Per Kudsk

A review of independent action compared to concentration addition as reference models for mixtures of compounds with different molecular target sites

From a theoretical point of view, it has often been argued that the model of independent action (IA) is the most correct reference model to use for predicting the joint effect of mixtures of chemicals with different molecular target sites. The theory of IA, however, relies on a number of assumptions that are rarely fulfilled in practice. It has even been argued that, theoretically, the concentration addition (CA) model could be just as correct. In the present study, we tested the accuracy of both IA and CA in describing binary dose-response surfaces of chemicals with different molecular targets using statistical software. We compared the two models to determine which best describes data for 158 data sets. The data sets represented 98 different mixtures of, primarily, pesticides and pharmaceuticals tested on one or several of seven test systems containing one of the following: Vibrio fischeri, activated sludge microorganisms, Daphnia magna, Pseudokirchneriella subcapitata, Lemna minor, Tripleurospermum inodorum, or Stellaria media. The analyses showed that approximately 20% of the mixtures were adequately predicted only by IA, 10% were adequately predicted only by CA, and both models could predict the outcome of another 20% of the experiment. Half of the experiments could not be correctly described with either of the two models. When quantifying the maximal difference between modeled synergy or antagonism and the reference model predictions at a 50% effect concentration, neither of the models proved significantly better than the other. Thus, neither model can be selected over the other on the basis of accuracy alone.

The Occurrence of Hormesis in Plants and Algae

This paper evaluated the frequency, magnitude and dose/concentration range of hormesis in four species: The aquatic plant Lemna minor, the micro-alga Pseudokirchneriella subcapitata and the two terrestrial plants Tripleurospermum inodorum and Stellaria media exposed to nine herbicides and one fungicide and binary mixtures thereof. In total 687 dose-response curves were included in the database. The study showed that both the frequency and the magnitude of the hormetic response depended on the endpoint being measured. Dry weight at harvest showed a higher frequency and a larger hormetic response compared to relative growth rates. Evaluating hormesis for relative growth rates for all species showed that 25% to 76% of the curves for each species had treatments above 105% of the control. Fitting the data with a dose-response model including a parameter for hormesis showed that the average growth increase ranged from 9±1% to 16±16% of the control growth rate, while if measured on a dry weight basis the response increase was 38±13% and 43±23% for the two terrestrial species. Hormesis was found in >70% of the curves with the herbicides glyphosate and metsulfuron-methyl, and in >50% of the curves for acifluorfen and terbuthylazine. The concentration ranges of the hormetic part of the dose-response curves corresponded well with literature values.

Eight principles of integrated pest management

The use of pesticides made it possible to increase yields, simplify cropping systems, and forego more complicated crop protection strategies. Over-reliance on chemical control, however, is associated with contamination of ecosystems and undesirable health effects. The future of crop production is now also threatened by emergence of pest resistance and declining availability of active substances. There is therefore a need to design cropping systems less dependent on synthetic pesticides. Consequently, the European Union requires the application of eight principles (P) of Integrated Pest Management that fit within sustainable farm management. Here, we propose to farmers, advisors, and researchers a dynamic and flexible approach that accounts for the diversity of farming situations and the complexities of agroecosystems and that can improve the resilience of cropping systems and our capacity to adapt crop protection to local realities. For each principle (P), we suggest that (P1) the design of inherently robust cropping systems using a combination of agronomic levers is key to prevention. (P2) Local availability of monitoring, warning, and forecasting systems is a reality to contend with. (P3) The decision-making process can integrate cropping system factors to develop longer-term strategies. (P4) The combination of non-chemical methods that may be individually less efficient than pesticides can generate valuable synergies. (P5) Development of new biological agents and products and the use of existing databases offer options for the selection of products minimizing impact on health, the environment, and biological regulation of pests. (P6) Reduced pesticide use can be effectively combined with other tactics. (P7) Addressing the root causes of pesticide resistance is the best way to find sustainable crop protection solutions. And (P8) integration of multi-season effects and trade-offs in evaluation criteria will help develop sustainable solutions.

Reproducibility of binary‐mixture toxicity studies

Binary-mixture studies often are conducted with the aim of elucidating the effect of one specific chemical on the biological action of another. The results can be interpreted in relation to reference models by the use of response-surface analyses and isobolograms. The amount of data needed for these analyses is, however, extensive, and the experiments therefore rarely are repeated. In the present study, we investigate the reproducibility of isobole shapes of binary-mixture toxicity experiments in terms of deviation from the reference model of concentration addition (CA), dose-level dependence, and isobole asymmetry. We use data from four herbicide mixtures tested in three to five independent experiments on the aquatic test plant Lemna minor and the terrestrial plant Tripleurospermum inodorum. The results showed that the variation both within and among experiments was approximately half the size for the aquatic test system compared to the terrestrial system. As a consequence, a consistent deviation from CA could be obtained in three of four herbicide mixtures for L. minor, whereas this was only the case for one or two of the herbicide mixtures tested on T. inodorum. For one mixture on T. inodorum, both CA synergism and antagonism were detected. Dose-dependent effects could not be repeated consistently, just as the asymmetry found in some isoboles could not. The study emphasizes the importance of repeating mixture toxicity experiments, especially for test systems with large variability, and using caution when drawing biological conclusions from the test results.

European Perspectives on the Adoption of Nonchemical Weed Management in Reduced-Tillage Systems for Arable Crops

Abstract Noninversion tillage with tine- or disc-based cultivations prior to crop establishment is the most common way of reducing tillage for arable cropping systems with small grain cereals, oilseed rape, and maize in Europe. However, new regulations on pesticide use might hinder further expansion of reduced-tillage systems. European agriculture is asked to become less dependent on pesticides and promote crop protection programs based on integrated pest management (IPM) principles. Conventional noninversion tillage systems rely entirely on the availability of glyphosate products, and herbicide consumption is mostly higher compared to plow-based cropping systems. Annual grass weeds and catchweed bedstraw often constitute the principal weed problems in noninversion tillage systems, and crop rotations concurrently have very high proportions of winter cereals. There is a need to redesign cropping systems to allow for more diversification of the crop rotations to combat these weed problems with less herbicide input. Cover crops, stubble management strategies, and tactics that strengthen crop growth relative to weed growth are also seen as important components in future IPM systems, but their impact in noninversion tillage systems needs validation. Direct mechanical weed control methods based on rotating weeding devices such as rotary hoes could become useful in reduced-tillage systems where more crop residues and less workable soils are more prevalent, but further development is needed for effective application. Owing to the frequent use of glyphosate in reduced-tillage systems, perennial weeds are not particularly problematic. However, results from organic cropping systems clearly reveal that desisting from glyphosate use inevitably leads to more problems with perennials, which need to be addressed in future research. Nomenclature: Catchweed bedstraw, Galium aparine L.; barley, Hordeum vulgare L.; maize, Zea mays L.; oilseed rape, Brassica napus L.; wheat, Triticum aestivum L. Resumen El cultivar sin inversión del suelo usando discos o picos, antes del establecimiento del cultivo, es la forma más común de reducir la labranza en sistemas de cultivos arables que incluyen cereales, colza y maíz en Europa. Sin embargo, nuevas regulaciones sobre el uso de plaguicidas podrían afectar la expansión de los sistemas de labranza reducida. La agricultura europea ha sido llamada a ser menos dependiente de los plaguicidas y a promover programas de protección de cultivos basados en los principios de manejo integrado de plagas (IPM). Los sistemas de labranza convencional sin inversión del suelo dependen totalmente de la disponibilidad de productos con glyphosate, y el consumo de herbicidas es mayoritariamente superior al compararse con sistemas de cultivo basados en el uso de arado. Malezas como zacates anuales y Galium aparine frecuentemente constituyen el principal problema de malezas en sistemas de labranza sin inversión del suelo y rotaciones de cultivos que además tienen proporciones muy altas de cereales de invierno. Existe la necesidad de rediseñar los sistemas de cultivos para permitir una mayor diversificación de las rotaciones de cultivos para así combatir estos problemas de malezas con un uso menor de herbicidas. Cultivos de cobertura, sistemas de manejo con residuos de cultivos, y tácticas que refuercen el crecimiento del cultivo en relación con el crecimiento de las malezas son también vistos como componentes importantes en los sistema IPM futuros, pero su impacto en los sistemas de labranza sin inversión del suelo necesita validación. Los métodos de control mecánico de malezas directo basados en implementos rotativos de deshierba, tales como azadones rotativos, han sido útiles en sistemas de labranza reducida donde la presencia de más residuos de cultivos y suelos menos trabajables son prevalentes, pero un mayor desarrollo de estos métodos es necesario para su aplicación efectiva. Debido al uso frecuente de glyphosate en sistemas de labranza reducida, las malezas perennes no son particularmente problemáticas. Sin embargo, resultados en sistemas de producción orgánicos han revelado claramente que el desistir del uso de glyphosate lleva inevitablemente a más problemas con malezas perennes, lo que necesita ser incluido en investigaciones futuras.

A general joint action model for herbicide mixtures

The assessment of mixture effects is usually done with isoboles which illustrate whether mixture effects are greater or smaller than would be expected on the basis of the individual activities of the herbicides. Under the assumption of similarity of response curves and by incorporating a function that can model the shape of isoboles, we can statistically test whether divergence from the Additive Dose Model (ADM) is significant. Two dose-response experiments with mixtures of either salt or ester formulations of MCPA and mecoprop-P and one experiment with tribenuron-methyl and mecoprop-P were analysed. Mixtures of tribenuron-methyl and a salt formulation of mecoprop-P showed antagonism. Mixtures of salt formulations of MCPA and mecoprop-P followed ADM, whilst ester formulations of the same compounds showed synergism. To get reliable estimates, the model requires mixture ratios covering the whole isobole

Toward a Reduced Reliance on Conventional Pesticides in European Agriculture

Whether modern agriculture without conventional pesticides will be possible or not is a matter of debate. The debate is meaningful within the context of rising health and environmental awareness on one hand, and the global challenge of feeding a steadily growing human population on the other. Conventional pesticide use has come under pressure in many countries, and some European Union (EU) Member States have adopted policies for risk reduction following Directive 2009/128/EC, the sustainable use of pesticides. Highly diverse crop production systems across Europe, having varied geographic and climatic conditions, increase the complexity of European crop protection. The economic competitiveness of European agriculture is challenged by the current legislation, which banned the use of many previously authorized pesticides that are still available and applied in other parts of the world. This challenge could place EU agricultural production at a disadvantage, so EU farmers are seeking help from the research community to foster and support integrated pest management (IPM). Ensuring stable crop yields and quality while reducing the reliance on pesticides is a challenge facing the farming community is today. Considering this, we focus on several diverse situations in European agriculture in general and in European crop protection in particular. We emphasize that the marked biophysical and socio-economic differences across Europe have led to a situation where a meaningful reduction in pesticide use can hardly be achieved. Nevertheless, improvements and/or adoption of the knowledge and technologies of IPM can still achieve large gains in pesticide reduction. In this overview, the current pest problems and their integrated management are discussed in the context of specific geographic regions of Europe, with a particular emphasis on reduced pesticide use. We conclude that there are opportunities for reduction in many parts of Europe without significant losses in crop yields.

Herbicidal effects of soil-incorporated wheat.

The hydroxamic acid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and the benzoxazolinones benzoxazolin-2-one (BOA) and 6-methoxybenzoxazolin-2-one (MBOA) have been identified as important allelochemicals in wheat. This study examines the possibility of exploiting the allelopathic properties of wheat as a weed control strategy by cultivating wheat as a precrop and incorporating plant residues into the soil before the next crop is sown. Different wheat varieties were cultivated in field plots during two seasons in both conventional and organic farming systems. Plants were sampled at various growth stages, and their contents of DIMBOA, MBOA, and BOA were determined by chemical analyses. The wheat samples were incorporated into soil, and the effect on germination and growth of 12 different weed species was examined in pot experiments under controlled conditions. In some cases significant effects were obtained, but the results were inconsistent and the effects were not correlated to the content of DIMBOA, MBOA, and BOA in the incorporated wheat plants. ED50 doses of the pure compounds were estimated in dose-response experiments in Petri dishes, and these turned out to be much higher than the predicted maximum concentrations of DIMBOA, MBOA, and BOA in the soil water following incorporation. The study shows that a prerequisite for exploiting the incorporation of wheat residues as a weed control strategy is the development of wheat varieties with an increased content of allelochemicals.

Robust cropping systems to tackle pests under climate change. A review

Agriculture in the twenty-first century faces the challenge of meeting food demands while satisfying sustainability goals. The challenge is further complicated by climate change which affects the distribution of crop pests (intended as insects, plants, and pathogenic agents injurious to crops) and the severity of their outbreaks. Increasing concerns over health and the environment as well as new legislation on pesticide use, particularly in the European Union, urge us to find sustainable alternatives to pesticide-based pest management. Here, we review the effect of climate change on crop protection and propose strategies to reduce the impact of future invasive as well as rapidly evolving resident populations. The major points are the following: (1) the main consequence of climate change and globalization is a heightened level of unpredictability of spatial and temporal interactions between weather, cropping systems, and pests; (2) the unpredictable adaptation of pests to a changing environment primarily creates uncertainty and projected changes do not automatically translate into doom and gloom scenarios; (3) faced with uncertainty, policy, research, and extension should prepare for worst-case scenarios following a “no regrets” approach that promotes resilience vis-à-vis pests which, at the biophysical level, entails uncovering what currently makes cropping systems resilient, while at the organizational level, the capacity to adapt needs to be recognized and strengthened; (4) more collective approaches involving extension and other stakeholders will help meet the challenge of developing more robust cropping systems; (5) farmers can take advantage of Web 2.0 and other new technologies to make the exchange of updated information quicker and easier; (6) cooperation between historically compartmentalized experts in plant health and crop protection could help develop anticipation strategies; and (7) the current decline in skilled crop protection specialists in Europe should be reversed, and shortcomings in local human and financial resources can be overcome by pooling resources across borders.

Modeling effects of herbicide drift on the competitive interactions between weeds.

Herbicides may drift onto road verges or natural areas adjacent to arable fields and affect nontarget plants. The effect of low doses of mecoprop-P on the competitive interactions and plant community dynamics was investigated in a model system using Capsella bursa-pastoris and Geranium dissectum as test plants. Dose–response experiments on single species showed that compared to G. dissectum, C. bursa-pastoris was more affected by mecoprop-P. Consequently, we expected that G. dissectum would outcompete C. bursa-pastoris when mecoprop-P was applied at a low dose in the competition experiment. Indeed, mecoprop-P had a significant effect on the interspecific competitive ability of both C. bursa-pastoris and G. dissectum. Our previous expectation, however, was not met: The interspecific competitive ability of both species increased significantly with the dose of the herbicide, and it was predicted that C. bursa-pastoris and G. dissectum are more likely to coexist in natural habitats with low concentrations of the herbicide compared to natural habitats with relatively high concentrations. The results from the dose–response experiments on the single species and the more laborious competition experiment approach, which is assumed to mimic the dynamics of plant communities more closely, show considerable discrepancies even though the experiments were performed at the same time and in the same greenhouse. This finding generally reduces the credibility of using single-species tests in ecological risk assessment of herbicide use.