A second survey of cereal weeds in central southern England

A survey of grass weeds of cereals in central southern England made in 1981 was repeated in 1982 between 28 June and 23 July. Dicotyledonous weeds were also assessed in 1982. A total of 1021 fields were surveyed, 702 in winter wheat. 198 in winter barley and 121 in spring barley. A total of twenty-four grass weeds were found and their levels of infestation were scored. The most frequently found grass weeds were the same as in 1981. In all cereals combined, these were Elymus (Agropyron) repens in 35% of fields, Avena fatua in 32%, Alopecurus myosuroides in 26% and Poa trivialis in 24%. Sixty-three species of dicotyledonous weeds were recorded and of these, eighteen species occurred in 2% or more of fields. The eight most frequent were Viola arvensis, Galium aparine, Stellaria media, Myosotis arvensis, Polygonum aviculare, Convolvulus arvensis, Bilderdykia (Polygonum) convolvulus and Lamium purpureum. Most species were fairly uniform in distribution, but Galium aparine, Convolvulus arvensis and Cirsium arvense were most frequent in the east while Viola arvensis was least frequent there. The cereals varied in weediness, 32% of winter barley, 23% of spring barley and only 7% of winter wheat fields had no weeds recorded.     

A survey of grass weeds in cereals in central southern England

A survey of grass weeds in cereals in nine areas of central southern England was made in summer 1981 with the primary purpose of determining the importance of Bromus sterilis. A total of 1477 fields of winter wheat, 715 of winter barley and 434 of spring barley were assessed by visually scoring the whole field for grass flower heads. In all, 19 species were found; their levels of infestation were scored. In winter cereals the most frequent species were Avena spp. in 32% of fields. Agropyron repens in 24%, Poa trivialis in 22% and Alopecurus myosuroides in 19%. Bromas sterilis was next most frequent in 9%. In spring barley the two most frequent species were Agropyron repens in 53% of the fields and Avena spp. in 52%. The third most frequent was Alopecurus myosuroides in 1 1%. Bromus sterilis was recorded in 12% of winter wheat and 4% of winter barley crops, but did not occur in spring barley. Of the 206 fields where it was present it occurred throughout the field in only 82 and it was confined to the headlands in the remainder.     

Evaluating the accuracy of mapping weeds in fallow fields using airborne digital imaging: Panicumeffusum in oilseed rape stubble

The potential accuracy of using airborne multispectral imaging to map weed patches rapidly in a fallow field has been evaluated. An image of a field of oilseed rape ( Brassica napus L.) stubble interspersed with Panicum effusum R. Br. was acquired using a four-camera airborne digital imaging system; recording in the infrared, red, green and blue wavebands. The image was converted into georectified weed maps using supervised and unsupervised classification procedures. Comparison of the airborne-derived maps with an accurate weed map compiled from a detailed ground survey demonstrated that weed:non-weed classification and mapping accuracies of better than 87% are possible. The limitations of assessing the accuracy of classified imagery using ground-truth data of similar spatial resolution are discussed.     

A preliminary survey of arable weeds in Britain

Details and results are given of the first of two surveys, which are designed to measure the changes taking place in the incidence of forty species of arable weeds in Britain.     

快捕净防除油菜田杂草的效果

近年来 ,随着油菜免耕移栽面积的不断增加 ,出现了油菜田杂草出草时间早、出草数量大、草害严重的新特点。根据调查 ,目前油菜田仍以禾本科杂草为主。为有效防除油菜田禾本科杂草 ,我们引进了日本曹达株式会社生产的 1 0 %快捕净ＥＣ进行了田间试验。1　材料与方法1 1　以看麦娘为主的油菜田杂草防除试验试验设 1 0 %快捕净ＥＣ30ｍｌ/亩、5%高效盖草灵ＥＣ(江苏丰山农药集团产 ) 6 0ｍｌ/亩及不用药 ,共 3个处理。重复 3次 ,随机区组排列 ,小区面积 1 5ｍ2 。用药日期为 2 0 0 0年1 2月 8日 ,用工农 1 6型喷雾机喷雾 ,对水量为 30ｋｇ/亩…     

Herbicide sensitivity of transgenic multiple herbicide-tolerant oilseed rape

Glyphosate and glufosinate-ammonium herbicide tolerance traits were combined into both winter and spring lines of Brassica napus L. This allowed the study of possible interactions between these transgenes in two genetic backgrounds when treated with a variety of herbicides. Selective herbicides that are commonly used within Brassica crops showed no adverse effects on the transgenic plants or their null controls. Lines containing both glyphosate and glufosinate transgenes remained tolerant to their respective herbicides, regardless of the presence of the second tolerance transgene. Lines containing only a single transgene retained tolerance to the encoded trait and did not show cross-tolerance to the second. Null lines were killed by either herbicide. All plant lines, regardless of their transgene content, were found to be equally susceptible to three herbicides (paraquat, metsulfuronmethyl and mecoprop), commonly used to remove volunteer B napus from succeeding crops and set-a-side land.     

Biological control methods of pest insects in oilseed rape

Parasitoids, predators, insect pathogenic fungi, nematodes and microsporidia have all shown promise in the biological suppression of the key target pest, the pollen beetle Meligethes aeneus in rapeseed, as well as in the control of other rapeseed pests. Under favourable conditions pollen beetles are locally and temporarily already under efficient natural control by one or several of these agents, but overall the pollen beetle remains the number one pest of rapeseed in Finland, as well as elsewhere in Europe. Conservation biological control to enhance natural control appears the most feasible approach to solve the problem. Field and simulation data are used to demonstrate how a simple change in the tillage practice may be enough to obtain efficient control of the pollen beetle. Several other options are, or will be available, subject to successful registration of microbial products based on the fungi Metarhizium anisopliae and Beauveria bassiana , and the nematode Steinernema feltiae . Strategies and methods of applying these agents have been developed to facilitate either inundative treatments, or ecosystem restoration to (re-)establish the presence of these agents in agricultural fields. Critical components of agricultural practice have been identified for maximising control by biological agents within a functioning IPM system.     

Seed dressings to control slug damage in oilseed rape

Slugs are major pests of oilseed rape that are poorly controlled by conventional bait pellets. A series of laboratory experiments investigated the potential of seed-dressings to control slug damage in this crop. Four compounds: metaldehyde, methiocarb, cinnamamide and 3,5-dimethoxycinnamic acid (DMCA) were tested at a range of doses for phytotoxicity and ability to reduce damage by Deroceras reticulatum (Müller). Metaldehyde and methiocarb were not phytotoxic at any doses, whereas all doses of cinnamamide and DMCA were. All compounds reduced slug damage, but metaldehyde and methiocarb consistently performed better than cinnamamide and DMCA. Metaldehyde and methiocarb seed-dressings were compared with baited pellets containing the same active ingredients at recommended field doses. The seed-dressings protected plants from damage by D reticulatum and Arion subfuscus (Draparnaud) as well as, or better than, baited pellets. We therefore recommend that metaldehyde and methiocarb should be field-tested as seed dressings to control slugs in oilseed rape.     

A systemic pathway in the infection of oilseed rape plants by Leptosphaeria maculans

In growth room regimes arranged to simulate field conditions which coincide with natural infection of oilseed rape by Leptosphaeria maculans , leaf inoculation resulted in systemic infection. After colonizing intercellular spaces in the spongy mesophyll of the lamina, the fungus reached a vascular strand and spread down the petiole mainly in xylem vessels or between cells of the xylem parenchyma and cortex, eventually invading and killing cells of the stem cortex and causing the stem canker symptom. The intercellular systemic phase of growth, which was biotrophic and virtually sytnptomless, occurred under a wide range of temperatures.     

A crop loss-related forecasting model for sclerotinia stem rot in winter oilseed rape

Sclerotinia stem rot (SSR) is an increasing threat to winter oilseed rape (OSR) in Germany and other European countries due to the growing area of OSR cultivation. A forecasting model was developed to provide decision support for the fungicide spray against SSR at flowering. Four weather variables-air temperature, relative humidity, rainfall, and sunshine duration-were used to calculate the microclimate in the plant canopy. From data reinvestigated in a climate chamber study, 7 to 11 degrees C and 80 to 86% relative humidity (RH) were established as minimum conditions for stem infection with ascospores and expressed as an index to discriminate infection hours (Inh). Disease incidence (DI) significantly correlated with Inh occurring post-growth stage (GS) 58 (late bud stage) (r(2) = 0.42, P /= Inh(i). Historical field data (1994 to 2004) were used to assess the impact of agronomic factors on SSR incidence. A 2-year crop rotation enhanced disease risk and, therefore, lowered the infection threshold in the model by a factor of 0.8, whereas in 4-year rotations, the threshold was elevated by a factor 1.3. Number of plants per square meter, nitrogen fertilization, and soil management did not have significant effects on DI. In an evaluation of SkleroPro with 76 historical (1994 to 2004) and 32 actual field experiments conducted in 2005, the percentage of economically correct decisions was 70 and 81%, respectively. Compared with the common practice of routine sprays, this corresponded to savings in fungicides of 39 and 81% and to increases in net return for the grower of 23 and 45 euro/ha, respectively. This study demonstrates that, particularly in areas with abundant inoculum, the level of SSR in OSR can be predicted from conditions of stem infection during late bud or flowering with sufficient accuracy, and does not require simulation of apothecial development and ascospore dispersal. SkleroPro is the first crop-loss-related forecasting model for a Sclerotinia disease, with the potential of being widely used in agricultural practice, accessible through the Internet. Its concept, components, and implementation may be useful in developing forecasting systems for Sclerotinia diseases in other crops or climates.     

Evaluation of selected commercial oilseed rape cultivars for early vigour,weed suppression and yield in southern New South Wales

The potential of oilseed rape to suppress weed growth while maintaining optimal yield and quality is not well understood under field conditions in Australia. This study, conducted in Condobolin and Wagga Wagga, New South Wales (NSW), during 2015 and 2016, examined a diverse range of commercial oilseed rape cultivars for their inherent ability to suppress weeds and maintain yields when in competition with natural weed infestations, with and without pre-emergent herbicide treatment. Cultivar differences were observed in oilseed rape canopy architecture and yield; however, early-season biomass, light interception, leaf area index and visual vigour ratings exhibited both year and location interactions. Cultivars with the highest biomass, light interception, leaf area indices and visual vigour were typically also the most weed-suppressive, in particular GT-50 and Hyola 600RR. Although crop and weed biomass accumulation differed significantly among cultivars for both location and year, weed biomass was inversely related to cultivar biomass in both years and locations. Hybrid Hyola and GT-50 cultivars exhibited up to 50% less weed biomass while maintaining consistently high levels of dry crop biomass. In addition, pre-emergent herbicide applications reduced weed infestation and contributed to higher crop yield in both locations and years. Given the consistent aboveground competitive ability of certain oilseed rape cultivars, our study demonstrated that diverse cultivar-dependent competitive traits such as early growth vigour, biomass production, absorption of photosynthetically active radiation and production and retention of crop residue significantly impacted weed establishment and total weed biomass. Our findings suggest that cultivar selection offers potential as a tool for maintaining suitable grain yield in the presence of weeds while potentially delaying the development of herbicide resistance through efficacious weed suppression.     

不同药剂控制油菜田杂草效果

油菜是吴江市主要经济作物,常年种植面积均在13000hm2以上。自20世纪90年代以来,由于长期单一使用精禾草克防治看麦娘,导致油菜田杂草草相发生了明显变化,以繁缕为主的双子叶杂草上升为主要优势种,给油菜生产带来了威胁。为了寻找适合于吴江市目前油菜田杂草草相的安全、高效新     

Prediction of competition between oilseed rape and Stellaria media

Ten experiments have investigated competition between winter oilseed rape and Stellaria media (common chickweed). Yield losses caused by this weed were often high, but differed greatly between experiments, 5% yield loss being calculated to be caused by 1.4–328 plants m^?2. Predictions of yield loss based on relative weed dry weights [weed dry weights/(crop + weed dry weights)] in December were somewhat less variable than those based on weed density, 5% yield loss being caused by 1.4–10.6% relative weed dry weight. The variations in yield loss were related to variations in the competitiveness of the oilseed rape and the S. media, caused by weather differences between years and sites, and the long period between weed assessment and harvest (8–10 months). However, despite the lack of precise relationships, there were indications that the greater the crop dry weights in December, the lower the final yield loss. Delayed sowing of oilseed rape until late September did not clearly increase the competitive effects of the weed compared with late August/early September sowings. Weed competition was not clearly affected by reduced crop density (44–113 plants m^?2), because of the compensatory ability of the lowest density. The results of the experiments are discussed in relation to the prediction of yield loss and, thus, possible adjustment of weed control strategies to meet expected crop losses.     

Predicting light leaf spot (Pyrenopeziza brassicae) risk on winter oilseed rape (Brassica napus) in England and Wales, using survey, weather and crop information

Data from surveys of winter oilseed rape crops in England and Wales in growing seasons with harvests in 1987–99 were used to construct statistical models to predict, in autumn (October), the incidence of light leaf spot caused by Pyrenopeziza brassicae on winter oilseed rape crops the following spring (March/April), at both regional and individual crop scales. Regions (groups of counties) with similar seasonal patterns of incidence (percentage of plants affected) of light leaf spot were defined by using principal coordinates analysis on the survey data. At the regional scale, explanatory variables for the statistical models were regional weather (mean summer temperature and mean monthly winter rainfall) and survey data for regional light leaf spot incidence (percentage of plants with affected pods) in July of the previous season. At the crop scale, further explanatory variables were crop cultivar (light leaf spot resistance rating), sowing date (number of weeks before/after 1 September), autumn fungicide use and light leaf spot incidence in autumn. Risk of severe light leaf spot (> 25% plants affected) in a crop in spring was also predicted, and uncertainty in predictions was assessed. The models were validated using data from spring surveys of winter oilseed rape crops in England and Wales from 2000 to 2003, and reasons for uncertainty in predictions for individual crops are discussed.     

Latent infection of winter oilseed rape by Leptosphaeria maculans

Plants of oilseed rape, cultivars Primer and Jet Neuf, were grown in a glasshouse and inoculated at G.S. 2.4–2.7 with pycnidiospores or ascospores of Leptosphaeria maculans. The plants were kept for a further 2–4 weeks at 14°C and then transferred, together with uninoculated plants, to a polythene tunnel in winter. The majority of stems of inoculated plants did not have macroscopic symptoms of L. maculans infection 6 weeks after inoculation. Examination of whole mounts of peripheral tissue and transverse sections of fixed and embedded portions of these stems revealed intercellular septate fungal hyphae, often deep in non-necrotic cortical tissue, in symptomless inoculated plants but not in uninoculated plants. L. maculans was recovered following surface sterilization of adjacent portions of the same stems. When symptomless inoculated plants were transferred to a glasshouse at 18–20°C, cankers soon developed. The significance of these latent mycelial infections to canker development in the field is discussed.