Unkrautflora in Mais

A weed monitoring conducted by Syngenta Agro GmbH in co-operation with the University of Hohenheim was carried out to evaluate the local and regional weed situation in maize in Germany. The fields were monitored at the two to six leaf stage of maize before weed control. A total of 2602 maize fields across Germany has been investigated from 2000 until 2004. Altogether 204 weed species (including volunteer crops) from 32 plant families have been recorded. The dicots were the predominant group with 166 species. The monocots were represented by 36 species and two species belonged to the family of Equisetaceae; volunteer crops were represented by 22 species. The most frequent species were Chenopodium spp. (79.7%) in particular Chenopodium album, followed by Stellaria media (61.0%), Fallopia convolvulus (55.7%), Echinochloa crus-galli (53.0%), Matricaria spp. (50.3%), Viola arvensis (47.8%), Polygonum aviculare (45.8%), Lamium spp. (41.6%), Galium aparine (39.7%) and Elytrigia repens (39.4%). The results demonstrate that with the exception of Echinochloa crus-galli, species usually considered for being typical for maize as e. g. Solanum nigrum, Amaranthus spp. and Galinsoga spp. are not dominating. Among the volunteer crops, rape was most abundant (17.2%). On average the weed density over all fields was 192 plants m^-2. The monitoring clearly shows that some weeds occur predominantly in certain areas as e. g. Solanum nigrum and Stellaria media in the north-west and Veronica spp. in the south of Germany. Beside climatic conditions differences in cropping systems and cultivation practices lead to a specific weed flora in maize. In comparison to similar investigations in the seventies of the last century, some species species as e. g. Veronica spp. and Viola arvensis have increased dramatically. This increase is mainly due to the use of sulfonylurea herbicides which are weak on these species. The increase of Geranium spp., weeds which are rather new in maize, is also linked to the low efficacy of the herbicides presently used on these species. All the species found during the five years monitoring are presented by their frequency of occurrence.     

Growth Acceleration of Seawater-Adapted Female Chinook Salmon Oncorhynchus tshawytscha by Constant Infusion of Recombinant Bovine Growth-Hormone Under Ambient Summer Conditions

Seawater-adapted female chinook salmon ( Oncorhynchus tshawytscha ) in their second summer were treated with one of three doses of recombinant bovine growth-hormone (rbGH) administered in a continuous fashion by osmotic pump for approximately five weeks. Untreated fish, sham-treated fish and fish treated with the low dose of hormone (0.003 μg/g bwt/day) did not differ significantly in their growth performance over the 10 week course of the experiment. By the end of the treatment period (week 6) the mean increases in fork length and weight for these groups were 7.6% and 38.9%, respectively. A dose-dependent enhancement of growth was observed for the fish treated with the mid (0.016 μg/g bwt/day) and high (0.078 μg/g bwt/day) doses of hormone. After 6 weeks, the fish given the mid dose of rbGH had gained 9.6% in fork length and 45.3% in weight, while the fish treated with the high dose of rbGH had gained 13.9% in fork length and 52.9% in weight. A significant increase in specific growth rate was observed for these latter two groups during the treatment period while condition factor declined in response to the high dose of rbGH. This experiment indicates that chronic administration of growth-hormone to chinook salmon can result in a dose dependent elevation of growth rate. Results are discussed in relation to previous attempts to accelerate the growth of Pacific salmon with growth-hormone and the potential for using recombinant growth-hormone to improve the production characteristics of salmon being cultured in seawater.     

Regionale Unterschiede in der Rapsunkrautflora Deutschlands

Data on weed species currently found in winter oilseed rape, the extent of their occurrence and regional distinctions were collected in autumn 2005 and 2006 from a total of 978 rape fields throughout Germany. Investigations took place on untreated sites at the six to eight leaf stage of rape. Weed frequencies and densities were determined by randomly placing a 0.1?m² quadrate frame ten times in each plot, identifying and counting all plants within the frame. Two year results are presented here with a main focus on regional distinctions in total weed infestation, species richness as well as differences in frequencies and densities of selected weed species between the federal states. As expected, the majority of weed species occurring in winter oilseed rape is not evenly spread over Germany. On the on hand there are weeds with a more or less limited distribution which can be frequently found in some regions but are absent in others while on the other hand several ubiquitous weed species mainly show regional differences in their densities. Sisymbrium officinale, Descurainia sophia, Centaurea cyanus, Anchusa sp., Sonchus sp., Rumex sp. or Euphorbia sp. are some of the weed species of mostly regional importance. In contrast statistically proofed differences in weed densities in the federal states of Germany were recorded for Capsella bursa-pastoris, Chenopodium album, Galium aparine, Lamium sp., Matricaria sp., Stellaria media, Thlaspi arvense, Veronica sp. and Viola arvensis. Total weed infestation level and the mean number of species per site also differed between the federal states of Germany.     

Agronomic traits contributing to nitrogen efficiency of winter oilseed rape cultivars

Reducing the high nitrogen (N) balance surpluses occurring in oilseed rape production through the cultivation of N-efficient cultivars is imperative for environmental reasons. In this study, seed yield and N efficiency parameters of oilseed rape cultivars grown under three N rates were investigated in field experiments performed during five years. Seed yields differed significantly among cultivars especially at limiting N supply, with significant shifts in cultivar ranking according to the N level. At high N supply, cultivar differences relied more on year effects. The importance of N efficiency parameters for yield varied owing to year and N rate effects. N uptake was an important parameter for yield at all N rates. While at low N, the duration of N uptake was most decisive, shoot N uptake capacity during vegetative growth was relatively more important under high N conditions. N utilization efficiency became more important with increasing N supply. At high N supply, cultivars with low seed N concentrations were superior in yield. Harvest index was also significantly correlated to yield across N rates; however, its importance depended much on environmental conditions. In conclusion, the specification of plant traits that might contribute to enhanced N efficiency in oilseed rape will depend very much on the N supply of the target environment and the target yield level.     

Low‐ammonia‐emission application methods can increase the opportunity for application of cattle slurry to grassland in spring in Ireland

Application of slurry in spring to grassland in north‐west Europe increases the efficiency of nitrogen recovery compared with the application in summer. In Ireland, however, more than 0·50 of slurry is applied in the summer. The splash‐plate method of application, most commonly used in Ireland, can make application in spring difficult because of the risk of contamination of grass with slurry, affecting subsequent silage quality and grazing preferences. This study evaluated the potential of low‐emission spreading methods to increase the opportunity for spring application of slurry using an agro‐meteorological modelling approach. Weather data from two weather stations were combined with data on grass growth from two nearby sites. Using three soil‐drainage classes (well, moderate and poor), each with a typical regime of grassland management, a database of soil moisture deficits, drainage, patterns of grazing and cover of grass herbage was developed for three hypothetical management systems, one for each soil drainage class, at each site. Simulations of four slurry application methods [splash‐plate (SP), band‐spreader (BS), trailing‐shoe (TS) and shallow‐injection (SI)], subject to a series of constraints, were compared over an 8‐year period (1998–2005) in order to determine the number of days during the period from 1 January to approximately 10 May of each year, when it was considered that grassland was suitable for application of slurry. These constraints were: (i) restrictions on spreading imposed by current legislation in Ireland; (ii) the period before occurrence of drainage or overland flow; (iii) soil trafficability; (iv) the time‐lag before a subsequent grazing or harvest event; and (v) herbage mass of the pasture. On well and moderately drained soils, the model predicted that the highest number of days available for slurry spreading was found for the TS method followed by the BS, SI and SP methods. There was no difference between application methods in the number of available days on poorly drained soils.     

Prevalence of the Bacterium Coxiella burnetii in Wild Rodents from a Canadian Natural Environment Park

Zoonotic diseases impact both wild and domestic animal populations and can be transmitted to humans through close contact with animal species. Reservoir species acting as vectors are major traffickers of disease. Rodents contribute to the transmission of Coxiella burnetii although little is known about its prevalence in wild animal populations. DNA was extracted from genital swabs collected from woodland jumping mice, deer mice, Southern red‐backed voles, Eastern chipmunks, North American red squirrels, as well as Southern and Northern flying squirrels collected from Algonquin Park, Canada. The presence of C. burnetii was determined through real‐time PCR. All species sampled had some prevalence of infection, except Eastern chipmunks, indicating wild rodents in Algonquin Park are reservoirs for C. burnetii. Emerging zoonotic diseases are linked to increasing globalization. Contact amongst individuals increases as crowding, habitat loss and fragmentation increase within wild spaces. Parks often act as a last refuge for wildlife but may also be an important transmission zone of wildlife disease to humans. Investigations that attempt to discover wild reservoir species of zoonotic disease are critically important to understanding the risk of pathogen exchange between wild and human populations.     

A tale of two wildfires; testing detection and prediction of invasive species distributions using models fit with topographic and spectral indices

Context

Developing species distribution models (SDMs) to detect invasive species cover and evaluate habitat suitability are high priorities for land managers.

Objectives

We tested SDMs fit with different variable combinations to provide guidelines for future invasive species model development based on transferability between landscapes.

Methods

Generalized linear model, boosted regression trees, multivariate adaptive regression splines, and Random Forests were fit with location data for high cheatgrass (Bromus tectorum) cover in situ for two post-burn sites independently using topographic indices, spectral indices derived from multiple dates of Landsat 8 satellite imagery, or both. Models developed for one site were applied to the other, using independent cheatgrass cover data from the respective ex situ site to test model transferability.

Results

Fitted models were statistically robust and comparable when fit with at least 200 cover plots in situ and transferred to the ex situ site. Only the Random Forests models were robust when fit with a small number of cover plots in situ.

Conclusions

Our study indicated spectral indices can be used in SDMs to estimate species cover across landscapes (e.g., both within the same Landsat scene and in an adjacent Landsat scene). Important considerations for transferability include the model employed, quantity of cover data used to train/test the models, and phenology of the species coupled with the timing of imagery. The results also suggest that when cover data are limited, SDMs fit with topographic indices are sufficient for evaluating cheatgrass habitat suitability in new post-disturbance landscapes; however, spectral indices can provide a more robust estimate for detection based on local phenology.