensis L.) in organic cropping systems showed that integrating 
two or more management strategies generally caused greater reductions in weed abundance than 
any method used alone (N Orloff, personal communication). Meta-analyses can also identify 
knowledge gaps and potential ways to improve experimental approaches. For example, a recent 
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review found that most experimental approaches assessing weed control of invasive plants 
evaluated efficacy of management techniques on short time frames (<1 year) and rarely included 
impacts on desirable vegetation or evaluations of control costs (Kettenring and Adams 2011). 
 We conducted a meta-analysis to review and summarize results from previously 
published studies involving Canada thistle management in annual cropping and perennial 
systems. Our objectives were to 1) assess short- and long-term effectiveness of management 
techniques for controlling Canada thistle, 2) compare short- and long-term effectiveness of 
different herbicide mechanism of action (MOA) groups for controlling Canada thistle, 3) 
determine if and how management techniques for Canada thistle control impact crop yield 
(annual cropping systems) or abundance of desired plants (perennial systems), and 4) identify 
knowledge gaps. These objectives were conducted separately for annual cropping systems (row 
crop and fallow fields) and perennial systems (pasture, rangeland, natural areas, etc.).  
 
Materials and Methods 
Literature Search and Study Inclusion. In December 2015 we conducted a literature search for 
Canada thistle using the Web of Science® (1864-2015) and Agricola® (1927-2015) databases. 
We used the keywords “Cirsium arvense,” “Carduus arvensis,” “Canada thistle,” “creeping 
thistle,” “Californian thistle,” and “field thistle.” We limited our search to articles written in 
English.  
 Following guidelines by Koricheva et al. (2013), all references underwent the following 
filtering process for their inclusion into the meta-analysis: (1) duplicate references from the two 
databases were removed, (2) abstracts and titles of retrieved articles were examined and clearly 
irrelevant literature (e.g., patents, studies about ecology or biology with no control treatments, 
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medical topics, genetics studies, pollination studies) was removed, and (3) full text of selected 
articles was examined and studies were included that met our pre-established inclusion criteria. 
Specifically, we included replicated field studies that assessed the relative efficacy of stand-alone 
or integrated weed management techniques taking place in annual cropping or perennial systems. 
We limited annual cropping system studies to cooler, temperate climatic regions specified as 
those that grew crops listed by the US Department of Agriculture state agriculture overview for 
the Northern Great Plains states (defined as Montana, Nebraska, North Dakota, South Dakota, 
and Wyoming): wheat (Triticum aestivum L.), hay (Medicago sativa L.), barley (Hordeum 
vulgare L.), peas (Pisum sativum), potatoes (Solamum tuberosum), lentils (Lens culinaris), corn 
(Zea mays L.), beans (Phaseolus vulgaris), canola (Brassica napus L.), safflower (Carthamus 
tinctorius), oats (Avena spp.), sugar beets (Beta vulgaris), sunflower (Helianthus annuus L.), 
sorghum (Sorghum bicolor (L.) Moench ssp. bicolor), millet (Panicum miliaceum L.), legumes 
(Medicago sativa L.), mustard (Brassica nigra (L.) W.D.J. Koch; Sinapis alba L.), and flaxseed 
(Linum usitatissimum L.) (USDA 2017). Perennial systems included rangelands, pastures, lawns, 
alfalfa, hay fields, and natural areas world-wide. 
 Studies utilizing herbicides were included only if the applied herbicide was approved for 
use according to Shaner (2014) and if it was applied within recommended rates (Greenbook 
2017; Shaner 2014). We followed terminology from Shaner (2014) and did not consider 
herbicides that had an unclassified MOA (e.g., sodium chlorate). We included studies with 
control/treatment comparisons that published quantitative response measurements for 
aboveground density, cover, biomass, frequency, survival, or percent control (measured from 0-
100%) of Canada thistle. Responses needed to be from established Canada thistle populations as 
7 
 
opposed to populations established artificially for testing purposes. The filtering process was 
conducted by a single author (S. Davis). 
Data Extraction and Synthesis. Following Gurevitch and Hedges (2001), we recorded means, 
measures of variation, and sample sizes for both control and treatment plots from published 
tables, within the text, or derived from published figures using WebPlotDigitizer (Rohatgi 
c2010-2017). Means included quantitative response measurements for aboveground density, 
cover, biomass, frequency, survival, or percent control of Canada thistle. We extracted additional 
information on type of system (annual versus perennial), study duration, and details of the 
treatment applied (e.g., herbicide type and rate, herbicide MOA group). Herbicide MOA groups 
followed the classification used in Shaner (2014) and were as follows: 2 (Acetolactate Synthase 
(ALS) or Acetohydroxy Acid Synthase (AHAS) Inhibitors), 4 (Synthetic Auxins), 5 (Inhibitors 
of photosynthesis at photosystem II site A), 6 (Inhibitors of photosynthesis at photosystem II site 
B), 9 (Inhibitor of 5-enolypyruvyl-shikimate-3-phosphate synthase (EPSPS)), 11 (Inhibitors of 
carotenoid biosynthesis (unknown target)), 27 (Inhibitors of 4-hydroxyhenyl-
pyruvatedioxygenase (4-HPPD)). We included a “mix” herbicide MOA group, which we defined 
as an herbicide application including two or more herbicides from different groups. We also 
extracted data, when available, on crop yield or abundance of desired plants to examine how 
Canada thistle management techniques impacted them. 
 Following Gurevitch and Hedges (2001), we developed a series of criteria to 
systematically extract data from the literature. If there were multiple types of response 
measurements within a study (e.g., density and cover), we selected one response type using a 
ranking process to avoid issues of non-independence. We ranked response measurements based 
on a pre-determined order of importance: 1) biomass, 2) cover, 3) density, 4) frequency, 5) 
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survival, and 6) percent control. Oftentimes, percent control response measurements did not 
include means for non-treated plots; therefore we assumed 0% control in non-treated plots. 
Additionally, percent control was transformed to the same scale as weed abundance 
measurements (i.e., biomass, cover, density, frequency, or survival) by subtracting percent 
control from 100. In this metric, lower numbers indicated more successful management.  
 For each published article, if more than one site or treatment were assessed, data were 
extracted from each situation being tested. For multifactorial studies, we considered the response 
to each treatment as an independent data point (Gurevitch and Hedges 2001). For example, if an 
article compared five different types of herbicide active ingredients applied at two different rates, 
we extracted data for each herbicide active ingredient and rate combination, for a total of 10 data 
points. Although this meant the same control group mean was included for more than one data 
point, it allowed us to maximize use of existing valuable data on effectiveness of management 
techniques (Gurevitch and Hedges 2001).  
 When multiple articles reported results on the same study across varying years, we used 
the data only once by extracting data from the latest set of observations. Many land managers 
apply management techniques every year for multiple years in a row, but in order to accurately 
compare short- and long-term control of Canada thistle, we only used response measurements 
that considered a single year of treatment. If responses to a single year of treatment were 
measured over multiple dates, we extracted data from two defined time periods (less than one 
year after treatment and one year or more after treatment) when possible and conducted separate 
analyses to compare short- versus long-term control. If there were repeated measures within our 
defined time periods, we only used the response from the longest time period since treatment 
(Gurevitch and Hedges 2001).  
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Data Analysis. For each data point, the effect size of a treatment was calculated as the log 
response ratio (lnR), where 
lnR = ln(XE/XC) = lnXE – lnXC [1] 
and XE and XC are means of experimental (treated) and control (non-treated) groups, respectively 
(Hedges et al. 1999). This variable quantifies the proportionate change that results from an 
experimental treatment and represents a meaningful approach to summarize and combine results 
of different studies (Hedges et al. 1999). We selected the response ratio for our analysis because 
it can be estimated without knowledge of sample sizes or variances (Adams et al. 1997). An 
example of an effect size measurement that utilizes measures of variance includes the 
standardized difference in means (e.g., Hedge’s D) (Koricheva et al. 2013). However, since 
many of our studies did not report measures of variation, we used the response ratio as our effect 
size measurement. Only 22% of data points from annual cropping systems and 2% of data points 
from perennial systems reported measures of variation.  
 The response ratio cannot be calculated when data points have response measurements 
equal to zero because one cannot take a logarithm of a zero value (Koricheva et al. 2013). 
Therefore, 10 data points from annual cropping systems and 11 data points from perennial 
systems were excluded from the analysis (<3% of data for each system type). Although we could 
not include these data points, using the response ratio as our effect size allowed us to include a 
large amount of data that did not report measures of variation.  
 We paired our response ratio with a nonparametric bootstrapping approach using a 
simplified weighting scheme. Meta-analyses using Hedge’s D as the effect size metric weight 
each effect size based on their relative sensitivity to measures of variance (Koricheva et al. 
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2013). However, since most of our studies lacked information about variance, we weighted each 
response ratio using sample sizes with the function FN, where 
FN= (nE x nC)/(nE + nC)  [2] 
and nE and nC represent the number of replicates for the experimental (treated) and control (non-
treated) groups, respectively (Adams et al. 1997). We used bootstrapping methods to calculate 
95% confidence intervals around the pooled effect size mean with 1,000 iterations for individual 
management techniques or herbicide MOA groups (Adams et al. 1997). Individual management 
techniques or herbicide MOA groups were considered effective at managing Canada thistle if the 
mean response ratio was negative and the 95% confidence interval did not overlap zero (Adams 
et al. 1997; Gurevitch et al. 1992). For example, a 50% reduction in Canada thistle relative to a 
control group is equivalent to an effect size of -0.7. Mean response ratios from different 
management techniques or herbicide MOA groups were considered to be different from one 
another if their 95% confidence intervals did not overlap (de Graaff et al. 2006; Ferreira et al. 
2015). Management techniques or herbicide MOA groups that had only one data point were 
included in figures to note knowledge gaps and should not be compared statistically to other 
management techniques or herbicide MOA groups because confidence intervals could not be 
calculated. All summaries and analyses were conducted in R statistical software (version 3.3.2), 
including the “plyr”, “ggplot2”, and “cowplot” packages (R Core Team 2016). 
 We conducted separate meta-analyses corresponding to each objective. First, we 
examined management techniques used for Canada thistle control in annual cropping and 
perennial systems. Management techniques included biocontrol, burn, competition, crop 
diversification, fertilizer, herbicide, herbicide integrated, mowing, mulch, non-herbicide 
integrated, soil disturbance, and water manipulation (Table 1). We included the categories of 
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herbicide integrated and non-herbicide integrated to examine the effectiveness of integrated 
multi-tactic techniques, with or without herbicides. For our analyses in annual cropping and 
perennial systems, we examined management at different time periods by conducting two meta-
analyses for each system, one for responses measured <1 year after treatment and another for 
responses measured ≥1 year after treatment. Next, we examined efficacy of different herbicide 
MOA groups (<1 year after treatment and ≥1 year after treatment). We did not compare 
additional specifics of individual management techniques (e.g., timing, types of biocontrol 
agents, herbicide rates) because this level of detail was outside the scope of our questions of 
interest and there was insufficient replication of specific practices within management techniques 
to adequately compare them. Finally, we compared the effect of management techniques on crop 
yield (annual) or abundance of desired plants (perennial). A positive response ratio indicated an 
increase in yield or abundance with treatment, while 95% confidence intervals overlapping zero 
indicated the management technique had no effect (Gurevitch et al. 1992). 
 Complete bibliographies of the articles used in our annual cropping and perennial 
system analyses are given in Supplemental Appendices 1 and 2. Information from each article 
used in our meta-analysis, including study location, system description, management techniques, 
herbicide MOA groups (if applicable), and study duration grouping, is shown in Supplemental 
Tables 1 and 2. 
  
Results and Discussion  
Canada Thistle Management in Annual Cropping Systems. We extracted data from 55 
articles published between 1957 and 2015, resulting in 650 total data points (Figure 1). The 
majority of studies took place in the United States (33 articles) and Canada (9 articles), while the 
12 
 
remaining took place in Denmark, England, Germany, Hungary, India, Iran, New Zealand, 
Norway, Poland, Serbia, and Sweden. Nearly three quarters (74%) of data points evaluated short-
term efficacy of Canada thistle management (<1 year).  
All management techniques studied were effective at reducing Canada thistle in annual 
cropping systems when measured <1 year after treatment (Figure 2a). However, herbicide 
integrated management techniques were most effective for short-term control (Figure 2a). 
Herbicide, herbicide integrated, and soil disturbance were more effective than biocontrol and 
crop diversification (Figure 2a). Many management techniques were also effective ≥1 year after 
treatment. Biocontrol, crop diversification, herbicide, herbicide integrated, mowing, non-
herbicide integrated, and soil disturbance all reduced Canada thistle ≥1 year after treatment 
(Figure 2b). Similar to effects <1 year after treatment, herbicide integrated management 
techniques were more effective than herbicide alone ≥1 year after treatment (Figure 2b). 
Additionally, herbicide integrated management techniques were similar to non-herbicide 
integrated management techniques ≥1 year after treatment (Figure 2b). Fertilizer had no effect on 
Canada thistle ≥1 year after treatment (Figure 2b). The availability of data for competition as a 
management technique in annual cropping systems was insufficient, with only one data point 
reporting treatment effects both <1 and ≥1 year after treatment.  
Although herbicide was the most studied management technique (79% of data points), 
other less studied management techniques were equally or more effective at controlling Canada 
thistle in annual cropping systems. For example, soil disturbance was as effective as herbicide <1 
year after treatment but has not been studied to the extent that control via herbicide has. 
Furthermore, biocontrol, crop diversification, mowing, and soil disturbance all had the same 
level of effectiveness as herbicide ≥1 year after treatment. Only two data points in our meta-
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analysis evaluated the long-term effectiveness of non-herbicide integrated management 
techniques, but these techniques resulted in improved control of Canada thistle versus herbicide 
alone (Figure 2b), highlighting the potential benefits of non-chemical multi-tactic strategies for 
Canada thistle control. 
Our meta-analysis also indicated that herbicide integrated management techniques 
resulted in greater reductions in Canada thistle than herbicide applied alone both <1 year and ≥1 
year after treatment (Figure 2a, 2b). Herbicide integrated management techniques examined 
across both time periods included herbicide + fertilizer (3 data points), herbicide + mowing (14 
data points), herbicide + soil disturbance (40 data points), and herbicide + soil disturbance + 
fertilizer (3 data points). Compared to herbicide used as a stand-alone technique, integrating 
herbicides with additional management techniques can help reduce crop injury and decrease the 
selective pressure towards the selection of herbicide resistance, while providing control of 
invasive perennial weed species (Miller 2016). 
All herbicide MOA groups reduced Canada thistle when measured <1 year after 
treatment (Figure 3a), while only half of the MOA groups tested ≥1 year after treatment were 
effective (Figure 3b). Less than one year after treatment, herbicide MOA groups 4, 6, 9, 11, 27, 
or mixes of MOA groups reduced Canada thistle more than herbicide MOA group 2 (Figure 3a). 
One year or more after treatment, herbicide MOA groups 4, 5 and 9 were effective at reducing 
Canada thistle (Figure 3b). However, herbicide MOA group 9 was slightly more effective than 
MOA group 4 (Figure 3b). Herbicide MOA group 4 (i.e., synthetic auxins) was most frequently 
tested ≥1 year after treatment (n=37) and included 2,4-D (32%), picloram (26%), and clopyralid 
(16%). Other MOA group 4 herbicides included dicamba, quinclorac, and MCPA (26%). 
Herbicide MOA group 5 (i.e., inhibitors of photosynthesis at photosystem II site A) assessed ≥1 
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year after treatment all consisted of atrazine in corn fields (n=6) (Parochetti 1974). Herbicide 
MOA group 9 (i.e., inhibitors of EPSPS, glyphosate) was used in 24 data points evaluated ≥1 
year after treatment. Herbicide MOA groups 2, 11, or mixes of MOA groups did not provide 
Canada thistle control ≥1 year after treatment. Two of ten data points for the mix treatment had a 
positive effect size (i.e., increased Canada thistle). These treatments were bromoxynil + MCPA 
and glyphosate + bromoxynil + MCPA used in spring wheat (Carlson and Donald 1988). 
Overall, results from short-term studies suggest that all herbicide MOA groups studied have 
similar effectiveness. However, if the goal of the land manager is to reduce the frequency of 
herbicide applications, herbicide MOA groups 4, 5, and 9 are promising options for longer-term 
control of Canada thistle in annual cropping systems.  
Canada thistle causes significant yield losses in the northern part of North America (Tiley 
2010), but our results suggest that management options can help reduce its impacts. In our meta-
analysis, 90 data points reported on how various management techniques for Canada thistle 
control were associated with improved crop yield of barley, canola, corn, rapeseed, spring wheat, 
sugar beets, and winter wheat (Figure 4). These techniques included biocontrol, crop 
diversification, herbicide, herbicide integrated, non-herbicide integrated, and soil disturbance. 
Biocontrol, herbicide, and herbicide integrated management techniques were similarly associated 
with increased crop yield (Figure 4). Crop diversification and non-herbicide integrated 
management techniques were associated with increased crop yield more than biocontrol and 
herbicide (Figure 4). However, herbicide was the only management technique that had more than 
three data points recording crop yield, emphasizing the need to include measurements of crop 
yield in study design. The availability of data for fertilizer as a management technique was 
15 
 
insufficient to make comparisons with other techniques, with only one data point reporting 
treatment effects.  
Canada Thistle Management in Perennial Systems. We extracted data from 45 articles 
published between 1958 and 2015, resulting in 376 total data points (Figure 1). The majority of 
these studies took place in the United States (28 articles) and New Zealand (11 articles), while 
the remaining took place in Australia (1 article), Canada (2 articles), Czech Republic (1 article), 
Turkey (1 article), and the United Kingdom (1 article). Perennial systems studied included alfalfa 
fields, grass for seed, natural areas, pastures, rangelands, and roadsides. More than half of data 
points (58%) evaluated short-term efficacy of Canada thistle management (<1 year).  
 Our meta-analysis revealed that biocontrol, competition, herbicide, herbicide integrated, 
mowing, mulch, and non-herbicide integrated management techniques reduced Canada thistle <1 
year after treatment (Figure 5a). Herbicide and herbicide integrated management techniques were 
most effective at reducing Canada thistle, compared to all other techniques (Figure 5a). Fertilizer 
had no effect on Canada thistle control, whereas water manipulation increased the density of 
Canada thistle <1 year after treatment (Figure 5a). The three water manipulation data points were 
from low, medium, and high levels of irrigation on plots with forage species; all levels of 
irrigation resulted in an increase in density of Canada thistle (Thrasher et al. 1963). Only one 
data point existed for the impact of burning on Canada thistle, so comparisons to other 
management techniques should not be made.  
 Many management techniques that were effective at reducing Canada thistle <1 year 
after treatment were also effective ≥1 year after treatment. These included biocontrol, herbicide, 
herbicide integrated, and mowing (Figure 5b). Although herbicide was equally effective as 
herbicide integrated <1 year after treatment, herbicide integrated was more effective than 
16 
 
herbicide alone ≥1 year after treatment (Figure 5b). Mowing was as effective as herbicide in 
controlling Canada thistle ≥1 year after treatment (Figure 5b). Mowing techniques included 
removing all vegetation to 5 cm using a sickle bar when Canada thistle was at early bud stage in 
a pasture (Grekul and Bork 2007), mowing alfalfa fields twice a year for hay (Hodgson 1958), 
and using a rotary mower set at 5 cm when Canada thistle was at bud stage in a pasture (Amor 
and Harris 1977). Even though competition decreased Canada thistle <1 year after treatment 
(Figure 5a), it had no effect on Canada thistle ≥1 year after treatment (Figure 5b).  
Similar to our annual cropping system results and the findings of other meta-analyses 
(Kettenring and Adams 2011), herbicide was the most studied management technique in 
perennial systems (61%). However, other management techniques were equally or more 
effective than herbicide for long-term control. Specifically, mowing was as effective as herbicide 
while herbicide integrated management techniques were more effective than herbicide applied 
alone ≥1 year after treatment. Herbicide integrated management techniques that resulted in long-
term control included herbicide + burn (1 data point), herbicide + competition (2 data points), 
herbicide + soil disturbance (1 data point), herbicide + competition + mowing (1 data point), and 
herbicide + competition + soil disturbance (1 data point). While herbicides are the primary 
method of weed control in most rangelands, this study emphasizes the need to develop integrated 
weed management programs to achieve long-term control of weeds and healthy plant 
communities (DiTomaso 2000). 
 All herbicide MOA groups reduced Canada thistle <1 year and ≥1 year after treatment 
(Figure 6a, 6b). Several herbicide MOA groups showed similar effectiveness in controlling 
Canada thistle. In particular, herbicide MOA groups 2, 4, and mixes of MOA groups were 
similar in effectiveness <1 year after treatment (Figure 6a). Herbicide MOA group 4 and mixes 
17 
 
of MOA groups showed higher effectiveness than herbicide MOA groups 5 and 6 <1 year after 
treatment (Figure 6a). Herbicide mixes included imazamox + bentazon, imazethapyr + bentazon, 
MCPB + bentazon, clopyralid + chlorsulfuron, and 2,4-D + chlorsulfuron. One year or more 
after treatment, herbicide MOA groups 2, 4, 9, and mixes of MOA groups were similar in 
effectiveness (Figure 6b). Herbicide mixes included dicamba + diflufenzopyr, 2,4-D + 
chlorsulfuron, and 2,4-D + metsulfuron. Herbicide MOA group 9 was represented in our meta-
analysis by only six data points that measured control ≥1 year after treatment. This group is 
likely seldom used in pastures and rangelands because it includes non-selective products which 
could injure desired perennial vegetation. Data for herbicide MOA group 6 ≥1 year after 
treatment and MOA group 11 in both time periods was insufficient to make comparisons with 
other groups, with only one data point for each MOA group reporting treatment effects. 
 Similar to our results in annual cropping systems, herbicide MOA group 4 was the most 
studied in perennial systems, with 81% of data points using this group across both time periods. 
Additionally, the majority of studies using mixes of MOA groups had group 4 as one of the 
ingredients (73% of data points). Herbicide MOA group 4 contains herbicides such as 2,4-D, 
dicamba, clopyralid, MCPA, and picloram that are considered important tools for managing 
perennial invasive species in rangelands and pastures (DiTomaso 2000; Morishita 1999). 
Common MOA group 4 herbicides used in studies in our meta-analysis included clopyralid 
(19%), 2,4-D (18%), dicamba (17%), a mix of two or more MOA group 4 herbicides (17%), and 
picloram (15%). Other MOA group 4 herbicides making up 15% of use in studies included 
aminopyralid, MCPB, and MCPA. In spite of the emphasis on MOA group 4 in past research, 
other MOA groups were just as effective at reducing Canada thistle ≥1 year after treatment (e.g., 
groups 2 and 9). 
18 
 
 Both competition and herbicide were similarly associated with increased abundance of 
desired plants in perennial systems (competition mean lnR= 0.45, 95% CI: 0.21 to 0.67, n=5; 
herbicide mean lnR= 0.20, 95% CI: 0.08 to 0.32, n=27), as demonstrated by thirty-two data 
points measuring alfalfa yield, seed yield, and grass biomass. For example, decreasing row 
spacing of alfalfa was associated with an increase in alfalfa yield and a reduction in Canada 
thistle density (Celebi et al. 2010). A total of three articles that utilized herbicides also recorded 
abundance of desired plants with contrasting results. Mesbah and Miller (2005) found an 
increase in alfalfa seed yield after applying a variety of herbicides (18 data points), and 
Gallagher and Vandenborn (1976) observed both increases and decreases in creeping red fescue 
(Festuca rubra L.) seed yield after applying herbicides (seven data points). In contrast, Krueger-
Mangold et al. (2002) observed a decrease in desired grass biomass after treating natural areas in 
the fall with glyphosate, a non-selective herbicide (two data points). It is important to note that 
other plant community components and ecosystem services may also change as a result of 
management efforts. For example, abundance of desired forbs may decrease as a result of 
broadleaf herbicide use (Ortega and Pearson 2010). Although no data points in our meta-analysis 
examined the response of native forbs to Canada thistle management techniques, the potential 
non-target effects on native forbs with broadleaf herbicides is an important concern. 
Incorporating herbicide use with other weed management strategies may help minimize such 
non-target impacts in perennial systems (Crone et al. 2009). 
General Management Recommendations. Our meta-analysis provides several general 
management recommendations for Canada thistle. First, in both annual cropping and perennial 
systems, land managers should consider integrating management techniques for enhanced long-
term control of Canada thistle, as this approach proved to be more effective than solely applying 
19 
 
herbicides. Second, despite herbicide being the most studied management technique, a variety of 
other management techniques resulted in similar control of Canada thistle in the short- and long-
term in annual cropping and perennial systems. This emphasizes the need to re-focus weed 
science research priorities by investigating alternative and integrated control methods more 
often. Third, herbicide MOA groups 4, 5, or 9 can be used for long-term control of Canada 
thistle in annual cropping systems. Finally, a variety of herbicide MOA groups can be used for 
long-term control of Canada thistle in perennial systems including groups 2, 4, 5, 9, and mixes of 
MOA groups. 
Future Research. First, our meta-analysis had limited data on certain non-chemical 
management techniques, such as burning, mulch, and water manipulation. However, some of 
these management techniques had negative effect sizes, suggesting these could be promising 
techniques for Canada thistle control. Additional management techniques, such as grazing, were 
not examined due to lack of papers addressing these. Therefore, increasing the amount of 
research devoted to non-chemical and integrated management techniques in annual cropping and 
perennial systems may help provide a broader range of management recommendations for 
Canada thistle control. Second, because short-term studies could misrepresent the impact of a 
management technique on a perennial species, we encourage researchers to conduct long-term 
evaluations on approaches to control Canada thistle. Finally, our meta-analysis, along with others 
(Koricheva and Gurevitch 2014; Philibert et al. 2012), highlights the need to include such basic 
information on means, measures of variation, and sample sizes in published articles related to 
invasive species management (Gurevitch and Hedges 2001; Gurevitch et al. 1992). Additionally, 
researchers should consider the importance of measuring not only weed control but also crop 
yield and abundance of desired plants, as well as other ecosystem services.  
20 
 
 
Acknowledgements 
The authors would like to thank the Montana Noxious Weed Trust Fund and the Montana Wheat 
and Barley Committee for funding this research. We would like to thank Sean MacKenzie for 
statistical analysis help. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
21 
 
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25 
 
Tables 
Table 1. Descriptions of management techniques used in articles included in the meta-analysis of 
Canada thistle. The number of data points associated with each type of system is indicated. 
Management technique Description Annual cropping Perennial 
Biocontrol Biological control using insects or 
pathogens 
24 20 
Burn Prescribed fire 0 1 
Competition Any method attempting to increase 
competitive ability including 
manipulating row spacing or 
revegetation 
2 48 
Crop diversification Adding cover crops or increasing 
crop rotation to a cropping system 
17 0 
Fertilizer Soil amendments including fertilizer 
or manure applied 
2 7 
Herbicide Applying herbicides 512 228 
Herbicide integrated Any combination of two or more 
management techniques with at least 
one method utilizing herbicides 
60 30 
Mowing Mechanical mowing or clipping 12 11 
Mulch Use of either plastic or organic 
mulches 
0 3 
26 
 
Non-herbicide 
integrated 
Combination of two or more 
management techniques, none 
including herbicides 
2 25 
Soil disturbance Mechanical control methods 
including tillage, cultivation, hoeing, 
or harrowing 
19 0 
Water manipulation Changing water availability through 
irrigation 
0 3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
27 
 
Figures 
 
Figure 1. Flow diagram depicting criteria applied during literature screening portion of the meta-
analysis of Canada thistle management. In each box, “n” is the number of articles described in 
that step. 
28 
 
 
Figure 2. Mean effect size (lnR) and 95% confidence intervals for Canada thistle abundance 
measured (a) <1 year or (b) ≥1 year after treatment in annual cropping systems as a function of 
management techniques. For each management technique, the number next to the confidence 
interval represents the number of data points that was used to calculate the mean. 
29 
 
 
Figure 3. Mean effect size (lnR) and 95% confidence intervals for Canada thistle abundance 
measured (a) <1 year or (b) ≥1 year after treatment in annual cropping systems as a function of 
herbicide mechanism of action groups. For each group, the number next to the confidence 
interval represents the number of data points that was used to calculate the mean. Groups are as 
follows: 2= ALS or AHAS inhibitors; 4= synthetic auxins; 5= inhibitors of photosynthesis at 
photosystem II site A; 6=inhibitors of photosynthesis at photosystem II site B; 9=inhibitor of 
EPSPS; 11=inhibitors of carotenoid biosynthesis; 27 = inhibitors of 4-hydroxyhenyl-
pyruvatedioxygenase (4-HPPD); and mix= includes two or more herbicides from different 
groups. 
 
 
30 
 
 
Figure 4. Mean effect size (lnR) and 95% confidence intervals for crop yield in annual cropping 
systems as a function of Canada thistle management techniques. For each management 
technique, the number next to the confidence interval represents the number of data points that 
was used to calculate the mean. 
31 
 
 
Figure 5. Mean effect size (lnR) and 95% confidence intervals for Canada thistle abundance 
measured (a) <1 year or (b) ≥1 year after treatment in perennial systems as a function of 
management techniques. For each management technique, the number next to the confidence 
interval represents the number of data points that was used to calculate the mean. 
32 
 
 
Figure 6. Mean effect size (lnR) and 95% confidence intervals for Canada thistle abundance 
measured (a) <1 year or (b) ≥1 year after treatment in perennial systems as a function of 
herbicide mechanism of action groups. For each group, the number next to the confidence 
interval represents the number of data points that was used to calculate the mean. Groups are as 
follows: 2= ALS or AHAS inhibitors; 4= synthetic auxins; 5= inhibitors of photosynthesis at 
photosystem II site A; 6=inhibitors of photosynthesis at photosystem II site B; 9=inhibitor of 
EPSPS; 11=inhibitors of carotenoid biosynthesis; and mix= includes two or more herbicides 
from different groups. 
  
33 
 
Appendix S1. References used in meta-analysis of Canada thistle management in annual 
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34 
 
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35 
 
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36 
 
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37 
 
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38 
 
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39 
 
Appendix S2. References used in meta-analysis of Canada thistle management in perennial 
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40 
 
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41 
 
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Krueger-Mangold J, Sheley RL, Roos BD (2002) Maintaining plant community diversity in a 
waterfowl production area by controlling Canada thistle (Cirsium arvense) using 
glyphosate. Weed Technol 16: 457-463 
McKay HC (1959) Control Canada thistle for greater profits. University of Idaho Rep 321. 16 p 
Meeklah FA, Mitchell RB (1984) Evaluation of herbicides for control of Californian thistle. 
Pages 20-23 in Proceedings of the New Zealand Weed and Pest Control Conference. New 
Zealand Plant Protection Society 
Melichar MW, Stafford MP (1989) Control of Canada thistle and musk thistle on roadside rights-
of-way with clopyralid and 2,4-D. Pages 72-73 in Proceedings of the Northeastern Weed 
Science Society 
Mesbah AO, Miller SD (2005) Canada thistle (Cirsium arvense) control in established alfalfa 
(Medicago sativa) grown for seed production. Weed Technol 19: 1025-1029 
Peterson SC, Parochetti JV (1978) Canada thistle (Cirsium arvense) control in timothy (Phleum 
pratense) and red-clover (Trifolium pratense) sward. Weed Sci 26: 215-220 
Samuel LW, Lym RG (2008) Aminopyralid effects on Canada thistle (Cirsium arvense) and 
native plant species. Invasive Plant Sci Manag 1: 265-278 
Sebastian JR, Beck KG, Owsley CJ (1992) Canada thistle control with metsulfuron, picloram, 
2,4-D, and split applications of 2,4-D and the sulfonylureas. Western Society of Weed 
Science. 2 p 
43 
 
Thrasher FP, Cooper CS, Hodgson JM (1963) Competition of forage species with Canada thistle, 
as affected by irrigation and nitrogen levels. Weeds 11: 136-138 
Tipping PW (2001) Canada thistle (Cirsium arvense) control with hexazinone in crown vetch 
(Coronilla varia). Weed Technol 15: 559-563 
Travnicek A, Lym R, Prosser C (2005) Fall-prescribed burn and spring-applied herbicide effects 
on Canada thistle control and soil seedbank in a northern mixed-grass prairie. Rangeland 
Ecol Manag 58: 413-422 
Vantoor R (1994) Effect of applying glyphosate and clopyralid by rotary weed wiper on 
Californian thistle in Southland. Pages 91-92 in Proceedings of the New Zealand Plant 
Protection Conference. New Zealand Plant Protection Society 
Wedryk S, Cardina J (2012) Smother crop mixtures for Canada thistle (Cirsium arvense) 
suppression in organic transition. Weed Sci 60: 618-623 
Whitson TD, Ferrell MA (1986) Evaluation of herbicides for Canada thistle control. Western 
Society of Weed Science. p 55 
Wilson R, Kachman S (1999) Effect of perennial grasses on Canada thistle (Cirsium arvense) 
control. Weed Technol 13: 83-87 
Wilson RG, Martin AR, Kachman SD (2006) Seasonal changes in carbohydrates in the root of 
Canada thistle (Cirsium arvense) and the disruption of these changes by herbicides. Weed 
Technol 20: 242-248 
Wilson RG, Michiels A (2003) Fall herbicide treatments affect carbohydrate content in roots of 
Canada thistle (Cirsium arvense) and dandelion (Taraxacum officinale). Weed Sci 51: 
299-304 
44 
 
Table S1. Article information used in meta-analysis of Canada thistle management in annual cropping systems. Articles that had 1 
information on crop yield are indicated by an * next to the citation. 2 
     
Study 
duration 
Citation Study location Annual cropping system 
description 
Management 
technique 
Herbicide 
groups 
<1 
year 
≥1 
year 
Armel et al. 2005 Delaware, United 
States 
corn herbicide 4, 27, mix X 
 
Asadi et al. 2013 
* 
Mashhad, Iran winter wheat biocontrol na X 
 
Bicksler and 
Masiunas 2009 
Illinois, United 
States 
fallow, cover crop- buckwheat, 
sudangrass, or sudangrass-
cowpea mix 
crop 
diversification 
na X X 
Blasko and 
Nemeth 2006 
Hungary corn herbicide 2, mix X X 
Bondarenko 1957 Ohio, United 
States 
fallow herbicide 11 
 
X 
   
herbicide 
integrated 
11 
 
X 
Brosten and 
Sands 1986 
Montana, United 
States 
fallow biocontrol na X X 
Carlson and 
Donald 1988 
North Dakota, 
United States 
spring wheat herbicide 9, mix X X 
Carson and 
Bandeen 1975 
Ontario, Canada fallow herbicide 4, 5 X 
 
Causey and Webb 
1990 
Delaware, United 
States 
corn herbicide mix X 
 
45 
 
Curtis and 
Haagsma 1986 
Alberta, Canada wheat, barley herbicide 4 X X 
Darwent et al. 
1994 
Alberta, Canada barley, canola-barley-barley, 
lentil-barley-barley, wheat-
barley-barley, field pea-wheat 
herbicide 9 
 
X 
Davies and Orson 
1987 
Norfolk and 
Essex, England 
winter wheat herbicide 2, 4 X 
 
 
Cambridge and 
March, England 
fallow herbicide 2, 4 
 
X 
Derscheid et al. 
1961 
South Dakota, 
United States 
oats herbicide 4 X X 
   
herbicide 
integrated 
4 X 
 
Donald 1993 North Dakota, 
United States 
fallow herbicide 4, 9 X 
 
Donald and Prato 
1992a 
North Dakota, 
United States 
spring wheat herbicide 4, mix X 
 
Donald and Prato 
1992b * 
North Dakota, 
United States 
spring wheat herbicide 2, 4 X 
 
Faravani and 
Khlaghani 2004 
Khorasan, Iran wheat herbicide 9, 2 X 
 
Glenn and 
Heimer 1994 * 
Maryland, 
United States 
corn herbicide 2, 4, 9, 
mix 
X 
 
Graglia et al. 
2006 
Slagelse, 
Denmark 
grass/clover, spring barley mowing na 
 
X 
  
red clover, spring barley soil disturbance na 
 
X 
Gronwald et al. 
2002 
Minnesota, 
United States 
soybean biocontrol na X 
 
46 
 
Hodgson 1958 * Montana, United 
States 
spring wheat fertilizer na 
 
X 
  
fallow, spring wheat, peas herbicide 4 
 
X   
spring wheat, potatoes and corn herbicide 
integrated 
4 
 
X 
Hoeft et al. 2001 Minnesota, 
United States 
soybean biocontrol na X 
 
   
herbicide 6 X 
 
Howatt et al. 
2006 
North Dakota, 
United States 
spring wheat herbicide 9, mix X 
 
Kirkland 1977 * Saskatchewan, 
Canada 
fallow herbicide 9 X 
 
   
herbicide 
integrated 
9 X 
 
Kluth et al. 2005 Lower Saxony, 
Germany 
fallow biocontrol na X 
 
Kwiatkowski 
2009 
Lublin, Poland spring barley crop 
diversification 
na X 
 
Lym and Deibert 
2005 
North Dakota, 
United States 
fallow herbicide 4, mix X X 
McKay 1959 Idaho, United 
States 
potatoes competition na 
 
X 
  
spring wheat fertilizer na 
 
X   
spring wheat herbicide 4 
 
X   
spring wheat-alfalfa herbicide 
integrated 
4 
 
X 
McKone 1989 Montana, United 
States 
barley herbicide 2, 4 X 
 
Miller 1987 * Wyoming, 
United States 
barley herbicide 2, 4, mix X 
 
47 
 
Miller and Lym 
1998 
North Dakota, 
United States 
corn, soybean herbicide 4, mix X 
 
   
soil disturbance na X 
 
Miller et al. 1989 
* 
Wyoming, 
United States 
barley herbicide 4, 5, mix X 
 
Miller et al. 1994 
* 
Wyoming, 
United States 
sugarbeets herbicide 4 X 
 
Naish 1975 New Zealand fallow herbicide 4 X 
 
O'Donovan et al. 
2001 * 
Alberta, Canada barley-canola herbicide 4 X 
 
O'Sullivan 1982 Alberta, Canada barley and wheat herbicide 2 X 
 
O'Sullivan and 
Kossatz 1982 * 
Alberta, Canada rapeseed herbicide 4 X 
 
O'Sullivan and 
Kossatz 1984a * 
Alberta, Canada rapeseed herbicide 4 X 
 
O'Sullivan and 
Kossatz 1984b * 
Alberta, Canada barley herbicide 4 X 
 
Parochetti 1974 Maryland, 
United States 
corn herbicide 5, 11 X 
 
Rabcewicz 1995 Alnarp, Sweden fallow soil disturbance na X 
 
Renner 1991 Michigan, United 
States 
sugarbeets herbicide 4 X 
 
Selleck and Baird 
1981 
Pennsylvania, 
United States 
corn and soybeans herbicide 9, mix X 
 
Singh and Malik 
1992 
Hisar, India fallow herbicide 4 X 
 
Terry and Wilson 
1964 
Essex, England winter wheat herbicide 5 X 
 
48 
 
Thomsen et al. 
2015 * 
As, Norway spring wheat crop 
diversification 
na 
 
X 
   
non-herbicide 
integrated 
na 
 
X 
Tolimir et al. 
2006 * 
Belgrade, Serbia corn soil disturbance na X 
 
Warden 1964 South Dakota, 
Minnesota, and 
Wisconsin 
United States 
fallow herbicide 4 X 
 
 
Montana, United 
States 
winter wheat herbicide 4 
 
X 
 
Minnesota, 
United States 
oats herbicide 4 
 
X 
Warnes 1974 Minnesota, 
United States 
fallow-corn herbicide 4 X X 
   
herbicide 
integrated 
4 X X 
   
soil disturbance na X 
 
Wedryk and 
Cardina 2012 
Ohio, United 
States 
fallow competition na X 
 
Westra and 
D'Amato 1988 
Colorado, United 
States 
winter wheat herbicide 2, 4, 9, 
mix 
X 
 
Zimdahl and 
Foster 1974 
Colorado, United 
States 
fallow herbicide 4, 5, 9, 
mix 
X X 
Zimdahl and 
Foster 1979 
Colorado, United 
States 
fallow herbicide 4, 5, 9, 
mix 
X 
 
Zimdahl and 
Foster 1993 
Colorado, United 
States 
fallow herbicide 2, 4, 9 X 
 
49 
 
Zuris et al. 1987 Nebraska, United 
States 
winter wheat-fallow herbicide 2 X X 
 3 
 4 
 5 
 6 
 7 
 8 
 9 
 10 
 11 
Table S2. Article information used in meta-analysis of Canada thistle management in perennial systems. Articles that had information 12 
on desired plant yield are indicated by an * next to the citation. 13 
     
Study duration 
Citation Study 
location 
Perennial system 
description 
Management 
technique 
Herbicide 
groups 
<1 
year 
≥1 
year 
Almquist 
and Lym 
2010 
Minnesota, 
United 
States 
range herbicide 4 X X 
50 
 
Amor and 
Harris 
1977 
Victoria, 
Australia 
pasture herbicide 4, 9, 11 X X 
   
mowing na X X 
Beck 1988 Colorado, 
United 
States 
pasture herbicide 4, mix X X 
Beck et al. 
1989 
Colorado, 
United 
States 
pasture herbicide 4 X X 
Biesboer et 
al. 1994 
Minnesota, 
United 
States 
natural area competition na X X 
Bixler et al. 
1991 
Washington, 
United 
States 
natural area, pasture herbicide 2, 4, mix X X 
Boerboom 
and Wyse 
1988 
Minnesota, 
United 
States 
pasture herbicide 6 
 
X 
Bourdot et 
al. 1993 
Canterbury, 
New 
Zealand 
pasture biocontrol na X X 
Bourdot et 
al. 2004 
Canterbury, 
New 
Zealand 
pasture biocontrol na X 
 
Bourdot et 
al. 2006 
Canterbury, 
New 
Zealand 
pasture biocontrol na 
 
X 
Bultsma et 
al. 1992 
Wyoming, 
United 
States 
range herbicide 4 
 
X 
51 
 
Celebi et 
al. 2010 * 
Van, Turkey alfalfa competition na 
 
X 
Clements 
et al. 2012 
Southampto
n, England 
pasture fertilizer na X 
 
Derscheid 
et al. 1961 
South 
Dakota, 
United 
States 
pasture herbicide integrated 4 X 
 
   
non-herbicide 
integrated 
na X 
 
Enloe et al. 
2007 
North 
Dakota, 
Colorado, 
and 
Wyoming, 
United 
States 
range, pasture herbicide 4, mix 
 
X 
Foote et al. 
1970 
Minnesota, 
United 
States 
roadside herbicide 4 
 
X 
Gaisler et 
al. 2008 
Liberec, 
Czech 
Republic 
natural area mowing na X 
 
   
mulch na X 
 
Gallagher 
and 
Vanden 
Born 1976 
* 
Alberta, 
Canada 
grass for seed herbicide 4 X X 
Gramig 
and 
North 
Dakota, 
range herbicide integrated 4 
 
X 
52 
 
Ganguli 
2015 
United 
States 
Grekul and 
Bork 2007 
Alberta, 
Canada 
pasture fertilizer na X 
 
   
herbicide 4 
 
X    
herbicide integrated 4 X 
 
   
mowing na 
 
X    
non-herbicide 
integrated 
na X 
 
Harrington 
et al. 2014 
Washington, 
United 
States 
meadow herbicide 4 
 
X 
Hartley and 
James 1979 
Hamilton, 
New 
Zealand 
pasture herbicide integrated 4 X 
 
   
non-herbicide 
integrated 
na X 
 
Hartley and 
Thomson 
1982 
Normany, 
New 
Zealand 
pasture herbicide 4 X 
 
   
mowing na X 
 
Harvey et 
al. 1993 
Canterbury, 
New 
Zealand 
pasture biocontrol na 
 
X 
Harvey et 
al. 1998 
Canterbury, 
New 
Zealand 
pasture biocontrol na X X 
Hodgson 
1958 
Montana, 
United 
States 
pasture, alfalfa herbicide integrated 4 
 
X 
53 
 
   
mowing na 
 
X 
Hurrell and 
Bourdot 
1996 
Canterbury, 
New 
Zealand 
pasture biocontrol na 
 
X 
   
mowing na X 
 
   
non-herbicide 
integrated 
na X 
 
Hurrell and 
Bourdot 
2001 
Canterbury, 
New 
Zealand 
pasture biocontrol na X 
 
Krueger-
Mangold 
2002 et al. 
* 
Montana, 
United 
States 
natural area herbicide 9 
 
X 
McKay 
1959 
Idaho, 
United 
States 
alfalfa competition na 
 
X 
   
herbicide integrated 4 
 
X 
Meeklah 
and 
Mitchell 
1984 
Otago, New 
Zealand 
pasture herbicide 4 X X 
   
herbicide integrated 4 X 
 
   
mowing na X 
 
Melichar 
and 
Stafford 
1989 
Iowa, 
Kentucky, 
and Indiana, 
United 
States 
roadside herbicide 4 X 
 
54 
 
Mesbah 
and Miller 
2005 * 
Wyoming, 
United 
States 
alfalfa herbicide 2, 4, 6, 
mix 
X 
 
Peterson 
and 
Parochetti 
1978 
Maryland, 
United 
States 
range herbicide 4 X 
 
Samuel and 
Lym 2008 
North 
Dakota, 
United 
States 
range herbicide 4 X X 
Sebastian 
et al. 1992 
Colorado, 
United 
States 
range herbicide 2, mix 
 
X 
Thrasher et 
al. 1963 
Montana, 
United 
States 
range fertilizer na X 
 
   
water manipulation na X 
 
   
non-herbicide 
integrated 
na X 
 
Tipping 
2001 
Maryland, 
United 
States 
range herbicide 5 X 
 
Travnicek 
et al. 2005 
North 
Dakota, 
United 
States 
range burn na X 
 
   
herbicide 4 X 
 
   
herbicide integrated 4 X 
 
Vantoor 
1994 
Southland, 
New 
Zealand 
pasture herbicide 9 
 
X 
55 
 
Wedryk 
and 
Cardina 
2012 
Ohio, United 
States 
pasture competition na X 
 
Whitson 
and Ferrell 
1986 
Wyoming, 
United 
States 
range herbicide 4 
 
X 
Wilson and 
Kachman 
1999 
Nebraska, 
United 
States 
pasture competition na X 
 
   
herbicide integrated 4, 9 X 
 
   
non-herbicide 
integrated 
na X 
 
Wilson and 
Michiels 
2003 
Nebraska, 
United 
States 
range herbicide 4 X 
 
Wilson et 
al. 2006 
Nebraska, 
United 
States 
pasture herbicide 4 X 
 
 14