Established native hedgerows on field borders suppress weeds on farms

Landscape complexity affects cover and species richness of weeds in Brazilian agricultural environments

Agroecological service crops are introduced into the vegetable crop rotation to provide agroecosystem services, and are a key strategy for weed management in organic systems. Organic farmers across Europe usually terminate these crops before cultivation of the subsequent cash crop, using them as green manure. Recently, the in-line tillage-roller crimper has attracted interest across Europe. It allows flattening the agroecological service crops and creates a narrow furrow that facilitates the fertilization and transplantation of organic vegetables. In Europe, most of the research on this technology has been carried out in Italy, and no studies are available analyzing its effect on weed density, weed species richness, and community composition in different vegetable crops, soils, and climatic conditions across Europe. We compared the effects of the usage of in-line tillage-roller crimper versus green manure on the weed abundance, species richness, and community composition in fourteen original datasets from five countries over 2 years. The support for a common effect of in-line tillage-roller crimper across trials was tested by means of a meta-analytic approach based on a weighted version of Stouffer’s method. Our results indicate that in-line tillage-roller crimper management reduced weed density by 35.1% on average in comparison with green manure, and this trend was significant across trials. Moreover, we document a significant reduction of weed species richness under this technique and significant but, in general, minor changes in the weed community composition across the trials. Therefore, this study provides for the first time a solid evidence of the effectiveness of this management technique to reduce weed density at the early stages of crop growth across a wide range of vegetable systems and production conditions in Europe. Nonetheless, it is important to note that the effect of this technology can be strongly affected by variations in cropping conditions.

Comparing Weed Abundance and Composition in Conventional Tillage vs. Early-Phase Conservation Agriculture Incorporating Winter Cover Crops

Semi-natural habitats (SNHs) in agricultural landscapes represent important refugia for biodiversity including organisms providing ecosystem services. Their spill-over into agricultural fields may lead to the provision of regulating ecosystem services such as biological pest control ultimately affecting agricultural yield. Still, it remains largely unexplored, how different habitat types and their distributions in the surrounding landscape shape this provision of ecosystem services within arable fields. Hence, in this thesis I investigated the effect of SNHs on biodiversity-driven ecosystem services and disservices affecting wheat production with an emphasis on the role and interplay of habitat type, distance to the habitat and landscape complexity. I established transects from the field border into the wheat field, starting either from a field-to-field border, a hedgerow, or a kettle hole, and assessed beneficial and detrimental organisms and their ecosystem functions as well as wheat yield at several in-field distances. Using this study design, I conducted three studies where I aimed to relate the impacts of SNHs at the field and at the landscape scale on ecosystem service providers to crop production. In the first study, I observed yield losses close to SNHs for all transect types. Woody habitats, such as hedgerows, reduced yields stronger than kettle holes, most likely due to shading from the tall vegetation structure. In order to find the biotic drivers of these yield losses close to SNHs, I measured pest infestation by selected wheat pests as potential ecosystem disservices to crop production in the second study. Besides relating their damage rates to wheat yield of experimental plots, I studied the effect of SNHs on these pest rates at the field and at the landscape scale. Only weed cover could be associated to yield losses, having their strongest impact on wheat yield close to the SNH. While fungal seed infection rates did not respond to SNHs, fungal leaf infection and herbivory rates of cereal leaf beetle larvae were positively influenced by kettle holes. The latter even increased at kettle holes with increasing landscape complexity suggesting a release of natural enemies at isolated habitats within the field interior. In the third study, I found that also ecosystem service providers benefit from the presence of kettle holes. The distance to a SNH decreased species richness of ecosystem service providers, whereby the spatial range depended on species mobility, i.e. arable weeds diminished rapidly while carabids were less affected by the distance to a SNH. Contrarily, weed seed predation increased with distance suggesting that a higher food availability at field borders might have diluted the predation on experimental seeds. Intriguingly, responses to landscape complexity were rather mixed: While weed species richness was generally elevated with increasing landscape complexity, carabids followed a hump-shaped curve with highest species numbers and activity-density in simple landscapes. The latter might give a hint that carabids profit from a minimum endowment of SNHs, while a further increase impedes their mobility. Weed seed predation was affected differently by landscape complexity depending on weed species displayed. However, in habitat-rich landscapes seed predation of the different weed species converged to similar rates, emphasising that landscape complexity can stabilize the provision of ecosystem services. Lastly, I could relate a higher weed seed predation to an increase in wheat yield even though seed predation did not diminish weed cover. The exact mechanisms of the provision of weed control to crop production remain to be investigated in future studies. In conclusion, I found habitat-specific responses of ecosystem (dis)service providers and their functions emphasizing the need to evaluate the effect of different habitat types on the provision of ecosystem services not only at the field scale, but also at the landscape scale. My findings confirm that besides identifying species richness of ecosystem (dis)service providers the assessment of their functions is indispensable to relate the actual delivery of ecosystem (dis)services to crop production.

Natural vegetation occurring on farms in field margins, fallow fields, ditch systems and neighboring forests, provides increased biodiversity, structural diversity, habitat for wildlife and beneficial insects, and can act as a protective buffer against agrochemical drift. Nevertheless, farmers frequently view these areas as non-productive and as potential sources of weeds, insect pests and diseases. Weed species richness and abundance were examined in crop fields in 2002–2003 at the Center for Environmental Farming Systems near Goldsboro, NC to determine if crop field weed infestation was associated with field margin management (managed versus unmanaged). Weed species abundance and richness were measured over two growing seasons on four occasions in crop fields along permanent transects that extended from the field edge toward the center of the field. The presence/absence of data for all plant species in the field margin was also recorded. For both margin types, managed and unmanaged, more weeds were found near the field edge than in the center of the field. Weed species richness was slightly higher in cropland bordering managed margins than in cropland along unmanaged margins. Several significant interactions led to an examination of nine dominant weed species in each field margin type and their distribution in crop fields. When all sampling dates were pooled, only 42 (40%) of 105 species identified in the field margins were observed in the crop field. Managed margins had lower species richness than unmanaged field margins—less than half the mean number of species (15 versus 6 species, respectively). Contingency table analysis did not reveal any association between plant species occurring in the margin and those found in the crop field. Furthermore, margin type and weed presence in the field margin were not effective predictors of weed occurrence in the crop field as determined by logistic regression.

Impact of integrated sheep grazing for cover crop termination on weed and ground beetle (Coleoptera:Carabidae) communities

SummaryWeed species diversity may benefit from organic farming due to enhanced temporal diversification of crop species in a rotation and omission of herbicide applications. However, in intensively managed conventional systems, little evidence exists as to what extent diversified crop rotations contribute to higher weed species richness. Using an on‐farm approach, the effect of crop rotation (organic, conventional diverse (CD) and conventional simple (CS) crop rotations) and weed control (with vs. without) on weed species richness, cover, community composition and crop biomass, was analysed in 24 winter wheat fields. Weed species with beneficial functions for invertebrates and birds were analysed separately. Weed species richness was higher in the organic crop rotation, but did not differ between CD and CS crop rotations. Weed control treatment reduced species richness in both conventional rotations, but not in the organic one. Redundancy analyses revealed that crop rotation intensity accounted for the largest part of the explained variation in weed species composition. Results from the study indicate that the maintenance of weed species richness and conservation of species with important ecological functions requires not only temporal diversification of crop species in the rotation, but also an adjustment of weed control strategies.

An investigation of the carabid and plant communities of a conventional and an organic potato crop was carried out in the west of Ireland from June to September 1999. At each site, carabids were sampled using 15 pitfall traps, and 2 × 2 m quadrats were used to assess weed and potato cover. A total of 17 carabid species (672 individuals) were trapped during the study with 11 species common to both sites. 82.4% of individuals were captured at the organic site compared with 17.6% at the conventional site. The reciprocal Berger-Parker diversity index was 3.4 and 2.2 for the organic and conventional sites, respectively. Pterostichus niger and P. melanarius constituted 48.3% of the total catch and were the most abundant of all species captured. However, of the catch at each site, Bembidion bruxellense (44.9%) and P. niger (29.1%) were the most abundant species at the conventional and organic sites, respectively. A total of 13 weed species were identified, 11 of which were found exclusively in the organic field. A positive relationship between weed species richness and carabid species richness was apparent with r (Spearman Rank Correlation Coefficient) = 0.679, p < 0.001). The relationship was stronger between carabid species richness and weed cover (r = 0.704, p < 0.001). Differences between the sites appear to be related to weed cover although other possible factors are discussed.

PMFG Inc, USA

Effect of crop management and climatic factors on weed control in sugarcane intercropping systems

Alley cropping agroforestry is a land use practice in which arable crops are grown between tree rows. In such agroforestry systems, non-crop herbaceous vegetation develops on the tree rows, resulting in understory vegetation strips (UVS). UVS are perceived both as reservoirs for weeds and opportunities for biodiversity conservation. The purpose of this study was to assess the contribution of UVS to (i) plant spillover and (ii) plant diversity conservation, depending on their functional structure and the farming system. Vegetation surveys were carried out in May 2017 in South-Western France over 16 winter cereal fields (8 alley cropping agroforestry systems and 8 pure crop controls), half under conventional farming and half under organic farming. Using data on plant functional traits related to dispersal strategies and response to agricultural disturbances, we explained the mechanisms involved in plant spillover between habitats. The study revealed that very few species were able to disperse far into crop alleys, except perennial species producing rhizomes and stolons whose spread has been favored by tillage. The presence of UVS in agroforestry fields did not increase weed-crop ratio (i.e. weed coverage / weed and crop coverage) in adjacent crop alleys. On the other hand, UVS harbored richer and more abundant floras (with high proportions of species rarely found in arable habitats) compared to crop alleys and pure crop controls, especially under conventional farming. The functional approach provided insights for weed management in alley cropping agroforestry systems in order to optimize plant diversity conservation without increasing weed-crop ratio. This study showed the relevance of using the functional approach to understand the mechanisms behind plant spillover in cropping systems that integrate semi-natural habitats.

Vegetation changes across edges of rainforest remnants

SummaryWeeds have negative impacts on crop production but also play a role in sustaining biodiversity in agricultural landscapes. This trade‐off raises the question of whether it is possible to promote weed communities with low competitive potential but high value to biodiversity. Here, we explored how weed communities respond to different vineyard management practices in South Africa's Western Cape, aiming to identify whether any specific practices are associated with more beneficial weed communities. Eight weed community characteristics representative of abundance, diversity and functional composition were used as indicators of competitive potential and biodiversity value. We explored how these responded to farm management strategy (organic, low input or conventional) and weed management practices (herbicides, tillage, mowing or combinations of these) using ordination and mixed models. Mown sites were associated with weed communities of high biodiversity value, with higher weed cover in both winter and summer, higher diversity and more native weeds. Mowing also promoted shorter weeds than either tillage or herbicides, considered to be less competitive with grapevines. However, high summer weed cover may be problematic where competition for water is critical, in which case tillage offers a method to limit summer weed cover that did not adversely affect diversity or native weeds. In contrast, herbicide‐treated sites had characteristics indicative of a lower biodiversity value and higher potential for competitiveness with few native weeds, lower diversity and relatively tall, small‐seeded weeds. Mowing in winter combined with tillage in spring may thus optimise the biodiversity benefits and production costs of Western Cape vineyard weeds.

Impact of managing cover crop residues on the floristic composition and species diversity of the weed community of pepper crop (Capsicum annuum L.)

The IR-4 program works to identify potential minor-use horticultural chemicals and evaluate them for phytotoxicity and efficacy. The objective of this experiment was to evaluate phytotoxicity and weed control of three unlabeled herbicides on field production of Hemerocallis spp. `Ming Toy'. Ten-cm pots of `Ming Toy' were planted into the field 16 July 2001. Each plot consisted of 3 plants per treatment with 6 replications in a completely random design. Each herbicide was analyzed as a separate experiment. Herbicide treatments consisted of clopyralid (0.14, 0.28, 0.56, or 1.1 kg·ha-1 a.i.), clethodim (125, 250, or 500 mL·L-1 a.i.), or bentazon (1.1, 2.2, or 4.4 kg·ha-1 a.i.). Data collected included weed number, percentage of weed coverage (% weed coverage), and phytotoxicity and foliar color ratings for `Ming Toy'. Clopyralid reduced total weed number 90 DAT although % weed coverage was similar or worse compared to the control treatment. Phytotoxicity 90 DAT was not significant for plants treated with clopyralid, but foliar color ratings were reduced. Application of clethodim to `Ming Toy' plots, regardless of rate, resulted in similar weed numbers compared to the control 49 DAT. Clethodim application, regardless of rate, reduced % weed coverage compared to the control treatment. Phytotoxicity 90 DAT was not significant, regardless of herbicide treatment, but foliar color ratings were lower for herbicide treated plants compared to the control. Bentazon, regardless of rate, reduced weed number and % weed coverage 49 DAT compared to the control. Phytotoxicity was similar to the control for plants treated with 1.1 kg·ha-1 a.i.