scholarly journals Accounting for the Economic Risk Caused by Variation in Disease Severity in Fungicide Dose Decisions, Exemplified for Mycosphaerella graminicola on Winter Wheat

2013 ◽  
Vol 103 (7) ◽  
pp. 666-672 ◽  
Author(s):  
D. E. te Beest ◽  
N. D. Paveley ◽  
M. W. Shaw ◽  
F. van den Bosch
Keyword(s):  
Probability Distribution ◽  
Risk Aversion ◽  
Disease Severity ◽  
Yield Loss ◽  
Grain Filling ◽  
Optimal Dose ◽  
Mycosphaerella Graminicola ◽  
Septoria Tritici ◽  
High Loss ◽  
Field Plots

A method is presented to calculate economic optimum fungicide doses accounting for the risk aversion of growers responding to variability in disease severity between crops. Simple dose-response and disease-yield loss functions are used to estimate net disease-related costs (fungicide cost plus disease-induced yield loss) as a function of dose and untreated severity. With fairly general assumptions about the shapes of the probability distribution of disease severity and the other functions involved, we show that a choice of fungicide dose which minimizes net costs, on average, across seasons results in occasional large net costs caused by inadequate control in high disease seasons. This may be unacceptable to a grower with limited capital. A risk-averse grower can choose to reduce the size and frequency of such losses by applying a higher dose as insurance. For example, a grower may decide to accept “high-loss” years 1 year in 10 or 1 year in 20 (i.e., specifying a proportion of years in which disease severity and net costs will be above a specified level). Our analysis shows that taking into account disease severity variation and risk aversion will usually increase the dose applied by an economically rational grower. The analysis is illustrated with data on Septoria tritici leaf blotch of wheat caused by Mycosphaerella graminicola. Observations from untreated field plots at sites across England over 3 years were used to estimate the probability distribution of disease severities at mid-grain filling. In the absence of a fully reliable disease forecasting scheme, reducing the frequency of high-loss years requires substantially higher doses to be applied to all crops. Disease-resistant cultivars reduce both the optimal dose at all levels of risk and the disease-related costs at all doses.

Surveys of speckled leaf blotch and other foliar diseases of wheat in Victoria, 1974 to 1978

1980 ◽  
Vol 20 (102) ◽  
pp. 94 ◽  
Author(s):  
JS Brown ◽  
RG Paddick
Keyword(s):  
Yield Loss ◽  
Mycosphaerella Graminicola ◽  
Septoria Tritici ◽  
Puccinia Recondita ◽  
Puccinia Graminis ◽  
Yield Losses ◽  
Leaf Blotch ◽  
Average Percentage ◽  
Leptosphaeria Nodorum ◽  
Glume Blotch

The severity of speckled leaf blotch (Mycosphaerella graminicola (Fuckel) Schroeter, Septoria tritici Rob. ex Desm.) in wheat crops was surveyed in the Wimmera during the 1974-77 seasons and in all the major wheat growing areas of Victoria in 1978. Speckled leaf blotch was found in all crops and the severity varied greatly within and between seasons. The average percentage of affected area on the penultimate leaf of main tillers was 24%, 28%, 1.5%, 0% and 9.4%, respectively, for the successive seasons. The corresponding grain yield losses were estimated at 19, 21, 5, 0 and 12% by using an experimentally derived relation between yield loss and disease severity. In 1978, glume blotch (Leptosphaeria nodorum (Miiller, Septoria nodorum (Berk.) Berk.), stem rust (Puccinia graminis Pers. f sp. tritici Erikss and Henn.), leaf rust (Puccinia recondita Rob. ex Desm. f sp, tritici Erikss) and powdery mildew (Erysiphe graminis DC. f sp. tritici E. Marchal) occurred in 8%, 3%, 1% and 0.5%, respectively, of the crops sampled. These surveys have shown speckled leaf blotch to be the most important foliar disease of wheat in Victoria.

scholarly journals Comparison of Severity Assessment Methods for Predicting Yield Loss to Rhizoctonia Foliar Blight in Soybean

Plant Disease ◽  
2006 ◽  
Vol 90 (1) ◽  
pp. 39-43 ◽  
Author(s):  
K. C. Stetina ◽  
S. R. Stetina ◽  
J. S. Russin
Keyword(s):  
Disease Severity ◽  
Yield Loss ◽  
Anastomosis Group ◽  
Foliar Blight ◽  
Relative Differences ◽  
Moderately Resistant ◽  
Field Plots ◽  
Pod Number ◽  
Severe Destruction ◽  
Group 1

Rhizoctonia foliar blight, caused by Rhizoctonia solani Kühn anastomosis group 1, causes rapid and severe destruction of soybean foliage and pods during hot, wet weather. The objectives of this study were to determine the yield components affected by this disease and whether rating pod damage or foliar damage provides a more reliable method of assessing disease severity relative to impact on yield. Disease severity in the moderately resistant cv. NK S57-11 and the susceptible cv. Buckshot 723 was assessed in field plots in 1996 and 1997 using foliar and pod ratings (0-to-10 scale corresponding to 0 to 100% of tissue affected). Based on results from regression analysis, pod number, seed number, and seed weight per plot decreased as disease severity increased, whereas the proportion of partially filled pods and the weight of 100 seed were not affected. Yield loss appeared to be due primarily to loss of entire pods. Foliar and pod assessments of disease severity correlated positively in 1996 (r = 0.8343) and 1997 (r = 0.5958) for both cultivars, which suggests that either method can be used to identify relative differences among cultivars. However, pod assessments accounted for more variability than foliar assessments under low-disease conditions. Plants exhibiting moderate to severe symptoms of Rhizoctonia foliar blight also retained green stems and pods at harvest, which was evidence of delayed maturity.

Influence of nitrogen on the development of Septoria epidemics in winter wheat

1995 ◽  
Vol 124 (3) ◽  
pp. 361-368 ◽  
Author(s):  
M. H. Leitch ◽  
P. D. Jenkins
Keyword(s):  
Winter Wheat ◽  
Field Experiments ◽  
Yield Loss ◽  
Flag Leaf ◽  
Leaf Tissue ◽  
Grain Filling ◽  
Septoria Tritici ◽  
Potential Yield ◽  
Subsequent Effect ◽  
The University

SUMMARYField experiments were undertaken at the University of Wales, Aberystwyth over two seasons to investigate the effects of N fertilizer rate and timing on the development of Septoria diseases (principally Septoria tritici) in winter wheat and its subsequent effect on crop growth. Rates of 100, 200 and 300 kg/ha N were applied at GS23, GS30, or split (GS23/30/38) in 1985/86 and 100 and 250 kg/ha N at GS23, GS30, GS23/30, or GS23/30/37 in 1987/88. Foliar diseases were allowed to develop or were controlled with fungicide. Early disease levels were temporarily enhanced soon after N application and were greater at the higher rates of N. In April and June a significant correlation between disease infection and concentration of N in leaf tissue was shown. Despite differences in the level of early infection, dry matter production up to and including anthesis was unaffected by disease. Infection during grain filling caused premature senescence of the flag leaf which significantly reduced grain yield, primarily through a reduction in grain size. Loss of yield was directly related to severity of disease on the flag leaf in early July, with a yield loss of 0·45% for every 1% increase in disease infection. The severity of Septoria post-anthesis increased with increasing rate of fertilizer N by an average of 11·1% per 100 kg/ha N (translating to a potential yield loss of 5% for each 100 kg/ha N given as fertilizer), but was unaffected by its timing of application.

scholarly journals Influence of Flower Thrips on Fusarium Hardlock Severity

Plant Disease ◽  
2007 ◽  
Vol 91 (11) ◽  
pp. 1423-1429 ◽  
Author(s):  
D. J. Mailhot ◽  
J. J. Marois ◽  
D. L. Wright
Keyword(s):  
Gossypium Hirsutum ◽  
Untreated Control ◽  
Yield Loss ◽  
Fusarium Verticillioides ◽  
Field Conditions ◽  
Control Group ◽  
Flower Thrips ◽  
The Impact ◽  
Field Plots

Cotton (Gossypium hirsutum) fiber is sometimes affected by hardlock, which is characterized by a failure of the fiber to expand outward from the boll at maturity. Because affected fiber is inaccessible to mechanical harvesters, yield loss can be considerable. Hardlock has been linked to infection by Fusarium verticillioides. The involvement of flower thrips (Frankliniella spp.), which are commonly found in cotton flowers, was explored. At 1100 h, approximately 10% of cotton flowers contained thrips that were carrying F. verticillioides. The effect of thrips and/or Fusarium in flowers and bolls was explored under greenhouse conditions. Exposing flowers to Fusarium and thrips resulted in bolls with the most severe symptoms. Exposure to either Fusarium or thrips alone resulted in more hardlock than was noted in the control group. The impact of thrips was also evaluated under field conditions. Field plots were treated with insecticides, a fungicide, both, or left untreated. Insecticides reduced thrips numbers and reduced hardlock severity. The fungicide had no impact on thrips numbers and was less effective at reducing hardlock. Combining insecticide and fungicide applications was no more effective than using insecticides alone, although it more frequently increased yield. The untreated control plots generally had the most severe hardlock and lowest yields. Reducing hardlock severity resulted in higher yields, although not consistently. These studies suggest that thrips increase the severity of hardlock, and reducing their numbers may diminish hardlock severity.

Microsatellite markers provide evidence for sexual reproduction of Mycosphaerella graminicola in Saskatchewan

Genome ◽  
2004 ◽  
Vol 47 (5) ◽  
pp. 789-794 ◽  
Author(s):  
M Razavi ◽  
G R Hughes
Keyword(s):  
Genetic Diversity ◽  
Genetic Variability ◽  
Sexual Reproduction ◽  
Primary Source ◽  
Mycosphaerella Graminicola ◽  
Septoria Tritici Blotch ◽  
Septoria Tritici ◽  
Allelic Series ◽  
Evolutionary Potential ◽  
Wheat Field

This study examined the genetic structure of a Saskatchewan population of Mycosphaerella graminicola, cause of the foliar disease Septoria tritici blotch of wheat. Such knowledge is valuable for understanding the evolutionary potential of this pathogen and for developing control strategies based on host resistance. Nine pairs of single-locus microsatellite primers were used to analyze the genomic DNA of 90 isolates of M. graminicola that were collected using a hierarchical sampling procedure from different locations, leaves, and lesions within a wheat field near Saskatoon. Allelic series at eight different loci were detected. The number of alleles per locus ranged from one to five with an average of three alleles per locus. Genetic diversity values ranged from 0.04 to 0.67. Partitioning the total genetic variability into within- and among-location components revealed that 88% of the genetic variability occurred within locations, i.e., within areas of 1 m2, but relatively little variability occurred among locations. Low variability among locations and a high degree of variability within locations would result if the primary source of inoculum was airborne ascospores, which would be dispersed uniformly within the field. This finding was confirmed by gametic disequilibrium analysis and suggests that the sexual reproduction of M. graminicola occurs in Saskatchewan.Key words: Mycosphaerella graminicola, SSR markers, sexual reproduction, genetic diversity.

scholarly journals Considerations for Verticillium Wilt Resistance Evaluation in Potato

Plant Disease ◽  
2007 ◽  
Vol 91 (4) ◽  
pp. 360-367 ◽  
Author(s):  
K. E. Frost ◽  
D. I. Rouse ◽  
S. H. Jansky
Keyword(s):  
Disease Severity ◽  
Verticillium Wilt ◽  
Yield Loss ◽  
Control Culture ◽  
In Planta ◽  
Disease Symptoms ◽  
Accuracy And Precision ◽  
Population Sizes ◽  
Pathogen Colonization ◽  
Time Accuracy

Verticillium wilt (Vw), caused by the soilborne fungi Verticillium dahliae and V. albo-atrum, is an important disease of potato (Solanum tuberosum). Host plant resistance is a promising method of Vw control. Culture-based methods that quantify the pathogen in host tissue often are used for Vw resistance screening. To evaluate the processing time, accuracy, and precision of these methods, 46 clones were planted in a field naturally infested with V. dahliae to collect data on visual disease symptoms, pathogen colonization, and yield. In 2002, disease severity explained 4.34% of the variability of yield loss, but the linear relationship between stem colonization and yield loss was not significant. In 2003, stem colonization explained 57.5% of the variability of yield loss, whereas disease severity explained 1.7% of the variability of yield loss. Correlations comparing clone ranks from repeated pathogen measurements indicated that culturing sap from individual stems or bulked stems generated more repeatable clone rankings than culturing dried stems. Clone rankings were more repeatable between years if pathogen measurements were made earlier in the growing season. The results indicate a need to characterize the effect of the environment on the relationship among pathogen population sizes in planta, disease symptoms, and yield loss.

scholarly journals Brown spot disease severity, yield and yield loss relationships in pigmented upland rice cultivars from East Nusa Tenggara, Indonesia

2020 ◽  
Vol 21 (4) ◽  
Author(s):  
Yosep S. Mau ◽  
Antonius Ndiwa ◽  
Shirly Oematan
Keyword(s):  
Disease Severity ◽  
Yield Loss ◽  
Upland Rice ◽  
Brown Spot ◽  
Yield Reduction ◽  
Rice Cultivars ◽  
Rice Varieties ◽  
Resistance Level ◽  
Spot Disease ◽  
Brown Spot Disease

Abstract. Mau YS, Ndiwa ASS, Oematan SS. 2020. Brown spot disease severity, yield and yield loss relationships in pigmented upland rice cultivars from East Nusa Tenggara, Indonesia. Biodiversitas 21: 1625-1634. Brown spot is one of the most devastating diseases of rice, which could lead to total yield loss. The disease has a worldwide distribution, more specifically in areas where water supply is scarce, most specifically in the dry upland areas. Almost all stages of rice are affected by the disease, where leaves and grains are mostly affected. Considerable differences exist in susceptibility to brown spot among rice varieties, which may cause a large variation in yield loss caused by the disease. Therefore, the resistance level of rice varieties and their yield reduction has to be regularly evaluated and updated. There are only a few reports on the relationship between brown spot severity with yield and yield loss of upland rice, and is even lacking in pigmented upland rice. The objectives of the present study were to assess the brown spot severity and resistance level in pigmented upland rice cultivars from East Nusa Tenggara Province, Indonesia, and to elucidate their relationships with yield and yield reduction. Twenty four pigmented upland rice genotypes were evaluated in the field during May to October 2019, and their disease responses and yields were recorded. Disease severity was observed weekly and used to calculate Area Under the Disease Progress Curve (AUDPC) for comparison among the genotypes. The relationships between disease severity and AUDPC with yield and yield loss were also examined. The results showed significant variation in brown spot severity and AUDPC, ranging from, respectively, 11.11% to 40.70% and 398.42%-days to 1081.30%-days. Yields and yield losses of test genotypes also varied substantially. Yields under diseased-free and diseased plots ranged from, respectively, 2.34 t ha-1 to 6.13 t ha-1 and 1.68 t ha-1 to 3.74 t ha-1 while yield loss was between 10.46% and 56.15%. Six genotypes were moderately resistant, four genotypes were moderately susceptible and 14 genotypes were susceptible to brown spot. Neither disease severity nor AUDPC had a linear relationship with yield but both exhibited positive and linear relationships with yield loss.

scholarly journals Reaction of winter wheat genotypes to infection by Mycosphaerella graminicola(Fuckel) Schroeter

2013 ◽  
Vol 55 (1) ◽  
pp. 233-246
Author(s):  
Ewa Mirzwa-Mróz ◽  
Czesław Zamorski
Keyword(s):  
Winter Wheat ◽  
Broad Spectrum ◽  
Mycosphaerella Graminicola ◽  
Wheat Breeding ◽  
Septoria Tritici ◽  
Wheat Cultivars ◽  
Breeding Lines ◽  
Wheat Genotypes ◽  
Winter Wheat Cultivars

The response of Polish winter wheat genotypes to <i>M.graminicola</i> (preliminary experiments and cultivar collections) was observed in different regions of Poland. Observations were carried out in 1995-1999. The winter wheat genotypes showed a broad spectrum of reaction to this pathogen. Between 1997 and 1999 the highest degree of infection on winter wheat breeding lines was noted in Kończewice. During this time no genotypes free from infection were observed (preliminary breeding experiments). Cultivars with no symptoms of <i>Septoria tritici</i> blotch (Leszczyńska Wczesna and Żelazna) were found among old genotypes in Słupia Wielka only in earlier experiments (1995-1996). In the years 1997-1999 the winter wheat cultivars were classified into groups on the basis of their response to the pathogen. The degree of infection for the majority cultivars was quite high.

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