Role of Fungicides in Maximizing Grain Yield of Barley1

Application of fungicides to cereals normally increases grain yield, this usually being accounted for by control of well-defined diseases. Sometimes, however, yield increases are obtained when apparently trivial amounts of defined diseases are present or when their control seems insufficient to explain the observed benefit. Explanation for these ← unexpected → increases have been sought in: a) control of ← weak → pathogens or organisms not considered pathogenic but which may accelerate leaf senescence, and b) direct effects of fungicides on the plant's physiology. Whatever the precise explanation in individual instances, we may ask whether there is some general relationship linking fungicidal action, plant growth and yield. In barley, recent studies of controlled epidemics of powdery mildew have shown: a) that there is a strong correlation between severity and duration of mildew and reduction in green leaf area (GLA) integrated over time; b) that the grain yield of plants is highly correlated (r values often approaching unity) with values of GLA integrated for the period from seedling emergence to anthesis. The data also show that retranslocation of stored carbohydrate, produced before anthesis, plays an important role in grain filling, and indicate that mildew post anthesis may have little effect on yield. The main implication of these studies is that, in barley, fungicide treatments which increase GLA prior to anthesis are likely to enhance yield. Evidently this may be achieved by different means (control of pathogens, including ← weak → pathogens, or by directly extending the functional life of leaves); the end result, in terms of grain yield, will, however, be the same.     

Diversity and Complexity of Erysiphe graminis f.sp. hordei Collected from Barley Cultivar Mixtures or Barley Plots Treated with a Resistance Elicitor

Powdery mildew populations were analysed to determine the effects of a resistance elicitor and cultivar mixtures on genetic complexity and diversity. Isolations were made from a range of spring barley monocultures and mixtures in a field trial, and characterised for virulence and RAPD profile. In a second trial, isolates were taken from a single mixture from untreated and resistance elicitor-treated areas and from the components of the mixture in monoculture. The mildew population was not only highly heterogeneous for virulence characteristics, but also proved heterogeneous within pathotypes for molecular markers, indicating the major impact of sexual recombination on population structure and the lack of clonal dominance. Various diversity measurements were compared and the value of dissimilarity measurement for revealing genetic distance within a population was highlighted. There was a trend towards increasing complexity as the season progressed, but there was no consistent relationship between cultivar or mixture, disease control treatment, fertiliser treatment, replicate or position in trial, and pathogen genotype. Whilst the resistance elicitor did reduce mildew by 78% in the first trial, and there was no interaction with fertiliser level in its expression, control was substantially less in the second trial. There were no differences between mildew isolates from elicitor and control treatments. It was felt that more effective and consistent resistance elicitors need to be developed before it can be stated that they are unlikely to be eroded by selecting resistant or adapted mildew genotypes.     

Comparison of lettuce diseases and yield under subsurface drip and furrow irrigation

ABSTRACT Subsurface drip and furrow irrigation were compared on lettuce (Lactuca sativa) cvs. Salinas and Misty Day for yield and incidence and severity of three important diseases of lettuce in the Salinas Valley, CA. Experiments were conducted between 1993 and 1995 during the spring and fall seasons. The diseases examined included lettuce drop (Sclerotinia minor), downy mildew (Bremia lactucae), and corky root (Rhizomonas suberifaciens). Replicated plots of subsurface drip and furrow irrigation were arranged in a randomized complete-block design. All plants were inoculated with S. minor at the initiation of the experiment during the 1993 spring season. Plots were not inoculated for downy mildew and corky root during any season nor were the plots reinoculated with S. minor. During each season, all plots were sprinkler irrigated until thinning, and subsequently, the irrigation treatments were begun. The furrow plots were irrigated once per week, and the drip plots received water twice per week. The distribution of soil moisture at two soil depths (0 to 5 and 6 to 15 cm) at 5, 10, and 15 cm distance on either side of the bed center in two diagonal directions was significantly lower in drip-irrigated compared with furrow-irrigated plots. Plots were evaluated for lettuce drop incidence and downy mildew incidence and severity at weekly intervals until harvest. Corky root severity and yield components were determined at maturity. Lettuce drop incidence and corky root severity were significantly lower and yields were higher in plots under subsurface drip irrigation compared with furrow irrigation, regardless of the cultivar, except during the 1994 fall season. Incidence and severity of downy mildew were not significantly different between the two irrigation methods throughout the study. The differential microclimates created by the two irrigation treatments did not affect downy mildew infection, presumably because the mesoclimate is usually favorable in the Salinas Valley. Subsurface drip irrigation is a viable, long-term strategy for soilborne disease management in lettuce in the Salinas Valley.     

Movement of barley powdery mildew within field plots

Movement of barley powdery mildew (caused by Erysiphe graminis f.sp. hordei ) within fields was investigated by sowing the barley cultivars Tyra and Jupiter side by side in two field plots, and trapping spores along transects within the plots. The trapped spores were tested for virulence on the two cultivars. The epidemic on Tyra developed quickly, and a gradient in the proportion of spores with virulence on Tyra was detected in the Jupiter half-plots. In the Jupiter half-plots, the epidemic was much less severe; and no mildew could be found in one plot. Movement of spores from one half of the plot to the other usually declined steeply in the first 4 m from the boundary, and was not detectable beyond 12 m. There were exceptions where the gradient was much shallower, and these were consistent with differences in wind direction.     

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.     

Biocontrol of seedling diseases of barley and wheat caused by Fusarium culmorum and Bipolaris sorokiniana: effects of selected fungal antagonists on growth and yield components

The purpose of this study was to verify, under natural conditions, biological control effects obtained in a former screening programme against Fusarium culmorum. The most successful antagonists against seedborne Fusarium culmorum and Bipolaris sorokiniana were isolates of Chaetomium sp., Idriella bolleyi and Gliocladium roseum. These results were also obtained when the antagonists were applied to B. sorokiniana-infected barley sown in field soil in pots. In field experiments, G. roseum gave the best control of F. culmorum in winter wheat. One month after sowing, germination increased by 170%, the disease index decreased by 73% and plant dry weight increased by 25%, compared to untreated plots. At harvest, the number of tillers per row was found to have increased by 53%, yield had increased by 160% and the 1000-grain weight had increased by 4%. For all evaluated parameters the effect was significantly different from the untreated plots and not significantly different from the plots treated with the fungicide, Sibutol LS 280. I. bolleyi gave a lower but still significantly effective control, when evaluated for disease index and numbers of tillers per row, while Chaetomium sp. did not show any reduction in the disease. Furthermore, in field experiments using barley infected with B. sorokiniana , a significant effect of G. roseum was demonstrated as increased plant dry weight after 1 month and increased 1000-grain weight at harvest. The disease-controlling effect of G. roseum on F. culmorum was shown in a field experiment with spring barley.     

Spatial aggregation of pathotypes of barley powdery mildew

Aggregation in the distribution of pathotypes of Erysiphe graminis f.sp. hordei , the barley powdery mildew pathogen, was investigated in field plots of 'Golden Promise', 'Proctor' and 'Tyra'. 'Golden Promise' and 'Proctor' have no effective mildew resistance alleles, whereas 'Tyra' has Mla1 , which was only effective against a proportion of the mildew population. Isolates of mildew were sampled according to a grid sampling scheme and their virulence spectra ascertained in order to group them according to pathotype. The populations were very diverse, and evidence for aggregation (quantified using join counts) was found only in the 'Tyra' plots, at distances of up to 1m. This aggregation was reduced in a subsequent sample. The results are consistent with a model in which mildew epidemics are started by a large number of initial infections, which then form diffuse, overlapping aggregations of clones. These aggregations then become more diffuse, so that the amount of aggregation reduces with time. The greater amount of aggregation seen in the 'Tyra' plots might have been caused by there being less initial inoculum with virulence towards that cultivar.     

Some studies of competition between Avena fatua L. and spring barley I. The influence of A. fatua on yield of barley

A. fauta reduced yields of spring barley in the majority of 51 experiments carried out during 1971 and 1972. Infestations ranging from 8 to 662 seedlings/m² in the spring resulted in yield reductions varying from nothing to 72%; in 11 experiments these exceeded 1–2 t/ha. Reductions in yield were poorly correlated with numbers of seedlings, panicles or wild oat seeds produced. However, there was a good correlation between yield loss and the dry weight of wild oats at harvest. Growth and competitive effects of wild oats differed between the two years. Grain losses were due mainly to reductions in the numbers of ear bearing barley tillers. The influence and significance of the effect of competition on the size of barley grains is discussed.     

THE INFLUENCE OF IRRIGATION, FERTILIZING AND MCPA ON THE COMPETITION BETWEEN SPRING CEREALS AND WEEDS

Summary. The average air-dry yield of weeds on fallow plots was about four times as large (2660 kg/ha) as the yield of weeds which developed among spring cereal crops (740 kg/ha). Application of fertilizers increased the number of weeds and their average weight on both irrigated and non-irrigated plots. Treatment with MCPA reduced the weed yield to 36% on fallow plots and to 26% on weedy cereal plots. It was more effective on fertilized plots than on unfertilized plots, but irrigation made little difference to its effectiveness. The space left by the destroyed weeds was mainly occupied by Agropyron repens . Oats were better able to compete with weeds than were wheat and barley. On unfertilized and non-irrigated plots spraying with MCPA (1-26 kg/ha) at the beginning of shooting significantly reduced the yields of weed-free barley. The yields of sprayed oats and wheat were also below the yields from the unsprayed although the reductions were not significant at the 5% level. However, on a number of fertilized and irrigated plots, both weedy and hand-weeded , on which the plants had better growing conditions, MCPA resulted in a significant increase in the grain yield of barley and oats.
Influence de l'irrigation, de la fertilisation et du MCPA sur la compétition entre céréales de printemps et mauvaises herbes     

Soil fumigation and crop rotation to control spraing disease in potatoes

Growing resistant potato cultivars is of little help in avoiding damage by spraing, because of regionally differing strains of tobacco rattle virus and of special requirements of the processing industry. On soil, fumigated in 1971 during autumn with a solution of dichloropropene-dichloropropane (660 g/l) at 250 l/ha, the vectorsTrichodorus spp., were effectively controlled and the tuber disorder did not appear in the next year's potato crop. But potatoes from the treated plots had an unacceptable off-flavour. In the second crop after treatment, control was still good and there was no difference in flavour between potatoes from treated and untreated plots. Disease incidence was significantly lower after spring barley than after sugarbeet, maize, or potatoes.     

Immigration of the barley mildew pathogen into field plots of barley

Immigration of the barley powdery mildew pathogen ( Erysiphe graminis f.sp. hordei ) into field plots of the spring barley variety Tyra (carrying the resistance allele Mla1 ) was investigated. Spores were trapped from the top of the plot canopies, as well as from control plots of wheat with no barley nearby. Comparison of the frequencies of virulent and avirulent single-colony isolates showed that the amount of immigration, relative to the amount of inoculum being produced within the plot, reduced very rapidly, until it could not be detected in the middle of the growing season (mid-June).     

Effect of Jasmonic Application on Economically Insect Pests and Yeald in Spring Wheat

Field trials were conducted in spring wheat to observe effects of jasmonic acid (JA) on aphids, thrips and wheat blossom midge (WBM). Two spring wheat varieties (Triso and Kadrilj) were sprayed twice, with two concentrations of JA plus control. Wheat pests and associated natural enemies (Coccinellidae, Empididae and Aphelinidae) were surveyed by direct count and sweep net methods. Thrips larvae and adults and WBM larvae were estimated by dissecting wheat ears. Wheat midge larvae were monitored using white traps in treated and untreated plots. At the end of season, wheat yield was assessed in treated and control plots. There was a significant difference in the number of insect pests and their natural enemies between treatments in both varieties. Plants in control plots had higher numbers of aphids, thrips and midges than in treated plots. There were more aphids, thrips and midges on the variety ??Triso?? than on ??Kadrilj??. JA application enhanced wheat yield in treated plots compared to control plots. The results indicated that JA mediated induction of plant defense in wheat plants can improve resistance against insect herbivores. JA could be used to develop environmentally sound crop management with reduced insecticide applications.     

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.     

Variation in the effects of take-all disease on grain yield and quality of winter cereals in field experiments

Relationships between take-all intensity and grain yield and quality were determined in field experiments on cereal crops using regression analyses, usually based on single-point disease assessments made during anthesis or grain-filling. Different amounts of take-all were achieved by different methods of applying inoculum artificially (to wheat only) or by using different cropping sequences (in wheat, triticale or barley) or sowing dates (wheat only) in crops with natural inoculum. Regressions of yield or thousand-grain weight on take-all intensity during grain filling were similar to those on accumulated disease (area under the disease progress curve) when these were compared in one of the wheat experiments. Regressions of yield on take-all intensity were more often significant in wheat than in the less susceptible crops, triticale and barley, even when a wide range of disease intensities was present in the latter crops. The regressions usually had most significance when there were plots in the severe disease category. Thousand-grain weight and hectolitre weight usually responded similarly to total grain yield. Decreased yield was often accompanied by a significant increase in the percentage of small grains. When severe take-all was present in wheat, regressions showed that nitrogen uptake was usually impaired. This was sometimes accompanied, however, by increased percentage nitrogen in the grain as a consequence of smaller grain size with decreased endosperm. Significant effects of take-all, both positive and negative, on Hagberg falling number in wheat sometimes occurred. Significant regressions of yield on take-all assessed earlier than usual, ie during booting rather than grain-filling in wheat and triticale and during anthesis/grain-filling rather than ripening in barley, had steeper slopes. This is consistent with observations that severe disease that develops early can be particularly damaging, whilst the crops, especially barley, can later express tolerance by producing additional, healthy roots. The regression parameters, including maximum potential yield (y-axis intercept) and the extrapolated maximum yield loss, also varied according to the different growing conditions, including experimental treatments and other husbandry operations. These differences must be considered when assessing the economic potential of a control measure such as fungicidal seed treatment.     

Epidemiological studies on powdery mildew of mungbean and urdbean

Abstract

Powdery mildew of mungbean (Vigna radiata L. Wilczek) and urdbean ( V. mungo L. Hepper) caused by Erysiphe polyponi DC during the winter/spring season is a severe constraint in the production of bean crops in the Chhattisgarh region of Madhya Pradesh. Keeping this in view, studies were made to understand the development of powdery mildew in relation to crops, varieties, weather conditions and their effect on yield. The first appearance of powdery mildew in 33 mungbean and 18 urdbean varieties was 1 week earlier during winter 1992–93 than winter 1991–92. Its development was most rapid each year when the average maximum temperature varied from 27.2 to 30.3°C, relative humidity from 67 to 90% during the morning and 12 to 38% at noon, and wind velocity from 2.3 to 4.1 km/h. A positive correlation occurred between mildew severity and temperatures and wind velocity in most of the varieties. However, the correlation with relative humidity was negative and significant except in a few varieties. The pooled infection rates (r)/unit/day on resistant mungbean and urdbean varieties was less than 0.1 with disease scores of 1–5 while in apparently slow mildewing varieties, rvalues were also less than 0.1 but showed a score of 7–9. The effect of disease levels on grain yield of urdbean had a negative and significant correlation. However, it was negative but not significant in the case of mungbean. Grain yield was considerably higher when the crops were protected with one spray of Bavistin (1 kg/ha in 5001 of water) followed by Sulfex (3 kg/ha in 5001 of water) than in the untreated control. The disease scores in sprayed plots were also markedly less and ranged between 0 and 5 as against 1 and 9 in the untreated control in different varieties.     

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.     

Comparison of Programmed and Supervised Control Systems for Field Crops1

The effects of increasing inputs of pesticides, nitrogen and growth regulators were studied in field trials in winter wheat and spring barley in southern Sweden. The trials also included a comparison of different strategies: no control, routine control and supervised control. In 1982 EPIPRE, a computerized pest and disease management system developed in the Netherlands, was included. High inputs of nitrogen only slightly influenced the yields. In winter wheat, routine control, comprising one insecticide and three fungicide sprays, heavily increased the yield and was more profitable than supervised control. On an average only 1.2 pesticide sprays were carried out in supervised plots. However, in spring barley supervised control was slightly more profitable than routine control comprising one fungicide and one insecticide application. The average number of sprays in supervised was 0.6 only. In both winter wheat and barley the yield increase for routine control significantly increased with increasing nitrogen level. In barley a significant relationship between number of aphids per tiller and yield increase could be proved.     

Modelling the economics of herbicide treatment in wheat and barley using data on prevented grain yield losses

Losses in grain yield prevented by controlling weeds were measured in 59 fields of (southern hemisphere) spring-sown wheat (Triticum aestivum L.) (cv, Otane) and 45 fields of spring-sown barley (Hordeum vulgare L.) (cv. Corniche) in five consecutive growing seasons from 1988/89 until 1992/93 in the Canterbury region of New Zealand. The losses were measured as the differences in yield between weeded and non-weeded plots located in randomly positioned pairs in the fields. In the first 2 years, the weeding was by push hoe in‘organically grown crops. For the last 3 years, the fields were under prophylactic herbicide regimens with nonweeded plots created by excluding commercial herbicide applications (made mostly in October for wheat and November for barley) with polyethylene sheets placed temporarily over the plots. For each season the distributions of yield losses were modelled using the normal distribution and probabilities of ‘breaking even’ on herbicide use derived by substituting cumulative probability density functions into a simple break-even model for herbicide use. The model assumed that herbicide application in the current crop has no flow-on economic effect for succeeding crops. The mean annual yield losses prevented by herbicide application were positively correlated with September and October rainfall for wheat and bailey respectively. As a consequence, the probabilities of breaking even on herbicide use increased with increasing spring rainfall. Using historical rainfall records, probabilities of breaking even were estimated for each of the 48 years from 1947 to 1994. Averaging over these years, the analysis revealed that at current grain prices prophylactic use of the commonly applied herbicides is likely to be uneconomic in 24% (95% confidence limits 6% and 50%) of fields of average-yielding Otane wheat and in 26% (95% confidence limits 1% and 91 %) of fields of average-yielding Corniche barley in Canterbury. It was concluded that there is potential for withholding herbicide treatments without jeopardizing profitability in these crops, particularly in seasons with low spring rainfall.     

Temporary partial breakdown of mlo-resistance in spring barley by sudden relief of soil water-stress under field conditions: the effects of genetic background and mlo allele

This study, carried out under field conditions, assessed the extent to which temporary breakdown of mlo- resistance, following relief of water-stress, was determined by genetic background and mlo allele. Commercial barley cultivars expressing the mlo gene for resistance to powdery mildew ( Erysiphe graminis ( Blumeria graminis ) f.sp. hordei ) were tested as well as doubled haploid progeny from spring barley genotypes, a proportion of which were sown in the field in two successive years. Plants were protected from natural rain by a mobile rain shelter and either watered by trickle-irrigation or allowed to dry. Percentage mildew infection resulting from natural inoculum was recorded and the doubled haploid genotypes were classified as resistant, intermediate or susceptible on the basis of their control (watered) treatment scores. In each of the three designated classes, particular genotypes developed infection levels, following relief of water-stress, that were higher than those observed on the well-watered controls. This was found not to be related to the mlo allele as there was no significant difference between the increases observed on resistant plants carrying mlo9 and resistant plants carrying mlo11 . Differences in the degree of breakdown of resistance were attributed to genetic background rather than to the specific mlo allele.     

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.