Effect of sowing dates and fertilizer on the severity of stem borer (Busseola fusca Fuller,Lepidoptera: Noctuidae) on sorghum in Eritrea

The influence of sowing date and fertilizer application on the incidence anddamage ofthe maize stemborer (Busseolafusca Fuller) in sorghum(Sorghumbicolor L.) was investigated at the Halhale Research Centre in Eritrea during 1997 - 99. The trials were conducted in a splitplot design with sowing date as the main plot and fertilizer as subplots. There were six sowing dates at an interval of 15 days starting fromearly April tomid-June. There were fertilized and unfertilized subplots. Data on larval count, per cent infestation, per cent deadheart, heading and maturity dates, plant height and yield were recorded for each plot. Fertilizer had no effect on the incidence and damage of the stem borer (B. fusca). There was no interaction between fertilizer and sowing dates on the larval population and damage by stem borers. Sowing date had a significant effect on stem borer incidence and damage levels. Early sowing dates (April 1 and 15) had a significantly lower number of larvae, infestation, deadheart and gave higher yields compared with the other sowing dates while late sowing dates (mid-May- mid-June) resulted in significantly higher infestation and damage. The highest infestation and damage were recorded from mid-May sowings. High stem borer infestations in delayed sowing was due to the coincidence of the susceptible stage of the crop (3 - 6 weeks after germination) with high populations ofstemborer larvae fromthe first generationin late June and July. Mid- and late sown crops were also later attacked by the second generation at the grain-filling stage in September- October. These results indicate that early planting (April) is effective in reducing stem borer damage on sorghum in the highlands of Eritrea.     

Quantitative aspects of Orobanche crenata infestation in faba beans as affected by abiotic factors and parasite soil seedbank

The interactions between the root parasitic weed Orobanche crenata Forsk. and its host plant faba bean ( Vicia faba L.) were quantified under controlled and field conditions at ICARDA's Tel Hadya research station. In the field experiments conducted in 1993–94 and 1994–95 faba beans were sown on two dates, in plots with 0, 50, 200 and 600 O. crenata seeds kg^–1 soil, under both limited and sufficient moisture supply. The effects of temperature on the duration of the early developmental stages of O. crenata were investigated in a growth chamber. The extent of O. crenata infestation was closely related to the number of parasite seeds in the soil. The seed-density treatment with 600 seeds kg^–1 soil resulted in complete crop failure. Furthermore, O. crenata infestation was higher under sufficient than under limiting water supply conditions, irrespective of sowing date. Only in the moderately infested plots, did shifting of the planting time of faba bean result in a significant decrease in parasite dry weight and an increase in crop seed yield. The timing of germination, attachment and further developmental stages of O. crenata was not related to faba bean growth stage and was affected primarily by soil temperature. The duration of O. crenata developmental stages was estimated using the thermal time concept. The relationship between total number of parasite attachments at the harvest of the faba bean crop and O. crenata seed density was dependent on maximum faba bean root-length density measured by the start of pod-filling in each treatment combination of sowing date and moisture supply. The results are discussed with reference to implications for the development of a dynamic simulation model for the prediction of faba bean yield losses caused by O. crenata .     

基于连续14年国家绿豆品种区域试验的中国绿豆品种产量和性状变化

利用GGE双标图、变异系数法、相关性分析、多元回归和聚类分析等方法,分析了2003—2016年共14 a国家绿豆品种区域试验中来自内蒙古自治区、黑龙江省、吉林省、辽宁省、山西省等12个绿豆主产省（市、自治区）的29个育种单位提供的130个参试品种的生育天数、株高、主茎节数、主茎分枝数、荚长、单株荚数、荚粒数、千粒重以及产量在春播组和夏播组的变异,并比较了性状间的相关性以及不同育种单位选育的绿豆品种的性状差异。结果表明：2003—2016年春播组和夏播组绿豆产量分别增加14.0%和25.4%,年均增幅分别为1.0%和1.8%;主茎分支数分别减少12.0%和15.9%;其他性状变化不明显。春播组绿豆主要农艺性状的变异系数为5.14%~17.01%,均值为11.33%;遗传多样性指数为1.91~2.08,平均为1.99。夏播组绿豆主要农艺性状的变异系数为5.96%~19.99%,均值为12.52%;遗传多样性指数为1.98~2.17,平均为2.07。相关性和偏相关性分析表明,春播组中产量与荚长、单株荚数和荚粒数显著正相关,与其他性状的相关性不明显;夏播组中产量与单株荚数和荚粒数显著正相关,与株高、主茎分支数和荚长显著负相关。多元回归分析表明,春播组绿豆生育天数、株高、主茎分支数、荚长和单株荚数共同决定产量60.9%的变异;夏播组绿豆株高、主茎分枝数、单株荚数、荚粒数和千粒重共同决定产量87.7%的变异。依托品种选育区域的聚类分析表明,65个春播组品种被分为4类,在北京市、河北省、山西省、河南省、山东省、吉林省和陕西省综合表现较好;65个夏播组品种被分为6类,在河南省、河北省和山东省综合表现较好。2003—2016年,国家每轮区试的绿豆品种产量稳步提升,表明我国绿豆育种水平有了一定提升;但品种遗传基础狭窄,育种方法多样化程度较低,缺少突破性品种。     

Modelling regional level spatial distribution of aphid (Lipaphis erysimi) growth in Indian mustard using satellite-based remote sensing data

Abstract

We developed a procedure for preparing a model for mapping spatially distributed zones of aphid pest (Lipaphis erysimi) outbreaks at a regional level. This study employed near-surface meteorological parameters derived from National Oceanic and Atmospheric Administration (NOAA) Television and Infra-Red Operational Satellites (TIROS) Operational Vertical Sounder (TOVS) data and field observations of disease infestation. The study area comprised three sites representing semi-arid and sub-humid regions of dominant Indian mustard (Brassica juncea L.)-growing regions of India. A model based on TOVS-derived cumulative surface air temperature and minimum specific humidity (SpH) was developed to estimate the date of ‘aphid onset’ (first appearance), date of peak infestation and location of severity with respect to aphid population density. Aphid population growth rate during the linear growth phase between aphid onset to peak was computed using SpH-weighted temperature and dates of sowing of the crop (crop age). Sowing dates of mustard crop, of northwest India, were obtained from spectral growth profiles derived from time series remote sensing (RS) products of the SPOT-4 VEGETATION sensor. Estimated dates of peak aphid infestation and peak population showed a strong match with the observed data. The location of peak aphid population density was depicted in each spatial grid of 25×25 km² for parts of northwest India. The simulated aphid population build-up and date of peak population density was validated with observed data for an unknown site in the Sriganganager district, Rajasthan state, India. Comparison of predicted dates of attaining peak aphid population with observations showed a deviation of ±7 days. After validation, the regional level model was applied over a large area of a mustard-growing region for varying dates of sowing, surface air temperature and specific humidity, to show the spatial distribution of aphid growing severity zones (population density) and to predict dates of severe aphid infestation (peak population) at each grid level in the region.     

Evaluation of integrated crop management strategies employed to cope with Striga infestation in permanent land use systems in southern Benin

Striga hermonthica and S. gesnerioides pose serious threats to cereal and cowpea production, endangering peoples' livelihoods on the Abomey plateau, Benin. A 2-year joint experiment was undertaken with farmers in two hamlets to investigate the potential of managing sowing dates of cowpea, sorghum transplanting, and trap cropping as ways of increasing agricultural production and reducing Striga damage. Early sowing of cowpea failed due to dry spells. Late sowing reduced cowpea yield due to water deficiency at the end of the growing season. Transplanting sorghum seedlings raised in fertilised or Striga-free nurseries doubled or tripled cereal yield and substantially reduced S. hermonthica infestation compared to direct early-sown sorghum. Transplanting sorghum from plant hills to fill gaps was unsuccessful. Trap crops such as cowpea and groundnut increased subsequent maize yield. Trap cropping had only a small effect on S. hermonthica infestation. The very poor soils in Somè central were a major constraint upon yield improvement to acceptable levels even after the introduction of the new crop (and Striga) management methods.     

Effect of host and inoculum patterns on take-all disease of wheat incidence,severity and disease gradient

The importance of the spatial aspect of epidemics has been recognized from the outset of plant disease epidemiology. The objective of this study was to determine if the host spatial structure influenced the spatio-temporal development of take-all disease of wheat, depending on the inoculum spatial structure. Three sowing patterns of wheat (broadcast sowing, line sowing and sowing in hills) and three patterns of inoculum (uniform, aggregated and natural infestation) were tested in a field experiment, repeated over 2 years. Disease (severity, root disease incidence, plant disease incidence and, when applicable, line and hill incidences) was assessed seven times during the course of each season and the spatial pattern was characterized with incidence-incidence relationships. In the naturally infested plots, disease levels at all measurement scales were significantly higher in plots sown in hills, compared to plots sown in line, which were in turn significantly more diseased than plots with broadcast sowing. Disease aggregation within roots and plants was stronger in line and hill sowing than in broadcast sowing. Analysis of the disease gradient in the artificially infested plots showed that the disease intensified (local increase of disease level) more than it extensified (spatial spread of the disease), the effect of the introduced inoculum was reduced by 95% at a distance of 15 cm away from the point of infestation. Yield was not significantly affected by sowing pattern or artificial infestation.     

Effects of soil moisture and sowing depth on the development of bean plants grown in sterile soil infested by <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">Trichoderma harzianum</Emphasis>

The effects of soil moisture (varying from 15% to 42% (v/v)) and sowing depth (1.5–6.0 cm) on the development of bean plants grown in sterile soil infested by the pathogen Rhizoctonia solani and its antagonist Trichoderma harzianum were studied under greenhouse conditions. The four possible combinations of soil infestation with both fungi were tested. Disease severity, percentage of plants emerged, plant height and dry weight were evaluated 3 weeks after sowing. Emergence rate and growth of plants inoculated only with R. solani were not affected by soil moisture, but in the presence of both fungi, plant emergence, plant height and dry weight significantly decreased when soil moisture diminished. Deep sowing significantly reduced the emergence rate and growth of those plants that were inoculated with R. solani only. However, when the soil was infested with both fungi, the effect of sowing depth was not significant. At a sowing depth of 6.0 cm, the percentage of plants emerged was 50% in the presence of T. harzianum, but only 6.7% when the pathogen was inoculated alone. The antagonist protected bean seedlings from pre-emergence damping-off, reduced disease severity and increased plant growth in the presence of R. solani, especially in moist soil.     

Introduction of exotic parasitic wasps for the control of Liriomyza trifolii (Dipt., Agromyzidae) in Senegal

Abstract

Liriomyza trifolii Burgess had first been reported from Senegal in 1980. Field surveys in 1982 revealed its presence in all vegetable growing areas of the country, heaviest damage being registered in the Cap Vert. Five indigenous eulophids (larval parasitoids) plus five other rare parasitoids, frequently parasitized over 90% of the flies. These rates were higher in insecticide free fields, and very much above the 30–40% reported for 1981. The most important parasitoids were Hemiptarsensus semialbiclava (Girault), which dominated in the second half of the dry season, and two Chrysonotomyia spp., which were more abundant in the rainy season. Surveys for exotic parasitoids indicated Diaulinopsis callichroma Crawford from Trinidad to be a promising species for introduction in the New World. This parasitoid, together with eight other chalcidoids (mostly larval parasitoids) and two braconids (larval‐pupal parasitoids), were collected in the field or received from established insectary cultures. They were studied and shipped for rearing and release in Senegal. Nine species were released at the end of 1982 and in 1983. Many were recovered shortly after release, but only Opius dissitus Muesebeck was recovered in later samples and became relatively abundant.     

Predicting the risk of weed infestation in winter oilseed rape crops

Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.     

Influence of tillage,planting date,and Bt cultivar on seasonal abundance and within-plant distribution patterns of thrips and cotton fleahoppers in cotton

Abstract

Thrips (Thysanoptera: Thripidae( and cotton fleahoppers, Pseudatomoscelis seriatus (Reuter( (Hemiptera: Miridae(, are considered to be significant economic pests of cotton in Texas, USA. A 2-year field study evaluated the influence of planting date, tillage practice, and Bt cotton on seasonal abundance patterns of thrips and cotton fleahoppers and their within-plant distribution patterns in cotton. Thrips were sampled visually while fleahoppers were sampled both visually and with a ‘beat bucket’ at weekly intervals throughout the growing season. Thrips infestations had two distinct peaks, with the first peak at the one to two main stem node leaf stage and the second peak during the flowering stage. Cotton fleahoppers had only one infestation peak at 13 – 15 weeks after planting (after crop cutout(. Average seasonal abundance of each pest was significantly influenced by tillage practice with higher numbers in conventional tillage compared with that in conservation tillage plots. Thrips abundance was similar between the two cultivars, whereas cotton fleahopper abundance was significantly higher in non-Bt cotton compared with that in Bt cotton. Thrips average seasonal abundance was significantly higher in timely planted cotton compared with that in late-planted cotton. Thrips were more prevalent in upper one-third vertical stratum (51%( followed by middle stratum (33%( and the lower stratum (16%(. Cotton fleahopper within-plant distribution was similar to that for thrips, with 65, 24, and 11% of the total abundance found in upper, middle, and lower one-third of the plant, respectively.     

Soybean stem fly,Melanagromyza sojae (Diptera: Agromyzidae), on Sumatra: Seasonal incidence and the role of parasitism

Abstract

The density of M. sojae and percentage parasitism was studied in unsprayed soybean at 18 farmers’ field sites in Aceh, North Sumatra and West Sumatra provinces, Indonesia, during 1992 and 1993. M. sojae generally infested soybean throughout the season; infestation was initially low, reached its peak from the fifth till the eighth week after planting and declined towards the end of the season. A complex of seven hymenopterous parasiloids had a high impact on the pest. Parasitism levels built up alongside with host density and remained high until just before harvest. The eucoilid Gronotoma sp. was the most prevalent species during the early and mid‐season; a complex of pteromalids became dominant towards the end of the season. In soybean planted successively at 2‐week intervals, the parasitism level in the first‐planted crop built up slowly, whereas the parasitism level in the third‐planted crop was high from the early crop stage onwards, which suggests that the third‐planted crop benefited from parasitism build‐up in the earlier‐planted crops. The role of parasitoids in controlling beanflies in unsprayed soybean is discussed.     

Effect of plant density on grain yield, root–length density and Orobanche crenata infestation in two faba bean genotypes

The effect of host plant cultivar and sowing density on Orobanche crenata Forsk. L. infestation in Vicia faba was studied in a field experiment in north–west Syria. Two faba bean genotypes. ILB 1814 (Syrian Local Large) and 402/29/84 (new breeding line from Egypt), were planted at four sowing densities. Whereas ILB 1814 was severely affected by O. crenata , 402/29/84 proved to be highly resistant. Sowing density did not have a significant effect on O. crenata dry weight in either genotype. However, the number of O. crenata attachments in ILB 1814 was positively correlated with plant density. The resistance of faba bean genotype 402/29/84 to O. crenata is due to: (a) less plant vigour and root–length density; (b) necrosis of host cells preventing O. crenata attack either before or just after penetration into the host root, or developing a barrier in the host root after the formation of a small tubercle: (c) early flowering and pod setting.     

Erarbeitung eines Testverfahrens zur Bestimmung der Protektiv- und Kurativleistung von Fungiziden bei der Bek?mpfung des Erregers der Stemphylium-Laubkrankheit Stemphylium botryosum in der Spargelkultur (Asparagus officinalis L.)

The foilage of Asparagus officinalis L. has a large contact surface for different leaf diseases, which can lead to profits cuts, especially by the causal pathogen of Stemphylium leaf spot, Stemphylium botryosum. The maintaining healthy of the foliage is an important precondition to achieve an optimal harvest in the following year. Therefore, it is necessary to describe the efficacy of currently approved plant protection products against S. botryosum in order to optimize the fungicide applications. In the context of greenhouse trials with asparagus seedlings a method should be developed to evaluate the preventive and curative efficacy of fungicides. At the beginning, stable, repeatable and homogeneous infections of S. botryosum needed to be achieved. Ad hoc the factors plant age (weeks after sowing date), inoculum (density of conidia per ml and concentration of malt), infection conditions (period of high relative humidity) and day of rating, as well as their influence on the occurrence of the symptoms, were investigated. With the exception of the factor plant age, the other factors had a significant effect on the infection. For the trials to evaluate the efficacy of fungicides, the analysed factors were defined. The age of the seedlings was six weeks after sowing, the inoculum was composed of 1,00?×?10⁵ conidia per ml combined with an 0,5% malt concentration, as infection condition the ??tunnel system?? with periodically high relative humidity was chosen. 13 days past infection was the optimal day of rating. To apply the seedlings with the fungicides, the registered application rate was reduced to 1/5. The trials to evaluate fungicides were conducted with the fungicides Signum^®, Rovral^® WG and two different testing agencies. At four consecutive application days, the plants were covered with fungicides. In the following, the infestation degree of stems in percent was evaluated. Additionally, the used S. botryosum-Isolates were biomolecularly investigated and the QoI- and SDHI resistance state determined.     

Ninth Commonwealth Conference on Plant Pathology

Abstract

Data on shoot borer, Chilo infuscatellus Snell., infestation and granulosis virus infection were collected from sugarcane planted during early and late main seasons and special season on 45, 60, 75 and 90 days after planting. The shoot borer infestation varied significantly among seasons of planting and age of the crop. It was low in March‐April planted crop compared to December‐January and special season planted crops owing to higher rainfall. The infestation was more on 45 and 60 days old crop compared to 75 and 90 days. The seasons of planting, age of the crop and stage of the host larva failed to have any significant influence on the virus infection.     

Bioresidual and integrated pest management status of a biorational agent and a novel insecticide against whitefly and its key parasitoids

The effects of continuous exposure of the adult and crawler stages of the whitefly, Trialeurodes vaporariorum, and adult of the parasitoids Encarsia formosa and Eretmocerus eremicus to spray deposits of potassium salts of a fatty acid and diafenthiuron applied at recommended rates were evaluated. French bean, Phaseolus vulgaris Prince, plants were sprayed and the adults confined on them using modified 5 cm Petri dishes. Fresh (4 - 5-h-old) deposits of fatty acids resulted in a 10.7% mortality rate of whitefly adults and 8.0 and 10.7% mortality rates of E. formosa and E. eremicus adults respectively, while fresh deposits of diafenthiuron resulted in a 62.7% mortality rate of whitefly adults and 12.0 and 14.7% mortality rates of E. formosa and E. eremicus respectively. The mortality rate (6.9 and 69.7%) of whitefly crawlers was recorded when exposed to 24-h-old deposits of fatty acids and diafenthiuron respectively. The mortality rate declined as the deposits aged. Adult parasitoid emergence from the treated pupae was unaffected. Spray deposits of diafenthiuron were effective against whitefly for up to 2-3 weeks in comparison with fatty acids, which were effective only when sprayed. Both products were harmless to adults as well as pupae of both parasitoids irrespective of the exposure period (age of deposits) tested (IOBC Class 1). These insecticides can be included in integrated pest management strategies against whitefly with the fatty acids used on horticultural crops.     

Fourth International Conference on Spices

Abstract

The present article suggests a simple procedure for estimating yield and production losses in a given crop and region. The utility of the procedure is illustrated by an empirical application to bean production in Cauca Valley, Colombia. Using data obtained from direct field observations on a panel of farms, a production function approach is used to estimate yield and production losses caused by each of the yield constraints identified. It is expected that such estimates will be useful for establishing agricultural research priorities. In an empirical analysis of bean production in Cauca Valley, six important yield limiting factors were identified. Unfavourable rainfall conditions caused a yield loss of about 32% and a total production loss of about US $1.2 million for the region during one growing season. The production losses caused by rust and bacterial blight were slightly smaller. Other important yield constraints were Empoasca kraemeri, angular leaf spot and the use of noncertified seed. Small production increases could be obtained by increasing input use and plant population.     

Effects of sowing date on severity of blight caused by <Emphasis Type="Italic">Ascochyta rabiei</Emphasis> and yield components of five chickpea cultivars grown under two climatic conditions in Tunisia

Five chickpea cultivars, Chitoui, Neyer, Kasseb, Beja 1 and Bouchra, were planted on three sowing dates at two Experimental Stations in Tunisia: Bou Salem in the north and the more southerly Mornag, where the climate is drier. Severity of blight, caused by Ascochyta rabiei, was measured on a 1–9 scale (defined) on vegetative parts and on pods as percent infected and percent infected that were empty. At both locations, disease was essentially absent on plants sown on the third dates but present on plants sown on the two earlier dates. At Bou Salem, disease severity was highest for the second sowing date whereas at Mornag it was highest for the first sowing date; but for each sowing date, disease severity was lower at Mornag than at Bou Salem. Yield components were measured as number of pods per plant, number of seeds per plant, number of seeds per 100 pods, 100 seed weight and weight of seeds per plant. Both disease severity and yield differed significantly among sowing dates (differently at each location) and also among cultivars for each sowing date, these differences depending both on sowing date and location. A lower yield was always associated with a higher disease severity, although the quantitative relationship differed between cultivars and locations. Cultivar Beja 1 had the lowest vegetative disease scores at both locations and both sowing dates 1 and 2. Beja 1 also scored well for all yield components. Plants sown on the third (latest) date gave the highest yields for all cultivars at both locations (except for an unusually high yield of Neyer at Mornag on sowing date 2), in some instances being more than double those from the earlier sowing dates. Thus, in contrast to other studies, late sowing did not result in yield loss.     

Foliar Sprays and Disulfoton Granules for the Control of Aphis gossypii on Okra

Abstract

Monocrotophos, omethoate, formothion, methomyl, pirimicarb and phosphamidon applied as foliar sprays were the most effective of insecticides evaluated in field trials for the control of Aphis gossypii Glov. on okra. Three applications were required to control infestations on plants sown during October to February. Disulfoton granules applied to the soil at sowing remained active for a long period, the duration depending on the method and rate of application. A dosage of 0.1 g a.i./plant hole was effective throughout the season. Residues of disulfoton and its metabolites in the harvested crop were negligible. Using such methods of aphid control, okra yields were increased by 97–119%.     

Potential of parasitoids to control populations of the weevil Ceutorhynchus obstrictus (Marsham) on winter oilseed rape

Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) is a major pest of oilseed rape in Europe and North America. The last decade has seen growing interest in the occurrence, importance and efficiacy of its parasitoids as biocontrol agents. The infestation of pods by C. obstrictus larvae and their parasitism rates were assessed in a total of nine commercially-grown crops and fifteen experimental plots of winter oilseed rape in 2004–2007. Pod samples were collected at the pod maturation stage and incubated in emergence traps. Emerged larvae, their exit holes and parasitoids were counted and identified; the percentage of infested pods and parasitism rates were calculated. Pod infestation by larvae increased continuously over the study period. The parasitism level was lowest in 2005 and increased thereafter up to 96%. The most abundant parasitoid was Trichomalus perfectus (Walker), but Mesopolobus morys (Walker) and Stenomalina gracilis (Walker) (Hymenoptera: Pteromalidae) were also reared from host larvae. This study showed that naturally-occurring ectoparasitoids of C. obstrictus were capable of becoming established as viable populations and have the potential to contribute to biological control of C. obstrictus.     

Verändern pfluglose Bodenbearbeitung und Frühsaaten die Unkrautvegetation im Winterraps?

Between 2005 and 2007 a total of 1364 oilseed rape (OSR) fields in 12 federal states of Germany was surveyed. Investigations took place in late autumn and included the identification and counting of all weeds in unsprayed parts of rape fields. Results on the impact of tillage intensity and crop sowing date on the level of total weed infestation, weed species number and weed flora composition in OSR fields are shown and those species identified which are sensitive to the analysed factors. Neither tillage intensity nor crop sowing date affect the level of weed infestation in OSR fields. In contrast, species richness was enhanced by non-inversion tillage as well as by an early crop sowing. While there were statistically proofed differences in the weed species composition of ploughed and unploughed OSR fields due to canonical correspondence analysis, the crop sowing date only had minor effects on species composition. Nevertheless, a multitude of single weed species was affected by tillage intensity and sowing date showing significantly differing relative frequencies and/or densities in fields with inversion and non-inversion tillage as well as between early and late sown crop. Among others Centaurea cyanus, Anchusa arvensis, A. spica-venti and Elymus repens were more abundant and partly reached higher densities after ploughing, whereas non-inversion tillage mainly favoured Galium aparine, Geranium spp. and Sisymbrium spp.. Lots of weed species tended to have higher populations when OSR was sown before August 15^th, species significantly increased by early sowing date were e. g. Centaurea cyanus, Convolvulus arvensis, Euphorbia spp. and Anchusa arvensis. However, only V. arvensis reached significantly higher densities when OSR was sown after September 1^st.