Pasture Weeds Research Articles

Tolerance of plantain (Plantago lanceolata) to translocated herbicides wiped on flower stems

ABSTRACT Growing plantain (Plantago lanceolata) within pastures reduces nitrate leaching following grazing. Plantain is usually grown with grass and clover species, making selective weed control challenging. One strategy to selectively remove tall weeds in pastures with mixed species is to apply herbicides using weed wipers. However, for many months of the year, plantain has upright leafless flower stems that will intercept herbicide applied using wipers. To determine if this means plantain might be damaged by wipers used in such swards, two glasshouse experiments tested the tolerance of mature plantain plants to the application of herbicides suitable for use in weed wipers (glyphosate, clopyralid, aminopyralid, dicamba, metsulfuron, picloram and triclopyr) to the flower stems. Aminopyralid (0.075% ai solution) and a low rate of glyphosate (1.8% ai) caused the least decrease in plantain biomass and should be safe for weed wiping within swards containing plantain. A higher rate of glyphosate (7.2% ai) and a glyphosate/metsulfuron mix (0.9% + 0.01% ai, respectively) caused the most damage to plantain, particularly following simulated rainfall after application. Thus, applying some herbicides using wipers should be possible for selective weed control within plantain swards even if rain falls soon afterwards, though field trials are required to fine-tune recommendations.

Composting Dairy Manure with Biochar: Compost Characteristics, Aminopyralid Residual Concentrations, and Phytotoxicity Effects

Aminopyralid (2-pyridine carboxylic acid, 4-amino-3, 6-dichloro-2-pyridine carboxylic acid) is an auxin herbicide that has been used widely to control broadleaf weeds in pasture and hay fields. With no post-application withdrawal time, aminopyralid absorbed into forage material can contaminate compost feed stocks such as hay, grass bedding material, and manure. Composts derived from such feed stocks raises concerns about after-effect injuries to sensitive crops by residual aminopyralids. Biochar (BC) additive may affect the composting process and immobilizes organic pollutants. This study examined the effect of composting dairy manure/sawdust 1:1 mixture containing 10 ppb (wet) of aminopyralid with 0%, 2%, 4%, and 10% (w/w) BC levels on chemical and biological characteristics of compost, residual aminopyralid concentration, and intensity of plant injury to tomato (Lycopersicon esculentum L.) plants after composting in 140 L plastic rotary drum reactors for two 6-month cycles. Biochar addition decreased organic matter degradation and intensified reduction in residual aminopyralid levels in a dose-dependent manner. Composting with BC concentrated more N, P, and K, caused mild plant injuries, and increased the above ground biomass compared to the no BC incorporation. Addition of BC for composting aminopyralid-contaminated dairy manure can increase the phyto safety level of compost while enhancing the key fertilizer values.

Genetic matching and the identification of a promising biocontrol agent validates a decision to survey natural enemies of Urena lobata in Malaysia

Urena lobata is a major introduced pasture weed in Vanuatu where a biocontrol program to mitigate its impacts commenced in 2018. There was considerable uncertainty regarding the native range of U. lobata, although published literature, coupled with very simple climate matching suggested that Southeast Asia should be the most promising region in which to survey for natural enemies. We, therefore, conducted surveys for candidate biocontrol agents in Malaysia and conducted genetic matching to compare plants growing in Vanuatu, Malaysia, and other regions in the invaded and purportedly native range of U. lobata. Surveys in Malaysia prioritized a tingid bug Haedus vicarius as a promising candidate agent for the biocontrol of U. lobata and subsequent host specificity testing confirmed it is sufficiently host specific to be released in Vanuatu. Genetic matching indicated that plants growing in Malaysia are a good match to plants present in Vanuatu, validating our selection of survey sites.

Embryotoxicity Induced by Triclopyr in Zebrafish (Danio rerio) Early Life Stage.

Triclopyr, an auxin-like herbicide that is widely employed for managing weeds in food crops and pastures, has been identified in various environmental settings, particularly aquatic ecosystems. Limited understanding of the environmental fate of this herbicide, its potential repercussions for both the environment and human health, and its insufficient monitoring in diverse environmental compartments has caused it to be recognized as an emerging contaminant of concern. In this study, we have investigated how triclopyr affects zebrafish, considering a new alternative methodology. We focused on the endpoints of developmental toxicity, neurotoxicity, and behavior of zebrafish embryos and larvae. We determined that triclopyr has a 96 h median lethal concentration of 87.46 mg/L (341.01 µM). When we exposed zebrafish embryos to sublethal triclopyr concentrations (0.5, 1, 5, 10, and 50 μM) for up to 144 h, we found that 50 µM triclopyr delayed zebrafish egg hatchability. Yolk sac malabsorption was significant at 0.5, 1, 5, and 10 µM triclopyr. In zebrafish larvae, uninflated swim bladder was significant only at 50 µM triclopyr. Furthermore, zebrafish larvae had altered swimming activity after exposure to 10 µM triclopyr for 144 h. In summary, these comprehensive results indicate that even low triclopyr concentrations can elicit adverse effects during early zebrafish development.

Competition reduces structural defense in an invasive thistle in the field

AbstractInvasive thistles reduce the productivity of pastures and rangelands because their structural defenses make them unpalatable to grazing livestock. However, plants potentially alter their growth patterns, including their allocation of resources to defense, in response to the presence of competing vegetation. Understanding the effects of competition on the structural defense of problematic pasture weeds can inform management plans that reduce the economic harm caused by these pests. We grew musk thistle (Carduus nutans L., also commonly called nodding thistle) in a fully crossed factorial field experiment in a single abandoned pasture in 2017 with two experimental factors: the level of thistle infestation (1 thistle or 5, resulting in densities of 4 or 20 plants m−2) and the presence or absence of grazing (simulated by weekly trimming of competing vegetation). We assessed the effects of treatments on defense by counting prickles >3-mm long on leaves. Our analysis included leaf age and leaf size as covariates. Competition reduced the number of prickles present on leaves. Regression analysis showed that an increase from, for example, 50 g to 200 g of competing vegetation within 50 by 50 cm study plots reduced the expected average number of prickles on intermediate-aged leaves with average length 25.5 cm by 76.9 prickles per leaf, or 41%. This pattern was similar for leaves of all ages, although the oldest leaves generally had fewer prickles than younger leaves. We did not observe differences in defense structures between plants neighbored by conspecifics and those neighbored by other competitors. Carduus nutans has been previously managed using high densities of grazers, and this practice may be more likely to damage less-defended individuals such as those we observed in our treatments with competition. This finding suggests that maintaining competition in pastures may increase C. nutans vulnerability to grazing.

Health and Environmental Hazards of the Toxic Pteridium aquilinum (L.) Kuhn (Bracken Fern).

Bracken fern (Pteridium aquilinum (L.) Kuhn) is ubiquitous and acts as a cosmopolitan weed in pastures and similar environments. Despite its historical uses, it presents risks due to toxicity. This study, conducted in the second half of 2023, aimed to assess the environmental and health hazards of P. aquilinum, primarily focusing on its carcinogenic compound, ptaquiloside. The literature was comprehensively reviewed using diverse databases, including PubMed, Web of Science, Scopus, and Google Scholar. Information was synthesized from original research articles, meta-analyses, systematic reviews, and relevant animal studies. Animals grazing on bracken fern face annual production losses due to toxin exposure. The substantial impact on biodiversity, animal health, and human well-being arises from the presence of ptaquiloside and related compounds in milk, meat, and water, along with the increasing global prevalence of P. aquilinum and its swift colonization in acidic soil and fire-damaged areas. The objectives were to identify major bioactive compounds and explore their effects at molecular, cellular, pathological, and population levels. Various cooking techniques were considered to mitigate toxin exposure, although complete elimination remains unattainable. Therefore, the findings emphasize the need for cautious consumption. In conclusion, continued research is necessary to better understand and manage its environmental and health implications.

Predicting the field host-range of Leptinotarsa undecimlineata: A candidate biocontrol agent for Solanum torvum in Vanuatu

The host specificity of Leptinotarsa undecimlineata Stål, a candidate biocontrol agent for Solanum torvum Sw. (turkey berry) a woody pasture weed in Vanuatu was investigated. In no-choice tests, adult L. undecimlineata beetles fed and oviposited on eggplant (Solanum melongena L.) plants, which also supported development of first instar L. undecimlineata larvae through to adult. A systematic review of field host records indicated that L. undecimlineata has never been reported to attack S. melongena throughout most of its native range in Mexico, the Antilles and Colombia, although minor and infrequent spillover attack has been observed in Central America. Choice oviposition, ‘multiple generation’ (continuation) tests, and the relative performance risk score approach (updated to use Firth’s bias reduced logistic regressions) were used to investigate the potential risk posed to S. melongena should L. undecimlineata be released in Vanuatu. The relative risk score approach was inconclusive, indicating a low but not zero risk of S. melongena being a persistent field host for both choice and no-choice tests. In contrast, the multiple generation tests demonstrated that L. undecimlineata cannot persist on S. melongena. Adult feeding was lower and significantly fewer eggs were laid on S. melongena compared to S. torvum in no-choice adult feeding and oviposition tests. The combination of tests used provided an explanation why only minor and infrequent spillover attack on S. melongena has been reported in parts of the native range of L. undecimlineata. We conclude that L. undecimlineata poses a very low risk to S. melongena should it be introduced into Vanuatu. However, the relative performance risk score approach requires further analyses using larger datasets to investigate the potential for threshold scores to be used to reliably predict risk.

Monitoring the Effect of Weed Encroachment on Cattle Behavior in Grazing Systems Using GPS Tracking Collars

Weed encroachment on grasslands can negatively affect herbage allowance and animal behavior, impacting livestock production. We used low-cost GPS collars fitted to twenty-four Angus crossbred steers to evaluate the effects of different levels of weed encroachment on animal activities and spatial distribution. The experiment was established with a randomized complete block design, with three treatments and four blocks. The treatments were paddocks free of weeds (weed-free), paddocks with weeds established in alternated strips (weed-strips), and paddocks with weeds spread throughout the entire area (weed-infested). Animals in weed-infested paddocks had reduced resting time and increased grazing time, distance traveled, and rate of travel (p < 0.05) compared to animals in weed-free paddocks. The spatial distribution of the animals was consistently greater in weed-free paddocks than in weed-strips or weed-infested areas. The effects of weed encroachment on animal activities were minimized after weed senescence at the end of the growing season. Pasture weed encroachment affected cattle behavior and their spatial distribution across the pasture, potentially impacting animal welfare. Further long-term studies are encouraged to evaluate the impacts of weed encroachment on animal performance and to quantify the effects of behavioral changes on animal energy balance.

Use of plant viruses as bioherbicides: The first virus-based bioherbicide and future opportunities.

Until recently, only a few plant viruses had been studied for use as biological control agents for weeds, but none was developed into a registered bioherbicide. This position changed in 2015 when the U.S. Environmental Protection Agency (EPA) granted an unrestricted Section 3 registration for tobacco mild green mosaic virus (TMGMV) strain U2 as an herbicide active ingredient (a.i.) for a commercial bioherbicide (SolviNix LC). It is approved for the control of tropical soda apple (TSA, Solanum viarum), an invasive 'noxious weed' in the United States. TSA is a problematic weed in cattle pastures and natural areas in Florida. The TMGMV-U2 product kills TSA consistently, completely, and within a few weeks after its application. It is part of the TSA integrated best management practice (BMP) in Florida along with approved chemical herbicides and a classical biocontrol agent, Gratiana boliviana (Coleoptera: Chrysomelidae). TMGMV is nonpathogenic and nontoxic to humans, animals, and other fauna, environmentally safe, and as effective as chemical herbicides. Unlike the insect biocontrol agent, TMGMV kills and eliminates the weed from fields and helps recycle the dead biomass in the soil. Here the discovery, proof of concept, mode of action, risk analyses, application methods and tools, field testing, and development of the virus as the commercial product are reviewed. Also reviewed here are the data and scientific justifications advanced to answer the concerns raised about the use of the virus as a herbicide. The prospects for discovery and development of other plant-virus-based bioherbicides are discussed. This article is protected by copyright. All rights reserved.

Phytosociological Survey of Weeds on Degraded and Well-Managed Pastures: Agronomical and Ecological Implications

The objective of this research was to carry out a survey of weeds in pastures in the Middle Valley of Paraíba do Sul, Rio de Janeiro State, Brazil, in order to subsidize weed management and pasture recovery. Weed identification and plant count were carried out in pastures with four levels of degradation, classified as low (N1), moderate (N2), strong (N3) and very strong (N4), with five replications. Thirty-nine weed species were identified and distributed into16 botanical families. Poaceae, Asteraceae and Fabaceae were the most relevant families. The number and density of weeds increased as the level of degradation decreased. The relative importance of weed species varied with the level of degraded pasture. The main weeds found in N1 were Melinis minutiflora, Desmodium incanum, Croton lundianus, Andropogon bicornis, and Imperata brasiliensis; in N2: Paspalum notatum, Melinis minutiflora, Imperata brasiliensis, Sida rhombifolia, and Desmodium incanum; in N3: Paspalum notatum, Melinis minutiflora, Sida rhombifolia, Eupatorium maximilianii, and Imperata brasiliensis; in N4: Paspalum notatum, Melinis minutiflora, Cynodon dactilon, Eupatorium maximilianii, and Imperata brasiliensis. The similarity index was high, showing the homogeneity of weeds among areas. The predominant species, considering all areas, were in increasing order of importance: Cynodon dactilon, Melinis minutiflora and Paspalum notatum. Decision-making about applying control measures could be marked out when the plant density reached out or exceed the average of 3.58 plants m-2.

Impacts of Aminopyralid on Tomato Seedlings

Effective aminopyralid herbicides are commonly used to control broadleaf weeds in cereals or pastures, but their residues in straw or manure may damage cultivated crops and reduce the yield. In our experiments, the response of tomato plants to aminopyralid at doses of 0.6, 1.5, 3, 7.5, and 15 g/ha was evaluated, and extracts from straw treated with the herbicide Mustang Forte were tested. As the concentration of aminopyralid increased, seed germination was delayed by 1 to 3 days, compared to the control, and all the germinating seeds were deformed already at the lowest concentration of 0.6 g/ha. With the increased concentration of aminopyralid, injury to tomato plants also increased, and at the highest applied dose of 15 g/ha, 93.75% of the tomato plants were damaged. The critical level of concentration of aminopyralid in the soil was determined between 3 and 7.5 g/ha. Treatment with aminopyralid influences plant height in the indeterminate cultivar from an aminopyralid concentration of 3 g/ha and in the determinate cultivar from a concentration of 7.5 g/ha, but not as significantly. Thus, this experiment suggests that in the indeterminate cultivar, aminopyralid has a greater effect on height than in the determinate cultivar. This varietal sensitivity should be subjected to further study.

Rural AI: Serverless-Powered Federated Learning for Remote Applications

With increasing connectivity to support digital services in urban areas, there is a realization that demand for offering similar capability in rural communities is still limited. To unlock the potential of artificial intelligence (AI) within rural economies, we propose rural AI—the mobilization of serverless computing to enable AI in austere environments. Inspired by problems observed in New Zealand, we analyze major challenges in agrarian communities and define their requirements. We demonstrate a proof-of-concept rural AI system for cross-field pasture weed detection that illustrates the capabilities serverless computing offers to traditional federated learning.

Californian thistle (Cirsium arvense): endophytes and Puccinia punctiformis.

Californian thistle (Cirisum arvense) is a troublesome weed in pastures and cropping systems. The fungal biocontrol agent Puccinia punctiformis, commonly referred to as thistle rust, performs inconsistently on C.arvense. Problems with P.punctiformis establishment and control of C.arvense may be attributable to differing plant endophytic populations in various environments. This article provides an overview of the relationships between endophytes and their host, but also between endophytes and pathogens with a focus on rust pathogens. This review provides insights into reasons why P. punctiformis performs inconsistently and identifies gaps in our knowledge. Filling these gaps may help to improve performance of this classical fungal biocontrol agent. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Morphoanatomical characterization to differentiate two biotypes of Paspalum virgatum

The species Paspalum virgatum L. is considered to be a pasture weed that causes great damage to livestock. There are two empirically identified biotypes that differ in leaf blade width. Thus, the objective of this work was to differentiate two biotypes of P. virgatum based on the main aspects of leaf morphology and anatomy. Morphological characterization used the leaves of the third node of each biotype with five replications for both of them. For anatomical characterization, the median part of the leaf of the third node was collected. The evaluations consisted in the main leaf morphoanatomical parameters. The biotypes differ in leaf area, leaf blade width, sheath length and diameter, and inflorescence and canopy height. The “narrow” leaf biotype showed lower stomatal density on both sides of the blade. Therefore, leaf blade width is valid as the basis for empirical observation of the difference between biotypes.

Solanum carolinense L.

<i>Solanum carolinense</i> L.

Simulating the population dynamics of barley grass (Hordeum spp.) and impacts of weed management strategies in a southern Australian lucerne (Medicago sativa) pasture

Context Barley grass (Hordeum spp. L.) is an annual, invasive grass weed of southern Australian crops and pastures, frequently associated with weight loss and carcass damage in sheep due to its sharp seeds. Knowledge gaps exist regarding optimal density thresholds for effective control to reduce impacts on animal production. The value of integrated weed management (IWM) over individual control options for reducing barley grass populations in pasture is also unknown. Aims We aimed to develop a model for simulating the population dynamics of barley grass within lucerne (Medicago sativa L.) pastures of southern Australia and to test the hypothesis that combining herbicides with mowing will be more effective for removing barley grass seedbanks over time than individual control measures. Methods The model was developed within Microsoft Excel and adapted from other annual grass models. The model takes a Monte Carlo approach to simulate control impacts on weed seedbanks over 10 years using five weed-control density thresholds. It was parameterised using data from recent experiments and available literature. Key results The most effective long-term control strategy for barley grass occurred with a density threshold of 5 seedlings m−2 by combining early and late herbicide applications, and by combining early and late herbicides with mowing, reducing the seedbank by 86% and 89%, respectively. Conclusions Simulation results showed that IWM programs were more effective than individual control options in reducing the barley grass seedbanks over 10 years, particularly at low weed densities (≤50 seedlings m−2). Implications Incorporation of this model into a bioeconomic grazing systems model will be valuable for determining the economic impacts and optimal weed-control strategies for minimising the effects of barley grass seed contamination in lamb production systems.

Effect of Rhizome Fragment Length and Burial Depth on the Emergence of a Tropical Invasive Weed Cyperus aromaticus (Navua Sedge)

Cyperus aromaticus (Navua sedge) is a problematic perennial weed in pastures and crops including sugarcane, banana, rice, and fruits and vegetables in tropical climates. It reproduces both via rhizomes and seeds. As a regenerative and storage organ, these rhizomes play an important part in the invasion, establishment, and persistence of this weed. To eliminate their regenerative ability, it is important to understand the regrowth potential with respect to rhizome fragment size and burial depth. This study evaluated the emergence of C. aromaticus from rhizomes in a controlled condition. Three different sizes of rhizome fragments were buried at seven depths of up to 20 cm in two soil types. The experimental measurements included (i) the time for tillers to emerge, (ii) the cumulative emergence of tillers, recorded weekly, and (iii) the number of underground emerging tillers. The cumulative shoot emergence and the number of underground tillers produced were found to be positively correlated with the initial length of the rhizome fragments and negatively correlated with the burial depth. The time for the emergence of the tillers was negatively correlated with the burial depth, and soil type had no significant effect on any of the parameters recorded. There was no emergence recorded from rhizomes buried at 15 cm depth and deeper, irrespective of their size. Our results indicate that the combination of the fragmentation of rhizomes into small pieces and a deep burial, below 15 cm, is an important aspect to control the regeneration of C. aromaticus from rhizomes, if tillage is carried out, and can therefore form a part of an integrated weed management strategy for this troublesome weed.

Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

AbstractNavua sedge (Cyperus aromaticus), a perennial monocot plant native to tropical Africa, is a major weed in pasture and cropping areas in the wet tropical regions of Australia and South Pacific countries. In grazing pasture lands, rapid growth and reproduction of unpalatable Navua sedge leads to displacement of co‐occurring pasture species and depletion of livestock carrying capacity and production. Understanding the interspecific competitive ability of Navua sedge with co‐occurring desirable grasses and in response to varying ecological scenarios (e.g., grazing and plant density) is critical for the management of the weed in pasture situations. In a glasshouse setting, two co‐occurring pasture species—humidicola (Urochloa humidicola) and Rhodes grass (Chloris gayana) were grown with Navua sedge, in pots using a replacement series model. For each Navua sedge weed–pasture species pair, the experimental setup comprised of four ratios in two densities under simulated grazing and nongrazing conditions of the pasture grasses. Navua sedge growth and reproduction was highest when it grew as a monoculture or when co‐occurring pastures were exposed to simulated grazing as this action, reduced the competitiveness of the pasture grasses. Overall and using biomass gained, tiller production and relative yield as indices of growth dynamics, Rhodes grass was more competitive against Navua sedge than humidicola in both grazed and nongrazed conditions especially under high plant density. These results suggest the potential to include competitive pastures in integrated management strategies for Navua sedge, but species selection and grazing practices may influence the effectiveness of this approach.

Wiper Application of Herbicides to Cirsium arvense

Wiper applicators allow herbicides to be selectively delivered to upright target weeds, thereby avoiding application to nearby lower-growing desirable pasture plants. In this research, we investigated the efficacy of wiper application of four herbicides, clopyralid, metsulfuron, glyphosate and a triclopyr/picloram mixture, to control Cirsium arvense (L.) Scop., a troublesome weed of pastures in New Zealand. The results showed that wiper application of herbicides was a useful technique for controlling C. arvense. In one trial when plants were treated at the post-flowering stage, stem density reductions in the following season of 93%, 90% and 82% were achieved following a double pass with a rotary weed wiper containing glyphosate, clopyralid and metsulfuron, respectively. A double pass gave better control of dense infestations of C. arvense than a single pass for glyphosate and triclopyr/picloram, but not for clopyralid and metsulfuron. Despite wiper applicators usually being selective, some damage to pastures was recorded, very likely due to rain falling soon after wiper application. Overall, the results of this study revealed that wiper application can be used to selectively control C. arvense when the plants are treated at the post-flowering stage, though only if plants are actively growing. In addition, among the herbicides tested, glyphosate appears to be the best choice when using weed wipers to manage C. arvense, as this herbicide caused the least damage to pasture plants if washed off afterwards by rain.

The diversity of microfungi associated with grasses in the Sporobolus indicus complex in Queensland, Australia.

There are five closely related Sporobolus species, collectively known as weedy Sporobolus grasses (WSG) or the rat's tail grasses. They are fast growing, highly competitive, unpalatable weeds of pastures, roadsides and woodlands. An effective biological control agent would be a welcomed alternative to successive herbicide application and manual removal methods. This study describes the initial exploratory phase of isolating and identifying native Australian microfungi associated with WSG, prior to evaluating their efficacy as inundative biological control agents. Accurate species-level identification of plant-pathogenic microfungi associated with WSG is an essential first step in the evaluation and prioritisation of pathogenicity bioassays. Starting with more than 79 unique fungal morphotypes isolated from diseased Sporobolus grasses in Queensland, Australia, we employed multi-locus phylogenetic analyses to classify these isolates into 54 fungal taxa. These taxa belong to 22 Ascomycete families (12 orders), of which the majority fall within the Pleosporales (>24 taxa in 7 families). In the next phase of the study, the putative species identities of these taxa will allow us to prioritise those which are likely to be pathogenic based on existing literature and their known ecological roles. This study represents the first step in a systematic, high-throughput approach to finding potential plant pathogenic biological control agents.