Weed Of National Significance Research Articles

Threatened stick-nest rats preferentially eat invasive boxthorn rather than native vegetation on Australia’s Reevesby Island

Context The incorporation of invasive plants into novel ecosystems often has negative effects, but it can also sometimes enhance ecosystem function. The threatened native rodent species Leporillus conditor (greater stick-nest rat) is extinct on the Australian mainland and now lives primarily on small islands off the coast of southern Australia. Many of these are degraded novel ecosystems invaded by African boxthorn (Lycium ferocissimum), a weed of national significance. However, L. conditor does not appear to be negatively affected by the presence of boxthorn, raising the question of how the two species co-exist. Aims To understand how L. conditor uses African boxthorn, we evaluated dietary composition of L. conditor on parts of Reevesby Island by comparing consumption of invasive boxthorn with that of native vegetation. Methods We identified three key vegetation types on the centre of the island and used point-intercept vegetation surveys to estimate relative availability of plant species in each. We then used micro-histological faecal analysis to estimate the proportions of each species in the diet of L. conditor, and quantified plant species selection by using selection ratios (use/availability). Key results Qualitative evidence of L. conditor activity suggested that it was mostly confined to vegetation with greater abundance of boxthorn than the other vegetation types (13.5%, compared with 5.7% total sampled vegetation). Furthermore, 51.7% of the faecal plant content and 11.8% of total sampled vegetation was African boxthorn, resulting in a selection ration for boxthorn of 4.4. Native species that appeared to be favoured food sources of L. conditor included Olearia axillaris, Myoporum insulare and Enchylaena tomentosa. Conclusions Stick-nest rats of Reevesby Island demonstrate a clear selection for African boxthorn, both in terms of diet (tested quantitatively) and nesting (from previous research and our field observations). Implications The strong selection of stick-nest rats for a declared noxious weed as its main food source and persistence of stick-nest rats on Reevesby Island require consideration with regards to vegetation management on islands where L. conditor occurs. More broadly, it highlights that some elements of novel ecosystems may have unexpected positive impacts on parts of original ecosystems.

Life cycle, host specificity and potential impact of a gall-inducing thrips Acaciothrips ebneri, a biological control agent for prickly acacia (Vachellia nilotica subsp. indica) in Australia

Prickly acacia (Vachellia nilotica subsp. indica (Benth.) Kyal. & Boatwr.; Fabales: Fabaceae) is a Weed of National Significance and a target for biological control in Australia. Currently there are no effective biological control agents for the weed in Australia. Based on genetic and climate matching, a gall thrips (Acaciothrips ebneri Karny; Thysanoptera: Phlaeothripidae) inducing rosette galls resulting in shoot tip dieback, was identified as a prospective biological control agent from Ethiopia. No-choice host-specificity tests were conducted on 59 test plant species in a high security quarantine in Brisbane, Australia. Acaciothrips ebneri is host-specific, inducing galls and reproducing only on prickly acacia. Acaciothrips ebneri, as predicted by the CLIMEX model, is suited to hot and arid western Queensland where major prickly acacia infestations occur. The Australian Government approved A. ebneri for field release in October 2022. This is the first time a true gall-inducing thrips has ever been approved as a weed biological control agent. Field releases commenced in January 2023 and are in progress. There are early signs of field establishment resulting in shoot tip die back in the field, and field release and monitoring will continue.

Fungi associated with seeds of the invasive grass Nassella trichotoma (serrated tussock) in its native range as prospective biological control agents

Context The South American grass Nassella trichotoma (serrated tussock) is widely distributed in central Argentina and one of the most damaging invasive species in Australia, New Zealand, and South Africa. In Australia, it is a weed of national significance. Aims Our aim was to characterise the fungi able to colonise N. trichotoma seeds buried at a site in south-western Buenos Aires province, Argentina, and measure their impact on seed survival and germination. Methods We tested the germination of healthy seeds at the beginning of the experiment (control). We buried 10 mesh bags containing 100 disinfected N. trichotoma seeds each, during 3 months in spring and autumn. At the end of each experiment, the contents of five of the bags were counted and classified as germinated, healthy, damaged, or disintegrated. Germination tests were then conducted with seeds of the latter three categories. The remaining seeds were used for recording fungal signs/symptoms, and the isolation of fungi. Key results We identified and described a diverse group of fungi associated with the seeds and a seasonal variation in the specific composition. Seeds showing fungal signs and/or symptoms germinated less than the control. Conclusions This is the first study on fungi associated with seeds of this species in the native range, which can affect their survival and longevity. Implications It is expected that studies on the seed microbiome may help us understand the differences in behaviour of the plant between ranges, and test the enemy-release hypothesis.

A novel stem-applied herbicide-capsule methodology for control of the invasive cactus Cereus uruguayanus

Cereus uruguayanus R.Kiesling is a naturalised, non-opuntioid cactus that has formed large and dense infestations at several locations in the northern Australian rangelands. Of the Cactoideae subfamily, it typically grows into a large, spiny, single- or multi-stemmed candelabra-shaped cactus. While not classified as a Weed of National Significance (WONS) in Australia, it is causing increasing concern, with some local governments declaring it under their local laws. Recent research has identified several herbicides that control C. uruguayanus by using a range of techniques, including basal-bark, cut-stump, foliar, and stem injection applications. Of these, stem injection is one of the recommended options where weeds grow among desirable vegetation because the risk of non-target damage is minimised. This study evaluated C. uruguayanus control using a range of encapsulated dry-formulation herbicides from BioHerbicides Australia (BHA Pty Ltd), using their novel stem-implantation system (Injecta®). In May 2018, an experiment was established in central Queensland to compare the efficacy of six encapsulated herbicides (aminopyralid + metsulfuron-methyl, clopyralid, glyphosate, hexazinone, metsulfuron-methyl, triclopyr + picloram) against an untreated control. Glyphosate was the fastest-acting herbicide, followed by aminopyralid + metsulfuron-methyl and metsulfuron-methyl, with triclopyr + picloram much slower to act. Nevertheless, all four herbicides eventually caused high mortality (≥85%). In contrast, clopyralid and hexazinone were ineffective at the applied rates. Future research is recommended to compare the cost effectiveness of this system against other techniques, particularly those used for stem-injection applications.

Effects of Climate Change on Weeds and Invasive Alien Plants in Sri Lankan Agro-Ecosystems: Policy and Management Implications

Changes in the climate have worsen the problems caused by weeds and invasive alien plants (IAPs) in agro-ecosystems at global scale resulting from their changes in the range and population densities. Over the past six decades, Sri Lanka has experienced a slow but steady increase in annual environmental temperature by 0.01–0.03°C. Increasing extreme events of rainfall, wetter wet seasons, and drier dry seasons are some of the characteristic features of the changes in the climate observed in Sri Lanka over the years. The Ministry of Environment (MOE) in Sri Lanka has established a National Invasive Species Specialist Group (NISSG) in 2012 and adopted the National Policy on Invasive Alien Species (IAS) in Sri Lanka, Strategies and Action Plan in 2016. Further, the MOE has developed and adopted protocols to assess the risk of IAS at pre- and post-entry level to the country while incorporating climate change concerns. Periodic risk assessments have being carried out to prioritize actions against IAS in Sri Lanka. The Ministry of Agriculture as adopted a National Weed Strategy (NWS) and has identified the Weeds of National Significance (WONS) under different priority crops. A study done in 2014 has clearly shown that weed control costs in agricultural lands in several district of Sri Lanka were nearly doubled during the years that experiencedEl NiñoSouthern Oscillation (ENSO). Further, studies have clearly indicated that IAPs also survive, expand and impact the continuously disturbed environments in agro-ecosystems.Panicum trichocladum, a species listed as a potential invasive based on the risk assessment done in 2016, has shown an increase in its population density and distribution in Sri Lanka during the last 2–3 years. However, weeds and IAPs in agro-ecosystems have drawn less attention of policy makers, scientists, and practitioners in relation to impact of climate change in island ecosystems. This paper focuses on the scientific evidence reported in agro-ecosystems in Sri Lanka on climate-related impacts on agriculturally important weeds and IAPs, and the efforts made to manage their introduction and spread across the country.

Chloroplast genome of silverleaf nightshade (Solanum elaeagnifolium Cav.), a Weed of National Significance in Australia

Solanum elaeagnifolium Cav. is a widely distributed weed and recognized as a Weed of National Significance in Australia. This study sequenced the chloroplast (cp) genome of S. elaeagnifolium, which is 155,049 bp in length, including a large single-copy region at 85, 426 bp, a small single-copy region at 18,419 bp and two inverted repeats at 25,602 bp. A total of 130 genes were annotated. The phylogeny among the S. elaeagnifolium and 42 Solanum chloroplast genomes suggested S. elaeagnifolium is closely related to Solanum species from the section of Melongena.

Genetic diversity and morphological variation in African boxthorn (Lycium ferocissimum) – Characterising the target weed for biological control

Lycium ferocissimum (African boxthorn) is a Weed of National Significance in Australia. Biological control may have potential to manage this weed, but taxonomic uncertainty needs to be addressed first to facilitate searches for potential agents. We sampled putative L. ferocissimum (i.e. tentatively identified morphologically in the field) across its native range in South Africa and introduced range in Australia. Morphometric and genetic analyses were conducted to confirm the species identity of these samples, and to assess morphological and genetic variation across both ranges. All samples collected in Australia were confirmed as L. ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L. ferocissimum across both South Africa and Australia was low, with no evidence of genetic structure. One of the two common chloroplast haplotypes found across Australia was found at only two sites in South Africa, both near Cape Town, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa putatively identified in the field as L. ferocissimum were genetically characterised as different (unidentified) Lycium species. Our morphometric analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L. ferocissimum, and thus morphological identification of the latter species in its native range may remain problematic. To ensure the correct Lycium species is surveyed for candidate biological control agents we suggest that individuals should be permanently tagged and putative morphological determinations supplemented with genetic analyses to confirm species identity.

Long term monitoring of recruitment dynamics determines eradication feasibility for an introduced coastal weed

Bitou bush (Chrysanthemoides monilifera subsp. rotundata) is a Weed of National Significance in Australia and has impacted a significant portion of the eastern coastline. Its discovery in Western Australia was, therefore, a cause for concern. Assessment and control of the isolated and well-defined population began in 2012. To assess the feasibility of eradication in Western Australia as a management outcome for bitou bush, we applied a rigorous data-driven quantification and prediction process to the control program. Between 2012 and 2018 we surveyed over 253 ha of land and removed 1766 bitou bush plants. Approximately 97 person-days were spent over the six years of survey. We measured the seed bank viability for five years starting in 2013, with the 2017 survey results indicating a decline of mean viable seeds/m2from 39.3 ± 11.4 to 5.7 ± 2.2. In 2018 we found only ten plants and no newly recruited seedlings in the population. No spread to other areas has been recorded. Soil core studies indicate that the soil seed bank is unlikely to persist beyond eight years. Eradication of the population in Western Australia, defined as five years without plants being detected, therefore remains a realistic management goal. The information generated from the documentation of this eradication program provides invaluable insight for weed eradication attempts more generally: novel detection methods can be effective in making surveys more efficient, all survey methods are not entirely accurate and large plants can escape detection, bitou bush seeds persist in the soil but become effectively undetectable at low densities, and migration of seed was unquantifiable, possibly compromising delimitation. Continued monitoring of the Western Australian population will determine how much of a risk these factors represent to eradication as the outcome of this management program.

Eco-physiological performance may contribute to differential success of two forms of an invasive vine, Dolichandra unguis-cati, in Australia

Invasive plant species are hypothesized as being more efficient at resource acquisition and use, resulting in faster growth than co-occurring non-invasive plant species. Nonetheless, some findings suggest that trait differences between invasive and non-invasive species are context dependent. In this study, two forms of an invasive vine species,Dolichandraunguis-cati, were used to test the context-dependent hypothesis.Dolichandraunguis-catiis a weed of national significance in Australia with two different forms: the ‘long pod’ (LP) and ‘short pod’ (SP). The two forms have different levels of distribution on the eastern Seaboard of the continent, with the SP form occurring extensively in both States of Queensland and New South Wales while the LP form is found only in isolated sites in South-East Queensland. This study examines whether differences in eco-physiological performance could be responsible for differential success of the two forms. A partially factorial experiment was set up in controlled conditions where potted plants of both forms were grown under two levels of light, water and nutrient resources (high and low) for 15 months. We measured several traits that are known to correlate with plant performance and resource use efficiency (RUE). The SP form exhibited higher values of carbon assimilation, RUE, number of subterranean tubers and leaf nitrogen than the LP form. However, the LP form produced greater biomass than the SP form, with the difference driven mainly by high resource conditions. The LP form displayed significantly higher phenotypic integration (number of traits significantly correlated) than the SP form in response to all treatments while the SP form exhibited higher phenotypic integration than the LP form in response to high resource conditions only. The SP form displayed traits that are well suited for successful colonization, possibly explaining its increased success in Australia, while the LP form possessed traits of opportunistic plants. Overall, we find that the two forms of the weedy vine deploy different carbon economies in response to resource conditions, which is evidence of the context-dependent trait hypothesis.

Salvinia molesta D.S. Mitch.

<i>Salvinia molesta</i> D.S. Mitch.

Complete chloroplast genome of Chilean needle grass, Nassella neesiana (Poaceae: Stipeae)

Nassella neesiana (Chilean needle grass) is a serious weed in Australia, and has been included in the list of Weeds of National Significance (WoNS). We present here, the complete chloroplast sequence of N. neesiana reconstructed from Illumina whole genome sequencing. The complete chloroplast sequence is 137,700 bp in size, and has similar gene content and structure as other published chloroplast genomes of Stipeae. The N. neesiana chloroplast genome is deposited at GenBank under accession number MF480752.

Assessing the invasion threat of non-native plant species in protected areas using Herbarium specimen and ecological survey data. A case study in two rangeland bioregions in Queensland

Naturalised non-native plants that become invasive pose a significant threat to the conservation of biodiversity in protected areas (areas dedicated and managed for long-term conservation of nature), economic productivity of agricultural businesses, and societal impacts including community, culture infrastructure and health. Quantifying the spread, potential dominance and invasion threat of these species is fundamental to effective eradication and development of threat mitigation policy. But this is often hampered by the lack of comprehensive data. This study used existing ecological survey data from 2548 sites and 64 758 Herbarium specimen records to document the status and abundance of non-native plants in two case study bioregions, Cape York Peninsula (CYP) and the Desert Uplands (DEU) in Queensland covering a total area of 186 697 km2. There were 406 non-native species in the CYP, 186 (45.6%) of which are known environmental weeds and 159 non-natives in DEU, of which 69 (43.5%) are environmental weeds. Inside the protected areas, there were 98 species of environmental weeds in CYP, 27 of which are listed as weeds of State significance (Weeds of National Significance (WONS), Queensland declared and non-declared pest plants categories). In DEU, there were 18 environmental weeds inside protected areas and none of them was listed as a weed of State significance. Non-native species that recorded foliage cover dominance in the ecological site data are generally recognised as environmental weeds in Queensland. The threat of weeds from outside of protected areas was serious, with 41 weeds of State significance found in CYP, five of which are WONS, and 25 weeds of State significance found in DEU, 10 of which are WONS.

Avian responses to an emergent, wetland weed

AbstractAfrican boxthorn (Lycium ferocissimum Solanaceae) is a Weed of National Significance in Australia. It is particularly problematic in Victoria and is thought to not only threaten native wildlife but also provide important habitat, particularly to birds, when there is no native alternative. In a wetland ecosystem such as a saltmarsh, boxthorn has the potential to increase structural complexity because it can stand as an emergent above surrounding vegetation. We compared bird assemblages and behaviour in saltmarsh vegetation with and without boxthorn in a coastal wetland in south‐east Australia. Species assemblage, but not richness, changed with the presence of boxthorn. The presence of singing honeyeaters (Lichenostomus virescens) and white‐fronted chats (Epthianura albifrons), the two most common native bird species (based on numerical and spatial dominance), appeared to drive these differences; singing honeyeaters preferred boxthorn while white‐fronted chats avoided it. The presence of boxthorn increased the seasonal availability of fruit and flowers, which was reflected by a high frequency of foraging for fruit and nectar where boxthorn was present. In saltmarshes without boxthorn, there was a higher frequency of foraging for insects. Some, but not all, species responded to increased structural complexity and fruit/floral resources provided by boxthorn. Consequently, management by reducing boxthorn is likely to alter bird communities and the usage of sites by some native species, thus management success should consider fine‐scale biodiversity objectives, such as managing for particular types or species of birds.

A Conceptual Model to Describe the Decline ofRubus anglocandicans(European Blackberry), a Weed of National Significance in Australia

A Conceptual Model to Describe the Decline ofRubus anglocandicans(European Blackberry), a Weed of National Significance in Australia

Identification and Phytotoxicity Assessment of Phenolic Compounds in Chrysanthemoides monilifera subsp. monilifera (Boneseed).

Chrysanthemoides monilifera subsp. monilifera (boneseed), a weed of national significance in Australia, threatens indigenous species and crop production through allelopathy. We aimed to identify phenolic compounds produced by boneseed and to assess their phytotoxicity on native species. Phenolic compounds in water and methanol extracts, and in decomposed litter-mediated soil leachate were identified using HPLC, and phytotoxicity of identified phenolics was assessed (repeatedly) through a standard germination bioassay on native Isotoma axillaris. The impact of boneseed litter on native Xerochrysum bracteatum was evaluated using field soil in a greenhouse. Collectively, we found the highest quantity of phenolic compounds in boneseed litter followed by leaf, root and stem. Quantity varied with extraction media. The rank of phenolics concentration in boneseed was in the order of ferulic acid > phloridzin > catechin > p-coumaric acid and they inhibited germination of I. axillaris with the rank of ferulic acid > catechin > phloridzin > p-coumaric acid. Synergistic effects were more severe compared to individual phenolics. The litter-mediated soil leachate (collected after15 days) exhibited strong phytotoxicity to I. axillaris despite the level of phenolic compounds in the decomposed leachate being decreased significantly compared with their initial level. This suggests the presence of other unidentified allelochemicals that individually or synergistically contributed to the phytotoxicity. Further, the dose response phytotoxic impacts exhibited by the boneseed litter-mediated soil to native X. bracteatum in a more naturalistic greenhouse experiment might ensure the potential allelopathy of other chemical compounds in the boneseed invasion. The reduction of leaf relative water content and chlorophyll level in X. bracteatum suggest possible mechanisms underpinning plant growth inhibition caused by boneseed litter allelopathy. The presence of a substantial quantity of free proline in the target species also suggests that the plant was in a stressed condition due to litter allelopathy. These findings are important for better understanding the invasive potential of boneseed and in devising control strategies.

Invasive Salix fragilis: altered metabolic patterns in Australian streams

Willows (Salix spp.) are listed as a weed of national significance in Australia. Despite this recognition, functional effects of willows on streams compared to native species are largely unknown. Leaves supply carbon to instream food webs, but may also act as surfaces for biofilm, and thus can contribute in different ways to stream metabolism. Salix fragilis L. and Eucalyptus camaldulensis Dehnh. leaves that had been colonised by biofilms were placed into chambers in laboratory conditions, and metabolic rates were measured. Gross Primary Production (GPP) of biofilms on E. camaldulensis leaves after 10 days of incubation were significantly greater than biofilms on S. fragilis leaves. S. fragilis leaves displayed greater rates of microbial decomposition per leaf mass. Autotrophic biomass was one hundred fold greater on E. camaldulensis leaves. The biofilm on E. camaldulensis leaves is likely to support a greater population of grazers, compared to S. fragilis. The alien S. fragilis leaves, therefore, are fuelling a different component of the food web to endemic E. camaldulensis leaves. Endemic Eucalyptus spp. leaves play an important role in temperate Australian streams as a substrate for autotrophic growth and provide a year round pathway for carbon to reach secondary invertebrate consumers.

Optimal dynamic control of invasions: applying a systematic conservation approach.

The social, economic, and environmental impacts of invasive plants are well recognized. However, these variable impacts are rarely accounted for in the spatial prioritization of funding for weed management. We examine how current spatially explicit prioritization methods can be extended to identify optimal budget allocations to both eradication and control measures of invasive species to minimize the costs and likelihood of invasion. Our framework extends recent approaches to systematic prioritization of weed management to account for multiple values that are threatened by weed invasions with a multi-year dynamic prioritization approach. We apply our method to the northern portion of the Daly catchment in the Northern Territory, which has significant conservation values that are threatened by gamba grass (Andropogon gayanus), a highly invasive species recognized by the Australian government as a Weed of National Significance (WONS). We interface Marxan, a widely applied conservation planning tool, with a dynamic biophysical model of gamba grass to optimally allocate funds to eradication and control programs under two budget scenarios comparing maximizing gain (MaxGain) and minimizing loss (MinLoss) optimization approaches. The prioritizations support previous findings that a MinLoss approach is a better strategy when threats are more spatially variable than conservation values. Over a 10-year simulation period, we find that a MinLoss approach reduces future infestations by ~8% compared to MaxGain in the constrained budget scenarios and ~12% in the unlimited budget scenarios. We find that due to the extensive current invasion and rapid rate of spread, allocating the annual budget to control efforts is more efficient than funding eradication efforts when there is a constrained budget. Under a constrained budget, applying the most efficient optimization scenario (control, minloss) reduces spread by ~27% compared to no control. Conversely, if the budget is unlimited it is more efficient to fund eradication efforts and reduces spread by ~65% compared to no control.

A Conceptual Model to Describe the Decline ofRubus anglocandicans(European Blackberry), a Weed of National Significance in Australia

A Conceptual Model to Describe the Decline of<i>Rubus anglocandicans</i>(European Blackberry), a Weed of National Significance in Australia

Karrikins promote germination of physiologically dormant seeds of Chrysanthemoides monilifera ssp. monilifera (boneseed)

SummaryPhysiological dormancy in weed species has significant implications for weed management, as viable seeds may persist in soil seedbanks for many years. The major stimulatory compound in smoke, karrikinolide (KAR1), promotes germination in a range of physiologically dormant weed species allowing targeted eradication methods to be employed. Control of Chrysanthemoides monilifera ssp. monilifera (boneseed), a Weed of National Significance in Australia, may benefit from adopting such an approach. In this study, we hypothesised that seeds of C. monilifera ssp. monilifera exhibit physiological dormancy, germinate more rapidly as dormancy is alleviated, show fluctuations in sensitivity to KAR1 and form a persistent soil seedbank. Seeds responded to 1 μM KAR1 (40–60% germination) even during months (i.e. March, April, July, August) when seeds were observed to be more deeply dormant (control germination: 7–20%). Seeds germinated readily over a range of cooler temperatures (i.e. 10, 15, 20, 20/10 and 25/15°C) and were responsive to KAR2 (~50% germination) as well. Eradication efforts for C. monilifera ssp. monilifera may benefit from use of karrikins to achieve synchronised germination from soil seedbanks, even at times of the year when C. monilifera ssp. monilifera seeds would be less likely to germinate, allowing more rapid depletion of the soil seedbank and targeted control of young plants.

A global review of weeds that can germinate from horse dung

SummaryTo assess the diversity of weed seeds dispersed via horse dung, we reviewed 15 studies on seed germination from horse dung – six from Europe, four from North America, three from Australia and one study each from Africa and Central America. Seed from 249 species from 43 families have been identified germinating from horse dung. Almost two‐thirds of the species were forbs and 33% graminoids, with over half being perennials and 32% annuals. Nearly every species (totalling 99% of those reviewed) is considered a weed somewhere, with 47% recorded as invasive and 19% international environmental weeds. Of the 2739 non‐native plants that are naturalized in Australia, 156 have been shown to germinate from horse dung. This includes 16 of the 429 listed noxious weeds in Australia and two weeds of national significance. Seed from 105 of the 1596 invasive/noxious plant species in North America have also been identified germinating from horse dung. Seed traits including seed size, length, width and mass affect dispersal via horse dung. Habitat disturbance from trampling facilitates germination of seedlings from dung in both natural and experimental studies. Some studies found that plants germinating from dung reach maturity and flower, while others found plants did not survive due to unfavourable growing conditions in the field. The diversity of species with seed that can germinate from horse dung highlights the potential of horses to disperse a range of seed over long distances. Whether such dispersal is beneficial or harmful depends on the plant and the context in which it germinates. To maintain the conservation value of protected areas, it is important to understand and manage the different potential weed dispersal vectors, including horses.