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Unkrautmanagement und Unkrautforschung sind an einem Wendepunkt. So sehen es jedenfalls zahlreiche Expertinnen und Experten. Herbizide kommen an ihre Grenzen durch Fortfall von Altwirkstoffen und die Zunahme schwerbekämpfbarer Unkrautpopulationen. Auflagen zur Verbesserung der Biodiversität sollen verordnet und die Herbizidmengen reduziert werden. Der Beitrag diskutiert die Problemursachen und mögliche Auswege. Das bisherige Herbizidsystem muss überarbeitet und die Auswirkungen auf öffentliche Güter müssen stärker in Bekämpfungsentscheidungen integriert werden.

Glyphosate is the most frequently used herbicide active ingredient in Germany. Studies regarding its usage in non-GMO arable farming are still rare even though it plays an important role in several agronomic situations. Therefore, we conducted a comprehensive survey, which was carried out among conventional German farms in Winter 2014/2015. Based on the results of this survey we analyzed via cluster analysis how types of farms differ in terms of glyphosate usage. An illustration of seven clusters allows deep insights into arable farm structures. The farm types can be distinguished regarding their tillage system and similar to this differentiation also concerning their intensity of glyphosate application. Furthermore, it becomes obvious that farm clusters with a higher level of glyphosate usage are characterized by a lower number of labourers per hectare, more arable land and/or enhanced cover cropping. Moreover, groups of farmers who rely more on glyphosate are more likely to state that they need glyphosate for herbicide resistance management. Farmers’ assessments of the economic importance of glyphosate usage vary depending on the type of farm. By means of the farm clusters, the most important situations of glyphosate usage can be further analyzed economically and scenarios for impact assessments can be made.

Increasing maize cultivation and changed cropping practices promote the selection of typical maize weeds that may also profit strongly from climate change. Predicting potential weed problems is of high interest for plant production. Within the project KLIFF, experiments were combined with species distribution modelling for this task in the region of Lower Saxony, Germany. For our study, we modelled ecological and damage niches of nine weed species that are significant and wide spread in maize cropping in a number of European countries. Species distribution models describe the ecological niche of a species, these are the environmental conditions under which a species can maintain a vital population. It is also possible to estimate a damage niche, i.e. the conditions under which a species causes damage in agricultural crops. For this, we combined occurrence data of European national data bases with high resolution climate, soil and land use data. Models were also projected to simulated climate conditions for the time horizon 2070 - 2100 in order to estimate climate change effects. Modelling results indicate favourable conditions for typical maize weed occurrence virtually all over the study region, but only a few species are important in maize cropping. This is in good accordance with the findings of an earlier maize weed monitoring. Reaction to changing climate conditions is species-specific, for some species neutral (E. crus-galli), other species may gain (Polygonum persicaria) or loose (Viola arvensis) large areas of suitable habitats. All species with damage potential under present conditions will remain important in maize cropping, some more species will gain regional importance (Calystegia sepium, Setara viridis).

In the past years, a large number of studies have examined various aspects of possible consequences of climate change for the biology and damage potential of arable weeds. However, there are merely a few examples that have comprehensively investigated individual weed species or arable crop systems within a clearly delimited geographical area. In the frame of the research co-operation KLIFF (Climate change impact and adaptation research for Lower Saxony), we tested an approach that combines a number of methods to span several scale levels and types of environmental factors, which was intended to provide as accurate as possible an estimate of the potential distribution and performance of individual arable weed species under the predicted future climate conditions. This approach was put to practice for the species Abutilon theophrasti, Amaranthus retroflexus, Echinochloa crus-galli, Datura stramonium, Iva xanthiifolia and Setaria viridis. We combined projections of the potential future distribution of the individual weed species based on a correlative distribution modelling approach (regional scale level) with pot experiments (local scale level) on the vegetative and generative performance of these species under climatic conditions predicted for the end of the current century for Lower Saxony. A synopsis revealed that the results obtained from the different approaches corresponded to a large extent. For A. retroflexus, D. stramonium, E. crus-galli, and S. viridis, both approaches indicated a neutral or positive effect of the predicted future climate on their potential distribution and performance, whereas the opposite was found for I. xanthiifolia. Merely for A. theophrasti, results of the two methods did not fully concur. Altogether, our results highlight that investigating climate change impact on weeds by combining several methods to span several scale levels allows fitting various data sets to a comprehensive picture for a delimited region. It has a number of strengths which may be augmented by the inclusion of further aspects. Therefore, this approach can be recommended for research of the regional impacts of climate change on arable weeds.

In the course of the past decennia, numerous shifts of the arable weeds flora have been observed as a result of climate change and of changes of land use and agricultural management practice. These shifts necessitate appropriate adaptations of weed management. The present study depicts alterations of the arable weeds flora of Lower Saxony based on data from two different sources, and describes recent changes of arable weeds management. We firstly conducted a questionnaire-based survey among plant protection consultants and experts of agronomy and plant protection in industry and the federal agriculture authorities. This survey was aimed at identifying which weed taxa have gained or lost relevance for management, and which tendencies with regard to their relevance is expected according to expert knowledge. In addition, the experts were asked for information on possible adaptations and challenges of weed management expected for the future. Secondly, we used protocols of plant protection trails published by the Lower Saxony chamber of agriculture in order to determine alterations of the weed management practice since the 1980s. The screened data gave a clear indication of an increase of the relevance during the past 30 years for a number of weed taxa, in particular for several millet taxa, Geranium species, Alopecurus myosuroides and Chenopodium album. In the evaluation of changes of the relevance of individual weed taxa, the impact of climate change cannot be segregated from effects of altered agricultural practices, which are in turn themselves influenced by climate change. Records of the agricultural practice have pointed out shifts in herbicide application dates which parallel altered sowing dates, e. g., an increase in the frequency of herbicide application in autumn rather than in spring for winter wheat. The recent shifts of weed flora and management practices can serve as a basis for the development of management adaptations for the future. To this purpose, a sound understanding of their causes is indispensable, and it needs to be complemented with knowledge obtained from climate change research. As with the interpretation of past shifts, in projections for the future it will not be possible to disentangle climate and management effects. For example, crop sequence is known to select for certain weed life history groups, and a concentration of maize cultivation can therefore enhance the positive effects of a warmer climate for thermophile summer annual weed taxa.

Glyphosate is the mostly used herbicide substance worldwide. Uses of glyphosate herbicides cover a wide range of crops and agronomical situations. During the last ten years, glyphosate use has increased in Germany. Thus, it is of specific interest to gather information on the current practice of its applications. In early 2011, a survey was carried out based on a postal and online inquiry of German farmers. The number of accessible valid answer sheets was 896. The study covered around 250000 ha of agricultural land, representing farms throughout Germany. The area of application was calculated (percentage), describing the proportion of application area from the cropping area of a specific crop. Large areas of oilseed rape (87.2 %), pulses (72.1 %) and winter barley (65.9 %) are treated with glyphosate. Predominating uses are (descending order): Stubble management, pre-sowing application and pre-harvest application (siccation).

Abstract: BACKGROUND: Although glyphosate is the most widely used herbicide in the European Union, little is known about the patterns of its usage in arable farming. Therefore, a nationwide survey of 2026 German farmers was analysed to obtain further knowledge about glyphosate applications in conventional European arable farming. Given its broad range of agri‐environmental and farm‐type conditions, Germany can be regarded as a suitable study region to represent Central European farming. The growing season 2013/2014 was set as a reference. RESULTS: Farmers who participated in the survey employ diverse patterns of glyphosate use. While 23% stated that they did not use glyphosate in the season in question, others applied glyphosate to their total arable area. However, most applications occurred on specific parts of the farm. Application patterns of oilseed rape, winter wheat, maize and sugar beet were studied in detail, and U‐shaped distributions of glyphosate use intensity were observed. The effects of farm type and management practices on glyphosate use patterns were mixed in the various crops. CONCLUSION: Motivation for glyphosate use differs widely within the farming community. Agricultural researchers, extension services and policy makers are recommended to mitigate vulnerabilities associated with glyphosate use, such as routine spraying and practices that increase selection pressure for the evolution of glyphosate‐resistant weeds. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Copyright of Julius-Kühn-Archiv is the property of Julius Kuehn Institut and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Julius-Kühn-Archiv is the property of Julius Kuehn Institut and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Julius-Kühn-Archiv is the property of Julius Kuehn Institut and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Julius-Kühn-Archiv is the property of Julius Kuehn Institut and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)