The influence of weeds on aphid-specific natural enemies in winter wheat

Aphid-specific predators, aphid parasitoids and aphid-pathogenic fungi were sampled in 1980 and 1981 in plots of winter wheat treated or not with herbicides. Aphids and their natural enemies were also sampled from three abundant weed species. Aphid-specific predators were scarce in both years of the study, probably because of the scarcity of cereal aphids in the experimental plots, and no significant treatment effects on this group were recored. The syrphid, Platycheirus manicatus, was the only predator recorded from the weeds. Cereal aphids and the weed aphids, Brachycaudus helichrysi and Cryptomyzus galeopsidis, were attacked by the same species of aphid-pathogenic fungi but by different parasitoids. In the first year more Sitobion avenae were infected by fungal pathogens in weedy plots than in treated plots, either because of higher humidity or because of the spread of infection from weed aphids, or a combination of both. Weed removal had little effect on those parasitoid species which attacked cereal aphids. The small populations of cereal aphids which were present in the plots were unaffected by herbicide treatments.     

Width of clover strips and wheat rows influence grain yield in winter wheat/white clover intercropping

Cereal–legume intercropping offers potential benefits in low-input cropping systems, where nutrient inputs, in particular nitrogen (N), are limited. In the present study, winter wheat (Triticum aestivum L.) and white clover (Trifolium repens L.) were intercropped by sowing the wheat into rototilled strips in an established stand of white clover.A field experiment was performed in two fields starting in two different years to explore the effects of width of the wheat rows and clover strips on the competition between the species and on wheat yields. The factors were intercropping (clover sole crop, wheat sole crop and wheat/clover intercropping), rototilled band width, sowing width and wheat density in a factorial experimental design that enabled some of the interactions between the factors to be estimated. The measurements included grain yield, ear density, grain weight, grain N concentration, dry matter and N in above-ground biomass of wheat, clover and weeds and profiles of photosynthetic active radiation (PAR) within the crop canopy.Intercropping of winter wheat and clover resulted in wheat grain yield decreases of 10–25% compared with a wheat sole crop. The yield reductions were likely caused by interspecific competition for light and N during vegetative growth, and for soil water during grain filling. N uptake in the wheat intercrop increased during late season growth, resulting in only small differences in total N uptake between wheat intercrops and sole crops, but increased grain N concentrations in the intercrop. Interspecific competition during vegetative wheat growth was reduced by increasing width of the rototilled strips from 7 to 14 cm, resulting in higher grain yields and increased grain N uptake. Increasing the sowing width of the wheat crop from 3 to 6 cm increased interspecific interactions and reduced wheat intraspecific competition during the entire growing season, leading to improved grain yields and higher grain N uptake.     

A model to simulate yield losses in winter wheat caused by weeds,for use in a weed management decision support system

The ‘within-season’ module of the Weed Manager decision support system (DSS) predicts the effect of twelve UK arable weeds on winter wheat yields and profitability. The model and decision algorithm that underpin the DSS are described and their performance discussed. The model comprises: (i) seedling germination and emergence, (ii) early growth, (iii) phenological development, (iv) herbicide and cultivation effects and (v) crop yield loss. Crop and weed emergence are predicted from the timing and method of cultivation, species biology, and the weather. Wheat and weeds compete for resources, and yield losses are predicted from their relative leaf area at canopy closure. Herbicides and cultural control methods reduce weed green area index, improving crop yield. A decision algorithm identifies economically successful weed management strategies based on model output. The output of the Weed Manager model and decision algorithm was extensively validated by experts, who confirmed the predicted responses to herbicide application were sufficiently accurate for practical use. Limited independent data were also used in the validation. The development of the module required integrating novel and existing approaches for simulating weed seedling establishment, plant development and decision algorithm design. Combining these within Weed Manager created a framework suitable for commercial use.     

The economics of fungicide use in winter wheat in southern Sweden

In southern Sweden, fungicide treatment of winter wheat is prevalent and recommended almost routinely against leaf blotch diseases. However, yield increases and hence the resulting net returns from fungicide use are highly variable within and between years. These variations raise questions about whether, when and how fungicides should be used. To help answer these questions, a thorough economic evaluation of fungicide use was carried out, based on results from untreated plots and fungicide-treated plots in trials in farmers' fields, 1983–2007. Scenarios with varying grain prices and costs of fungicide treatment were evaluated and examined. Doubling and tripling the grain price led to the largest impact on the net return from fungicide treatment, followed by increasing cost of the fungicide. Other costs were of minor importance. The mean net return from fungicide use was no more than 12 € ha⁻¹ over the 25 years (2008 grain prices and costs used in calculations). Furthermore, the mean net return was negative in 10 years and less than 50% of the entries were profitable to treat in 11 years. Changes over time and changes in controllable factors (e.g. fungicide and cultivar choice, crop rotation, techniques) and uncontrollable factors (e.g. emerging and new diseases, price relations) influenced the profitability of fungicide use. Fungicide use was in fact more profitable (mean net return 21 compared with 3 € ha⁻¹) during the latter part of the period (1995–2007) than in the earlier part (1983–1994). Improved decision support systems in a holistic framework based on sound economics are urgently needed.     

Potential allelopathic influence of certain pasture weeds

Laboratory and growth chamber research was conducted to determine the potential allelopathy of tissue harvested from certain weeds commonly found in pastures. Results of bioassays indicated that the weeds dogfennel and mayweed chamomile are potentially allelopathic to alfalfa and Italian ryegrass seedlings. Leaf-tissue extracts from the two weed species reduced seedling growth more than stem and root extracts. In most experiments alfalfa seedlings were influenced more than Italian ryegrass seedlings and seedling growth was influenced more than seed germination. Leaf tissue from the weed species mixed into potting soil at a concentration as low as 0.25% (w/w) significantly reduced alfalfa and Italian ryegrass plant development and foliage production. Extract and tissue concentration used in this research were estimated to be similar to concentrations expected to occur within the pasture ecosystem and below concentrations that would result in hypertonicity in the bioassays.     

The selection of winter wheat varieties for whole-crop cereal conservation

Ten commercial varieties of winter wheat were sampled at different stages of growth, and dry mailer (DM) yields and potential nutritional quality, as determined by modified acid detergent fibre concentration (MADF), were measured. Maximum yields for the different varieties were spread over a four-week period, when the DM content was above 350 g kg⁻¹. When the varieties were harvested for conservation as either fermented (DM 380 g kg⁻¹) or alkaline (DM 580 g kg⁻¹) whole crop, the mean MADF concentration was similar at both harvests, with large differences recorded between varieties. At both harvests the quality of the crops was sharply increased by raising the cutting height from 10 to 40 cm above ground level.     

The influence of daylength on final leaf number in spring wheat

The influence of daylength on final leaf number was determined in four field-sown wheat cultivars with no vernalisation requirement. Leaf and primordium appearance was monitored in plots sown at two-month intervals during an annual cycle. The timing of the response to daylength varied substantially among cultivars. In one, final commitment of the last leaf primordium occurred close to the time of initiation of that primordium while, in another cultivar, commitment did not occur until terminal spikelet or later. In the other two cultivars, commitment occurred midway through spikelet initiation. Late timing of response to daylength is a useful adaptation that allows cultivars with no vernalisation response sown autumn to set more leaves than when sown in spring, and hence to delay flowering. Based on the analysis, a simple iterative procedure was developed that successfully predicted final leaf number, the dates of appearance of the flag ligule and anthesis for one of the cultivars grown in an independent experiment.     

Field studies on abscisic acid and embryonic germinability in winter wheat

Wheat (Triticum aestivum L.) cultivars differ in resistance to preharvest sprouting, which can occur when rains precede harvest. The objective of this study was to determine of sprouting resistance was related to endogenous levels of embryonic abscisic acid (ABA) and/or to the degree of embryonic sensitivity (capability of ABA to block embryonic germination) to exogenously applied ABA. Embryonic ABA levels and sensitivity were compared during the grain development period in 1983 and 1984 in a sprouting-resistant cultivar, ‘Brevor’, and a susceptible cultivar, ‘Greer’. The ABA levels were influenced by environment and year but not by cultivar, except at the soft-dough/ hard-dough transition stage of development in both years and at hard-dough stage in 1983. At those stages, Brevor had higher levels of free ABA than Greer. Embryonic ABA level and rate of germination of dissected embryos in water were not related, but the rate of germination was reduced by exogenous ABA (5×10⁻⁵M), and was reduced more in Brevor than in Greer. Differences in embryonic sensitivity to ABA, modulated by environmental conditions during the grain-filling period, may contribute to cultivar differences in resistance to preharvest sprouting.     

Reconciling alternative models of phenological development in winter wheat

Simulation of the timing of anthesis in wheat crops is achieved using two very different approaches. The older of these simulates progress to flowering by calculating the duration of phases between significant events on the shoot apex. The alternative method tracks development through leaf appearance, using the prediction of final mainstem leaf number to control the duration of the phase from emergence to flowering. Although these methods appear to differ substantially, we show in this paper that the number of leaves on the mainstem when the stage of terminal spikelet occurs is extremely tightly coupled to final mainstem leaf number. We conclude that accurate prediction of the terminal spikelet stage or similar prediction of mainstem leaf number amount to the same thing, so reconciling the methods.     

Yield response to pre-emergence control of broad-leaved weeds in winter cereals with isoxaben in France

A series of 59 trials was designed to assess the yield response to the control of broad-leaved weeds in winter cereals in the 1982/83, 1983/84 and 1984/85 seasons. When apllied pre-emergence to winter cereals, isoxaben provided season-long control of a wide spectrum of broad-leaved weeds including Veronica spp., Viola spp., Stellaria media, Aphanes arvensis, Papaver rhoeas and Matricaria spp. In 22 trials on winter barley and 37 trials on winter wheat treated pre-emergence with isoxaben in the autumn, mean yield increases of 0 · 22 t/ha and 0 · 14 t/ha respectively were recorded over that produced by herbicide combinations applied as post-emergence treatments in the spring. The mean yield increases with isoxaben over untreated controls were 0 · 30 t/ha and 0 · 26 t/ha on winter barley and winter wheat respectively.     

Effect of chemical and biological treatments on take-all of winter wheat

Several chemical and biological treatments were evaluated for control of take-all, caused by Gaeumannomyces graminis var. tritici, on winter wheat (Triticum aestivum). None of the treatments resulted in an effective suppression of take-all (percentage of roots with symptoms or whiteheads) or an increase in yield in naturally or artificially infested field experiments over 3 years. In a controlled-environment study triadimenol, imazalil and a combination of carboxin and thiram reduced the percentage of plants infected, and inoculating soil with G. graminis var. graminis gave good control. Disease development in field studies was limited in the fall. The greatest disease development occurred in the spring with the increase in soil temperatures. The lack of control of take-all by fungicides, such as triadimenol, which have been reported to be effective in other studies is discussed in relation to the development of the disease in south-eastern USA.     

Freezing tolerance of winter wheat plants frozen in saturated soil

Winter wheat is sown in the autumn and harvested the following summer, necessitating the ability to survive subfreezing temperatures for several months. Autumn months in wheat-growing regions typically experience significant rainfall. Hence, the wheat plants usually are exposed to freezing temperatures when they have high moisture content and are growing in very wet soil. Both of these conditions are conducive to freezing stresses different from those that occur under lower moisture conditions. This study was conducted to seek genetic variability among winter wheat lines and their progeny in the ability to tolerate freezing in saturated soil. Fully acclimated seedlings in saturated soil were frozen to a narrow range of temperature conditions that resulted in about 50% mortality of the most freezing tolerant lines studied. The temperature of the soil near the crowns of the plants was recorded every 2 min throughout each freezing episode. The following components were then determined for each freezing episode: the amount of time the plants remained in subfreezing temperature before all freezable water had been converted to ice; the rate of cooling from the freezing temperature to the minimum temperature; the minimum temperature; the length of time the plants remained at the minimum temperature; the rate of temperature increase from the minimum to 0 °C after freezing; and the total amount of time the plants were actually frozen. Partial regression analysis revealed the minimum temperature significantly influenced survival in all of the progeny populations, while the other five components significantly influenced survival in some, but not all of the populations, suggesting genotypic differences in the ability to tolerate variation in specific aspects of the freezing process. Evidence from progeny populations suggested that improved freezing tolerance was associated with decreased sensitivity to the length of time held at the minimum temperature and increased responsiveness to the post-freezing warming rate. Further analysis of this kind of variation may enable the genetic combining of sources of tolerance of the stresses imposed by specific components of the freezing process, leading to cultivars with improved tolerance of freezing in saturated soil.     

Chemical control of weeds in wheat (Triticum aestivum L.) in Iran

Experiments were conducted in 2006–2007 at six research stations of the Iranian Plant Protection Research Institute to study the efficacy of different herbicides to control weeds in wheat. Treatments included mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (WG) at 45 + 45 + 135 g a.i./ha, respectively, sulfosulfuron at 21, 31.5, 42 and 51 g a.i./ha, chlorsulfuron at 15 g a.i./ha, bromoxynil plus MCPA at 600 g a.i./ha with clodinafop propargyl at 64 g a.i./ha, sulfosulfuron plus metsulfuron-methyl at 36 g a.i./ha, mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (OD) at 15 + 3 + 45 g a.i./ha, respectively, and a full season weed-free control. Herbicides were applied at wheat tillering. Results showed that sulfosulfuron plus metsulfuron-methyl, and bromoxynil plus MCPA with clodinafop propargyl resulted in satisfactory weed control and wheat grain yield at most locations. Weed control efficacy of both formulations of mesosulfuron-methyl plus iodosulfuron-methyl-sodium was variable across locations. Efficacy of the OD formulation appears to depend upon location, so that application of this herbicide at Shiraz and Gorgan resulted in better weed control compared to use of the WG. Satisfactory performance of the OD formulation at Gorgan and Shiraz could be attributed in part to the even pattern of rainfall distribution during the growing season and wheat cultivar used, respectively. With respect to grain yield, however, the OD formulation was better than WG formulation at most of the locations.     

基于CBERS卫星遥感的冬小麦产量估测研究

对冬小麦产量进行遥感监测预报,有利于农业管理部门及时获取冬小麦区域产量信息,便于其制定有效的栽培管理措施,达到增产的目的。中巴资源卫星（CBERS-02）CCD影像具有较高的空间分辨率和较丰富的光谱信息,对植被及作物长势信息具有较强的探测能力。以江苏省泰兴市为例,进行了基于CBERS-02卫星遥感和小麦估产模型的冬小麦产量监测预报研究。在利用计算机分类结合人机交互式判读解译的基础上,结合GPS样点信息校验,进行冬小麦种植面积提取;利用影像提取的冬小麦NDVI数据,反演叶面积指数、生物量信息等,结合冬小麦估产模型,计算单点产量信息。经过线性转换,对整个区域的冬小麦产量进行分级监测预报,叠加样点的产量信息检验,最终制作了区域的冬小麦产量分级专题图。结果表明,冬小麦种植面积解译精度在90%以上,分级估产精度达到85%以上。中巴资源卫星影像数据基本能满足冬小麦长势监测和产量预报的需要,可以在实际农业生产中推广应用。     

冬季茶园虫病草无公害防治技术

冬季气温低,茶园虫、病、草除越年生杂草外,均停止生长发育,以不同形式进行越冬。越冬时期长,是一年最有利的防治时期。在防治策略上仍应坚持“预防为主,综合防治”的植保方针,认真做好茶园冬季虫、病、草的防治,减少越冬基数,为来年春茶丰产丰收,打下基础。     

Simulating multiple pest damage in varying winter wheat production situations

The production situation–injury profile paradigm can be used as a framework to assess the harmfulness of multiple-pest complexes in a changing agriculture. A mechanistic simulation model for wheat, WHEATPEST, was developed to incorporate drivers of (i) variable production situations and (ii) their related injury profiles. The model simulates the harmful effects of pathogens, pests, and weeds in a simple, open, generic manner. Simulation drivers were derived from published reports, in particular through a meta-analysis of highly detailed farmers’ field surveys in the United Kingdom and the Netherlands. Preliminary analysis of the model's performances indicates that WHEATPEST conforms with available published reports in a range of production situations and injury profiles. While improvement on some components of the model are discussed, this work points at the need for the collection of cross-disciplinary, reasonably accurate, and standardised data at a system's level, and at the usefulness of modelling tools for basic research and policy.     

Model predictions of winter rainfall effects on N dynamics of winter wheat rotation following legume cover crop or fallow

Winter rainfall in a Mediterranean region varies from year to year. Both release of inorganic N from soil organic matter (SOM) or a legume cover crop (LCC) and subsequent nitrate movement in the soil profile are strongly affected by winter rainfall, through its effects on soil water status and on vertical flux. N accumulation of a LCC also varies over years due to weather effects on growth. Thus, these two factors need to be taken into account for efficient use of SOM-N and LCC-N in a wheat (Triticum aestivum L.) rotation. To determine how winter weather might affect the performance of wheat-fallow rotations that include an LCC grown and incorporated during the fallow year, we used the CERES-wheat model and a 46-season weather record to simulate N dynamics of 2-year unfertilized and irrigated winter-LCC wheat systems with high LCC (236 kg N ha⁻¹) or low LCC (118 kg N ha⁻¹) inputs. Unfertilized and fertilized fallow-wheat controls were also simulated. Within a given LCC input value, coefficients of variation for total seasonal N supply (the sum of predicted wheat N uptake, N leaching and inorganic soil N at wheat maturity) over years were <15%, despite the fluctuating winter rainfall (CV 48%). Average N leaching was predicted to be highest in the high LCC input system (108 kg N ha⁻¹), followed by the low LCC input system (86 kg N ha⁻¹) and midseason-intensive and planting-intensive fertilized wheat-fallow systems (82 and 72 kg N ha⁻¹, respectively), and least in the unfertilized wheat-fallow system (54 kg N ha⁻¹). N leaching exceeded 100 kg N ha⁻¹ in 4, 20, 16, 18, and 29 seasons out of 46 seasons, respectively, in the unfertilized and planting-intensive and midseason-intensive fertilized wheat-fallow rotations and in wheat rotations with low and high LCC inputs. There was no difference in predicted wheat yield among the four systems with N inputs from fertilizer or LCC, but yield was lower in the unfertilized wheat-fallow rotation. If the goal of use of LCC was to attain the same yield level as high LCC input or fertilized wheat system while diminishing the risk of N leaching, the low LCC input case met this goal in the short term. However, a simple balance sheet using the model showed that the N balance of the low LCC input system was −147 kg N ha⁻¹ season⁻¹, if we assumed 50% of LCC-N was derived from atmospheric fixation. The low-LCC-input system could therefore fail to maintain inherent soil N fertility in the long term unless nearly 100% LCC-N was derived from fixation.     

Evidence for the influence of weeds on corky ringspot persistence in alfalfa and Scotch spearmint rotations

Corky ringspot disease (CRS) of potato is caused by tobacco rattle virus (TRV). The virus is transmitted by the stubby root nematode (Paratrichodorus allius) in the Pacific Northwest potato-producing regions. Alfalfa (Medicago sativa L.) and Scotch spearmint (Mentha cardiaca Baker) rarely serve as hosts for TRV. Therefore,P. allius reared on these plants for 1 to 3 months are cleansed of TRV in greenhouse trials. However, weeds in alfalfa and Scotch spearmint rotation crops may serve as hosts for the virus. In greenhouse trials, hairy nightshade (Solanum sarrachoides), prickly lettuce (Lactuca serriola), henbit (Lamium amplexicaule) and, green foxtail (Setaria viridis) grown alone were found to be suitable hosts ofP. allius, whereas Powell amaranth (Amaranthus powellii) was not. ViruliferousP. allius added to hairy nightshade, prickly lettuce, henbit, green foxtail, or Powell amaranth in mixtures with alfalfa and/or Scotch spearmint occasionally remained viruliferous over a 3-to 4-month period, whereasP. allius maintained on weed-free alfalfa or Scotch spearmint became virus-free after 1 to 2 months. Potato grown in soil containingP. allius that had been maintained on weed-alfalfa or weed-Scotch spearmint mixtures for 3 to 4 months exhibited slight to severe CRS symptoms on new tubers, whereas potato following weed-free Scotch spearmint or alfalfa were free from CRS symptoms. Severe CRS symptoms on potato tubers were only observed when potatoes were grown in soil containingP. allius that were maintained on hairy nightshade or hairy nightshade mixtures with alfalfa or Scotch spearmint. These preliminary data suggest that the presence of weeds that serve as hosts of both TRV and P.allius may nullify the positive effects of growing alfalfa or Scotch spearmint for CRS control. Targeted control efforts of known weed hosts may be required to successfully eliminate CRS from fields using alfalfa and Scotch spearmint rotational crops.