Reduced herbicide rates: present and future

Applying herbicides at rates lower than the label recommendation has been the rule rather than the exception in Denmark since the late 1980’s. Justifications for reducing herbicide rates can be 1) that the dominant weed species in the field are very susceptible to the herbicide, i.e. even reduced rates will result in maximum effects, 2) that the conditions at and around the time of application, e.g. growth stage of weeds, crop vigour and climatic condition are optimum promoting the activity of the herbicide and thus allows for the use of reduced herbicides rates, or 3) that less than maximum effects are accepted because the weed flora is not considered to have a significant effect on crop yield. “Crop Protection Online-Weed” (CPO-Weed) is a web-based decision support system that was developed to support farmers in their choice of herbicide and herbicide rate. CPO-Weed will, based on information on crop development and status and the composition of the weed flora, provide farmers with a list of herbicide solutions often recommending the use of reduced rates. The potential of CPO-Weed to reduced herbicide input has been proven in numerous validation trials. In recent years the use of reduced herbicide rates has been linked to the increasing number of cases of non-target resistance in outcrossing grass weed species like Alopecurus myosuroides and Lolium ssp. The underlying hypothesis is that the least susceptible individuals in the population will survive the use of reduced rates and that recombination will lead to a gradual increase in the resistance level in the weed population. This scenario is only valid if the use of reduced herbicide rates is prompted by acceptance of a lower effect but not if a high susceptibility of the weed species present in the field or optimum conditions are the reasons for reducing herbicide rates. This is an aspect that is often overlooked in the on-going discussion on herbicide rates and resistance. Large weed population increases the risk of selecting resistant weed biotypes because the likelihood that resistant plants are present in the population increases with population size. Preventing the build-up of large weed populations is a key objective in integrated pest management (IPM). If the use of herbicide is combined with non-chemical weed control methods the risk of resistance will be reduced further, i.e. in an IPM scenario the use of reduced herbicides rates will be less likely to promote herbicide resistance even if it is triggered by an acceptance of lower effects.        Keywords: Crop Protection Online, dose response curve, herbicide rate, herbicide resistance, integrated pest management, IPM Reduzierter Herbizidaufwand: heute und zukünftig Zusammenfassung  Seit den späten 1980-er Jahren ist in Dänemark die Anwendung von Herbiziden mit geringeren Aufwandmengen als bei der Zulassung vorgesehen eher die Regel als die Ausnahme. Den Aufwand herabzusetzen kann begründet sein, indem 1) die dominierenden Unkrautarten gegenüber dem Herbizid sehr empfindlich sind, d. h., dass selbst mit verminderten Aufwandmengen eine vollständige Wirkung erreicht werden kann, 2) die Bedingungen zum Anwendungszeitpunkt, z. B. das Entwicklungsstadium der Unkräuter, die Entwicklung der Kultur und die Witterung für die Herbizidwirkung günstig sind und daher verringerte Aufwandmengen erlauben, oder 3) weil angenommen werden kann, dass die Verunkrautung keine signifikante Auswirkung auf den Ertrag haben wird. “Crop Protection Online-Weed” (CPO-Weed) ist ein Internet-basiertes Beratungs-System, das dem Landwirt bei der Auswahl des Herbizids und der Aufwandmenge helfen soll. CPO-Weed wird aufgrund der Informationen über den Entwicklungsstand der Kulturpflanzen und der Zusammensetzung der Verunkrautung dem Landwirt eine Liste von Herbiziden, oft reduzierten Aufwand empfehlend, liefern. Das Potential von CPO-Weed hinsichtlich reduzierten Herbizidaufwands ist in zahlreichen Wirksamkeitsversuchen nachgewiesen worden. In letzter Zeit ist die Anwendung reduzierter Herbizidmengen mit den zunehmenden Fällen von Resistenz bei zum Outbreeding neigenden Unkrautarten wie Alopecurus myosuroides und Lolium ssp. in Verbindung gebracht worden. Die Hypothese ist, dass die am wenigsten empfindlichen Individuen der Population den reduzierten Herbizidaufwand überleben und allmählig das Resistenzniveau der Unkrautpopulation ansteigen lassen. Dieses Scenario trifft nur zu, wenn eine verringerte Herbizidmenge eine geringere Wirkung erzielt, aber nicht, wenn die hohe Empfindlichkeit einer vorkommenden Unkrautart oder optimale Anwendungsbedingungen die Herabsetzung des Herbizidaufwands begründeten. Das ist ein Gesichtspunkt, der in der laufenden Diskussion über reduzierten Herbizidaufwand und Resistenz oft übersehen wird. Große Unkrautpopulationen erhöhen die Gefahr, resistente Biotypen zu selektieren, denn die Wahrscheinlichkeit des Vorkommens resistenter Pflanzen wächst mit der Populationsgröße. Die Entwicklung starker Verunkrautung zu verhindern ist ein Hauptanliegen des Integrierten Pflanzenschutzes (IPS). Wenn die Anwendung von Herbiziden mit nichtchemischen Methoden der Unkrautbekämpfung kombiniert wird, kann die Resistenz-Gefahr weiter herabgesetzt werden, d. h., im Rahmen des IPS ist es weniger wahrscheinlich, dass reduzierte Herbizid-Aufwandmengen Herbizidresistenz fördern, auch wenn dabei geringere Wirkungen hingenommen werden. Stichwörter: Crop Protection Online, Dosis-Wirkungskurve, Herbizidaufwand, Herbizidresistenz, Integrierter Pflanzenschutz, IP

Glucosinolate hydrolysis products for weed control

Glucosinolates are allelochemicals present in all Brassica plants. Upon hydrolysis by endogenous enzymes they produce a series of biologically active compounds, such as isothiocyanates and their deriva-tives among others. These compounds have marked fungicidal, nematocidal and herbicidal effects and therefore their use as biodegradable natural products for crop protection has attracted much attention in the last years. A number of these compounds, either individually or in combination, were tested against Sinapis alba and Lollium perenne in Petri dishes bio-assays. C50 values as low as 0.7 and 0.2 mM were obtained. This may open the possibility for using glucosinolate hydrolysis products as herbicides

Glucosinolate hydrolysis compounds for weed control

Glucosinolates are allelochemicals present in all Brassica plants. Upon hydrolysis by endogenous enzymes they produce a series of biologically active compounds, such as isothiocyanates and their deriva-tives among others. These compounds have marked fungicidal, nematocidal and herbicidal effects and therefore their use as biodegradable natural products for crop protection has attracted much attention in the last years. A number of these compounds, either individually or in combination, were tested against Sinapis alba and Lollium perenne in Petri dishes bio-assays. C50 values as low as 0.7 and 0.2 mM were obtained. This may open the possibility for using glucosinolate hydrolysis products as herbicides

An Integrated Weed Management framework: A pan-European perspective

Initiatives to reduce the reliance of agriculture on pesticides, including the European Union (EU) Directive 2009/128/EC on the sustainable use of pesticides (SUD), have yet to lead to widespread implementation of Integrated Pest Management (IPM) principles. Developments in weed management have strongly focused on increasing the efficiency of herbicides or substituting herbicides with other single tactics such as mechanical control. To increase sustainability of agricultural systems in practice, a paradigm shift in weed management is needed: from a single tactic and single growing season approach towards holistic integrated weed management (IWM) considering more than a single cropping season and focusing on management of weed communities, rather than on control of single species. To support this transition, an IWM framework for implementing a system level approach is presented. The framework consists of five pillars: diverse cropping systems, cultivar choice and establishment, field and soil management, direct control and the cross-cutting pillar monitoring and evaluation. IWM is an integral part of integrated pest management (IPM) and adopting IWM will serve as a driver for the development of sustainable agricultural systems of the future

Determination of the Effect of Co-cultivation on the Production and Root Exudation of Flavonoids in Four Legume Species Using LC–MS/MS Analysis

Flavonoids play a key role in the regulation of plant−plant and plant−microbe interactions, and factors determining their release have been investigated in most of the common forage legumes. However, little is known about the response of flavonoid production and release to co-cultivation with other crop species. This study investigated alterations in the concentration of flavonoids in plant tissues and root exudates in four legumes [alfalfa (Medicago sativa L.), black medic (Medicago polymorpha L.), crimson clover (Trifolium incarnatum L.), and subterranean clover (Trifolium subterraneum L.)] co-cultivated with durum wheat [ Triticum turgidum subsp. durum (Desf.) Husn.]. For this purpose, we carried out two experiments in a greenhouse, one with glass beads as growth media for root exudate extraction and one with soil as growth media for flavonoid detection in shoot and root biomass, using LC−MS/MS analysis. This study revealed that interspecific competition with wheat negatively affected legume growth and led to a significant reduction in shoot and root biomass compared with the same legume species grown in monoculture. In contrast, the concentration of flavonoids significantly increased both in legume biomass and in root exudates. Changes in flavonoid concentration involved daidzein, genistein, medicarpin, and formononetin, which have been found to be involved in legume nodulation and regulation of plant−plant interaction. We hypothesize that legumes responded to the co-cultivation with wheat by promoting nodulation and increasing exudation of allelopathic compounds, respectively, to compensate for the lack of nutrients caused by the presence of wheat in the cultivation system and to reduce the competitiveness of neighboring plants. Future studies should elucidate the bioactivity of flavonoid compounds in cereal-legume co-cultivation systems and their specific role in the nodulation process and inter-specific plant interactions such as potential effects on weeds

Művészet, hatalom, illúzió

Plant Gene Ontology terms associated with the combined assembly of all tissues and growth stage of A. spica-venti. BP; biological processes, MF; metabolic function, CC; cellular component. (PNG 34 kb