Effects of the herbicide dicamba on nontarget plants and pollinator visitation

Pesticide Exposure and Effects on Non-Apis Bees

Bees are essential pollinators of many crops and wild plants, and pesticide exposure is one of the key environmental stressors affecting their health in anthropogenically modified landscapes. Until recently, almost all information on routes and impacts of pesticide exposure came from honey bees, at least partially because they were the only model species required for environmental risk assessments (ERAs) for insect pollinators. Recently, there has been a surge in research activity focusing on pesticide exposure and effects for non-Apis bees, including other social bees (bumble bees and stingless bees) and solitary bees. These taxa vary substantially from honey bees and one another in several important ecological traits, including spatial and temporal activity patterns, foraging and nesting requirements, and degree of sociality. In this article, we review the current evidence base about pesticide exposure pathways and the consequences of exposure for non-Apis bees. We find that the insights into non-Apis bee pesticide exposure and resulting impacts across biological organizations, landscapes, mixtures, and multiple stressors are still in their infancy. The good news is that there are many promising approaches that could be used to advance our understanding, with priority given to informing exposure pathways, extrapolating effects, and determining how well our current insights (limited to very few species and mostly neonicotinoid insecticides under unrealistic conditions) can be generalized to the diversity of species and lifestyles in the global bee community. We conclude that future research to expand our knowledge would also be beneficial for ERAs and wider policy decisions concerning pollinator conservation and pesticide regulation.

Anaerobic Degradation of Dicamba via a Novel Catabolic Pathway by a Consortium Enriched from Deep Paddy Soil

Dicamba is widely used in the paddy field to control broadleaf weeds. Dicamba easily migrates to deep soil, which is anoxic; however, the anaerobic catabolism of dicamba in paddy soil is still unknown. In this study, an anaerobic dicamba-degrading consortium was enriched from deep paddy soil. The consortium completely degraded 0.83 mM dicamba within 7 days. Five metabolites were identified, one of which is a new metabolite, 2,5-dichlorophenol, and a novel anaerobic dicamba degradation pathway was proposed. 2.5 mM dicamba, 1.5-2.0% NaCl, and 20 mM electron acceptors Na2SO4, NaNO3, and FeCl3, and 0.5 mM or more of metabolites 3-CP and 2,5-DCP strongly inhibited the degradation efficiency. During enrichment, the microbial community of the consortium was significantly changed with OTU numbers, and diversity decreased. The study is valuable to elucidate the catabolism and ecotoxicology studies of dicamba in paddy soil and to facilitate the engineering application of anaerobic technology to treat dicamba-manufacturing wastewater.

The consequences of synthetic auxin herbicide on plant-herbivore interactions

Although herbicide drift is a common side effect of herbicide application in agroecosystems, its effects on the ecology and evolution of natural communities are rarely studied. A recent shift to dicamba, a synthetic auxin herbicide known for 'drifting' to nontarget areas, necessitates the examination of drift effects on the plant-insect interactions that drive eco-evo dynamics in weed communities. We review current knowledge of direct effects of synthetic auxin herbicides on plant-insect interactions, focusing on plant herbivory, and discuss potential indirect effects, which are cascading effects on organisms that interact with herbicide-exposed plants. We end by developing a framework for the study of plant-insect interactions given drift, highlighting potential changes to plant developmental timing, resource quantity, quality, and cues.

Fertilizer and herbicide alter nectar and pollen quality with consequences for pollinator floral choices

Background

Pollinating insects provide economically and ecologically valuable services, but are threatened by a variety of anthropogenic changes. The availability and quality of floral resources may be affected by anthropogenic land use. For example, flower-visiting insects in agroecosystems rely on weeds on field edges for foraging resources, but these weeds are often exposed to agrochemicals that may compromise the quality of their floral resources.

Methods

We conducted complementary field and greenhouse experiments to evaluate the: (1) effect of low concentrations of agrochemical exposure on nectar and pollen quality and (2) relationship between floral resource quality and insect visitation. We applied the same agrochemcial treatments (low concentrations of fertilizer, low concentrations of herbicide, a combination of both, and a control of just water) to seven plant species in the field and greenhouse. We collected data on floral visitation by insects in the field experiment for two field seasons and collected pollen and nectar from focal plants in the greenhouse to avoid interfering with insect visitation in the field.

Results

We found pollen amino acid concentrations were lower in plants exposed to low concentrations of herbicide, and pollen fatty acid concentrations were lower in plants exposed to low concentrations of fertilizer, while nectar amino acids were higher in plants exposed to low concentrations of either fertilizer or herbicide. Exposure to low fertilizer concentrations also increased the quantity of pollen and nectar produced per flower. The responses of plants exposed to the experimental treatments in the greenhouse helped explain insect visitation in the field study. The insect visitation rate correlated with nectar amino acids, pollen amino acids, and pollen fatty acids. An interaction between pollen protein and floral display suggested pollen amino acid concentrations drove insect preference among plant species when floral display sizes were large. We show that floral resource quality is sensitive to agrochemical exposure and that flower-visiting insects are sensitive to variation in floral resource quality.

Triazine Herbicide and NPK Fertilizer Exposure: Accumulation of Heavy Metals and Rare Earth Elements, Effects on Cuticle Melanization, and Immunocompetence in the Model Species Tenebrio molitor

The increasing use of agrochemicals, including fertilizers and herbicides, has led to worrying metal contamination of soils and waters and raises serious questions about the effects of their transfer to different levels of the trophic web. Accumulation and biomagnification of essential (K, Na, Mg, Zn, Ca), nonessential (Sr, Hg, Rb, Ba, Se, Cd, Cr, Pb, As), and rare earth elements (REEs) were investigated in newly emerged adults of Tenebrio molitor exposed to field-admitted concentrations of a metribuzin-based herbicide and an NPK blend fertilizer. Chemical analyses were performed using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) supported by unsupervised pattern recognition techniques. Physiological parameters such as cuticle melanization, cellular (circulating hemocytes), and humoral (phenoloxidase enzyme activity) immune responses and mass loss were tested as exposure markers in both sexes. The results showed that NPK fertilizer application is the main cause of REE accumulation in beetles over time, besides toxic elements (Sr, Hg, Cr, Rb, Ba, Ni, Al, V, U) also present in the herbicide-treated beetles. The biomagnification of Cu and Zn suggested a high potential for food web transfer in agroecosystems. Gender differences in element concentrations suggested that males and females differ in element uptake and excretion. Differences in phenotypic traits show that exposure affects metabolic pathways involving sequestration and detoxification during the transition phase from immature-to-mature beetles, triggering a redistribution of resources between sexual maturation and immune responses. Our findings highlight the importance of setting limits for metals and REEs in herbicides and fertilizers to avoid adverse effects on species that provide ecosystem services and contribute to soil health in agroecosystems.

The effects of glyphosate, pure or in herbicide formulation, on bumble bees and their gut microbial communities

The widespread use of glyphosate-based formulations to eliminate unwanted vegetation has increased concerns regarding their effects on non-target organisms, such as honey bees and their gut microbial communities. These effects have been associated with both glyphosate and co-formulants, but it is still unknown whether they translate to other bee species. In this study, we tested whether glyphosate, pure or in herbicide formulation, can affect the gut microbiota and survival rates of the eastern bumble bee, Bombus impatiens. We performed mark-recapture experiments with bumble bee workers from four different commercial colonies, which were exposed to field relevant concentrations of glyphosate or a glyphosate-based formulation (0.01 mM to 1 mM). After a 5-day period of exposure, we returned the bees to their original colonies, and they were sampled at days 0, 3 and 7 post-exposure to investigate changes in microbial community and microbiota resilience by 16S rRNA amplicon sequencing and quantitative PCR. We found that exposure to glyphosate, pure or in herbicide formulation, reduced the relative abundance of a beneficial bee gut bacterium, Snodgrassella, in bees from two of four colonies when compared to control bees at day 0 post-exposure, but this reduction became non-significant at days 3 and 7 post-exposure, suggesting microbiota resilience. We did not find significant changes in total bacteria between control and exposed bees. Moreover, we observed an overall trend in decreased survival rates in bumble bees exposed to 1 mM herbicide formulation during the 7-day post-exposure period, suggesting a potential negative effect of this formulation on bumble bees.

Particle drift simulation from mesotrione and rimsulfuron plus thifensulfuron-methyl mixture through two nozzle types to field and vegetable crops

Potential for off-target movements follows every herbicide application. Because the launch of acetolactate synthase (ALS)- and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide-tolerant crops will increase the treated area, there is a need to assess the possible negative consequences of any particle drift from those herbicides. Drift happens with every pesticide application, requiring mitigation. Various factors influence drift. Some, such as nozzle type, working pressure, and boom height, can be managed. Others, such as wind, are not easy to manage. In our study, an herbicide tank mixture of mesotrione with rimsulfuron plus thifensulfuron-methyl was sprayed in a low-speed wind tunnel to simulate drift. The airspeed was set at 4.4 m s^-1, representing the labeled upper limit for applications. The herbicide solution was sprayed through XR110015 and TTI110015 nozzles. Eight crops were exposed to herbicide drift treatments and biomass data were collected. Droplet size spectra and tracer depositions were evaluated. Tracer deposition was on average threefold higher in all downwind distances (0.5, 1, 2, 3, 4, 6, 9, and 12 m) from the XR nozzle in comparison to the TTI nozzle. As a consequence, greater biomass reduction was recorded for applications with the XR compared to the TTI nozzle from 1 to 12 m downwind. At 12-m distance, biomass was decreased by 7-78% using XR nozzle while 1-27% using the TTI nozzle. Because drift can injure crops, it is very important to mitigate drift from application of formulations containing mesotrione and rimsulfuron plus thifensulfuron-methyl in combination. This can be done by selecting the appropriate nozzle and ensuring optimal distances between crops.

Impact of volatility reduction agents on dicamba and glyphosate spray solution pH, droplet dynamics, and weed control

BACKGROUND

Regulations in 2021 required the addition of a volatility reduction agent (VRA) to dicamba spray mixtures for postemergence weed control. Understanding the impact of VRAs on weed control, droplet dynamics, and spray pH is essential.

RESULTS

Adding glyphosate to dicamba decreased the solution pH by 0.63 to 1.85 units. Across locations, potassium carbonate increased the tank-mixture pH by 0.85 to 1.65 units while potassium acetate raised the pH by 0.46 to 0.53 units. Glyphosate and dicamba in tank-mixture reduced Palmer amaranth control by 14 percentage points compared to dicamba alone and decreased barnyardgrass control by 12 percentage points compared to glyphosate alone 4 weeks after application (WAA). VRAs resulted in a 5-percentage point reduction in barnyardgrass control 4 WAA. Common ragweed, common lambsquarters, and giant ragweed control were unaffected by herbicide solution 4 WAA. Dicamba alone produced a larger average droplet size and had the fewest driftable fines (% volume < 200 μm). Potassium acetate produced a larger droplet size than potassium carbonate for D_v0.1 and D_v0.5 . The addition of glyphosate to dicamba decreased droplet size from the entire spray droplet spectrum (D_v0.1 , D_v0.5 , D_v0.9 ).

CONCLUSION

A reduction in spray pH, droplet size, and weed control was observed from mixing dicamba and glyphosate. It may be advisable to avoid tank-mixtures of these herbicides and instead, apply them sequentially to maximize effectiveness. VRAs differed in their impacts on spray solution pH and droplet dynamics, but resulted in a minimal negative to no impact on weed control. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Interspecific variation in resistance and tolerance to herbicide drift reveals potential consequences for plant community co-flowering interactions and structure at the agro-eco interface

BACKGROUND AND AIMS

When plant communities are exposed to herbicide 'drift', wherein particles containing the active ingredient travel off-target, interspecific variation in resistance or tolerance may scale up to affect community dynamics. In turn, these alterations could threaten the diversity and stability of agro-ecosystems. We investigated the effects of herbicide drift on the growth and reproduction of 25 wild plant species to make predictions about the consequences of drift exposure on plant-plant interactions and the broader ecological community.

METHODS

We exposed potted plants from species that commonly occur in agricultural areas to a drift-level dose of the widely used herbicide dicamba or a control solution in the glasshouse. We evaluated species-level variation in resistance and tolerance for vegetative and floral traits. We assessed community-level impacts of drift by comparing the species evenness and flowering networks of glasshouse synthetic communities comprised of drift-exposed and control plants.

KEY RESULTS

Species varied significantly in resistance and tolerance to dicamba drift: some were negatively impacted while others showed overcompensatory responses. Species also differed in the way they deployed flowers over time following drift exposure. While drift had negligible effects on community evenness based on vegetative biomass, it caused salient differences in the structure of co-flowering networks within communities. Drift reduced the degree and intensity of flowering overlap among species, altered the composition of groups of species that were more likely to co-flower with each other than with others and shifted species roles (e.g. from dominant to inferior floral producers, and vice versa).

CONCLUSIONS

These results demonstrate that even low levels of herbicide exposure can significantly alter plant growth and reproduction, particularly flowering phenology. If field-grown plants respond similarly, then these changes would probably impact plant-plant competitive dynamics and potentially plant-pollinator interactions occurring within plant communities at the agro-ecological interface.

Biology, Genetic Diversity, and Conservation of Wild Bees in Tree Fruit Orchards

Different species of bees provide essential ecosystem services by pollinating various agricultural crops, including tree fruits. Many fruits and nuts depend on insect pollination, primarily by wild and managed bees. In different geographical regions where orchard crops are grown, fruit growers rely on wild bees in the farmscape and use orchard bees as alternative pollinators. Orchard crops such as apples, pears, plums, apricots, etc., are mass-flowering crops and attract many different bee species during their bloom period. Many bee species found in orchards emerge from overwintering as the fruit trees start flowering in spring, and the active duration of these bees aligns very closely with the blooming time of fruit trees. In addition, most of the bees in orchards are short-range foragers and tend to stay close to the fruit crops. However, the importance of orchard bee communities is not well understood, and many challenges in maintaining their populations remain. This comprehensive review paper summarizes the different types of bees commonly found in tree fruit orchards in the fruit-growing regions of the United States, their bio-ecology, and genetic diversity. Additionally, recommendations for the management of orchard bees, different strategies for protecting them from multiple stressors, and providing suitable on-farm nesting and floral resource habitats for propagation and conservation are discussed.

Monarch Butterfly Ecology, Behavior, and Vulnerabilities in North Central United States Agricultural Landscapes

The North American monarch butterfly (Danaus plexippus) is a candidate species for listing under the Endangered Species Act. Multiple factors are associated with the decline in the eastern population, including the loss of breeding and foraging habitat and pesticide use. Establishing habitat in agricultural landscapes of the North Central region of the United States is critical to increasing reproduction during the summer. We integrated spatially explicit modeling with empirical movement ecology and pesticide toxicology studies to simulate population outcomes for different habitat establishment scenarios. Because of their mobility, we conclude that breeding monarchs in the North Central states should be resilient to pesticide use and habitat fragmentation. Consequently, we predict that adult monarch recruitment can be enhanced even if new habitat is established near pesticide-treated crop fields. Our research has improved the understanding of monarch population dynamics at the landscape scale by examining the interactions among monarch movement ecology, habitat fragmentation, and pesticide use.

Herbicide spray drift from ground and aerial applications: Implications for potential pollinator foraging sources

A field spray drift experiment using florpyrauxifen-benzyl was conducted to measure drift from commercial ground and aerial applications, evaluate soybean [Glycine max (L.) Merr.] impacts, and compare to United States Environmental Protection Agency (US EPA) drift models. Collected field data were consistent with US EPA model predictions. Generally, with both systems applying a Coarse spray in a 13-kph average wind speed, the aerial application had a 5.0- to 8.6-fold increase in drift compared to the ground application, and subsequently, a 1.7- to 3.6-fold increase in downwind soybean injury. Soybean reproductive structures were severely reduced following herbicide exposure, potentially negatively impacting pollinator foraging sources. Approximately a 25% reduction of reproductive structures up to 30.5-m downwind and nearly a 100% reduction at 61-m downwind were observed for ground and aerial applications, respectively. Aerial applications would require three to five swath width adjustments upwind to reduce drift potential similar to ground applications.

Bumblebees can be Exposed to the Herbicide Glyphosate when Foraging

Herbicides are the most widely used pesticides globally. Although used to control weeds, they may also pose a risk to bee health. A key knowledge gap is how bees could be exposed to herbicides in the environment, including whether they may forage on treated plants before they die. We used a choice test to determine if bumblebees would forage on plants treated with glyphosate at two time periods after treatment. We also determined whether glyphosate and its degradation product aminomethylphosphonic acid were present as residues in the pollen collected by the bees while foraging. Finally, we explored if floral resources (nectar and pollen) remained present in plants after herbicide treatment. In general bees indiscriminately foraged on both plants treated with glyphosate and controls, showing no avoidance of treated plants. Although the time spent on individual flowers was slightly lower on glyphosate treated plants, this did not affect the bees' choice overall. We found that floral resources remained present in plants for at least 5 days after lethal treatment with glyphosate and that glyphosate residues were present in pollen for at least 70 h posttreatment. Our results suggest that bees could be exposed to herbicide in the environment, both topically and orally, by foraging on plants in the period between herbicide treatment and death. Identifying this route of exposure is a first step in understanding the risks of herbicides to bees. The effects of herbicides on bees themselves are uncertain and warrant further investigation to allow full risk assessment of these compounds to pollinating insects. Environ Toxicol Chem 2022;41:2603-2612. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Putting pesticides on the map for pollinator research and conservation

Wild and managed pollinators are essential to food production and the function of natural ecosystems; however, their populations are threatened by multiple stressors including pesticide use. Because pollinator species can travel hundreds to thousands of meters to forage, recent research has stressed the importance of evaluating pollinator decline at the landscape scale. However, scientists’ and conservationists’ ability to do this has been limited by a lack of accessible data on pesticide use at relevant spatial scales and in toxicological units meaningful to pollinators. Here, we synthesize information from several large, publicly available datasets on pesticide use patterns, land use, and toxicity to generate novel datasets describing pesticide use by active ingredient (kg, 1997–2017) and aggregate insecticide load (kg and honey bee lethal doses, 1997–2014) for state-crop combinations in the contiguous U.S. Furthermore, by linking pesticide datasets with land-use data, we describe a method to map pesticide indicators at spatial scales relevant to pollinator research and conservation.

Measurement(s)	LD50 • Pesticide • area of cropland • land cover
Technology Type(s)	dose response design • Survey • remote sensing
Factor Type(s)	pesticide active ingredient • contact vs. oral • state • year • crop group
Sample Characteristic - Organism	Apis mellifera
Sample Characteristic - Environment	cropland ecosystem
Sample Characteristic - Location	contiguous United States of America

High Doses of Pesticides Induce mtDNA Damage in Intact Mitochondria of Potato In Vitro and Do Not Impact on mtDNA Integrity of Mitochondria of Shoots and Tubers under In Vivo Exposure

It is well known that pesticides are toxic for mitochondria of animals. The effect of pesticides on plant mitochondria has not been widely studied. The goal of this research is to study the impact of metribuzin and imidacloprid on the amount of damage in the mtDNA of potato (Solanum tuberosum L.) in various conditions. We developed a set of primers to estimate mtDNA damage for the fragments in three chromosomes of potato mitogenome. We showed that both metribuzin and imidacloprid considerably damage mtDNA in vitro. Imidacloprid reduces the rate of seed germination, but does not impact the rate of the growth and number of mtDNA damage in the potato shoots. Field experiments show that pesticide exposure does not induce change in aconitate hydratase activity, and can cause a decrease in the rate of H₂O₂ production. We can assume that the mechanism of pesticide-induced mtDNA damage in vitro is not associated with H₂O₂ production, and pesticides as electrophilic substances directly interact with mtDNA. The effect of pesticides on the integrity of mtDNA in green parts of plants and in crop tubers is insignificant. In general, plant mtDNA is resistant to pesticide exposure in vivo, probably due to the presence of non-coupled respiratory systems in plant mitochondria.

Searching for biomarkers of early detection of 2,4-D effects in a native tree species from the Brazilian Cerrado biome

Biodiversity in the Brazilian Cerrado biome has been declining sharply with the continued expansion of agriculture and the excessive use of herbicides. Thus, the aim of this study was to evaluate the morphophysiological and biochemical responses in Dipteryx alata plants to various doses of the herbicide 2,4-D. Specific biomarkers that characterize the phytoindicator potential of this species were determined. Gas exchange, chlorophyll a fluorescence, photosynthetic pigments, and the activities of antioxidant enzymes and cellulase were performed after 24, 96 and/or 396 hours after 2,4-D application (HAA). The herbicide caused higher antioxidant enzymatic activity 24 HAA and damage to the photosynthetic machinery after 96 HAA. Reduction in gas exchange, chlorophyll content, and photochemical traits were observed. Increased respiratory rates, non-photochemical quenching, and carotenoid concentrations in 2,4-D-treated plants were important mechanisms in the defense against the excess energy absorbed. Furthermore, the absence of leaf symptoms suggested tolerance of D. alata to 2,4-D. Nevertheless, changes in the photosynthetic and biochemical metabolism of D. alata are useful as early indicators of herbicide contamination, especially in the absence of visual symptoms. These results are important for early monitoring of plants in conserved areas and for preventing damage to sensitive species.

Damage and recovery from drift of synthetic-auxin herbicide dicamba depends on concentration and varies among floral, vegetative, and lifetime traits in rapid cycling Brassica rapa

Herbicides can drift from intended plants onto non-target species. It remains unclear how drift impacts plant functional traits that are important for fitness. To address this gap, we conducted an experiment where fast cycling Brassica rapa plants were exposed to one of three drift concentrations (0.5%, 1%, 10%) of synthetic-auxin dicamba. We evaluated damage to and capacity of floral and vegetative traits to recover as well as lifetime fitness by comparing treated plants to controls. Response to dicamba exposure was concentration-dependent across all traits but varied with trait type. At 0.5% dicamba, three out of five floral traits were affected, while at 1% dicamba, four floral traits and one out of two vegetative traits were negatively impacted. At 10% dicamba all floral and vegetative traits were stunted. Overall, floral traits were more responsive to all dicamba drift concentrations than vegetative traits and displayed a wide range of variation ranging from no response (e.g., pistil length) to up to 84% reduction (ovule number). However, despite floral traits were more affected across the dicamba drift concentrations they were also more likely to recover than the vegetative traits. There was also variation among lifetime traits; the onset of flowering was delayed, and reproductive fitness was negatively affected in a concentration-dependent manner, but the final biomass and total flower production were not affected. Altogether, we show substantial variation across plant traits in their response to dicamba and conclude that accounting for this variation is essential to understand the full impact of herbicide drift on plants and the ecological interactions these traits mediate.

The Importance of Forests in Bumble Bee Biology and Conservation

Declines of many bumble bee species have raised concerns because of their importance as pollinators and potential harbingers of declines among other insect taxa. At present, bumble bee conservation is predominantly focused on midsummer flower restoration in open habitats. However, a growing body of evidence suggests that forests may play an important role in bumble bee life history. Compared with open habitats, forests and woody edges provide food resources during phenologically distinct periods, are often preferred nesting and overwintering habitats, and can offer favorable abiotic conditions in a changing climate. Future research efforts are needed in order to anticipate how ongoing changes in forests, such as overbrowsing by deer, plant invasions, and shifting canopy demographics, affect the suitability of these habitats for bumble bees. Forested habitats are increasingly appreciated in the life cycles of many bumble bees, and they deserve greater attention from those who wish to understand bumble bee populations and aid in their conservation.

Effects of glyphosate spray-drift on plant flowering

Recent studies have shown that sub-lethal doses of herbicides may affect plant flowering, however, no study has established a direct relationship between the concentrations of deposited herbicide and plant flowering. Here the aim was to investigate the relationship between herbicide spray drift deposited on non-target plants and plant flowering in a realistic agro-ecosystem setting. The concentrations of the herbicide glyphosate deposited on plants were estimated by measuring the concentration of a dye tracer applied together with the herbicide. The estimated maximal and average deposition of glyphosate within the experimental area corresponded to 30 g glyphosate/ha (2.08% of the label rate of 1440 g a.i./ha) and 2.4 g glyphosate/ha (0.15% label rate), respectively, and the concentrations decreased rapidly with increasing distance from the spraying track. However, there were not a unique relation between distance and deposition, which indicate that heterogeneities of turbulence, wind speed and/or direction can strongly influence the deposition from 1 min to another during spraying. The effects of glyphosate on cumulative flower numbers and flowering time were modelled using Gompertz growth models on four non-target species. Glyphosate had a significantly negative effect on the cumulative number of flowers on Trifolium pratense and Lotus corniculatus, whereas there were no significant effects on Trifolium repens, and a positive, but non-significant, effect on number of flowers on Cichorium intybus. Glyphosate did not affect the flowering time of any of the four species significantly. Lack of floral resources is known to be of major importance for pollinator declines. The implications of the presented results for pesticide risk assessment are discussed.

Effects of Low Doses of Herbicides on Different Endpoints in the Life Cycle of Nontarget Terrestrial Plants

Herbicide drift may cause adverse effects on natural and seminatural plant communities, and it has been debated whether the current ecological risk assessments are adequate to protect nontarget terrestrial plant species. In the present study, 9 nontarget terrestrial plant species with different lifespans (3 annual/6 perennial) belonging to 6 different plant families were exposed to 4 herbicides with different modes of action at the vegetative (6-8 leaf) and reproductive (bud) stages separately. The plant tests were conducted under controlled conditions in 2 greenhouses, 1 located in Denmark and 1 in Canada. For both growth stages, effects were recorded on vegetative (above-ground biomass 3 wk after treatment) and reproductive endpoints (number and germinability of seeds). In most cases, responses following exposure at the juvenile stage were greater than responses following exposure at the reproductive stage. For the combinations of herbicides and plant species included in the present study, we found that the sensitivities of vegetative and reproductive endpoints were equal, or else vegetative endpoints were more sensitive than reproductive endpoints. We also found that annual species were more sensitive than perennial species. The overall conclusions cover many different response patterns, and it is evident that some effects may not be found in the currently used standard tests. Generally, more pronounced effects were obtained in Denmark compared with Canada, highlighting the fact that even under standardized test conditions and following common guidelines, several uncontrollable factors can still induce variable results. Environ Toxicol Chem 2021;40:1389-1404. © 2021 SETAC.

A real-world implementation of a nationwide, long-term monitoring program to assess the impact of agrochemicals and agricultural practices on biodiversity

Biodiversity has undergone a major decline throughout recent decades, particularly in farmland. Agricultural practices are recognized to be an important pressure on farmland biodiversity, and pesticides are suspected to be one of the main causes of this decline in biodiversity. As part of the national plan for reduction of pesticides use (Ecophyto), the French ministry of agriculture launched the 500 ENI (nonintended effects) monitoring program in 2012 in order to assess the unintended effects of agricultural practices, including pesticide use, on biodiversity represented by several taxonomic groups of interest for farmers. This long-term program monitors the biodiversity of nontargeted species (earthworms, plants, coleoptera, and birds), together with a wide range of annual data on agricultural practices (crop rotation, soil tillage, weed control, fertilizers, chemical treatments, etc.). Other parameters (e.g., landscape and climatic characteristics) are also integrated as covariates during the analyses. This monitoring program is expected to improve our understanding of the relative contribution of the different drivers of population and community trends. Here, we present the experience of setting up the 500 ENI network for this ambitious and highly complex monitoring program, as well as the type of data it collects. The issue of data quality control and some first results are discussed. With the aim of being useful to readers who would like to set up similar monitoring schemes, we also address some questions that have arisen following the first five years of the implementation phase of the program.

Defining and validating regenerative farm systems using a composite of ranked agricultural practices

Background: Ongoing efforts attempt to define farms as regenerative to aid marketers, policymakers, farmers, etc. The approach needs to balance precision with function, and must be transparent, simple, scalable, transferable, incorruptible, and replicable. Methods: We developed practice-based scoring systems to distinguish regenerative cropland and rangeland, and validate them based on whether these scores scaled with regenerative goals on actual farm operations. Study systems included cornfields of the Upper Midwest, almond orchards of California, and rangeland systems of the Northern Plains. Response variables included soil carbon and organic matter, soil micronutrients, water infiltration rates, soil microbial communities, plant community structure, invertebrate community structure, pest populations, yields, and profit. Results: Regenerative outcomes were strongly correlated with our approach to farm scoring. Soil organic matter, fine particulate organic matter, total soil carbon, total soil nitrogen, phosphorous, calcium and sulfur all increased alongside regenerative matrix scores in one or both of the cropping systems. Water infiltration rates were significantly faster in more regenerative almond orchards. Soil bacterial biomass and Haney soil health test scores were higher as cropland incorporated more regenerative practices. Plant species diversity and biomass increased significantly with the number of regenerative practices employed on almonds and rangelands. Invertebrate species diversity and richness were positively associated with regenerative practices in corn, almonds, and rangelands, whereas pest populations and almond yields were unaffected by the number of regenerative practices. Corn yields were negatively associated with more regenerative practices, while almond yields were unaffected by the number of regenerative practices. Profit was significantly higher on more regenerative corn and almond operations. Conclusions: Our scoring system scaled positively with desired regenerative outcomes, and provides the basis for predicting ecosystem responses with minimal information about the farming operation. Natural clusters in the number of regenerative practices used can be used to distinguish regenerative and conventional operations.

Better Together? Combining Cover Crop Mulches, Organic Herbicides, and Weed Seed Biological Control in Reduced-Tillage Systems

Organic vegetable farmers rely heavily on labor-intensive tillage for weed management, which adversely affects soil health and harms beneficial insects that consume crop pests and weed seeds. Using cover crop residues as a weed-suppressive mulch enables some reduction in tillage, and combining this tool with recently developed organic herbicides may further enhance weed suppression in vegetable production. However, organic herbicides may also adversely affect beneficial insects, and their nontarget effects are unknown. Here, we examine the combined impacts of cultural and chemical tools on weed cover while monitoring activity of beneficial epigeal insects and measuring rates of weed seed biological control to assess potential nontarget effects of organic herbicides. In a 2-yr experiment, we compared three cover crop mulch treatments and three organic herbicide treatments (capric/caprylic acid, corn gluten meal, and herbicide-free) in a reduced-tillage system. Organic herbicides led to no reductions in beneficial insect activity nor weed seed biocontrol. In both years, capric/caprylic acid herbicide and cover crop mulches reduced weed pressure relative to a fallow control treatment, whereas corn gluten meal had no effect. In year 2, a combination of cover crop mulch with organic herbicide had the greatest weed suppression relative to the fallow control. Integrated weed management is a perpetual challenge, but our results suggest that organic herbicides used in concert with cover crop mulch may enhance weed control and reduce the need for tillage, with limited collateral damage to natural enemies.

Plant protection product residues in plant pollen and nectar: A review of current knowledge

Exposure to Plant Protection Products, PPPs, (fungicides, herbicides and insecticides) is a significant stressor for bees and other pollinators, and has recently been the focus of intensive debate and research. Specifically, exposure through contaminated pollen and nectar is considered pivotal, as it presents the highest risk of PPP exposure across all bee species. However, the actual risk that multiple PPP residues might pose to non-target species is difficult to assess due to the lack of clear evidence of their actual concentrations. To consolidate the existing knowledge of field-realistic residues detected in pollen and nectar directly collected from plants, we performed a systematic literature review of studies over the past 50 years (1968-2018). We found that pollen was the matrix most frequently evaluated and, of the compounds investigated, the majority were detected in pollen samples. Although the overall most studied category of PPPs were the neonicotinoid insecticides, the compounds with the highest median concentrations of residues in pollen were: the broad spectrum carbamate carbofuran (1400 ng/g), the fungicide and nematicide iprodione (524 ng/g), and the organophosphate insecticide dimethoate (500 ng/g). In nectar, the highest median concentration of PPP residues detected were dimethoate (1595 ng/g), chlorothalonil (76 ng/g), and the insecticide phorate (53.5 ng/g). Strong positive correlation was observed between neonicotinoid residues in pollen and nectar of cultivated plant species. The maximum concentrations of several compounds detected in nectar and pollen were estimated to exceed the LD_50s for honey bees, bumble bees and four solitary bee species, by several orders of magnitude. However, there is a paucity of information for the biggest part of the world and there is an urgent need to expand the range of compounds evaluated in PPP studies.

Herbicides as anthropogenic drivers of eco-evo feedbacks in plant communities at the agro-ecological interface

Herbicides act as human-mediated novel selective agents and community disruptors, yet their full effects on eco-evolutionary dynamics in natural communities have only begun to be appreciated. Here, we synthesize how herbicide exposures can result in dramatic phenotypic and compositional shifts within communities at the agro-ecological interface and how these in turn affect species interactions and drive plant (and plant-associates') evolution in ways that can feedback to continue to affect the ecology and ecosystem functions of these assemblages. We advocate a holistic approach to understanding these dynamics that includes plastic changes and plant community transformations and also extends beyond this single trophic level targeted by herbicides to the effects on nontarget plant-associated organisms and their potential to evolve, thereby embracing the complexity of these real-world systems. We make explicit recommendations for future research to achieve this goal and specifically address impacts of ecology on evolution, evolution on ecology and their feedbacks so that we can gain a more predictive view of the fates of herbicide-impacted communities.

Effects of Herbicides on Flowering

Herbicides have been shown to reduce flower production and to delay flowering, with results varying among herbicides and tested plant species. We investigated the effects of herbicides on flowering in an extensive greenhouse study conducted in Canada and Denmark. The effects of low doses of 5 different herbicides (bromoxynil, ioxynil + bromoxynil, metsulfuron-methyl, clopyralid, and glyphosate), simulating realistic drift scenarios (1 and 5% recommended field rates), on plant flowering were examined using 9 wild plant species exposed at either the seedling (6- to 8-leaf) or flower bud stage. Following herbicide exposure, initial flowering date as well as flower production over time were recorded over the growing period. The effect of herbicides on cumulative flower numbers and flowering time were modeled using Gompertz growth models. Significant delays to peak flowering and/or reductions in flower production were observed in at least one plant species for all tested herbicides, with glyphosate often exhibiting the greatest negative effects, that is, plant death. Except for ioxynil + bromoxynil, there was no clear evidence of either the seedling or the flower bud stage being more sensitive. Overall, 58% of all species × life stage × herbicide treatments resulted in either a statistically significant or a strong decline in flower production with herbicide application rates up to 5% of recommended field rates, whereas significant or strong delays in peak flowering were also detected but were slightly less common. Effects at 1% label rates were minimal. Simultaneous delays to peak flowering and reductions in total flower production occurred in approximately 25% of all cases, indicating that herbicide application rates simulating realistic drift scenarios would likely have negative effects on wild floral communities. Environ Toxicol Chem 2020;39:1244-1256. © 2020 SETAC.

Dipteryx alata, a tree native to the Brazilian Cerrado, is sensitive to the herbicide nicosulfuron

The expansion of land use for agricultural interests and the excessive use of herbicides are among the causes of biodiversity losses in the Brazilian Cerrado biome. Therefore, we aimed to test the hypothesis that Dipteryx alata Vogel, a common species in this biome, is sensitive to nicosulfuron because of its high phytotoxicity. We evaluated physiological, biochemical and morphological responses in D. alata plants exposed to increasing doses of the herbicide. Young plants were transplanted to 10 L pots containing substrate composed of soil and sand (2:1) after fertilization. After an acclimation period, the following doses of nicosulfuron were applied: 0 (control), 6, 12, 24, 48, and 60 g a.e. ha^-1. The experiment was conducted in a randomized block design factorial scheme with six doses of nicosulfuron, three evaluation times, and five replicates per treatment. The effects of the herbicide were assessed by measuring gas exchange, chlorophyll a fluorescence, photosynthetic pigments, membrane permeability, antioxidant enzymes and acetolactate synthase. Nicosulfuron altered the photosynthetic machinery and enzymatic metabolism of D. alata. Reductions in physiological traits, increased catalase and ascorbate peroxidase activities, enhanced malondialdehyde concentrations rate of electrolyte leakage and decreased acetolactate synthase activity in response to nicosulfuron all suggest that D. alata is sensitive to this herbicide.

Comparative Assessment of Vegetative and Reproductive Terrestrial Plant Species Endpoints from Exposure to Herbicides and Potential Environmental Implications: A Review

To investigate whether vegetative endpoints are protective of reproductive endpoints in terrestrial plant risk assessments (RAs) for authorization of plant protection products (PPPs), we assessed differences in sensitivity to herbicides between these parameters. Published literature and unpublished proprietary data generated for the registration of PPPs were used to compile a database. If reproductive endpoints were systematically more sensitive than the vegetative endpoints on which regulatory decisions are presently based, a concern could be raised about the protectiveness of the current RA process. Vegetative and reproductive endpoints were assessed considering further potentially relevant parameters. Reproductive endpoints were compared with vegetative endpoints of juvenile plants or with those of mature plants. Direct comparison by substance-species combination proved to be most adequate and was used to calculate quotients by effect level. In addition, we assessed the spread between different effect levels, estimating by which factor the conservatism would increase if effect rate (ER)50 endpoints were replaced by ER25 or ER10 endpoints with otherwise unchanged test parameters. Reproductive endpoints were found to be similarly sensitive as vegetative endpoints derived in nontarget terrestrial plant (NTTP) studies conducted following Organisation for Economic Co-operation and Development (OECD) or US Office of Chemical Safety and Pollution Prevention (OCSPP) guidelines. A switch from vegetative to reproductive endpoints would therefore not significantly change the conservatism (less than a factor of 1.5), whereas the change from ER50 to ER10 would (by a factor of ~5 to 6). However, because ecotoxicological tests on terrestrial plants bear intrinsic high variability that prevents the reliable detection of effects at the 10% effect level, ER10 endpoints are not a reliable basis for RA. No particular family, genus, or species with clusters of distinctly insensitive vegetative and sensitive reproductive endpoints could be identified that would call for regular testing of reproductive endpoints. Also, from the data set available, no specific herbicidal modes of action could be singled out for acting particularly on reproductive endpoints. Integr Environ Assess Manag 2020;16:166-183. © 2019 SETAC.

Effects of Sublethal Doses of Herbicides on the Competitive Interactions Between 2 Nontarget Plants, Centaurea cyanus L. and Silene noctiflora L

Plant competitive interactions influence the effect of herbicides, and the effect of competitive interactions on plant responses may be important to include in the ecological risk assessment of herbicides. In the present study the effect of competitive interactions and sublethal doses of 2 herbicides on plant species was investigated in competition experiments and fitted to empirical competition models. Two nontarget species commonly found in agroecosystems (Centaurea cyanus L. and Silene noctiflora L.) and 2 herbicides (glyphosate and metsulfuron methyl) were used in separate experiments. Plants were sprayed at the 6- to 8-leaf stage. Effects of herbicide treatments and plant density were modeled by generalization of a discrete hyperbolic competition model. The 10% effective dose (ED10) was calculated for C. cyanus. All experiments showed that as density increased, plants were negatively affected. Furthermore, in all cases, C. cyanus remained a better competitor than S. noctiflora. Nevertheless, the density of S. noctiflora (competitor) was an influential element in determining the ED10 of C. cyanus measured at the mature stage. With herbicide exposure, the competitive interactions were further altered; C. cyanus was less affected by glyphosate when S. noctiflora increased to high density. In contrast, at the young stage, conspecific density was important in determining the sensitivity of C. cyanus to metsulfuron methyl, whereas the density of the competitor S. noctiflora had a limited influence. Overall, the results demonstrate the importance of integrating the effect of herbicide and species interactions measured at the reproductive stage into the ecological risk assessments of pesticides. Environ Toxicol Chem 2019;38:2053-2064. © 2019 SETAC.

Multiphase Porous Electrochemical Catalysts Derived from Iron-Based Metal-Organic Framework Compounds

Herbicide use has attracted attention recently due to potential damage to human health and lethality to the honey bees and other pollinators. Fenton reagent treatment processes can be applied for the degradation of herbicidal contaminants from water. However, the need to carry out the normal Fenton reactions under acidic conditions often hinders their practical application for pollution control. Herein, we report on the synthesis and application of multiphasic porous electro-Fenton catalysts prepared from calcinated metal-organic framework compounds, CMOF@PCM, and their application for the mineralization of herbicides in aqueous solution at circum-neutral pH. CMOF nanoparticles (NPs) are anchored on porous carbon monolithic (PCM) substrates, which allow for binder-free application. H₂O₂ is electrochemically generated on the PCM substrate which serves as a cathode, while ·OH is generated by the CMOF NPs at low applied potentials (-0.14 V). Results show that the structure and reactivity of the CMOF@PCM electro-Fenton catalysts are dependent on the specific MOF precursor used during synthesis. For example, CMIL-88-NH₂, which is prepared from MIL-88(Fe)-NH₂, is a porous core-shell structured NP comprised of a cementite (Fe₃C) intermediate layer that is sandwiched between a graphitic shell and a magnetite (Fe₃O₄) core. The electro-Fenton production of hydroxyl radical on the CMOF@PCM composite material is shown to effectively degrade an array of herbicides.

Pesticides and pollinators: A socioecological synthesis

The relationship between pesticides and pollinators, while attracting no shortage of attention from scientists, regulators, and the public, has proven resistant to scientific synthesis and fractious in matters of policy and public opinion. This is in part because the issue has been approached in a compartmentalized and intradisciplinary way, such that evaluations of organismal pesticide effects remain largely disjoint from their upstream drivers and downstream consequences. Here, we present a socioecological framework designed to synthesize the pesticide-pollinator system and inform future scholarship and action. Our framework consists of three interlocking domains-pesticide use, pesticide exposure, and pesticide effects-each consisting of causally linked patterns, processes, and states. We elaborate each of these domains and their linkages, reviewing relevant literature and providing empirical case studies. We then propose guidelines for future pesticide-pollinator scholarship and action agenda aimed at strengthening knowledge in neglected domains and integrating knowledge across domains to provide decision support for stakeholders and policymakers. Specifically, we emphasize (1) stakeholder engagement, (2) mechanistic study of pesticide exposure, (3) understanding the propagation of pesticide effects across levels of organization, and (4) full-cost accounting of the externalities of pesticide use and regulation. Addressing these items will require transdisciplinary collaborations within and beyond the scientific community, including the expertise of farmers, agrochemical developers, and policymakers in an extended peer community.

Bee Viruses: Ecology, Pathogenicity, and Impacts

Bees-including solitary, social, wild, and managed species-are key pollinators of flowering plant species, including nearly three-quarters of global food crops. Their ecological importance, coupled with increased annual losses of managed honey bees and declines in populations of key wild species, has focused attention on the factors that adversely affect bee health, including viral pathogens. Genomic approaches have dramatically expanded understanding of the diversity of viruses that infect bees, the complexity of their transmission routes-including intergenus transmission-and the diversity of strategies bees have evolved to combat virus infections, with RNA-mediated responses playing a prominent role. Moreover, the impacts of viruses on their hosts are exacerbated by the other major stressors bee populations face, including parasites, poor nutrition, and exposure to chemicals. Unraveling the complex relationships between viruses and their bee hosts will lead to improved understanding of viral ecology and management strategies that support better bee health.

Plant reproduction is altered by simulated herbicide drift to constructed plant communities

Herbicide drift may have unintended impacts on native vegetation, adversely affecting individual species and plant communities. To determine the potential ecological effects of herbicide drift, small plant community plots were constructed using 9 perennial species found in different Willamette Valley (OR, USA) grassland habitats. Studies were conducted at 2 Oregon State University (Corvallis, OR, USA) farms in 2 separate years, with single and combined treatments of 0.01 to 0.2× field application rates (f.a.r.) of 1119 g ha-1 for glyphosate (active ingredient [a.i.] of 830 g ha-1 acid glyphosate) and 560 g ha-1 a.i. for dicamba. Plant responses were percentage of cover, number of reproductive structures, mature and immature seed production, and vegetative biomass. Herbicide effects differed with species, year, and, to a lesser extent, farm. Generally, 0.1 to 0.2× f.a.r. of the herbicides were required to affect reproduction in Camassia leichtlinii, Elymus glaucus, Eriophyllum lanatum, Festuca idahoensis, Iris tenax, and Prunella vulgaris. Eriophyllum lanatum also had a significant increase in percentage of immature seed dry weight with 0.01× f.a.r. of dicamba or the combination of glyphosate plus dicamba. Other species showed similar trends, but fewer significant responses. These studies indicated potential effects of low levels of herbicides on reproduction of native plants, and demonstrated a protocol whereby species growing in a constructed plant community can be evaluated for ecological responses. Environ Toxicol Chem 2017;36:2799-2813. Published 2017 SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Root-level exposure reveals multiple physiological toxicity of triazine xenobiotics in Arabidopsis thaliana

Herbicides are pollutants of great concern due to environmental ubiquity resulting from extensive use in modern agriculture and persistence in soil and water. Studies at various spatial scales have also highlighted frequent occurrences of major herbicide breakdown products in the environment. Analysis of plant behavior toward such molecules and their metabolites under conditions of transient or persistent soil pollution is important for toxicity evaluation in the context of environmental risk assessment. In order to understand the mechanisms underlying the action of such environmental contaminants, the model plant Arabidopsis thaliana, which has been shown to be highly responsive to pesticides and other xenobiotics, was confronted with varying levels of the widely-used herbicide atrazine and of two of its metabolites, desethylatrazine and hydroxyatrazine, which are both frequently detected in water streams of agriculturally-intensive areas. After 24h of exposure to varying concentrations covering the range of triazine concentrations detected in the environment, root-level contaminations of atrazine, desethylatrazine and hydroxyatrazine were found to affect early growth and development in various dose-dependent and differential manners. Moreover, these differential effects of atrazine, desethylatrazine and hydroxyatrazine pointed to the involvement of distinct mechanisms directly affecting respiration and root development. The consequences of the identification of additional targets, in addition to the canonical photosystem II target, are discussed in relation with the ecotoxicological assessment of environmental xenobiotic contamination.

Ecological intensification to mitigate impacts of conventional intensive land use on pollinators and pollination

Worldwide, human appropriation of ecosystems is disrupting plant–pollinator communities and pollination function through habitat conversion and landscape homogenisation. Conversion to agriculture is destroying and degrading semi‐natural ecosystems while conventional land‐use intensification (e.g. industrial management of large‐scale monocultures with high chemical inputs) homogenises landscape structure and quality. Together, these anthropogenic processes reduce the connectivity of populations and erode floral and nesting resources to undermine pollinator abundance and diversity, and ultimately pollination services. Ecological intensification of agriculture represents a strategic alternative to ameliorate these drivers of pollinator decline while supporting sustainable food production, by promoting biodiversity beneficial to agricultural production through management practices such as intercropping, crop rotations, farm‐level diversification and reduced agrochemical use. We critically evaluate its potential to address and reverse the land use and management trends currently degrading pollinator communities and potentially causing widespread pollination deficits. We find that many of the practices that constitute ecological intensification can contribute to mitigating the drivers of pollinator decline. Our findings support ecological intensification as a solution to pollinator declines, and we discuss ways to promote it in agricultural policy and practice.

Reducing Freshwater Toxicity while Maintaining Weed Control, Profits, And Productivity: Effects of Increased Crop Rotation Diversity and Reduced Herbicide Usage

Increasing crop rotation diversity while reducing herbicide applications may maintain effective weed control while reducing freshwater toxicity. To test this hypothesis, we applied the model USEtox 2.0 to data from a long-term Iowa field experiment that included three crop rotation systems: a 2-year corn-soybean sequence, a 3-year corn-soybean-oat/red clover sequence, and 4-year corn-soybean-oat/alfalfa-alfalfa sequence. Corn and soybean in each rotation were managed with conventional or low-herbicide regimes. Oat, red clover, and alfalfa were not treated with herbicides. Data from 2008-2015 showed that use of the low-herbicide regime reduced freshwater toxicity loads by 81-96%, and that use of the more diverse rotations reduced toxicity and system dependence on herbicides by 25-51%. Mean weed biomass in corn and soybean was <25 kg ha^-1 in all rotation × herbicide combinations except the low-herbicide 3-year rotation, which contained ∼110 kg ha^-1 of weed biomass. Corn and soybean yields and net returns were as high or higher for the 3- and 4-year rotations managed with the low-herbicide regime as for the conventional-herbicide 2-year rotation. These results indicate that certain forms of cropping system diversification and alternative weed management strategies can maintain yield, profit, and weed suppression while delivering enhanced environmental performance.

Herbicide resistance and biodiversity: agronomic and environmental aspects of genetically modified herbicide-resistant plants

Farmland biodiversity is an important characteristic when assessing sustainability of agricultural practices and is of major international concern. Scientific data indicate that agricultural intensification and pesticide use are among the main drivers of biodiversity loss. The analysed data and experiences do not support statements that herbicide-resistant crops provide consistently better yields than conventional crops or reduce herbicide amounts. They rather show that the adoption of herbicide-resistant crops impacts agronomy, agricultural practice, and weed management and contributes to biodiversity loss in several ways: (i) many studies show that glyphosate-based herbicides, which were commonly regarded as less harmful, are toxic to a range of aquatic organisms and adversely affect the soil and intestinal microflora and plant disease resistance; the increased use of 2,4-D or dicamba, linked to new herbicide-resistant crops, causes special concerns. (ii) The adoption of herbicide-resistant crops has reduced crop rotation and favoured weed management that is solely based on the use of herbicides. (iii) Continuous herbicide resistance cropping and the intensive use of glyphosate over the last 20 years have led to the appearance of at least 34 glyphosate-resistant weed species worldwide. Although recommended for many years, farmers did not counter resistance development in weeds by integrated weed management, but continued to rely on herbicides as sole measure. Despite occurrence of widespread resistance in weeds to other herbicides, industry rather develops transgenic crops with additional herbicide resistance genes. (iv) Agricultural management based on broad-spectrum herbicides as in herbicide-resistant crops further decreases diversity and abundance of wild plants and impacts arthropod fauna and other farmland animals. Taken together, adverse impacts of herbicide-resistant crops on biodiversity, when widely adopted, should be expected and are indeed very hard to avoid. For that reason, and in order to comply with international agreements to protect and enhance biodiversity, agriculture needs to focus on practices that are more environmentally friendly, including an overall reduction in pesticide use. (Pesticides are used for agricultural as well non-agricultural purposes. Most commonly they are used as plant protection products and regarded as a synonym for it and so also in this text.).