Poa Annua on Sub‐Antarctic Macquar

DR LAURA WILLIAMS (Orcid ID : 0000-0002-7468-5159)

Article type : Original Article

Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub-Antarctic Macquarie Island

L K WILLIAMS 1, B M SINDEL 1, P KRISTIANSEN 1, S C WILSON 1 & J D SHAW 2

1 School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia and 2 Centre for Biodiversity and Conservation Science, School of Biological Sciences, The University of Queensland, St Lucia, Queensland, Australia

Received 21 July 2018

Revised version accepted 1 January 2019

Subject Editor: David Clements, Trinity Western University, Canada

Running head: Efficacy of invasive plant management

Correspondence: Laura Williams, School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia. Tel: (+61) 438 065 206; E-mail: [email protected]

Author Manuscript

This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/WRE.12355

Summary Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub-Antarctic temperatures and their off-target impacts may increase eradication success. With interest in controlling non-native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub-Antarctic biotype) in sub-Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub- Antarctic Macquarie Island through field-based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub- Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one-off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site-specific testing of control methods and understanding off-target impacts of control when managing alien plant species in protected areas.

Keywords: Eradication, alien, weed, off-target impacts, Southern Ocean Islands, annual meadow grass, wintergrass

Introduction Author Manuscript Biological invasions negatively impact ecosystems worldwide and protected areas are not immune to invasion. Attempts to eradicate invasive species are becoming increasingly common in protected areas (Foxcroft et al., 2013), however success is difficult to achieve. A review of 173 eradications worldwide found only half to be successful, with success less likely in natural habitats (Pluess et al., 2012). Most successful eradications have

This article is protected by copyright. All rights reserved targeted vertebrates. Plants have been more difficult to eradicate, generally because the targeted populations have had persistent seed banks which are difficult to remove and also due to high fecundity of the invasive plants resulting in large populations. Plants are also often cryptic and small in size and the attractive baits and traps that aid animal eradication are not applicable to plants (Panetta & Timmins, 2004; Simberloff, 2013). Small populations of alien plants have been eradicated worldwide, yet successful eradication of established alien species is rare in protected areas with only a few documented cases, mainly from islands (Genovesi, 2011).

The Southern Ocean Islands (SOI) consist largely of protected areas (Shaw, 2013), yet over 280 alien plant species have become established (McGeoch et al., 2015). Most of the alien species have limited impact due to their restricted distributions, but some threaten sub-Antarctic ecosystems (Gremmen et al., 1998; Frenot et al., 2005; le Roux et al., 2013). To date, nine successful plant eradications have been recorded from the SOI (Greve et al., 2017; Shaw, 2013, Department of Primary Industries, unpublished data). All of these populations covered just a small area (or were single plants) and all but one were removed physically (McGeoch et al., 2015; Greve et al., 2017). Managers in the region are now considering controlling or eradicating more widespread and established populations (Shaw, 2013; Greve et al., 2017). Some attempts have already been made, but have been unsuccessful due to established seed banks and logistical difficulties associated with managing alien plants in this region (Shaw, 2013).

Many factors contribute to the success or failure of an eradication programme, including population size and distribution and invasion characteristics of the target species (Panetta & Timmins, 2004; Simberloff, 2013). Based on short-comings of eradication attempts in protected areas, we have identified two factors that are important to assess when eradicating alien plants from protected areas such as the SOI. First, it is essential to have a thorough understanding of the efficacy of control methods prior to implementation of a management program. In many control programmes management methods are trialled and refined over the course of the project (Hilton & Konlechner, 2010; Cooper et al., 2011; Ryan et al., 2012; Hamilton et al., 2015). This approach can be highly successful for rapid response situations and dealing with small populations. Eradication of established populations is more difficult (Panetta & Timmins, 2004) and a trial-and-error approach may reduce efficiency and increase the timeframe and cost of the programme. Second, it is essential to consider any possible off-target impacts of the control methods used and these are rarely understood (Power et al.). There is a growing body of evidence suggesting that alien plant management can have negative or unexpected outcomes on species other than the target (Caut et al., 2009; Rinella et al., 2009) and this needs to be a fundamental objective of alien species management programmes within protected areas (Buckley & Han, 2014).

The importance of understanding the efficacy of control methods used and their potential negative impacts is illustrated by the recent eradication of two invasive Agrostis species on Macquarie Island. A quick response was required, given the high rate of spread of these species in the sub-Antarctic, and so the plants, roots and surrounding soil was removed. The first attempt was unsuccessful, with a second treatment required

the following year (DepartmentAuthor Manuscript of Primary Industries, Parks, Water and the Environment, unpublished data) which was destructive, leaving large, deep holes denuded of vegetation which have been slow to recover (Williams, personal observation). If the efficacy and impact of various control methods had been known, eradication of this species could have been more effective and less destructive.

This article is protected by copyright. All rights reserved Poa annua (L.) or wintergrass, is considered the worst weed in the SOI based on its widespread distribution and impact (McGeoch et al., 2015). Management of P. annua is being considered on several SOI (de Villiers et al., 2006, Hughes et al., 2015) and an eradication attempt is underway on King George Island in Antarctica. Aspects of the ecology of the species on the SOI are relatively well known, in particular its perenniality, habit of growing in expansive, dense mats and preference of colonising disturbed, nutrient enriched sites (Walton, 1975; Copson, 1984; Frenot et al., 1998; Williams et al., 2018). Extensive research has been undertaken on P. annua in temperate turf grass, where it is difficult to control due to its high plasticity and tolerance of varied environmental conditions (Branham & Calhoun, 2005; Christians, 2006). Physical methods (Beard et al., 1978), herbicides (Finlayson & Dastcheib, 2000, Toler et al., 2007; Cross et al., 2012), biological methods (Gange et al., 1999) and environmental manipulation (Baldwin, 1993) provide some degree of control, but success is highly variable depending on the biotype of P. annua and environmental conditions. This makes it essential to test the efficacy of P. annua control methods under colder SOI conditions using the perennial biotype of P. annua found across most of the SOI.

Macquarie Island is a SOI of high conservation status, designated as a Nature Reserve, Biosphere Reserve and World Heritage Area. Over forty native plant species are present on the island, many of which are found across the SOI (Baker & Duretto, 2016). Seven non-native plant species have established. Four species were individual plants/isolated populations and have been removed (Baker & Duretto, 2016), while three remain widespread, Cerastium fontanum (Baumg.), P. annua and Stellaria media (L.) Vill (Sindel et al., 2017). Poa annua has been present on Macquarie Island since the late 1800s and is distributed across the island, found in all habitats although at different densities (Williams et al., 2018). Eradication of P. annua on Macquarie Island is not a current consideration, however research into the control of P. annua on Macquarie Island will inform management of the species on other SOI islands where the species is less widely distributed and eradication may be feasible.

We aimed to quantify the efficacy of a number of physical and chemical control methods that have proven effective on P. annua in temperate turf grass, under sub-Antarctic temperature conditions, and to assess the off-target impacts of these control methods on native grass species. This information will assist in more effective management of P. annua and other future weed incursions throughout the SOI and Antarctica. It should also highlight the importance of investing concerted thought into controlling invasive species in protected areas, of carefully considering a range of different control options and of ensuring these control methods do not cause off-target impacts.

Materials and methods Review and selection of control methods A review of the literature was undertaken using several search engines and search terms to identify all possible methods used for P. annua control. We selected scalping, hoeing, trimming and hand weeding as appropriate control methods becauseAuthor Manuscript they are legally allowable in Australia, logistically feasible in the sub-Antarctic and have proven effective for P. annua control elsewhere. We selected herbicides that were registered for the control of P. annua in Australia with relatively low toxicity and low soil persistence to better suit a protected area.

Physical control

This article is protected by copyright. All rights reserved In the austral summer of 2013 (January/February), we established four study sites on Macquarie Island across an altitudinal and P. annua cover gradient (Fig 1). Bauer Bay Beach and Tractor Rock were located at low altitude (< 50 m above sea level) with high P. annua cover (> 60 %) and Bauer Bay Slope and Doctor’s Track at mid altitude (100-150 m above sea level) with medium P. annua cover (15-50 %).

At each of the sites, four replicates of four treatments were established. Treated plots were 1 m × 1 min size and the treatments were: control (no disturbance); trimming (vegetation to 2 cm above ground level cut and removed); scalping (removal of all above-ground vegetation and roots and soil to a depth of 10 cm); and hoeing (digging and mulching of vegetation and soil leaving highly disturbed biomass in place). The number of species (species richness) and percentage cover of each vascular species was recorded within each quadrat immediately prior to treatment (January/February 2013) and again in December 2013, February/March 2014 and April 2015. During analysis, the two alien species other than P. annua found in plots were omitted to obtain an exact measure of native species richness.

In December 2013, another five sites (Fig 1) were established as above but with an additional treatment of hand weeding (selective manual removal of P. annua plants and roots where possible). Lower Boot Hill, Mt Power and Upper Boot Hill were at high altitude (> 250 m above sea level) with low P. annua cover (< 10 %), Sawyer Creek was at mid altitude (100-150 m above sea level) with medium P. annua cover (15-50 %) and The Nuggets at low altitude (< 50 m above sea level) with high P. annua cover (> 60 %). Species presence and cover were measured prior to treatment in December 2013 and again in February/March 2014 and April 2015.

Fig. 1 near here

Chemical control Herbicides were trialled ex-situ due to strict land management regulations preventing herbicide use on Macquarie Island. Experiments were undertaken in light and temperature-controlled conditions similar to those on Macquarie Island (5°C, 37 Watt fluorescent lights delivering 12 hours of light per day). Poa annua and three common native co-occurring grass species (Agrostis magellanica Lam., Festuca contracta Kirk., Poa foliosa Hook. f.) (Copson 1984) were collected from Macquarie Island in March 2013 and March 2014 and grown at The University of New England, Armidale, NSW, Australia in a typical sand/peat soil from Macquarie Island in individual pots (75 mm diameter, 105 mm high).

We quantified the efficacy and selectivity of 11 herbicides (plus a control) on P. annua (Herbicide screening experiment) (Table 1). Herbicides were selected which were documented to be phytotoxic to P. annua when applied post-emergence, have low acute mammal toxicity and low to medium soil adsorption (more

appropriate in environmentallyAuthor Manuscript sensitive sites) as described on the herbicide labels and safety data sheets. For each treatment, five P. annua plants and five plants of each native grass species (A. magellanica, F. contracta, P. foliosa) were sprayed with the herbicide (or water for the control) in an enclosed container to ensure no cross- contamination or spray drift. Herbicide was applied using a hand-held spray bottle (total of 3.18 ml applied per plant across an area of 0.28 m2) 70 cm above the plant. Plants were monitored for 12 weeks until no further

This article is protected by copyright. All rights reserved plant deaths occurred for 14 days, and injury rating (damage to shoots) scored weekly using the European Weed Research Council’s rating system where 1 = no effect and 9 = plant dead. Dead/live/unhealthy shoot dry weight, proportion of dead/live/unhealthy shoots, root length and height data were also collected but these factors either correlated with injury rating or were not as consistent as injury rating and so were not further investigated in any of the experiments.

Table 1 near here

The most effective and selective herbicides determined in the aforementioned experiment (glyphosate, rimsulfuron, trifloxysulfuron sodium) were then trialled on P. annua and the native grass species at four application rates (plus an unsprayed control): 0.25, 0.5, 1 and 2 times the recommended label rate. The same methods were used as above, except with four replicates of each treatment and plants monitored for 10 weeks. A further experiment was conducted to assess application method (brushed or sprayed). The herbicides were applied to additional P. annua plants at 0.5 and 1 times the recommended rate using a paint brush (2 strokes/plant, four replicates per treatment) to compare with the sprayed P. annua plants as described above.

Data analysis Data were analysed using R version 3.5.0 (R Core Team, 2018). For the physical control trial, t-tests were used to test for differences in the cover of P. annua between different time periods (months), with P. annua cover as the response variable and time as the explanatory variable. Time was non-significant; therefore, a linear model was used to assess treatment effects at the final time period with P. annua cover as the response variable and treatment and site as the explanatory variables. Variances and normality were checked and the data was transformed using square root to stabilise the variances, and back-transformed means and confidence intervals are presented. Native species richness data from the physical control trial varied over time (months) so the data were analysed using the linear mixed effects function from the nlme package in R. Time, treatment and site were modelled as fixed effects and plots were used as the random effects. Given the ordinal nature of the response variable (injury rating) for the herbicide screening, herbicide rate and application method data, general linear models with a Poisson distribution were applied with herbicide type, rate and method as the explanatory variables as 3-way factorials. The dispersion and goodness of fit of each model were checked and found to be satisfactory. The estimated marginal means and 95 % confidence intervals (CI) for the treatments in all models were calculated using the emmeans function in the emmeans package in R. Significant differences between the means were assessed based on the overlap of the CIs (Afshartous & Preston, 2010).

Results Efficacy of physical control methods on Poa annua Author Manuscript For sites established for both 16 and 27 months, t-tests indicated no significant difference in P. annua cover in the physical control trials between the start and end of the monitoring period (P ≥ 0.05). Therefore, data was only further investigated for the final time period. At sites established for 16 months, site (4 df, P < 0.002), treatment (4 df, P < 0.001) and the interaction site × treatment (16 df, P = 0.02) were significant (Fig. 2). For

This article is protected by copyright. All rights reserved sites established for 27 months, treatment was not significant (3 df, P = 0.15) but site (3 df, P < 0.001) and the interaction site × treatment (9 df, P = 0.004) was significant (Fig. 3). None of the treatments significantly reduced P. annua cover at any site in comparison with the control treatment. The scalping and hoeing treatment at Lower Boot Hill, hoeing treatment at Mount Power and scalping treatment at Bauer Bay Slope actually increased P. annua cover (Figs. 2, 3). The initial cover of P. annua (based on site differences) did not influence the success of any treatment.

Figs. 2, 3 near here

Efficacy of chemical control methods on Poa annua In the herbicide screening experiment, there was a significant difference in injury rating between the herbicides (11 df, P < 0.001). Of the 11 herbicides tested, six (dithiopyr, ethofumesate, flupropanate, imazamox, methabenzthiazuron and simazine) were not effective on P. annua. Of the five herbicides which were effective on P. annua (amitrole, clethodim, glyphosate, rimsulfuron and trifloxysulfuron sodium, Fig. 4), glyphosate, rimsulfuron and trifloxysulfuron sodium were observed to be more selective of the native grasses in preliminary tests (data not shown). These three herbicides were selected for a further trial, to assess their efficacy and selectivity at different application rates and using different application methods.

Fig. 4 near here

In the herbicide rates experiment, the injury rating of P. annua varied significantly between the different herbicides (2 df, P < 0.001) and rates (4 df, P < 0.001). The interaction term herbicide x rate was not significant (6 df, P = 0.29) (Fig. 5). All rates of glyphosate, and 0.5, 1.0 and 2.0 rates of trifloxysulfuron sodium were effective on P. annua, significantly injuring the shoots of the plant compared with the control treatment (Fig. 5). Rimsulfuron was not effective at any rate. There was no significant difference in the efficacy of each herbicide among different rates (Fig. 5).

Fig. 5 near here

For the application method experiment, there was a significant difference in injury rating between the

herbicides (3 df, P = 0.001)Author Manuscript (Fig. 6). All herbicides were effective on P. annua in comparison with the control. Rate (1 df, P = 0.68), application method (1 df, P = 0.49) and the interaction terms herbicide x rate (2 df, P = 0.86), herbicide x application method (3 df, P = 0.75), rate x application method (1 df, P < 0.80) and herbicide x rate x application method (2 df, P = 0.30) were non-significant, indicating both application methods and all herbicides and rates were equally effective on P. annua.

Fig. 6 near here

Impact of control methods on native species For native species richness, month was significant in both the 16 (2 df, P < 0.001) and 27 (3 df, P = 0.02) month sites of the physical control experiments (Figs. 7, 8), indicating native species richness changed over time. However, there was no significant change in native species richness in the control treatment between the initial measurement (prior to treatment) and the final measurement at any site (Figs. 7, 8). There was also no significant difference in native species richness in treated plots between the initial and final measurement periods, although there may have been differences at other time periods explaining the significance of month. Treatment was significant for the 16 month sites (4 df, P = 0.03) but not the 27 (3 df, P = 0.93) month sites. The interaction term was not significant for either data set (16 df, P = 0.10 and 9 df, P = 0.14 respectively).

Figs. 7, 8 near here

In the herbicide rates experiment, species was significant (3 df, P < 0.001), as was the interaction term herbicide × species (6 df, P = 0.003) (Fig. 5). The interactions of rate × species (12 df, P = 0.48) and herbicide × rate × species (18 df, P = 0.70) were not significant. Glyphosate was selective for A. magellanica and P. foliosa at low rates (0.25 and 0.25 and 0.5 respectively), with no significant difference in injury rating in comparison with the control. The analysis suggests it was selective towards F. contractor at all rates, however this may have been due to the high variation in injury rating within the control treatment. Rimsulfuron did not cause any significant damage to any of the three native grass species at any rate except for 2.0 times the recommended rate. Trifloxysulfuron did not cause any significant damage to any of the native grass species at any rate (Fig. 5).

Discussion We tested a range of methods for the control of P. annua and identified those most effective in the sub- Antarctic. Perhaps unsurprisingly, given the ecology of P. annua, and the use of on-off treatments, physical control exhibited little success in controlling P. annua on Macquarie Island. Herbicides, however, showed potential in selectively controlling P. annua. Physical control methods were ineffective for control of P. annua when applied as one-off treatments, likely due to the continual thick mats of P. annua on Macquarie Island, the presence of a dense seed bank below the treated soil (Williams et al., 2016), plants producing abundant seed adjacent to the trial plots, disturbance stimulating germination, and the ability of damaged plants to recover following disturbance (Walton, 1975; Haussmann et al., 2013). Despite some evidence that trimming and hand Author Manuscript weeding can control P. annua in temperate turf grass (Beard et al., 1978; Itoh et al., 1996), these treatments were ineffective on Macquarie Island, probably because a prolonged effort is required to prevent further seeding and deplete the soil seed bank. Hand weeding of P. annua and removal of the soil and seed bank to a depth of 10 cm is showing potential as an effective control method in the Antarctic Peninsula (Galera et al., 2017). There,

This article is protected by copyright. All rights reserved plants are small and scattered and growing in gravely soils and low density vegetation that would aid removal. Hand weeding may be effective for small, scattered plants growing on gravely or sandy soil on Macquarie Island. However, the most abundant P. annua occurs as thick monocultures on peaty soils, with dense intertwined root systems making it impossible to pull out the plants without leaving the roots behind, which subsequently reshoot. In areas with low P. annua density, physical treatments may be more effective if applied several times to deplete the soil seed bank. However, even several treatments are unlikely to be effective where P. annua grows as dense mats with a significant root system that is difficult to remove. Although none of the physical control methods were effective on P. annua on Macquarie Island, the final amount of P. annua cover did vary with site. This was a reflection of the different P. annua densities at the sites prior to treatment.

The herbicides dithyopyr, ethofumesate, flupropanate, imazamox, methabenzthiazuron and simazine are registered for the control of P. annua in Australia and the USA and give effective control of P. annua in temperate turf grass (Cross et al., 2012: Gaines et al., 2012). These herbicides were not effective at sub- Antarctic temperatures, possibly confounded by the timing of application and differences in the morphology of P. annua collected from the wetter, cooler climate of Macquarie Island (McCullough & Hart, 2006). Amitrole, clethodim, glyphosate, rimsulfuron and trifloxysulfuron sodium all show effective control of P. annua in temperate turf grass (Finlayson & Dastcheib, 2000; Cross et al., 2012) and showed some degree of efficacy at sub-Antarctic temperatures. Glyphosate and trifloxysulfuron sodium had high efficacy on P. annua and were still highly effective at rates lower than the recommended rate.

Physical disturbance treatments had little impact on native species richness in this study, although this may be attributed to the small size of the trial plots. If methods such as scalping or hoeing were employed at a landscape scale, damage to native vegetation may occur directly or indirectly by altering nitrogen and carbon cycling, depleting native seed banks and/or making soil more prone to landslips which are already common on Macquarie Island.

The response of the native grass species to the different herbicide treatments was variable. Rimsulfuron did not unduly damage the shoots of the native grass species, but it was not effective on the target species. Glyphosate caused significant damage to A. magellanica and P. foliosa at high rates, but both glyphosate and trifloxysulfuron sodium show the potential to be selective towards native grass species at low rates. Glyphosate is documented elsewhere to show high efficacy (Finlayson & Dastcheib, 2000; Toler et al., 2007) and selectivity at low rates (Finlayson & Dastcheib, 2000). The greater efficacy of glyphosate and trifloxysulfuron for controlling P. annua than native species on Macquarie Island may be due to morphological and physiological differences between species, such as leaf area and surface characteristics. The soft, thin leaves of P. annua starkly contrast with the narrow, thicker laminae of A. magellanica, inrolled leaves of F. contractor and glaucous laminae of P. foliosa, which may help repel sprayed herbicides.

These results highlight the importance of understanding the efficacy of control methods prior to Author Manuscript implementing a control programme, and particularly the importance of site-specific testing. Methods such as scalping, hoeing and hand weeding have been used successfully in P. annua control programmes in temperate areas. When applied as one-off applications in the sub-Antarctic, they were ineffective. If these had been implemented in a wide scale management programme without prior testing, significant time and resources

This article is protected by copyright. All rights reserved would have been wasted. Further, we now have a better understanding of whether these control methods may negatively impact some of the native plant species found on SOI.

These research findings give us some insight into what control methods may be the most effective and least damaging for the management of P. annua in the SOI. When the species has high cover or numerous populations, one-off physical control methods, or even short-term management initiatives, are likely to be ineffective and undesirable. This is due to the positive response of P. annua to physical disturbance and the perenniality of the species on Macquarie Island (Williams et al., 2018), meaning that existing plants need to be removed and re-establishment of P. annua from the seed bank prevented. An integrated weed management programme incorporating glyphosate application at low rates on high density P. annua infestations to prevent further seed set, combined with targeted physical control of any emerging seedlings for up to four years until the seed bank is depleted (Williams et al., 2016) may be successful. For coastal areas with abundant, thick lawns of P. annua and very low densities of native grass species, given the potential for native grasses to persist following low rates of glyphosate application, such management may be effective at reducing P. annua with minimal damage to the native vegetation. More research is required into the effects of glyphosate on the forbs on Macquarie Island. Removal of dense P. annua populations may require action to regenerate the native vegetation. In medium and low density P. annua infestations, where there is a high cover of native species able to suppress the emergence and establishment of P. annua seedlings, spot-spraying or brushing glyphosate directly onto P. annua (potentially useful in these windy environments), or hand weeding individual plants until the seed bank is depleted, may be more effective.

Throughout the SOI and Antarctica, new populations of non-native species are still being detected, with further incursions likely to occur (Hughes et al., 2015). The management of non-native plants is a priority action for most islands (de Villiers et al., 2006; Shaw, 2013; Hughes et al., 2015, McGeoch et al., 2015). Where new incursions are detected, we advocate rapid response. Where species are widespread and physical removal techniques and herbicides are being applied at larger scales, there should be prior research to determine the efficacy of these techniques and to highlight any environmental impacts caused by the control action. Our research underlines the importance of site-specific assessment of control methods, whilst also understanding the impact of these control methods on the native species prior to widespread management. Undertaking such assessments can inform decision makers and managers in future invasive species control in high conservation protected areas, such as the SOI, where the cost of management actions is high and there is strong public perception of their wilderness and pristine values (de Villiers et al., 2006). Author Manuscript

This work was supported by Australian Antarctic Science Program (AAS 4158), University of New England (Australian Postgraduate Award), Tasmanian Parks and Wildlife (access to Macquarie Island) and Australian Antarctic Division (logistical support). We thank Luis Rodriguez Pertierra for assistance in the field. All authors designed the experiments and field surveys. LK Williams collected and analysed the data and prepared the manuscript. All other authors provided ideas and feedback. BM Sindel and SC Wilson provided assistance in the field. Data have been uploaded to the Australian Antarctic Data Centre: https://data.aad.gov.au/, project 4158.

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List of Figures Fig. 1 Physical control sites on Macquarie Island were located at low altitude with high Poa annua cover (circles), mid altitude with medium P. annua cover (squares) or at high altitude with low P. annua cover (triangles). Sites established for 16 months are shown by grey symbols, sites established for 27 months are shown by black symbols. Fig. 2 Poa annua cover 16 months after treatment at Lower Boot Hill (LBH), Mount Power (MP), the Nuggets (NUG), Sawyer Creek (SC) and Upper Boot Hill (UBH). Error bars represent 95 % confidence intervals. Fig. 3 Poa annua cover 27 months after treatment at Bauer Bay Beach (BBB), Bauer Bay Slope (BBS), Doctor’s Track (DT) and Tractor Rock (TR). Error bars represent 95 % confidence intervals. Fig. 4 Mean injury rating of Poa annua 12 weeks after the application of herbicides, where an injury rating of 1 indicates no effect to the plant and an injury rating of 9 indicates plant death. Error bars represent 95 % confidence intervals.

Fig. 5 Mean injury rating of non-native Poa annua and three native grass species at 0.25, 0.5, 1 and 2 times the recommended application rate, 10 weeks after application, where an injury rating of 1 indicates no effects to the plant and an injury rating of 9 indicates plant death. Error bars represent 95 % confidence intervals. Fig. 6 Mean injury rating of Poa annua plants 10 weeks after the application of herbicides using a brush or spray application method at 0.5 and 1 times the recommended rate, where an injury rating of 1 indicates no effects to the plant and an injury rating of 9 indicates plant death. Error bars represent 95 % confidence intervals. The black symbols differentiate the control treatment from the herbicide treatment. Fig. 7 Mean species richness of treated plots 0, 3 and 16 months after treatment, at Lower Boot Hill (LBH), Mount Power (MP), the Nuggets (NUG), Sawyer Creek (SC) and Upper Boot Hill (UBH). Error bars represent 95 % confidence intervals. Fig. 8 Mean species richness of treated plots 0, 11, 14 and 27 months after treatment, at Bauer Bay Beach (BBB), Bauer Bay Slope (BBS), Doctor’s Track (DT) and Tractor Rock (TR). Error bars represent 95 % confidence intervals.

Table 1 Concentrations of herbicides used in the screening experiment

Active ingredient Product name Active Rate of Additional surfactants ingredient product concentration Author Manuscript Control (water) - - - - amitrole Amitrole T 250 g/L 11 L/ha clethodim Select 240 g/L 0.5 L/ha Bonza at 1 L/100 L dithiopyr Dimension 2EW 240 g/L 3.5 L/ha

This article is protected by copyright. All rights reserved ethofumesate Tramat 500 500 g/L 0.8 L/ha flupropanate Scuffle 745 g/L 3 L/ha Chemwet at 100 ml/ 100 L glyphosate Roundup attack 570 g/L 1.25 L/ha imazamox Raptor WG 700 g/kg 0.045 kg/ha Chemwet at 200 ml/100 L methabenzthiazuron Juggler 700 700 g/kg 3 kg/ha rimsulfuron Coliseum 250 g/kg 0.1 kg/ha Chemwet at 250 ml/ 100 L simazine Simazine 500 900 g/kg 24 kg/ha trifloxysulfuron sodium Envoke 750 g/kg 0.03 kg/ha Chemwet at 0.24 %

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Table 1

Active ingredient Product name Active Rate of Additional surfactants ingredient product concentration Control (water) - - - - Amitrole Amitrole T 250 g/L 11 L/ha Clethodim Select 240 g/L 0.5 L/ha Bonza at 1 L/100 L Dithiopyr Dimension 2EW 240 g/L 3.5 L/ha Ethofumesate Tramat 500 500 g/L 0.8 L/ha Flupropanate Scuffle 745 g/L 3 L/ha Chemwet at 100 ml/ 100 L Glyphosate Roundup attack 570 g/L 1.25 L/ha Imazamox Raptor WG 700 g/kg 0.045 kg/ha Chemwet at 200 ml/100 L Methabenzthiazuron Juggler 700 700 g/kg 3 kg/ha Rimsulfuron Coliseum 250 g/kg 0.1 kg/ha Chemwet at 250 ml/ 100 L Simazine Simazine 500 900 g/kg 24 kg/ha Trifloxysulfuron sodium Envoke 750 g/kg 0.03 kg/ha Chemwet at 0.24 % Author Manuscript