Bärbel Gerowitt

Impact of climate change on weeds in agriculture: a review

Over the past decades, climate change has induced transformations in the weed flora of arable ecosystems in Europe. For instance, thermophile weeds, late-emerging weeds, and some opportunistic weeds have become more abundant in some cropping systems. The composition of arable weed species is indeed ruled by environmental conditions such as temperature and precipitation. Climate change also influences weeds indirectly by enforcing adaptations of agronomic practice. We therefore need more accurate estimations of the damage potential of arable weeds to develop effective weed control strategies while maintaining crop yield. Here we review the mechanisms of responses of arable weeds to the direct and indirect effects of climate change. Climate change effects are categorized into three distinct types of shifts occurring at different scales: (1) range shifts at the landscape scale, (2) niche shifts at the community scale, and (3) trait shifts of individual species at the population scale. Our main conclusions are changes in the species composition and new species introductions are favored, which facilitate major ecological and agronomical implications. Current research mainly considers processes at the landscape scale. Processes at the population and community scales have prevalent importance to devise sustainable management strategies. Trait-climate and niche-climate relationships warrant closer consideration when modeling the possible future distribution and damage potential of weeds with climate change.

Occurrence and distribution of important weed species in German winter oilseed rape fields

Data on weed species currently found in winter oilseed rape, the extent of their occurrence and regional distinctions were collected in autumn 2005, 2006 and 2007 from a total of 1463 oilseed rape (OSR) fields throughout Germany. Investigations took place in untreated parts of OSR fields at the four to six leaf stage of rape. Weed frequencies and densities were determined by randomly placing a 0.1 m2 square frame ten times in each plot, identifying and counting all plants within the frame. Results presented here mainly focus the distribution of important weed species and differences in their frequencies and densities between German Federal states.The majority of weed species occurring in winter oilseed rape is not evenly spread over Germany. There are weed species with a limited distribution which can be frequently found in some regions but are absent in others. Sisymbrium officinale, Descurainia sophia, Centaurea cyanus, Anchusa spp., Sonchus spp., Rumex spp. or Euphorbia spp. are some weed species with mainly regional importance. Several ubiquitous weed species show regional differences in their densities. Capsella bursa-pastoris, Chenopodium album, Galium aparine, Lamium spp., Matricaria spp., Stellaria media, Thlaspi arvense, Veronica spp. and Viola arvensis were among the most frequent weed species in OSR in all German federal states though sometimes differing significantly in regional densities. Recent field observations reporting an increased spreading of Geranium spp., Sisymbrium spp. or Anchusa arvensis in intense OSR cropping areas are verified by these results.

A survey of on-farm acceptance of low-input measures in intensive agriculture

Low-input measures is used as a generic term for all measures involving a reduced intensity of agricultural management to enhance the quality of biotic or abiotic goods. Intensive agricultural regions have the lowest share of implemented low-input measures, though they have to resolve the most serious nature conservation and environmental problems. To understand the conditions for a better implementation of these measures in intensive agricultural areas, we carried out a written survey among 865 farmers in intensively-used arable regions. The adoption patterns of arable and grassland measures were compared. The determining factors were analysed by logistic regression. Arable measures, such as mulch seeding, that claim a high share of the arable area often have comparatively slight restrictions and cause windfall gains. However, our results show that their adoption increases the ratio of probability of a subsequent implementation of low-input measures on grasslands by 0.05. This means that these arable measures can act as starting measures for probably more valuable low-input measures on grasslands. Furthermore, the relation of the farmers with their subsidising institution proved to have an influence in our analysis. With every next best rating the farmers give for their relation with their subsidising institution, the ratio of probability for the adoption of low-input measures on arable land rises by 0.3. We also detected a strong positive influence of defined contact persons within the subsidising institution on the probability of adopting grassland measures, with a ratio of probability of 4.802. These findings show that the subsidising institution has in many respects a central influence on the decision process of the farmer to adopt low-input measures. The described determinants reveal new insights usable for improving the off-farm conditions of an increased implementation of low-input measures in intensively-used arable regions.

Response of the two rare arable weed species Lithospermum arvense and Scandix pecten-veneris to climate change conditions

Rare weeds are currently under pressure due to intensifying arable management practices, and as a consequence of climate change, these practices will likely become even more intensive, together with a greater uniformity of land use. As a result, ecological stresses will increase for most species of rare weeds, in some cases leading to their further decline or even extinction. Moreover, climate change will alter the suitability of the environment for many plants, since average temperatures are predicted to increase and precipitation extremes to become more common. For most arable weed species it is unclear, whether the anticipated changes in environmental conditions are disadvantageous or beneficial. Little is known about specific biological responses of rare weeds to climate changes, and this study attempts to close some of these knowledge gaps. Here, the rare arable weed Lithospermum arvense and the endangered arable species Scandix pecten-veneris were investigated with regard to the effects of higher temperature and different crop densities on flowering time, shoot development, plant height, dry mass and seed production. Semi-field experiments were conducted with winter wheat crop for 3 years, involving 48 climate cages, in which every second was a variant of warmer temperature and contrasting crop density. We observed that S. pecten-veneris flowered earlier under warmer conditions and had fewer seeds and less biomass in the dense wheat crop compared to control conditions, while L. arvense grew taller, it produced fewer seeds in the high density crop. We suggest that such data concerning the biological responses of weeds can improve the precision of bioclimatic distribution models. Finally, we discuss strategies, such as relocation or non-intrusive management practices, for preventing further disappearances of rare arable weeds. Our results should be of considerable interest for the fields of plant ecology, biodiversity research and conservation.

Influence of selected potato cultivars on the reproduction rate of the aphid species Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas).

The influence of potato cultivar (Solanum tuberosum L. cvs. Albatros, Borwina, Fasan, Kormoran, Pirol, Salome, Romanze and Terrana) and leaf zone on the reproduction rate of green peach aphid, Myzus persicae (Sulzer) and potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae), was assessed in glasshouse experiments. Aphids were caged in five leaf zones of each cultivar. M. persicae prefers senescent leaves. Fecundity and reproductive rate of M. persicae were greater on the lower leaves than on upper leaves (P< 0.001). The total fecundity and reproduction rate of M. euphorbiae were greater on the upper leaves than on lower leaves (P< 0.001). The results showed that the reproduction rate of M. persicae and M. euphorbiae differed significantly (P< 0.05) among cultivars.ZusammenfassungUntersuchungen zum Einfluss der Kartoffelsorten (Solanum tuberosum L. Sorten Albatros, Borwina, Fasan, Kormoran, Pirol, Salome, Romanze und Terrana) und der Blattetage auf die Vermehrungsrate der Grünen Pfirsichblattlaus, Myzus persicae (Sulzer) und der Gestreiften Kartoffellaus, Macrosiphum euphorbiae (Thomas) (Homoptera: Aphididae) wurden im Gewächshaus durchgeführt. Die Blattläuse wurden in Käfigen auf 5 Blattetagen pro Kartoffelsorte isoliert. M. persicae bevorzugte die alten Blätter. Die Fruchtbarkeit und die Reproduktionsrate von M. persicae waren auf den unteren Blättern höher als auf den oberen Blättern (P < 0.001). Insgesamt waren die Fruchtbarkeit und die Reproduktionsrate von M. euphorbiae auf den oberen Blättern höher als auf den unteren Blättern (P < 0.001). Die Ergebnisse ergaben signifikante (P < 0.05) Unterschiede für die Reproduktionsraten von M. persicae und M. euphorbiae bei den Kartoffelsorten.

Weed seed survival during anaerobic digestion in biogas plants.

Anaerobic digestion using animal manure and crop biomass is increasingly being used to produce biogas as a durable alternative to fossil fuel. The sludge, the leftover after processing, is returned to the field as a crop fertilizer. If weed seeds survive anaerobic digestion, the use of contaminated sludge poses a phytosanitary risk. The conditions that seeds are likely to encounter in biogas plants, and the effect of these, in particular temperature, on seed viability were reviewed. Knowledge on seed defence mechanisms and how these might protect seeds from inactivation in biogas reactors was summarized. Mechanisms of seed inactivation can be classified as thermal, biological and chemical. Weed species with hard seeds (physical dormant), high thermoresistance, a thick seed coat or adapted to endozoochory were identified as high-risk species. Specific seed traits could be used in future tests to circumvent extensive testing of seeds in biogas reactors.

The probability of maize biomass contamination with weed seeds

Anaerobic digestion in biogas reactors generates a semi-solid leftover, the digestate, which is frequently used as a crop fertiliser. If weed seeds in the maize biomass that is used for feedstock survive the process of anaerobic digestion, the use of digestate could contribute to the spread of weeds. We investigated here the probability that weeds enter the biogas production chain via maize biomass. Five organic and four conventional maize fields were sampled to determine the identity, density and biomass of the weeds present, and the number and viability of seeds produced. This was done separately for plant parts below and above the anticipated cutting height of the maize crop, close to the anticipated harvest date. Weed density varied from 56 to 568 weeds m−2 and weed seed production from 886 to 229 256 seeds m−2. Conventional fields tended to have lower weed biomass, lower seed production, and lower proportion of the seeds above the cutting height of maize, with lower seed viability. The main weeds were Chenopodium album and Echinochloa crus-galli. In general, either weed plants were small and produced few seeds that were largely found below the cutting height of maize, or they were tall and produced numerous seeds that were largely found well above the cutting height. Given the numbers of weed seeds produced per hectare in this study, it is likely that some will survive anaerobic digestion in biogas plants, although in low numbers, as seed survival during anaerobic digestion tends to be low.

Important maize weeds profit in growth and reproduction from climate change conditions represented by higher temperatures and reduced humidity

Climate change is predicted to result in rising temperatures and reduced precipitation during spring and summer in Central Europe. As a consequence, crops and weeds will be affected. Our study focuses on the three weed species in maize Amaranthus retroflexus , Echinochloa crus-galli and Setaria viridis . These weeds occur numerously in European maize fields and populations are likely to further increase. Yet, there is a lack of knowledge about particular biological strategies of the weeds. Our study focuses on how the weed species respond biologically to the climate change conditions. Experiments were conducted in two climate chambers with a 2°C difference in temperature and the warmer one with 13% less humidity. Emergence, development, biomass and seed production were determined of the weeds grown individually in pots and grown within maize. All tested weed species were taller during the first weeks under the climate change scenario. At later growth phases there was a trade-off between traits measured during vegetative growth and at the time when seeds were produced. To summarize the results, the weed species profited in the order E. crus-galli , S. viridis and A. retroflexus from the climate change conditions. Knowledge of the weeds biological responses to the predicted conditions helps to reduce their long-term population development by targeting crop protection measures at specific growth phases of the weeds. To ensure control of the tested weed species under climate change conditions various weed management strategies are necessary.

Anwendungsmuster von Pflanzenschutzmitteln in Winterweizen und Winterraps

ZusammenfassungSeit 2000 werden in Deutschland Anstrengungen unternommen, um einen Überblick über die tatsächlich stattfindenden Pflanzenschutzmittelanwendungen zu bekommen. Für den vorliegenden Artikel wurden Schlagkarteidaten von Betrieben in Mecklenburg-Vorpommern bezüglich der durchgeführten Pflanzenschutzmaßnahmen in den Jahren 2000 bis 2004 ausgewertet. Die Ergebnisse werden für 97 Schläge mit Winterweizen und 68 Schläge mit Winterraps vorgestellt.Die Pflanzenschutzintensität wird durch die Behandlungshäufigkeit, die Anzahl eingesetzter Präparate und den Behandlungsindex beschrieben. Häufigkeit und Zusammensetzung von Tankmischungen verschiedener Präparate und Pflanzenschutzmittelgruppen werden dargestellt. Darüber hinaus wird gezeigt, dass die Verwendung reduzierter Aufwandmengen zu einer geringeren Bekämpfungsintensität auf den Schlägen beigetragen hat.AbstractFrom the year 2000 on, different steps have been taken to study the real extent of pesticide use in Germany. For this paper, the data of farms in North East Germany were examined for the chemical plant protection measures carried out between 2000 and 2004. Results are presented for 97 winter wheat fields and 68 fields of oil seed rape.Pesticide use intensity is described as frequency of use, number of pesticides used, and treatment frequency index. Number and composition of tank mixtures are given in detail. More over it can be shown that the use of reduced dosages contributes to smaller overall pesticide use intensity.

Zur Bedeutung betrieblicher Faktoren für die Pflanzenschutzmittel-Intensität im Ackerbau

ZusammenfassungIn Europa sind die Landwirte aufgefordert, den Einsatz von Pflanzenschutzmitteln zu verringern. Die Höhe der Pflanzenschutzmittel-Intensität im Ackerbau hängt von einer großen Anzahl von Faktoren ab. Ziel der vorliegenden Studie ist es, Faktoren im Betrieb sowie im Pflanzenschutz-Management zu identifizieren, die mit geringeren oder höheren Behandlungsintensitäten in Zusammenhang stehen. Von 30 Betrieben in zwei Untersuchungsregionen (Fläming, Oder-Spree), in denen die Intensität der Pflanzenschutzmittel-Anwendungen über einen zehnjährigen Untersuchungszeitraum in fünf Ackerbaukulturen erfasst wurde, analysiert die vorliegende Studie zehn Betriebe. Von dieser Stichprobe der Gesamt-Anzahl der untersuchten Betriebe waren Ertragsdaten sowie Angaben zur feldspezifischen Bodengüte verfügbar. Zur Beschreibung des quantitativen Umfangs sowie der betrieblichen Unterschiede in der Anwendung von chemischen Pflanzenschutzmitteln wird die Kennziffer Behandlungsindex verwendet. Einflussfaktoren auf die Intensität des Pflanzenschutzmittel-Einsatzes werden mittels multipler Regressionen analysiert.Die Ergebnisse zeigen, dass betriebliche Faktoren, wie Ziele und Ausstattungen sowie das Wissen und die Wahrnehmungen der Entscheidungsträger, die Pflanzenschutz-Intensität beeinflussen. Der Pflanzenschutzmittel-Einsatz unterscheidet sich, unabhängig von der Bodengüte, zwischen Ackerbau- und Gemischtbetrieben. Betriebe mit besseren Böden innerhalb einer Region setzten mehr Pflanzenschutzmittel ein. Die Intensität des Pflanzenschutzes steigt mit sinkendem Arbeitskräftebesatz. Sie war höher in Familienbetrieben als in anderen untersuchten Rechtsformen. Die Pflanzenschutz-Intensitäten standen in engem Zusammenhang zur Ertragsfähigkeit, gemessen als Ackerzahl. Die Ergebnisse verdeutlichen jedoch, dass sich die Ertragswirkung der eingesetzten Pflanzenschutzmittel zwischen den untersuchten Kulturen unterscheidet. Zukünftig sollte der Einsatz von Pflanzenschutzmitteln im Kontext mit betriebswirtschaftlichen Zielen diskutiert werden sowie Wissen und Wahrnehmungen der Landwirte hinsichtlich des Integrierten Pflanzenschutzes entwickelt werden. Dabei sind je nach Betriebs-Ziel unterschiedliche Wege erfolgversprechend.AbstractIn Europe, farmers are encouraged to reduce pesticide use. Pesticide use intensity in arable farming depends on many factors. Numerous studies report a high variance in pesticide use between farms. The aim of the present study is to identify farm specific determinants for the intensity of pesticide use. We investigated which farm characteristics and pesticide management factors are related to lower or higher pesticide use intensity. Data on chemical plant protection measures of 30 farms in two districts of North East Germany were examined for five field crops from 2005 until 2014. In the present study we investigated the pesticide use intensities described as Standardized Treatment Index (STI) of ten representative farms. Yield data and information on the field-specific soil quality were available from these ten farms. We used multiple regressions to estimate the relationship between farm characteristics and pesticide use.The results demonstrate that pesticide use will be affected by farm specific factors, like objectives and equipment such as knowledge and perceptions of decision makers. Pesticide use intensity differs between arable and mixed farms independent of soil characteristics. Farms with more fertile soils use higher amounts of pesticides. The analyses demonstrated that pesticide use decreases with increasing labor availability. STIs of family farms are highest compared to other investigated legal forms. Pesticide use intensities are strongly related to productiveness. The results show that influences of pesticides on yield differ between the investigated crops.The present study further demonstrates that pesticide use has to be discussed in an economic context. Knowledge and perception of farmers must be developed with regard to integrated pest management. For success a diverse approach is required, depending on the farmer’s objectives.