Weed Establishment Research Articles

Influence of strip-tillage and winter cover crops on weeds and yield in organic pepper

Increasing vegetation diversity within crop fields through cover cropping has been advocated as an additional tool for managing weeds. As such, field experiments were conducted over two field seasons to compare the influence of four cover cropping/tillage tactics on weeds, time spent manually removing weeds and marketable yields in organic bell peppers (Capsicum annuum). The four treatments included: (1) conventional till (CT), (2) no-till (NT), (3) strip till after roller-crimping (ST-RC), and (4) strip till with a living mulch between crop rows (ST-LM). Impacts of cover crop on the number of weeds encountered during the study differed according to how cover crops were managed, row region (intra- and inter-row) and weed characteristic (life cycle, type) and was not always consistent. The ST-LM treatment generally had the least amount of weed establishment and ground coverage in the inter-row crop area. The CT treatment contained more weeds than all treatments in intra- and inter-row areas in year 1. Perennial weeds were generally found in greatest biomass in the inter-row area of the NT treatment. Weeding times varied among years and were similar among treatments in season 1. However, in year 2, less time was required for hand weeding in CT than NT and ST-RC. The CT treatment contained the highest marketable fruit yield during year 1. However, in year 2 fruit yields were similar among treatments. Red clover can be used as a living mulch to effectively reduce weed pressure in vegetable crops, however competition between the clover and cash crop must be minimized, and additional intra-row weed management may be necessary.

Current and future glyphosate use in European agriculture

AbstractThere has been a longstanding and contentious debate about the future of glyphosate use in the European Union (EU). In November 2023, the European Commission approved the renewal of the use registration for glyphosate for a further 10 years. Nevertheless, the EU Farm to Fork strategy calls for a 50% reduction in pesticide use by 2030. In November 2022, the European Weed Research Society organised a 2 day workshop to identify critical glyphosate uses in current EU cropping systems and to review the availability of glyphosate alternatives. Workshop participants identified four current, critical uses in EU cropping systems; control and management of perennial weeds, weed control in conservation agriculture, vegetation management in tree and vine crops and herbicide resistance management. There are few herbicide alternatives that provide effective, economic, broad‐spectrum control of weeds, particularly perennial weeds. Mechanical weed control, and in particular, soil cultivation is the most obvious glyphosate alternative. However, this is not possible in conservation agriculture systems and, in general, increased soil cultivation has negative impacts for soil health. Emerging technologies for precision weed control can enable more targeted use of glyphosate, greatly reducing use rates. These technologies also facilitate the use and development of alternative targeted physical weed control (e.g. tillage, lasers, electricity), reducing the energy and environmental costs of these approaches. In tree crops, the use of organic and inorganic mulches can reduce the need for glyphosate use. In general, reduced use of glyphosate will require an even greater focus on integrated weed management to reduce weed establishment in agroecosystems, increase weed management diversity and limit the use of alternative resistance‐prone herbicides.

Boosting species evenness, productivity and weed control in a mixed meadow by promoting arbuscular mycorrhizas.

Lowland meadows represent aboveground and belowground biodiversity reservoirs in intensive agricultural areas, improving water retention and filtration, ensuring forage production, contrasting erosion and contributing to soil fertility and carbon sequestration. Besides such major ecosystem services, the presence of functionally different plant species improves forage quality, nutritional value and productivity, also limiting the establishment of weeds and alien species. Here, we tested the effectiveness of a commercial seed mixture in restoring a lowland mixed meadow in the presence or absence of inoculation with arbuscular mycorrhizal (AM) fungi and biostimulation of symbiosis development with the addition of short chain chito-oligosaccharides (CO). Plant community composition, phenology and productivity were regularly monitored alongside AM colonization in control, inoculated and CO-treated inoculated plots. Our analyses revealed that the CO treatment accelerated symbiosis development significantly increasing root colonization by AM fungi. Moreover, the combination of AM fungal inoculation and CO treatment improved plant species evenness and productivity with more balanced composition in forage species. Altogether, our study presented a successful and scalable strategy for the reintroduction of mixed meadows as valuable sources of forage biomass; demonstrated the positive impact of CO treatment on AM development in an agronomic context, extending previous observations developed under controlled laboratory conditions and leading the way to the application in sustainable agricultural practices.

Ornamental Rhizoma Peanut: Perceptions and Use by Florida Consumers

Ornamental rhizoma peanut (Arachis glabrata Benth.; ORP) is a low-maintenance groundcover for use in urban and residential landscapes. Despite its availability since 2002, consumer insights on ORP have never been assessed. Online surveys are readily accepted by academic researchers as a valuable research tool. An online survey was distributed to 5820 Floridians with the objective to assess the use and perceptions of ORP by consumers. A total of 907 survey responses were received. Most respondents identified themselves as home gardeners (89%), white (93%), female (75%), and over age 65 (60%). Out of several turfgrass alternative benefits, respondents most valued reducing herbicide/pesticide and fertilizer/water usage and preventing weed establishment (χ2 = 204, df = 6, P < 0.001). The ORP selection purchased by respondents was predominately unknown. Most preferred ORP to flower heavily and frequently and maintain a canopy height below 20 cm in the landscape with infrequent mowing. Survey data show there is a potentially large consumer demand for ORP in Florida, but product availability, branding, and consumer access and engagement with information sources require additional focus in the coming years.

Drivers of growth and establishment of the invasive plant Rumex acetosella within Andean fallow systems

Intensification of crop rotations and associated agricultural practices are reducing the capacity of traditional fallows to restore soil fertility and provide forage in Andean cropping systems. While the implementation of improved fallows offers great promise to enhance forage provision and maintain soil productivity, effects of these practices on the establishment of problematic weeds, including non-native plant species, remain poorly understood. To address this knowledge gap, we studied: i) how biotic and abiotic environmental factors influence the establishment and productivity of weeds in traditional fallows; and ii) to what extent improved fallows can help control weedy vegetation in smallholder rotations of the high Andes. Specifically, in this research, we focused on the invasive plant species Rumex acetosella L., which is a common concern of farmers throughout the central Peruvian Andes. We leveraged a multi-site, participatory research trial established in 2017 across eight communities in the region to understand the main drivers of R. acetosella presence and productivity. We used a total of 82 sites, each with paired treatments of traditional fallow (control with natural revegetation) and improved fallow (seeded with Vicia sativa L. and Avena sativa L.). Prior to treatment establishment we measured soil texture, pH, soil organic matter content as well as exchangeable macro-nutrients. Vegetation data was recorded in each treatment and divided into four categories: 1) A. sativa, 2) V. sativa, 3) R. acetosella, and 4) other weeds, and weighed to determine the relative biomass contribution of each. From these data, we calculated an index for R. acetosella pressure, weed pressure, and forage productivity. Our findings indicate that improved fallows greatly suppress weedy vegetation relative to unmanaged controls, including the invasive R. acetosella. Multivariate analyses suggested that R. acetosella abundance was associated with the presence of other non-planted weeds and predictors of soil fertility. The mean R. acetosella index in improved fallows was significantly lower compared to traditional fallows. We found R. acetosella biomass to be greater at lower productivity sites, i.e., those at higher elevations with cooler climates and sites with less fertile soils. Our findings indicate that if the fallow portion of a rotation is kept productive via adequate soil fertility inputs, the biomass of weeds, including the alien R. acetosella, is dramatically reduced.

Discrepancies between the drivers of alpha and beta plant diversity in arable field margins.

Field margins are major habitats for biodiversity conservation and ecosystem functioning in agricultural landscapes, but biotic homogenization of plant communities threatens their ecological and agronomic functions. Our objective is to determine the drivers of plant diversity in field margins for conservation and restoration purposes. To do so, we assessed the effects of field margin structure and long-term management over 20 years (1995-2015) on the taxonomic and functional α- and β-diversity, and the functional composition of herbaceous plant communities. In 2015, we surveyed 302 field margins in bocage landscapes of Brittany, northwestern France. Results were very similar between taxonomic and functional diversity but revealed important discrepancies between the drivers of α- and β-diversity. Deep ditches, mowing and grazing increased α-diversity but did not affect β-diversity. Denser hedgerows had lower α-diversity than other field margins but strongly contributed to β-diversity by harbouring more unique sets of species or life strategies. Long-term herbicide spraying in field margins and cropping intensity in adjacent habitats did not affect α-diversity, but had more complex effects on β-diversity and selected for common weeds. All in all, preservation of dense hedgerows, abandonment of herbicide spraying, and protection against agrochemical drifts are key measures to prevent the establishment of common weeds and biotic homogenization of herbaceous plant communities in field margins. Above all, our study shows how important it is to go beyond α-diversity to make robust conservation and restoration decisions.

The twolined spittlebug (Hemiptera: Cercopidae) invades Hawaiʻi: establishment, biology, and management of a destructive forage grass pest

Abstract The twolined spittlebug, Prosapia bicincta (Say) (Hemiptera: Cercopidae), is a major economic pest of turfgrass, forage grass, and sugarcane. Native to the southeast United States, it impacts rangelands and the landscape trade by damaging pastures, golf courses, urban landscapes, and lawns. This insect pest was reported and confirmed in Hawaiʻi for the first time in 2016, the first species in the family Cercopidae to invade Hawaiʻi. On Hawaiʻi Island, P. bicincta is severely devastating Hawaiʻi’s beef cattle industry. Since its initial detection, P. bicincta has rapidly expanded its range across an estimated 72,183 ha area on Hawaiʻi Island, and it continues to disperse to new locations. In areas of high infestation, this pest has caused 100% dieback of key pasture grasses for livestock forage, including kikuyu (Pennisetum clandestinum Hochst. Ex Chiov) and pangola (Digitaria eriantha Steud) grasses, leading to the establishment of low-quality forage grasses and weeds. Additionally, this pest may affect the Hawaiʻi landscape trade and impact golf courses, urban landscapes, and homeowners. The taxonomy, detection history, range, biology, ecology, economic damage, and management strategies for P. bicincta are discussed.

Climate and pest interactions pose a cross-landscape management challenge to soil and water conservation

Climate change and biological invasions by plant pests (weeds), agriculture and forest insect pests (insects), and microbial pests (plant pathogens) are complex interactive components of global environmental change. The influence of pest distribution and prevalence across landscapes are challenging the conservation and sustainability of natural resources, agricultural production, native biological diversity, and the valuable ecosystem services they provide (Huenneke 1997; Vitousek 1997; Juroszek and von Tiedemann 2013; Ziska and Dukes 2014). Since 2000, numerous scientific studies indicate accelerating climate change is posing substantial risks to natural and managed systems in North America (IPPC 2022). Intensified droughts, large-scale wildfires, and increased demands for limited surface and groundwater water supplies in arid regions are threatening the sustainability of irrigated agriculture and contributing to economic losses (Stewart et al. 2020), while extreme rainfall events are contributing to severe riverine and urban flooding across the United States. Climate change affects crops, rangelands, forests, and natural areas directly through the immediate effects of temperature, precipitation, and atmospheric carbon dioxide (CO₂) levels and thereby impacts production and management systems. These effects are amplified by climate-driven increases in weed, insect, and plant pathogen problems that further complicate related factors such as water, nutrient, and pest management (Walthall et al. 2013). Changing climates also alter physiological, ecological, and evolutionary processes that can support increased establishment, invasiveness, local spread, and geographic range changes of weeds, insects, and plant pathogens (Chidawanyika et al. 2019; Gallego-Tevár et al. 2019; Ziska et al. 2019) that have cascading effects on soil and water quality, and human livelihoods. Thus, a need exists for cross-habitat and landscape/watershed-scale perspectives to improve understanding of mechanisms underlying pest fitness and impacts within and across integrated systems.

Climate Change and Pathways Used by Pests as Challenges to Plant Health in Agriculture and Forestry

Climate change already challenges people’s livelihood globally and it also affects plant health. Rising temperatures facilitate the introduction and establishment of unwanted organisms, including arthropods, pathogens, and weeds (hereafter collectively called pests). For example, a single, unusually warm winter under temperate climatic conditions may be sufficient to assist the establishment of invasive plant pests, which otherwise would not be able to establish. In addition, the increased market globalization and related transport of recent years, coupled with increased temperatures, has led to favorable conditions for pest movement, invasion, and establishment worldwide. Most published studies indicate that, in general, pest risk will increase in agricultural ecosystems under climate-change scenarios, especially in today’s cooler arctic, boreal, temperate, and subtropical regions. This is also mostly true for forestry. Some pests have already expanded their host range or distribution, at least in part due to changes in climate. Examples of these pests, selected according to their relevance in different geographical areas, are summarized here. The main pathways used by them, directly and/or indirectly, are also discussed. Understanding these pathways can support decisions about mitigation and adaptation measures. The review concludes that preventive mitigation and adaptation measures, including biosecurity, are key to reducing the projected increases in pest risk in agriculture, horticulture, and forestry. Therefore, the sustainable management of pests is urgently needed. It requires holistic solutions, including effective phytosanitary regulations, globally coordinated diagnostic and surveillance systems, pest risk modeling and analysis, and preparedness for pro-active management.

How Do Long Term Crop Rotations Influence Weed Populations: Exploring the Impacts of More than 50 Years of Crop Management in Serbia

Crop rotation is known as an eco-friendlier approach, as provides diversification in crop management systems, modifies intensive pressure on the agricultural ecosystem, utilizes various soil horizons, and prevents the establishment of specific pests and weeds. We set out here a study on the farms that have been managed over 50 years of specific continuous crop management programs. The experimental treatments were in a different management system: monoculture of maize, winter wheat, and soybean, 2-year crop rotation (winter wheat–maize) with and without chemical fertilizer, and 3-year crop rotation (winter wheat–soybean–maize) with and without chemical fertilizer and manure. We took soil samples six times from 2014 to 2017 prior to sowing and after harvesting each year. Weed seeds were extracted from soils and identified and counted by species. We, upon the data of a long term experiment of crop rotation, could conclude that crop rotations with more crops in the sequence are significantly effective in maintaining weed populations, a low-input crop production could reach a constant low population below an important damaging density, and therefore will be a more sustainable crop production while chemical fertilizers would change the soil’s chemical and structure and imbalance the plant population diversity and manures with high weed seed infestations have the potential to totally eradicate crop rotation effects, Therefore, clean manures or compost are highly recommended.

Climate effect on Avena fatua field emergence dynamics: A 38‐year experiment in the semiarid Pampean region of Argentina

Climate events modulate weed population dynamics mainly by influencing field seedling emergence patterns. Field experiments aiming to study the influence of climate on the early-stage establishment of weeds are of utmost importance from a practical and strategic decision-making management point of view. The objective of this study was to analyse the effect of climate variations on the field emergence dynamics of Avena fatua in the southwest area of the semiarid Pampean region of Argentina. Field emergence patterns of A. fatua were monitored from 1977 to 2015. Seedling counts were destructively sampled at weekly intervals. Three quadrats (1 m2 each) were randomly distributed on a 5 ha experimental field with a high natural population density of A. fatua in the absence of a crop. Results show that the emergence strategy of this species is highly plastic with a striking variation in response to year-to-year climate signals. Avena fatua field emergence strategies were classified as staggered, early, medium and late based on both chronological and hydrothermal-time parameters. In the short-term, precipitation regimes during both the after-ripening and emergence phases largely explained the resulting emergence strategy. In the long-term, the combined effect of a reduction in both the precipitation frequency and the mean minimum temperature correlated with an increase in the staggered emergence pattern. Results also point out the adaptability of A. fatua in the area under study, further suggesting a bet-hedging fitness strategy that could diminish the risk of population decline under changing climate scenarios. From an agronomic perspective, the occurrence of staggered emergence patterns with an extended emergence window would complicate the definition of the optimal time for weed control. Thus, tailoring decisions based on the Southern Oscillation Index (SOI) episodes (neutral, negative or positive) forecast plus the implementation of weed emergence models could lead to more accurate and sustainable weed management decisions.

Allelopathic Potential of Hemp: Implications for Integrated Weed Management

Evolved resistance to herbicides necessitates alternative weed control strategies. Allelopathic crops show promise as an alternative to exogenous herbicides and could be used to reduce establishment, growth, and reproduction of weeds. Individual cannabinoids and terpenes found in hemp (Cannabis sativa L.) show allelopathic potential, but allelopathic effects of plant residue have not been characterized. A laboratory assay found that crude, acetone-soluble hemp extracts diluted to 2.5 mg mL−1 reduced the germination of a bioindicator species. However, tested concentrations below 2.5 mg mL−1 were not more effective than the no-extract control treatment at reducing germination. A greenhouse study found that soil-incorporated hemp residue was not more effective than a maize (Zea mays L.) residue treatment comparison in reducing plant growth. However, a simulated chaff line experiment in the greenhouse showed that the equivalent of 378 g m−2 hemp residue on the soil surface can effectively reduce and delay the germination of waterhemp [Amaranthus tuberculatus (Moq.) Sauer] in comparison to bare-soil, or a maize residue treatment comparison. Together, these results show that incorporated hemp residue will likely not be an effective weed control practice. However, chaff lining hemp residue may be an effective practice for the control of certain weeds and warrants further research in a field setting.

Impact of Rotational Sequence Selection on Weed Seedbank Composition in Australian Broadacre Crops

The use of competitive crops in successional rotations has been shown to reduce the growth and establishment of annual weeds by the depletion of the weed seedbank in broadacre cropping systems. However, the impact of specific crop rotational sequences contributing to weed seedbank density has not been quantified in the Riverina region of southern Australia. Trials were established in two locations in 2014–2018 to quantify the impact of selected annual rotations featuring grain, pulse, and pasture crops on weed infestation and seedbank dynamics with a focus on winter and summer annual weeds. The weed seedbank dynamics were evaluated by a twice-annual soil sampling regime (at planting and harvest), followed by soil sample screening for weed propagule germination and seedling establishment in a subsequent controlled-environment screening performed from 2014–2020. The weed seedling density decreased in the cereal rotations in years experiencing average to above-average rainfall, as crops established a dense canopy leading to reduced weed establishment and fecundity. Several rotational treatments were effective in suppressing the weed propagule numbers over time, including those using dual-purpose cereals only or a canola break-crop along with the cereals. Rotational selection can be an important and cost-effective tool in integrated weed management systems when applied over multiple growing seasons.

Evaluation of Barley Cultivars for Competitive Traits in Southern New South Wales.

The potential of multi-purpose barley (Hordeum vulgare L.) cultivars to suppress weeds while maintaining optimal yield and grain quality has been reported but not recently evaluated in replicated field trials performed under southern Australian field conditions. Therefore, to investigate this potential, aboveground competitive traits were assessed in nine genetically diverse commercial barley cultivars in 2015, 2016 and 2017, in two locations in the Riverina region of NSW in replicated field trials performed in the absence of pre-emergent herbicide treatment. Crop and weed establishment, early vigour, leaf area index, photosynthetically active radiation (PAR) and biomass were assessed at various crop growth stages, including early growth, vegetative, flowering, grain fill and harvest. Cultivar differences in crop and weed biomass accumulation at ~50, 100 and 150 days after planting were noted at both locations. Early barley biomass accumulation was inversely related to weed biomass in both locations and most years, suggesting strong (over 90%) potential for heritable competitive barley interference against weeds. The current study also observed a positive relationship between PAR light interception and crop biomass in all three years at both locations, suggesting that PAR light interception contributed positively to crop biomass accumulation by directly increasing photosynthesis (50–70%) and growth or indirectly influencing weed biomass accumulation (10–15%) and weed interference (50–75). Partial least squares modelling was performed with 2015 and 2016 datasets to assess the interactions between crop developmental traits and weed suppression. Cultivars exhibiting enhanced early vigour and PAR light interception were generally more weed suppressive under optimal higher soil moisture conditions. Our results indicate that the choice of barley cultivar has a significant impact on weed establishment, fecundity and seedbank dynamics. The use of competitive barley genotypes is, thus, a cost-effective strategy to reduce weed seedbank numbers over time and may reduce potential herbicide use.

Weed Management in Oilseed Crops - A Review

Oilseed crops are slow growing during the initial growth period. In oilseeds, weeds caused yield reduction by 15-60 percent. Hence it is very essential to control weeds during the critical period of crop-weed competition. Weed management options in the majority of oilseed crops are limited, therefore, adoptions of multiple options of weed management using ‘little hammers’ considering preventive, cultural, mechanical, chemical, and biotechnological approaches are important. Integrated weed management (IWM) is a system approach to minimize weed populations below the economic threshold level. Among different weed management practices, cultural practices minimized the crop-weed competition up to large extent. Further, mechanical measures and herbicidal weed management are ‘large hammers’ or single large methods of weed control, but that may lead to the development of another level of problems like shift in weed flora, development of difficult-to-control weeds, issues of herbicide resistance, establishment of perennial weeds, etc. Thus, the aforesaid problems can be overcome by suitably adopting IWM, since it mixes the use of different available weed control methods in a balanced way by managing the weeds effectively, and sustainably provides higher production without harming the environment.

Intercropping red clover with intermediate wheatgrass suppresses weeds without reducing grain yield

AbstractIntermediate wheatgrass (IWG) [Thinopyrum intermedium (Host) Barkworth & Dewey] is the first commercially produced perennial grain crop in the United States. Intercropping legumes with IWG has the potential to enhance dual‐purpose grain and forage production and contribute to weed control in organic management systems. We compared IWG with annual winter wheat (Triticum aestivum L.) in monoculture and intercropped with red clover (Trifolium pratense L.) in a 3‐yr experiment in central New York. Grain yield of IWG was lower than wheat in all years, partly due to lower tiller fertility and seed size in IWG. Compared with grain yield of 1,212 kg ha–1 in the first year, IWG grain yield was 83% (202 kg ha–1) and 64% lower (441 kg ha–1) in the second and third years, respectively. Intermediate wheatgrass straw production increased 40% from 5,541 to 7,785 kg ha–1 over 3 yr while wheat straw yield declined from 5,167 to 3,533 kg ha–1. Red clover did not affect grain or straw yield of either crop but reduced weed biomass and weed species richness. Weed communities in IWG plots were dominated by perennial grasses by the second year of production, whereas annual weeds were dominant in wheat throughout the experiment. Preventing establishment of perennial weeds that will persist in perennial grain cropping systems should be a management priority. High forage production observed when comparing IWG and wheat suggest opportunities for including IWG in integrated crop–livestock systems where IWG's higher forage yield and quality has higher utility.

Intra-specific kin recognition contributes to inter-specific allelopathy: A case study of allelopathic rice interference with paddy weeds.

Species interactions and mechanisms affect plant coexistence and community assembly. Despite increasing knowledge of kin recognition and allelopathy in regulating inter-specific and intra-specific interactions among plants, little is known about whether kin recognition mediates allelopathic interference. We used allelopathic rice cultivars with the ability for kin recognition grown in kin versus non-kin mixtures to determine their impacts on paddy weeds in field trials and a series of controlled experiments. We experimentally tested potential mechanisms of the interaction via altered root behaviour, allelochemical production and resource partitioning in the dominant weed competitor, as well as soil microbial communities. We consistently found that the establishment and growth of paddy weeds were more inhibited by kin mixtures compared to non-kin mixtures. The effect was driven by kin recognition that induced changes in root placement, altered weed carbon and nitrogen partitioning, but was associated with similar soil microbial communities. Importantly, genetic relatedness enhanced the production of intrusive roots towards weeds and reduced the production of rice allelochemicals. These findings suggest that relatedness allows allelopathic plants to discriminate their neighbouring collaborators (kin) or competitors and adjust their growth, competitiveness and chemical defense accordingly.

Spatial patterns of weed dispersal by wintering gulls within and beyond an agricultural landscape

Abstract Non‐frugivorous waterbirds disperse a wide variety of plants by endozoochory, providing longer‐dispersal distances than other mechanisms. Many waterbirds visit both agricultural and natural landscapes during their daily movements, but potential bird‐mediated dispersal of weed plants within and from agricultural landscapes to other habitats is commonly overlooked. Gulls (Laridae) are expanding in numbers and increasingly exploiting anthropogenic habitats worldwide, with possible growing implications for the spread of weeds. Yet, to date, there are no studies on the spatial distribution of weed dispersal by waterbirds. We developed a plant dispersal model based on movements of 19 Larus fuscus using ricefields, via GPS telemetry. We combined daily movements with two curves estimating the retention times of plant seeds in their guts: (a) an experimental curve based on retention time in captivity for four weeds with dry fruits known to be dispersed by gulls: Juncus bufonius, Cyperus difformis, Polypogon monspeliensis and the alien Amaranthus retroflexus; (b) a theoretical curve based on the interspecific scaling relationship between body mass and mean retention time. Median dispersal distances of weed plant seeds by gulls ranged between 690 and 940 m, but maximum distances exceeded 150 km. The theoretical retention time model showed higher median dispersal distances than the experimental retention time model. Spatial patterns of weed deposition were very similar between retention time methods, and most strongly depended on gull movements. Variation between individual gulls had little influence on seed shadows. About 92% of all seeds (>10,000 intact seeds per day) were dispersed within the ricefield area of 370 km2. The remaining 8% of seeds were deposited beyond ricefields into other habitats, 42% of which reached moist environments (other irrigated agriculture, rivers and natural wetlands) presumably suitable for weed establishment. Synthesis. Gulls can disperse weed plants over long distances across a mosaic of habitats. This implies exchange of weed plant species between human‐dominated and natural areas by waterbirds as dispersal vectors. This spatial study highlights the importance of non‐frugivorous birds for long‐distance plant dispersal, which is generally an overlooked mechanism in studies aiming to predict and manage expansion of weed plants.

Allelopathy of Sorghum Residues on Weed Establishment Is Affected by Hybrid, Phenolic Acid Contents and Environment

Sorghum species are well known for allelopathic potential toward weeds and other crops. Sorghum above-ground residues mediate allelopathic activity through production and release of many allelochemicals including phenolic acids. Information is limited on selection of grain sorghum hybrids with high allelopathic potential and assessment of sorghum residue phenolic activity in soil under field conditions. This study was carried out to investigate several grain sorghum hybrids for allelopathic potential for suppressing weed growth in the field in the subsequent growing season; and to investigate the involvement of phenolic substances released into soil on the establishment of weeds. The weed seedbank was affected by environmental conditions that led to different weed densities subjected to suppression by residues in soil. Differential allelopathy was identified among the sorghum hybrids suggesting that improved selection may increase production and release of allelochemicals in new hybrids to control weeds inexpensively, easily, and environmentally friendly. Tillage type (till vs no-till) had variable effects on weed suppression. Soil type, environment, sorghum hybrid traits and cultural practices complicate the use of allelopathy in weed control and benefits gained from this potentially environment friendly weed control practice. Well-planned management will be required to successfully integrate allelopathic crops into sustainable crop production.

Tillage practices affect weeds differently in monoculture vs. crop rotation

Reduced tillage practices are widely considered to be more sustainable than conventional tillage practices, but many producers remain reluctant to reduce tillage due to difficulties controlling weeds. Crop rotation is often put forward as the best means to manage weeds in reduced tillage systems, but uncertainties remain around how different tillage practices and crop rotations interact. Here, we assess the effects of four different tillage practices on weed seedbank density and composition in wheat (Triticum aestivum) monoculture (WWWW), and two different rotations, wheat-medic-wheat-medic (annual medic, Medicago spp.; WMWM), and wheat-canola-wheat-lupin (Brassica napus, Lupinus spp.; WCWL). We use data across a whole four-year rotation period from a long-term experiment replicated at two sites in South Africa’s winter rainfall region. The four tillage practices assessed follow a gradient of soil disturbance: conventional tillage (CT, soil inversion through ploughing), minimum tillage (MT, shallow soil loosening), no tillage (NT, direct drilling with tine openers) and zero tillage (ZT, direct drilling with disc openers). Our results indicate that tillage type had no effect on weeds within the wheat monoculture. Both crop rotations generally had lower weed densities and reduced dominance of grass weeds than the monoculture, but under ZT weed seed bank density in both rotations was similar to that found in monoculture. Thus the use of ZT with crop rotation is antagonistic in this system, possibly due to more limited chemical weed control options than in CT, MT and NT, or due to crop residue cover promoting weed establishment. Subsequently, we recommend that producers in the region seeking to reduce tillage opt for NT rather than ZT, and avoid a wheat monoculture. Weed researchers and agronomists should be wary of other such antagonistic interactions between weed management practices in different systems.