Browsing by Subject "Herbicide efficacy"

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Integrated weed management in intensive cropping systems : towards reduction of herbicide input
(2016) Jäck, Ortrud; Gerhards, Roland
Weed control in conventional cropping is commonly done using herbicides. Those, however, can have negative side-effects on the environment. The objective of this thesis is to investigate the potential of reducing herbicide input into cropping systems with a focus on two of the most important staple crops, maize and winter wheat. The thesis is divided into five main sections, dealing with different topics, i.e.: 1. Determination of herbicide efficacy 2. Efficacy of reduced herbicide dosages in maize 3. Efficacy of reduced herbicide dosages in winter wheat 4. Integrated weed management 5. Long-term effect of reduced herbicide dosages To examine herbicide efficacy at reduced dosages it is necessary to conduct a wide range of dose-reponse experiments. They are usually time and labour consuming and the assessment of herbicide efficacy is often not objective. To overcome these issues, a novel method for assessing herbicide efficacy using bi-spectral imaging was tested. The results show at the example of Bromus japonicus that weed coverage assessed with the bi-spectral camera system can serve as a non-destructive, rapid and objective method to assess herbicide efficacy. In field experiments the potential for reducing herbicide dosages in summer maize was investigated with several common herbicides and herbicide mixtures. These experiments show that it is possible to reduce herbicide dosages for weed control in maize without influencing weed control efficacy and crop yield. However, the extent to which dosages can be reduced without loss in efficacy is dependent on the herbicide used and the weed growth stage. One of the herbicide tested in the field (topramezone) is usually applied together with a methylated seed oil (MSO) adjuvant. Adjuvants play an important role for herbicide efficacy, but the mechanism for enhancing herbicide efficacy is often not clear, yet. To examine the mechanism of MSO in enhancing efficacy of topramezone, several experiments were conducted. Efficacy of topramzone was significantly increased by addition of MSO. The results show that MSO enhances the uptake and translocation of topramezone in the two tested weed species. Furthermore, physical properties of the spray solution were altered. More precisely, surface tension and thus the contact angle on the leaf was decreased. These results can explain why MSO adjuvant enhances topramezone efficacy. To investigate the potential of reducing herbicide dosages in winter wheat and its impact on weed seed production, experiments were conducted using A. fatua as weed. The results show, that dosages of the four tested herbicides could be tremendously reduced without loss in efficacy. However, A. fatua seed production was influenced by winter wheat competitiveness and herbicide mode of action and did not necessarily follow herbicide efficacy. These results on the one hand highlight the potential of herbicide dosage reduction for controlling A. fatua in winter wheat. But on the other hand, the results point out that decision on herbicide dosage reduction should not only be made on basis of herbicide efficacy data but also on its influence on weed seed production. Reduction of herbicide input cannot only be achieved by reducing herbicide dosages, but also by applying non-chemical weed control methods. These methods may not be able to fully replace herbicide usage, but they can serve as tool to reduce weed pressure and competitiveness. Field experiments were carried out to investigate the effect of adjusted winter wheat seeding rate and nitrogen fertilization on Calystegia hederacea abundance and herbicide control efficacy. The results show that increased seeding rate reduces density of this weed while enhancing herbicide efficacy. Lowering nitrogen fertilization rate towards Nmin based fertilization increased density of C. hederacea. This study points out how adjustment of agronomic parameters can influence weed competitiveness and can serve in enhancing weed control efficacy by herbicides. It had been shown in several studies that cover crops or undersown crops can effectively suppress weed growth. This suppression may not only be due to competition for resources, but also by chemical interaction via allelopathic active compounds. To examine the allelopathic effect of several cover crops, pot and laboratory experiments were carried out. These experiments show, that effects of the tested cover crops can be growth promoting or inhibiting, and are dependent on the species and extract concentration. Furthermore, cover crops can also affect growth of the crop. To discuss the long-term effect of reduced herbicide dosages on weed population development, a simulation model was set-up at the example of winter wheat and A. fatua. Different strategies for herbicide input reduction were simulated. This paper highlights the potential of reducing total herbicide input without population increase, while keeping grain yield and net return at high level. The presented articles work out the risks and potential for herbicide dosage reduction and point out the possibilities of using integrated weed management options for enhancing weed suppression.