Take-all and grain yields in sequences of winter wheat crops testing fluquinconazole seed treatment applied in different combinations of years

A seed treatment containing fluquinconazole as the only active ingredient was tested in sequences of up to six consecutive crops of winter wheat. It was applied or not applied in each year, and was tested in all possible combinations with treatments applied in previous years. Take‐all was controlled effectively, and grain yield usually increased, when the disease intensity was moderate or severe in non‐treated crops, but control of the most severe take‐all did not result in acceptable yields or grain quality. Treatment of a first wheat or second wheat with little take‐all did not usually benefit the subsequent crop. Non‐treatment of a crop grown after a treated, diseased crop usually resulted in a marked increase in disease, indicating that treatment had delayed progress of the epidemic. Take‐all was controlled by treatment of a crop grown after a treated, diseased crop but the amount of control and of increased yield was often less than that in a treated crop grown after a non‐treated crop in the same crop sequence. Similar effects of seed treatment were apparent in crops grown on a site with take‐all decline. The alternative fungicide, silthiofam, applied as a seed treatment in the later years of some experiments, was usually as effective as fluquinconazole. From these experiments, it is recommended that: a) fluquinconazole seed treatment should be applied to a second or third wheat crop, grown after a first wheat crop that was managed to avoid rapid take‐all development (e.g. by avoiding very early sowing); b) a break crop should follow the treated crop; c) the seed treatment should not normally be used in longer sequences of wheat or on take‐all decline soil unless it is planned to follow the treated crop with a non‐cereal break.     

Strategies for control of eyespot (Pseudocercosporella herpotrichoides) in UK winter wheat and winter barley

This review considers strategies for control of eyespot (Pseudocercosporella herpotrichoides) in winter wheat and winter barley in the UK. Varietal resistance to eyespot may take the form of direct resistance to the growth of the pathogen in the stem base or of indirect tolerance to eyespot through resistance to lodging. The French variety Cappelle-Desprez has been a source of resistance for most UK wheat varieties and a new source of resistance in wild goat grass has been discovered recently. Use of fungicides for control of eyespot increased rapidly after the introduction of the highly effective MBC fungicides in the 1970s, but has decreased recently because UK populations of P. herpotrichoides are now predominantly resistant to MBC fungicides and alternative fungicides are more expensive. Historically, cultural methods, especially crop rotation, have been important in the control of eyespot. The importance of cultural control of eyespot is now increasing because more non-cereal break crops are being grown and fungicide use is declining.     

Effects of foliar sprays of azoxystrobin on take-all in wheat

Average percentages of winter wheat plants with severe take‐all were decreased by up to half by azoxystrobin applied as foliar sprays in four field experiments. Decreased take‐all in three of the experiments was associated with increased grain yield but effects on other diseases may have contributed to these responses. Standard fungicide sprays were ineffective. The effects differed, but not consistently, among different cultivars that were tested in three of the experiments. One, two or three sprays of azoxystrobin or kresoxim‐methyl, in autumn, spring or summer, were tested in the fourth experiment. Unlike azoxystrobin, kresoxim‐methyl had no consistent effects but a smaller amount was applied. Two or three sprays of azoxystrobin were more effective than a single spray but their timing was unimportant. Such control of a root disease by a foliar‐applied fungicide is unusual but may help to explain some of the unexpectedly large yield responses to azoxystrobin that have been reported. This relatively broad‐spectrum fungicide may have the potential to contribute to the practical management of take‐all but further research is needed to determine how best to exploit its effects consistently.     

Effects of sowing date and volunteers on the infectivity of soil infested with Gaeumannomyces graminis var. tritici and on take-all disease in successive crops of winter wheat

In a field experiment on winter wheat, take‐all on plants and the infectivity of the soil were studied in crop sequences with different combinations of sowing dates. Take‐all was negligible in the first wheat crop, but thereafter the mean disease intensity (measured using a take‐all rating, TAR, with a maximum of 300) was 108, 190, 118 and 251 in the second to fifth successive crops. In each growing season, the disease differed amongst sequences and built up more rapidly and was more intense on plants sown in mid‐September than on plants sown in mid‐October. In late‐sown plots, where volunteers had been present during the mid‐September to mid‐October period, take‐all reached an intensity intermediate between that in early‐sown plots and that in late‐sown plots that had been kept free of volunteers. Volunteers, therefore, partially offset the expected beneficial effect of decreased disease with later sowing. Differences in take‐all amongst sequences were most pronounced in the second wheat crop and early sowing of the previous wheat increased intensity of disease. In the following (third) crop, differences in disease intensity amongst sequences were smaller. Soil infectivity (measured by seedling bioassay after harvest) built up progressively from a low level after the first crop to peak after the third crop. In this build‐up phase, soil infectivity estimates were always numerically greater after harvest of early‐sown treatments than after later‐sown treatments, although never significant at P= 0.05. The greatest difference (P= 0.06) was recorded in October before sowing of the third crop, where the comparison was between soil after two previous early sowings and soil after two previous later sowings and control of volunteers. In the same autumn, presence of green cover (i.e. volunteers) was associated with a smaller loss of soil infectivity between harvest and later sowing than occurred in an absence of green cover. In 2^nd–4^th crops, where comparisons were available and mean TARs indicated moderate levels of take‐all, sowing later had no yield benefit, despite more take‐all and greater soil infectivity associated with early sowing. Important considerations for the management of crops at risk of take‐all are 1) choosing appropriate sowing dates to minimize take‐all or to encourage take‐all decline and 2) controlling volunteers and weed hosts where crops are sown late to minimise take‐all.     

Fungal Communities and Disease Symptoms on Stem Bases of Wheat and Barley and Effects of Seed Treatments Containing Fluquinconazole and Prochloraz

Three successive crops of winter wheat or barley were grown as second, third and fourth cereals. Communities of fungi on shoot bases, identified after isolation on agar media, were more diverse (determined by number of taxa identified) on wheat than on barley, and their diversity increased from year to year. Diversity was not affected by seed treatments containing fluquinconazole or prochloraz. Eyespot (caused by Tapesia spp.) and brown foot rot (caused by Fusarium spp. or Microdochium nivale ) increased from year to year. Eyespot, brown foot rot (after the first year) and sharp eyespot (which remained infrequent), assessed in summer (June), affected wheat more than barley. Eyespot severity was increased slightly on barley by treatments containing fluquinconazole, formulated with or without prochloraz, in the second year (third cereal), when it was also decreased slightly on wheat by fluquinconazole plus prochloraz, except in plots where the treatment had been applied for two successive years. The increases or decreases in eyespot in the second year were accompanied by, respectively, decreases or increases in the frequency of Idriella bolleyi where fluquinconazole was applied alone. Although the eyespot pathogen Tapesia yallundae (but not Tapesia acuformis ) is sensitive to fluquinconazole in vitro , seed treatment, applied principally to control take-all disease, is likely to have only a small effect against eyespot (or other stem-base diseases), and then only on wheat and when formulated with prochloraz.     

Effect of Morpholine Systemic Fungicides on the Chloroplast Pigments of Wheat and Maize

Abstract

The growth, chlorophyll and carotenoid contents of wheat and maize seedlings as influenced by a soil drench of 250 μM of tridemorph or fenpropimorph, were studied. It was found that the length of the shoot, primary leaf, and root, as well as the leaf area were significantly reduced in the fungicide treated seedlings. Although the dry matter percentage was higher in the treated seedlings as compared to the control, the fresh or dry weight per shoot remained lower in the fungicide treated seedlings. The chloroplast pigments in the treated seedlings of both crops were unaffected, suggesting that the fungicides had no significant effect on the chlorophyll or carotenoid biosynthesis.     

The influence of host plant,nitrogen fertilization and fungicide application on the abundance and seasonal dynamics of vesicular-arbuscular mycorrhizal fungi in arable soils of northern Germany

The present investigation examines whether the crop plant, increased nitrogen (N) fertilization and fungicide application influence the pattern of vesicular-arbuscular mycorrhizal fungi (VAM) populations. For this purpose, two arable field locations in Lower Saxony (Hotteln and Langreder) were chosen and the formation of mycorrhiza, spore density, number of infectious propagules (MPN) and frequency of spore types within VAM populations were investigated. The influence of crop plants was examined over two cultivation periods (1986/1987 and 1987/1988) in Hotteln, comparing winter wheat, winter barley and sugar beet. The effects of increased N fertilization and fungicide application were investigated on winter wheat in Langreder in the cultivation period 1988 only. Both the frequency of mycorrhizal infection and the spore dynamics in soil differed with the crops grown. Spore density and MPN increased until harvesting when host plants (winter wheat, winter barley) were cultivated, whereas both diminished with a non-host plant (sugar beet). Different spore types increased or decreased, according to the plant species grown, but the predominating types of the location remained constant. Increased N fertilization caused marginal inhibition of mycorrhizal infection and sporulation on winter wheat, whereas both leaf and base application of fungicides resulted in minor increases in mycorrhizal colonization of roots and sporulation in soil. Both increased N fertilization and fungicide application distinctly decreased the sporulation of one type in May, but the characteristic compositions of the VAM populations remained unchanged.     

Removal of pesticides from white wine by the use of fining agents and filtration

The effects of four clarification agents (bentonite, charcoal, PVPP and potassium caseinate) on the removal of residues of three fungicides (famoxadone, fluquinconazole and trifloxystrobin) applied directly to a racked white wine, elaborated from Airen variety grapes from the D.O. Region of Jumilla (Murcia, Spain) are studied. The clarified wines were filtered with 0.45 microm nylon filters to determine the influence of this winemaking process in the disappearance of fungicide residues. Hydro-alcoholic solutions with the three fungicides at concentrations of 1 and 2 ppm were then added through intense stirring to each of the containers. Two hours later, the corresponding clarifying agent was added with intense stirring for some minutes. The containers were then sealed and left to settle for five days. Once the clean wines had been racked, they were filtered through nylon 0.45 microm pore filters. All assays were performed three times. Analytical determination of fluquinconazole and trifloxystrobin was performed by gas chromatography with an electron captor detector (ECD), while that of famoxadone was made using an HPLC-DAD. For the three fungicides, the highest elimination is produced with the clarification by charcoal, reaching Levels of removal of 100% in all cases. For the four clarifying agents, the highest elimination is produced for the fluquinconazole residues. The fungicide which is retained most in the lees is famoxadone, since it has the lowest solubility of the three pesticides studied. The highest percentage of residues in the lees is obtained for the assay with charcoal. The filtration process of the clarified wines using the four agents studied is not effective, since the elimination percentage is generally lower than 10% of the initial residues in the non-clarified wines.     

The importance of weather and agronomic factors for the overwinter survival of yellow rust (Puccinia striiformis) and subsequent disease risk in commercial wheat crops in England

Disease survey data from 4475 randomly selected crops of wheat from England and Wales during 1985–2000 showed that yellow rust was most prevalent in 1988, 1989, 1990, 1998 and 1999. Disease severity on the upper two leaves was low as >95% crops had received foliar fungicides. Factors affecting the presence or absence (incidence) of yellow rust were investigated using random effects logistic regression (general linear mixed model). This enabled crop management (risk) variables for individual crops to be combined with meteorological variables measured at the county level. Two models are presented that analysed the effect of host genotype on incidence either solely through yellow rust resistance rating (Model 1) or by including both resistance rating (fixed effect) and cultivar (fitted as a random term) (Model 2). In both models, the percentage of crops with yellow rust decreased with cultivar disease resistance ratings ≥3, the occurrence of severe frosts (P < 0.05) of timing of fungicide sprays, previous cropping or summer weather. The use of risk variables associated with overwintering survival may help adjust fungicide inputs to seasonal risk.     

The potential of non-pathogenic Gaeumannomyces spp., occurring naturally or introduced into wheat crops or preceding crops, for controlling take-all in wheat

Take‐all disease (Gaeumannomyces graminis var. tritici) in wheat crops is known to be suppressed by naturally occurring antagonistic fungi, closely related to the pathogen, that infect grasses and cereals. This form of suppression was re‐investigated because of the changing importance and role of grass weeds and grass covers in arable farming. Natural populations of the competitive fungus Gaeumannomyces cylindrosporus, allowed to develop under rye‐grass, were more effective than artificially introduced populations in suppressing the development of take‐all in following wheat crops. To be effective, the antagonist needs to be present before the start of wheat cropping. Introducing G. cylindrosporus, but not G. graminis var. graminis (a potential antagonist that is faster growing), into a previous crop, or just after the previous crop, sometimes suppressed take‐all, but the effect was small. It is concluded that, for any future attempts at biocontrol by these fungi, they should be introduced into a preceding crop not susceptible to take‐all. Take‐all inoculum in the soil should be at a minimum and effective hosts of the take‐all pathogen must not be present as weeds or volunteers.     

Effects of some systemic imidazole and triazole fungicides on white clover and symbiotic nitrogen fixation by Rhizobium trifolii

Effects of prochloraz, imazalil, diclobutrazol, triadimefon and propiconazole were studied. Compared with most systemic fungicides previously tested they were all relatively toxic to R. trifolii on agar. Effects of soil residues of the compounds on the growth and nitrogen fixing capacity of white clover were measured. The lowest concentration of the fungicides used was that which would be present if all the active ingredient from a single application remained unchanged and evenly distributed in the top 5 cm of soil. This concentration of diclobutrazol decreased the size and weight of 11-wk-old clover plants. The rate of nitrogen fixation was reduced by twice this concentration and root nodulation by four times this amount. None of the other fungicides had any significant effect. The possibility of field application of diclobutrazol to cereals causing damage to clover crops is discussed. It is questionable whether harmful soil residues will ever accumulate from normal usage of the fungicide but exceeding the recommended rate of application, or application to cereals undersown with clover, might cause undesirable effects on the clover.     

Inhibition of efflux transporter-mediated fungicide resistance in Pyrenophora tritici-repentis by a derivative of 4'-hydroxyflavone and enhancement of fungicide activity

Populations of the causal agent of wheat tan spot, Pyrenophora tritici-repentis, that are collected from fields frequently treated with reduced fungicide concentrations have reduced sensitivity to strobilurin fungicides and azole fungicides (C14-demethylase inhibitors). Energy-dependent efflux transporter activity can be induced under field conditions and after in vitro application of sublethal amounts of fungicides. Efflux transporters can mediate cross-resistance to a number of fungicides that belong to different chemical classes and have different modes of action. Resistant isolates can grow on substrata amended with fungicides and can infect plants treated with fungicides at levels above recommended field concentrations. We identified the hydroxyflavone derivative 2-(4-ethoxy-phenyl)-chromen-4-one as a potent inhibitor of energy-dependent fungicide efflux transporters in P. tritici-repentis. Application of this compound in combination with fungicides shifted fungicide-resistant P. tritici-repentis isolates back to normal sensitivity levels and prevented infection of wheat leaves. These results highlight the role of energy-dependent efflux transporters in fungicide resistance and could enable a novel disease management strategy based on the inhibition of fungicide efflux to be developed.     

Pyrosequencing reveals the impact of foliar fungicide application to chickpea on root fungal communities of durum wheat in subsequent year

Frequent application of foliar fungicide is essential for chickpea production due to the susceptibility of this plant to ascochyta blight. Chlorothalonil, pyraclostrobin, and boscalid are commonly used to control the disease in Saskatchewan. While fungicides are meant to target specific fungal pathogens, they may impact non-target organisms and alter soil microbial community structure. The effects of the typical 5-time foliar fungicide application program to chickpea CDC Vanguard on the fungal communities associated with seminal and adventitious roots of the following durum wheat crop were studied in a 2 yr field experiment. Root fungal communities were characterized through analysis of the ITS1 region of root metagenomic DNA at the genus level. One hundred and seven fungal genera were detected in durum wheat roots. Fusarium was predominant in both years. A three-way interaction of fungicide application, root type and year on fungal community structure was detected. Unlike Fusarium, the relative abundances of the genera Olpidium, Alternaria, and Cryptococcus were greater in 2010, a very wet year. Fungicide application to chickpea increased the relative abundance of Fusarium in the seminal roots of a subsequent durum crop in 2009, but did not affect the relative abundance of Fusarium in 2010. We could not detect a significant impact of fungicide application to chickpea on durum wheat yield in the subsequent year. The effect of changes in root fungal communities on durum wheat grain yield is discussed.     

我国主粮作物的化学农药用量及其温室气体排放估算

现代农业中化学农药在提高作物产量中发挥着重要的作用,但是我国普遍存在过量用药现象,导致环境污染和危害食品安全.基于2012年的全国性农户问卷调查,本研究分析了2011年我国水稻、小麦和玉米使用农药现状,并估算了它们的温室气体排放.结果表明: 这3种作物至少使用了54种杀虫剂、24种杀菌剂和50种除草剂,其中32%的水稻种植农户使用了生物农药.全国3种作物使用了30.8 kt杀虫剂、16.5 kt杀菌剂和58.3 kt除草剂,它们的温室气体排放总量为1.5 Tg Ce,杀虫剂、杀菌剂和除草剂的排放分别占23.8%、16.9%和59.3%.南方区的农药用量占全国用量的51%;全国水稻、小麦和玉米的单位产量农药用量分别是0.22、0.18和0.24 g·kg^-1粮食,3种作物用药总量分别为44.4、21.4和39.7 kt,温室气体排放分别为665.5、250.1和547.5 Gg Ce;在不同农药种类中,有机磷类杀虫剂占我国所用杀虫剂总量的69%,苯丙咪唑类、有机磷类、唑类和有机硫类等杀菌剂占杀菌剂总量的87%,酰胺类、有机杂环类和有机磷类等除草剂占除草剂总量的85%.因此,减少农药用量,对于我国粮食安全和环境安全及减少农业温室气体排放都具有重要意义.     

Studies on the tolerance of Erysiphe graminis f. sp. hordei to systemic fungicides

Successive sowings of glasshouse-grown barley plants were treated with either tridemorph, ethirimol or both fungicides, and inoculated with an initially fungicide-sensitive isolate of Erysiphe graminis f. sp. hordei. The time taken for symptoms to appear, compared with that for untreated plants, decreased with successive sowings. This was interpreted as evidence for the increase in the frequency of fungicide-tolerant propagules in the pathogen population. Effective mildew control was obtained by the use of either or both fungicides in trial plot and field crops. Seedling assays for tolerance to tridemorph and ethirimol showed that tolerance was more evident in treated than in untreated crops in June. Some mildew populations partially tolerant to one fungicide also showed reduced sensitivity to the other. By July a response intermediate between tolerant and sensitive was recorded on all the plots, probably indicating the mixing of fungal populations from adjacent plots. Larger numbers of tolerant isolates were found in random samples from treated than from untreated crops.     

Disease Development and Buildup of Resistance to Oxadixyl in Potato Crops Inoculated with Phytophthora infestans as Affected by Oxadixyl and Oxadixyl Mixtures: Experimental and Simulation Studies

Simulator predictions for the effect of oxadixyl and oxadixyl mixtures on the control of late blight in potato crops inoculated with Phytophthora infestans and the buildup of fungal resistance to oxadixyl were compared with data obtained in field experiments. The simulator, which considered fungus, fungicides and crop variables, predicted accurately the effect of fungicide sprays (oxadixyl, oxadixyl mixed with mancozeb, and oxadixyl mixed with mancozeb and cymoxanil) on blight development. The model predicted accurately both resistance buildup and infection in non-treated crops and in crops treated with oxadixyl alone or in a mixture with mancozeb (SAN 518F), but overestimated the control efficacy of the three-way mixture Pulsan.     

Soil-applied fungicides for controlling take-all in field experiments with winter wheat

Soil treatment fungicides were tested against take-all (Gaeumannomyces graminis var. tritici) in three field experiments with winter wheat. Fungicides were applied as drenches either before sowing in autumn, and incorporated by rotary harrowing, or to the crop in spring. The most effective treatments were autumn applied benomyl (20 kg/ha) and nuarimol (0·55-4·4 kg/ha). However, the highest nuarimol concentration depressed yield. Benomyl sometimes induced a resurgence of take-all in the second wheat crop after treatment. Nuarimol had no adverse effects in subsequent crops, and neither fungicide hindered the onset of take-all decline in a third crop after treatment. The possible value of soil treatment in future control strategies is discussed.     

Grain yield and incidence of take-all (Ophiobolus graminis Sacc.) in wheat grown in different crop sequences

The yield of wheat and the incidence of take-all were measured in crops grown in six different 4-year sequences, repeated in 3 successive years. The first crop of winter wheat grown after oats or beans yielded 13–23 cwt/acre (1632–2887 kg/ha) more grain than wheat after wheat or barley. Spring wheat after oats yielded 2–5 cwt/acre (250–625 kg/ha) more than spring wheat after wheat. The smaller yields of wheat after wheat or barley were caused mostly by greater prevalence of take-all. Regression analysis indicates that each 1 % increase in straws with take-all decreased yield of winter wheat by 0·6%. Take-all was more prevalent in the second and third successive wheat crops after oats than in the fourth crop.     

A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systems

A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose–response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance.