Browsing by Person "Hurle, Karl"

Now showing 1 - 3 of 3

Bromus-Arten in Winterweizen: Verbreitung, Bedeutung und Populationsdynamik
(2005) Moray, Ralph; Hurle, Karl
The increase of reduced tillage in agriculture and winter cereal dominated crop rotations has lead to a rise of annual and perennial grass weeds in the last decades. One of these are Bromus species that occur worldwide in cereal growing areas. In Germany they also attract more and more interest because of their increasing distribution. Therefore an inves-tigation was conducted to assess the current situation of Bromus species in Germany, competition, population biology and control. Additionally, control strategies were designed on the basis of analyses of population-dynamical parameters. A survey carried out in Germany, showed that Bromus sterilis and B. secalinus were found to be the dominant species. The problems that were predominantly mentioned were yield loss and difficulties at harvest which mostly appear in winter wheat. Their occurrence is closely connected with reduced tillage, early seeding and winter cereal dominated crop rotations whereas Bromus densities can be reduced effectively with a mouldboard plough or the increase of spring crops in crop rotation. In dicot. crops the chemical control was regarded as very good, whereas in cereals between good to sufficient. All of the survey participants expected a further distribution of Bromus species on arable land. Field trials were conducted on three locations over a period of three years to investigate the competition of B. sterilis, B. secalinus, B. tectorum and B. japonicus in winter wheat. Weed density and seeding date of winter wheat were considered for the species competition studies. The trials showed that distinct yield losses could be recorded in winter wheat depending on the different Bromus species. Thresholds where calculated based on the relationship between weed density and yield loss. The thresholds for the Bromus species in winter wheat were below the values given in literature for other grass weeds in winter cereals. This highlights the strong competitiveness of the species. Additionally the results showed that with late seeding the weed density decreases distinctively and thereby the yield loss can be reduced by half. Greenhouse trials on the efficiency of the three in Germany registered herbicides for the control of Bromus species showed, that a sufficient control of B. sterilis and B. secalinus could not always be achieved with the recommended dose. The simulation of the population dynamics showed clearly that with reduced tillage and direct seeding in a winter wheat monoculture without control measures a very fast increase of densities within two growing seasons up to a density-dependent level where high yield losses can be expected. In contrast mouldboard ploughing can control the species to 100 % as a depth of seeds of 10 cm already reduces emergence by half and seeds in the trials showed to have longevity in soil of no longer that 12 months. Moreover, it was demonstrated that the soil cultivation has a higher influence on the development of the weed population than the different seeding dates of winter wheat. The simulation under the influ-ence of herbicide application suggested, that it is possible to practice a winter cereal dominated crop rotation without yield losses. From the results of the investigations it can be concluded that Bromus as a problem in win-ter cereal dominated crop rotation in our latitudes will increase. In fact the control with available herbicides is not always sufficient, but for economical reasons integrated control strategies can not always be considered although quite a good control is given. Therefore one can presume that in future the control of Bromus in winter cereals still will be based on the use of herbicides and that these weed species will be as common in win-ter cereals as it became Alopecurus myosuroides and Apera spica-venti.
Unkrautbekämpfung in Zuckerrüben - Ermittlung der Kritischen Periode
(2003) Kobusch, Henner; Hurle, Karl
Early leaf stages of sugar beet are very sensitive to weed competition, which is a major reason for the absence of thresholds for weed control in sugar beet. In combination with non-selective herbicides, the use of herbicide resistant sugar beets appears to allow the control of weeds at a later date than usual applications of common selective herbicides. Therefore, it is necessary to know the critical period, in which the crop should be weed free in order not to loose yield. The influencing factors of the critical period are the moment until weed can be tolerated (beginning of the critical period) and the moment after weed can be tolerated (end of the critical period). The primary objective of the present work was the establishment of a parameter, which would allow a determination of the critical period independent of location and season. Therefore, triannual field trials were carried out at three different sites in the Ukraine and in Stuttgart-Hohenheim in order to evaluate the suitability of different parameters. In addition, by use of a glufosinat resistant sugar beet transformant, the practicability of the critical period was investigated. Application of the critical period and moreover the definition of a general period threshold requires a reference value defining the beginning and end of the critical period which is both independent of location and season. The primary aim of this work was to establish a parameter, which fulfills this condition. All parameters relate to the growth of sugar beet or of the weed quantify their interaction. The following parameters were investigated: the leaf stage of the sugar beet, the weed and sugar beet coverage level, the relative weed coverage, the temperature sum and the intensity of weed shading of the beets. The investigation took place at three separate sites in the Ukraine and in Stuttgart-Hohenheim enabling the effect of different sites to be taken into account. A uniform sugar beet leaf stage until and after weeds could be tolerated was not found. The leaf stage until weeds could be tolerated varied between the 2 and 10 leaf stage. Similarly the leaf stage after which the weeds could be tolerated varied between the 2 and 12 leaf stage of the beet. A uniform and therefore location and year-independent degree of sugar beet coverage and weed coverage relating to leaf stage was not found at the beginning of the critical period at the Hohenheim site (1999 and 2000) and Poltava (1999) in the Ukraine. The degree of weed cover varied at the beginning of the critical period between 96.7% and 66.5% in Hohenheim. The same applies to the degree of sugar beet coverage which varies between 5.3% and 15%. The difference between the two levels of coverage is almost completely compensated by the parameter relative weed coverage. At the Hohenheim site it only varied between 94.8% and 84.5%. The minimum value was found at Poltava with 83.8%. On this basis, a maximum relative weed coverage of 83 % can be tolerated without significant yield loss. Herewith, a decisive parameter is defined as a measure for timing weed control in sugar beets. However, an important requirement is the availability of efficient control methods at this certain point of time. In a further step an attempt was made to apply the critical period in relation to the leaf stage of the beet by using a glufosinate resistant sugar beet transformant. In no trail it could be waited with glufosinate applications until the beginning of the critical period. The latest leaf stage, when glufosinate application had to start in Poltava and Vinnitsa was the 6-leaf stage, whereas the critical period began at the 10- or 12-leaf stage. A limiting factor for the definitive application of the beginning of the critical period was shown in the field trials by a decreasing tolerance of the glufosinate resistant transformant at ever later leaf stages of beet development. Prediction model investigations confirmed this correlation. In addition to the effect of the leaf stage the effect of weather conditions was also apparent. The increase in air humidity from 50 % to 80 % led to an increase in NH3 concentration in the resistant transformant, regardless of its leaf stage. NH3 is found in non-resistant plants due to the inhibition of glutamine-synthetase by glufosinate, which leads to cell death. The largest increase in NH3 when the air humidity was increased from 50 % to 80 % occurred at the youngest leaf at the 6-leaf stage. In addition to the dependency of NH3 concentration on leaf stage the effect of leaf age was also apparent. Concluding, the control of weeds, related to the leaf stage of glufosinate resistant sugar beet, has to be done before the critical period begins. Unfortunately, technologies, which offer the possibility to control weeds by an integration of the critical period, are so far not available.
Zur Diversität von Galium aparine L.-Herkünften
(2003) Ernst, Vera; Hurle, Karl
G. aparine is known as a very adaptable and worldwide distributed plant species. It is one of the worst weed species in numerous crops causing severe problems. Occasionally, a high degree of variability of G. aparine regarding to morphological and phenological characteristics was reported as well as to its herbicide susceptibility. Because of these observations and the necessity to gain more information about the biology and ecology of this species to perform a successful control of this weed in the field the variability of G. aparine was investigated. In comparative studies 24 field populations of different origins within Europe were used. For some of these populations the history of field management for the last few years was known. Additionally to the field populations one population from a hedgerow and one population of G. spurium has been further characterized. One central aim of these studies was the determination of the susceptibility of the populations against different herbicides. Furthermore the morphology and phenology of the different populations were also characterized. The variability of selected populations was examined by RAPD-PCR, too. The results of herbicide susceptibility tests showed that field populations of G. aparine reacted differently to the various herbicides. The largest differences in susceptibility were observed for the test herbicide, where one population showed a 6,8-fold higher tolerance than the most susceptible population (ED90). Low variability was detected for Mecoprop-P and Cinidon-ethyl, where populations differed at a factor of at most 1,5 and 1,7, respectively. Nearly all populations could be controlled with reduced herbicide concentrations compared to the recommended dosages. No resistant population was observed. Further, no significant differences between field populations and the hedgerow population could be detected. In several experiments the population of G. spurium tended to react slightly more susceptible towards the herbicides than G. aparine. A correlation between herbicide susceptibility and chemical control measures as described in the field history of the few past years could not be observed. The results with the test herbicide and Cinidon-ethyl might be interpreted as natural variability, because the active agents have not been on the market before sampling of the plants. Populations from adjacent fields showed as different susceptibilities as populations from distant fields, so that no regions with populations predominantly expressing significant levels of susceptibility or tolerance could be identified. The morphological and phenological tests showed that all populations differed regarding to many parameters. For most parameters the differences between the populations were in an identical range and persistently the populations differed at a maximum factor of 1,2-1,5. Higher differences than at this scale could be observed for the size of cotyledons, the number of seeds and the seminal yield. For the last parameter the largest differences could be observed with a maximum factor of 2,4 between the population with the smallest and highest seminal yield. Further, some populations showed a stronger habit than others. In a cluster analysis the G. aparine populations were divided into four groups. There was no difference between the field populations and the hedgerow population, but the population of G. spurium was, as expected, clearly different from G. aparine. An analysis of correlation revealed correlations for several parameters. For example, an early beginning of flowering was accompanied by a higher seminal yield. Some characteristics could furthermore be correlated with the geographic origin of the populations. Populations from northern and western locations often tended to have a less stronger habit than populations from the southern regions. Furthermore the onset of flowering was delayed compared to the populations from the more southern regions. The different characteristics could not been explained with the field history of the populations. Certainly the field history as well as climatic and geographic factors may have influenced the different morphology and phenology of the populations. In summary no morphological and phenological differences were detected between more sensitive or less sensitive populations. The results of the RAPD-PCR showed that 17 out of 40 tested primers were suitable to indicate polymorphisms between the different populations. They have been used to calculate the genetic similarity of the populations. The resulting genetic similarity of the G. aparine populations including the hedgerow population was between 93 and 97 %. G. spurium differed clearly from Galium aparine. No correlations could be detected between the results of the molecular and the morphological, phenological and herbicide susceptibility tests.