The effect of powdery mildew (Erysiphe graminis f. sp. hordei) and leaf rust (Puccinia hordei) on spring barley in New Zealand. I. Epidemic development, green leaf area and yield

Powdery mildew and leaf rust caused large yield losses in spring barley grown near Christchurch, New-Zealand, in two seasons. Disease present during early growth stages was as damaging to yield as disease late in the season. Moderate leaf rust severities after anthesis were most damaging when combined with earlier mildew epidemics. Later growth did not compensate for reduced yield potential induced by early infection. This was attributed, at least in part, to an effect on leaf size, and therefore on green leaf area, at later growth stages. There was a closer relationship, by regression analysis, of yield to green leaf area than to disease severity in three cultivars.
The three cultivars. which differed in yield potential and disease resistance, were not equally sensitive to disease. It is proposed that high yielding cultivars may be the most sensitive to yield constraint by disease.     

Interactions of fungicides and leaf saprophytes

Phylloplane micro-organisms may metabolise substances present on the leaf surface, they may interact with leaf pathogens and they may be involved in the process of senescence. The effects of fungicides on many leaf saprophytes are, however, largely unknown. Studies under both field and laboratory conditions have indicated that wide spectrum protectant fungicides, such as captan, captafol and zineb, are as effective against the saprophytic flora as they are against plant pathogens. If the leaf surface microflora is restricted by fungicides then antagonism towards pathogens will also be reduced, but beneficial results may ensue if the microbial impact on senescence is lessened. Field trials with barley have demonstrated that it is possible to delay senescence by using fungicide sprays.     

Evaluation of the systemic activity of simeconazole in comparison with that of other DMI fungicides

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) in plants was compared with those of eight other sterol demethylation inhibitor (DMI) fungicides. Simeconazole prevented the infection of Blumeria graminis (DC) Speer f sp hordei Marchal on barley leaves within a radius of several centimeters from the edge of local treatment on the leaves when the compound was separated from the leaves by glass coverslips. This reveals that simeconazole has prominent vapour-phase activity. Simeconazole showed excellent curative activity against barley powdery mildew when treated 1-3 days after inoculation. Furthermore, this indicates that simeconazole has notable translaminar activity because, when the compound was applied onto either the adaxial or abaxial leaf surface, it showed excellent efficacy against powdery mildew on the opposite side of the leaf surface of barley and cucumber. Simeconazole also showed excellent efficacy against barley powdery mildew by soil drench 24h after inoculation. This suggests that simeconazole was absorbed very quickly into the barley plant after treatment. The permeability of the compound through cuticular membranes prepared from tomato fruits was about 20% at 22 h after the treatment and was much superior to that of the other DMI fungicides tested.     

Optimierte Strategien zur Krankheitsbekämpfung in der Gerste unter Berücksichtigung neuer Erkenntnisse zur Epidemiologie des Blattfleckenkomplexes

The leaf spot complex constitutes an increasing challenge for integrated pest control in barley. The complex consists of biotic and abiotic factors causing early ripening after a rapid loss of green leaf area, in particular in upper, exposed leaves. Severe symptoms appear late in the growing season after heading. The experience from recent years shows that the control of the leaf spot complex improves yield. Best control is achieved by new, effective fungicides. Efficiency is improved by late fungicide application and is dose-dependent. In contrast, late treatments provide poor control of early appearing diseases. For a successful disease control in barley good efficiency in the control of the leaf spot complex appears based on a sufficient control of the other diseases. For optimization of disease control, we require improved knowledge of the epidemics of the leaf spot complex and of the contribution of individual biotic and abiotic factors. Besides the weather, the fungal pathogen Ramularia collo-cygni and its photodynamic toxins play a mayor role in symptom development. By combination of conventional and molecular diagnostics we aim at a better understanding of the complex as a basis for early and reliable prediction of epidemics. Because non fungicidal factors like the physiological plant age play a significant role in the occurrence of the leaf spot complex, they should be taken into account for integrated control.     

Fungicide Treatment Increases Yield of Cereal Cultivars by Reducing Disease and Delaying Senescence1

The results of 21 winter wheat and 32 spring barley trials done in the United Kingdom showed that cultivars differed significantly in their yield response to a standard fungicide treatment. Regression analyses showed that yield responses were significantly related to disease reduction, particularly that of mildew, although the proportion of variance accounted for was small. Measurements made on seven winter wheat trials indicated that the percentage of leaf area remaining green after anthesis was increased by the fungicide treatment to a greater extent than could be attributed to disease reduction alone. In some of these trials, yield responses were more closely correlated with the increase in leaf area remaining green than with disease reduction.     

Unexpected Effects of Fungicides on Cereal Yields1

Field experiments with barley have generally shown a good relationship between disease and yield. However, in some experiments the yield response is greater than would be expected from the level of disease. In contrast, other trials have shown a reduction of yield following applications of tridemorph to spring barley. On winter wheat, trials in Germany have shown a poor relationship between disease incidence and yield following application of carbendazim or captafol at GS 30–31. About 10 96 of these responses were negative, although there was an average yield increase of 2–3 %. Similarly, in a series of trials in Britain an average yield increase of 3 % was not related to disease level. In these trials about 25 % of results showed no increase in yield. The carbendazim fungicides, and also certain others, have some cytokinin-like activity and it is possible that this is related to extended green leaf survival. Other interactions with host-cell chemistry can be envisaged. Fungicides also influence stability of the leaf microflora. By this effect they may favour diseases such as Typhula and Rhizoclonia, or else suppress secondary pathogens (Alternaria, Cladosporium) at the end of the season.     

Optimization of chemical control of Pseudoperonospora cubensis on cucumber in Ukraine

Downy mildew ( Pseudoperonospora cubensis ) is one of the most harmful diseases of cucumber in Ukraine. At high disease severity, the growing season is considerably shortened and yield is reduced. The most effective method of control is the development of resistant cultivars but, in the absence of absolutely resistant forms, control with fungicides remains very important. The effectiveness of such treatment depends on the dates of application, the number of sprays and the efficacy of the fungicides used. An improved scheme is presented, based on three components: use of cultivars with increased resistance; application of highly effective systemic + contact fungicides; and reliable short-term forecasting of disease appearance. The predictors for downy mildew forecasting are: sum of effective temperatures, weather index, duration of leaf wetness, concentration of sporangia in air and latent period of disease development. These conditions determine'critical days'for disease development. The first fungicide spray on less susceptible cultivars is recommended on the first critical day, and the next on the day of appearance of first disease symptoms. This scheme allows the fungicide load to be approximately halved, while ensuring higher yield.     

Occurrence and molecular characterization of strobilurin resistance in cucumber powdery mildew and downy mildew

ABSTRACT Between 1998 and 1999, control failure of powdery mildew (Podosphaera fusca) and downy mildew (Pseudoperonospora cubensis) by the strobilurin fungicides azoxystrobin and kresoxim-methyl was observed in cucumber-growing areas of Japan. Results from inoculation tests carried out on intact cucumber plants and leaf disks clearly showed the distribution of pathogen isolates highly resistant to azoxystrobin and kresoximmethyl. Fragments of the fungicide-targeted mitochondrial cytochrome b gene were polymerase chain reaction amplified from total pathogen DNA and their sequences analyzed to elucidate the molecular mechanism of resistance. A single point mutation (GGT to GCT) in the cytochrome b gene, resulting in substitution of glycine by alanine at position 143, was found in resistant isolates of downy mildew. This substitution in cytochrome b seemed to result in high resistance to strobilurins in this pathogen. The same mutation was found in some but not all resistant isolates of powdery mildew. This study suggests that a mutation at position 143 in the target-encoding gene, resulting in an amino acid substitution, was probably a major cause of the rapid development of high strobilurin resistance in these two pathogens.     

Some studies on the systemic activity of the thiophanate fungicides in plants

Three closely related fungicides, thiophanate (NF 35), thiophanate methyl (NF 44) and NF 48 have been found to be active against a wide range of diseases including the powdery mildews of apple, cucumber and barley; apple and pear scab and grey mould of soft fruit. This paper deals with the preliminary experiments to compare their relative mobilities and biological persistence in crop plants, using the powdery mildews as indicator infections. NF 44 and NF 48 in particular showed a high degree of systemic activity by root uptake and persistence of action against barley and cucumber mildew but very little systemic activity against apple mildew on potted rootstocks. They have also displayed trans-laminar and localised movement towards the leaf apex in sprayed cucumber and barley leaves but movement was not so marked in sprayed apple leaves. NF 48 was also active as a seed dressing against loose smut of barley.     

Effect of fungicide treatment on yield of winter wheat and spring barley cultivars

Analyses of the results of 21 winter wheat and 32 spring barley trials showed that cultivars differed significantly in their yield response to a standard fungicide treatment. Responses were also strongly influenced by differences between sites and between years. Regression analyses showed that responses were significantly related to reductions in foliar disease, particularly that of mildew, although the proportion of variance accounted for was small. Measurements made on seven winter wheat trials indicated that the percentage of leaf area remaining green after anthesis was increased by the fungicide treatment to a greater extent than could be attributed to reduction in foliar disease alone. In one of these trials, yield response was more closely correlated with the increase in leaf area remaining green than with reduction in foliar disease.     

Fungicide and nitrogen applications in relation to the improvement of disease control and yield in winter barley

In crops of winter barley, cvs Igri and Halcyon, crop structure and intensity of foliar diseases were altered by delaying the main top dressing of nitrogen until mid-April. A single application of fungicide then was sufficient to decrease substantially the severity of fungal disease and improve grain yield at harvest.
Disease control and yield responses were greatest when fungicides were applied during a 3-week period after the main nitrogen application in April. No additional yield benefits were obtained by making two fungicide applications at growth stage (GS) 31 and GS 39.     

A web-based decision support system for integrated management of cereal pests

The models in the Danish decision support system (DSS) PC-Plant Protection (PC-P) have been developed during the past 15 years of research on cereal pests in Denmark. Recently, the system was reintroduced as a web-based DSS and is now called Crop Protection Online (CPO). CPO includes models for powdery mildew, rusts, septoria, rhynchosporium, net blotch, eyespot, aphids and leaf beetle larvae and is based on empirical data on: (i) the specific effect of each plant protection product; (ii) control thresholds; (iii) importance of pests according to growth stage; (iv) variation in susceptibility to pathogens among cultivars; and (v) influence of weather on the development of pests. The system has been validated in numerous trials and has proved to give good control of pathogens at low product inputs. The margin of product use has been similar or better compared with standard treatments included in the field trials. In trials where CPO was compared with other DSS, CPO resulted in the lowest input of fungicides, measured as TFI (TFI expresses the ratio applied doses/standard doses throughout a growing season) and the highest margin over product use. Differences in the prices of fungicides and in the grain price may change that. The system is under development in Poland and the Baltic countries, and is also ready for export to other countries.     

Evaluation of systemic fungicides for use in the glasshouse industry

The primary evaluation of ten fungicides for the control of cucumber powdery mildew (Sphaerotheca fuliginea), tomato leaf mould (Cladosporium fulvum) and tomato grey mould (Botrytis cinerea) indicated that nine of them were systemically active against one or more of the pathogens when applied as soil drenches. Benomyl, thiophanate, thiophanate-methyl, thiabendazole and Cela W52A showed activity against all three diseases, but dimethirimol, triarimol and dodemorph were more specific and mainly active against cucumber powdery mildew. An in vitro bioassay generally indicated that fungitoxicity was not translocated from sprayed to unsprayed leaves, and though toxicity to B. cinerea, following soil drenches of benomyl, thiophanate and thiophanate-methyl, was detected by bioassay in leaf sap and calyces it was not detected in fruit. Furthermore, extended evaluation of benomyl for the control of grey mould on cropping tomotoes showed that in the presence of abundant B. cinerea inoculum, benomyl soil drench treatment effectively controlled flower and leaf infection but not fruit ghost-spotting.     

The Effect of Fungicides on the Microbial Balance in the Phyllosphere1

The sensitivity to fungicides of saprophytic fungi colonizing cereal leaves (mainly ←pink→ yeasts, Sporobolomyces spp.; ← white → yeasts, Cryptococcus spp.; Aureobasidium pullulans and Cladosporium spp.) is discussed. Fungicides like dithiocarbamates, captafol, benzimidazoles and tridemorph reduce the saprophytic microflora, while others have little or no effect. The fungicides are mostly effective for 2–3 weeks after the treatment. When evaluating the consequences of a disturbance of the microbial balance we should realize that the saprophytes are able to antagonize a number of necrotrophic pathogens of cereal leaves and ears (Cochliobolus sativus, Septoria nodorum, Fusarium culmorum, Pseudocercosporella herpotrichoides, Colletotrichum graminicola). This antagonism is based on nutrient competition, which reduces the superficial development of the pathogen before penetration, resulting in a reduction of infection of about 50 % or more. This interaction seems particularly important when saprophytes compete successfully for extraneous nutrients from pollen grains or aphid honeydew, which will otherwise stimulate infection.     

The development of the leaf rust,Puccinia hordei,population during winter,spring and early summer in 11 winter barley cultivars

The overwintering and the epidemic development in spring of leaf rust was studied in 11 winter barley cultivars at two different sites near Wageningen in 1976/1977. The amount of leaf rust decreased through the winter at both sites. Cultivars differed considerably in the amount of leaf rust in late winter. Both the moment and the rate of increase of leaf rust after the winter varied with cultivars. The ultimate amount of leaf rust in a cultivar was therefore determined by three factors: The amount of overwintering leaf rust, the onset of leaf rust increase and the rate of increase. The latter was determined by the partial resistance of the cultivar. Why the epidemics did not start at the same moment is yet unknown. The differential overwintering could be explained from the amounts of leaf rust and powdery mildew at the start of the winter, the effect of powdery mildew being a negative one. The correlation coefficient between the values observed in March and those predicted from the December leaf rust and powdery mildew readings was 0.93. In a second experiment carried out in 1979/1980 with six winter barley cultivars chosen from the first experiment the powdery mildew was succesfully excluded by treatment with fungicides. There was no decrease in the leaf rust over the winter nor a differential cultivar effect on overwintering.     

Residual effects of triadimefon in soil on powdery mildew and yield of spring barley

Residual triadimefon (or a breakdown product), from a spray application (2 kg/ha) to field soil in 1978, significantly decreased powdery mildew on spring barley throughout two subsequent growing seasons, with consequent yield increases of 42% in 1980 and 18% in 1981.
In other field experiments triadimefon applied to soil at rates >0.06 kg/ha decreased mildew in barley growing in the soil 11 months later. In these experiments triadimefon, but not benomyl, imazalil or prochloraz (all at 0.5 kg/ha) significantly decreased mildew up to harvest and increased yield by 22%.
Triadimefon incorporated into a loam soil and a peat-based compost at rates >0.1 ng/g significantly decreased mildew on barley grown in pots under glasshouse conditions. Plants grown in the treated compost at the same time but in isolated pots supplied with filtered moistened air and capillary watering required more triadimefon (>100 ng/g) in soil for significant mildew control.
Despite strong adsorption of triadimefon to soil (Kd 19.4), an active substance appears to remain available for uptake and translocation by barley plants over long periods. The sensitivity of barley mildew to extremely small residues of triadimefon is discussed in relation to the siting of field experiments on mildew control. The implications for widespread commercial use of formulations containing triadimefon are discussed in relation to disease control practice in cereal growing systems.     

两种候选甲氧基丙烯酸酯类杀菌剂对黄瓜霜霉病的作用方式

20%唑胺菌酯EC、20%SYP-3998 SC是甲氧基丙烯酸酯类候选杀菌剂,为探索两药剂对黄瓜霜霉病的作用方式,采用盆栽植株喷雾-叶碟法、叶碟喷雾法、盆栽植株喷雾-叶碟法分别测定两药剂对黄瓜霜霉病的保护、治疗及持效期,并采用离体叶片法、叶碟法测定二者对黄瓜霜霉病的铲除作用.结果表明:20%唑胺菌酯EC和20%SYP-3998 SC具有良好的保护、治疗及铲除作用.两药剂的铲除作用表现在能抑制黄瓜霜霉病菌病斑扩展、孢子囊产生及孢子囊再侵染,与孢子囊混合接种能显著降低孢子囊的致病性.此外,20%唑胺茵酯EC和20%SYP-3998 SC具有7～10天的持效期;20%唑胺茵酯EC预防、治疗、铲除效果及持效性均优于20%SYP-3998 SC及对照药剂25%嘧菌酯SC.     

Barley yield losses due to defoliation of upper three leaves either healthy or infected at boot stage by <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis>

This paper evaluates, in the greenhouse and under natural conditions, barley yield losses due to defoliation treatments of the upper three leaves either healthy or infected at the boot stage by Pyrenophora teres f. teres. Defoliation was assumed as a loss of a similar leaf area caused by net blotch disease severity of 100%. Contribution to grain yield was defined herein as a difference between defoliation treatments and a treatment where plants lost all their upper three leaves. In contrast, yield losses referred to differences in yield between defoliations and the control. In the greenhouse, removal of the antepenultimate leaf did not affect any yield component. For main stems, defoliating upper three leaves reduced grain yield by 30% and this was mainly due to flag leaf removal. These losses were similar to those induced by net blotch disease under natural conditions, but were of 42% for all tillers. Grain yield losses due to disease severity were not equivalent to the defoliation effect of a similar healthy leaf area. On the other hand and for a significant contribution to grain yield, flag leaf was dependent on the presence of the other two leaves. Inoculation and defoliation of 21 cultivars induced similar grain yield losses of 32%. However, biotic stress reduced by 40% the contribution of their upper three leaves. Under field conditions, yield losses were not significant until barley plants lost more than one upper leaf and flag leaf contribution was equivalent to that of the remaining leaves. Characteristic roots, defined as leaf coefficients for plant performance, were 0.13, 0.06 and 0.01 for the flag, penultimate and antepenultimate leaves, respectively. Because antepenultimate leaves become trivial at the boot stage, we propose that coefficients of the remaining leaves should be used when modelling yield losses due to barley foliar diseases.     

A Compromised Mlo Pathway Affects the Response of Barley to the Necrotrophic Fungus Bipolaris sorokiniana (Teleomorph: Cochliobolus sativus) and Its Toxins

ABSTRACT In search of new durable disease resistance traits in barley to control leaf spot blotch disease caused by the necrotrophic fungus Bipolaris sorokiniana (teleomorph: Cochliobolus sativus), we developed macroscopic and microscopic scales to judge spot blotch disease development on barley. Infection of barley was associated with cell wall penetration and accumulation of hydrogen peroxide. The latter appeared to take place in cell wall swellings under fungal penetration attempts as well as during cell death provoked by the necrotrophic pathogen. Additionally, we tested the influence of a compromised Mlo pathway that confers broad resistance against powdery mildew fungus (Blumeria graminis f. sp. hordei). Powdery mildew-resistant genotypes with mutations at the Mlo locus (mlo genotypes) showed a higher sensitivity to infiltration of toxic culture filtrate of Bipolaris sorokiniana as compared with wild-type barley. Mutants defective in Ror, a gene required for mlo-specified powdery mildew resistance, were also more sensitive to Bipolaris sorokiniana toxins than wild-type barley but showed less symptoms than mlo5 parents. Fungal culture filtrates induced an H2O2 burst in all mutants, whereas wild-type (Mlo) barley was less sensitive. The results support the hypothesis that the barley Mlo gene product functions as a suppresser of cell death. Therefore, a compromised Mlo pathway is effective for control of biotrophic powdery mildew fungus but not for necrotrophic Bipolaris sorokiniana. We discuss the problem of finding resistance traits that are effective against both biotrophic and necrotrophic pathogens with emphasis on the role of the anti-oxidative system of plant cells.     

Effects of fungicide movement between plots in field experiments

Interactions between plots of spring barley which were either unsprayed, or sprayed with triadi mefon or tridemorph to control powdery mildew ( Erysiphe graminis f.sp. hordei ) were measured in experiments of balanced design in 1978 and 1979. The average amounts of mildew in untreated plots with triadimefon-reated neighbours on the predominaotly up-wind side were usually less than half those in untreated plots with tridemorph-treated neighbours on the up-wind side. Triadiniefon-treated plots had most effect on the adjacent sides of their untreated neighbours but there was evidence that their influence extended across the whole widths of these neighbouring plots. Amounts of mildew in tridemorph-treated plots were increased by untreated neighbours.
Differences in amounts of disease between these plots of spring barley with differently treated neighbours had no significant effects on grain yield. However, in a rando'mized block experiment with spring wheat in 1975 there was evidence that similar inter-plot interactions caused consider able bias in the yield data. Possible causes of the observed effects are discussed.