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See detailModeling the Main Fungal Diseases of Winter Wheat: Constraints and Possible Solutions
El Jarroudi, Moussa ULiege; kouadio, Louis; Tychon, Bernard ULiege et al

in Advances in Plant Pathology (2018)

The first step in the formulation of disease management strategy for any cropping system is to identify the most important risk factors. This is facilitated by basic epidemiological studies of pathogen ... [more ▼]

The first step in the formulation of disease management strategy for any cropping system is to identify the most important risk factors. This is facilitated by basic epidemiological studies of pathogen life cycles, and an understanding of the way in which weather and cropping factors affect the quantity of initial inoculum and the rate at which the epidemic develops. Weather conditions are important factors in the development of fungal diseases in winter wheat, and constitute the main inputs of the decision support systems used to forecast disease and thus determine the timing for efficacious fungicide application. Crop protection often relies on preventive fungicide applications. Considering the slim cost−revenue ratio for winter wheat and the negative environmental impacts of fungicide overuse, necessity for applying only sprays that are critical for disease control becomes paramount for a sustainable and environmentally friendly crop production. Thus, fungicides should only be applied at critical stages for disease development, and only after the pathogen has been correctly identified. This chapter provides an overview of different weather-based disease models developed for assessing the real-time risk of epidemic development of the major fungal diseases (Septoria leaf blotch, leaf rusts and Fusarium head blight) of winter wheat in Luxembourg. [less ▲]

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See detailImproving fungal disease forecasts in winter wheat: A critical role of intra-day variations of meteorological conditions in the development of Septoria leaf blotch
El Jarroudi, Moussa ULiege; kOUADIO, Louis; EL JARROUDI, Mustapha et al

in Field Crops Research (2017), 213

Meteorological conditions are important factors in the development of fungal diseases in winter wheat and are the main inputs of the decision support systems used to forecast disease and thus determine ... [more ▼]

Meteorological conditions are important factors in the development of fungal diseases in winter wheat and are the main inputs of the decision support systems used to forecast disease and thus determine timing for efficacious fungicide application. This study uses the Fourier transform method (FTM) to characterize temporal patterns of meteorological conditions between two neighbouring experimental sites used in a regional fungal disease monitoring and forecasting experiment in Luxembourg. Three meteorological variables (air temperature, relative humidity, and precipitation) were included, all conducive to infection of wheat by Zymoseptoria tritici cause of Septoria leaf blotch (STB) in winter wheat, from 2006 to 2009. The intraday, diurnal, dekadal and intra-seasonal variations of the meteorological variables were assessed using FTM, and the impact of existing contrasts between sites on the development of STB was analyzed. Although STB severities varied between sites and years (P ≤ 0.0003), the results indicated that the two sites presented the same patterns of meteorological conditions when compared at larger temporal scales (diurnal to intra-seasonal scales, with time periods >11 h). However, the intraday variations of all the variables were well discriminated between the sites and were highly correlated to STB severities. Our findings highlight and confirm the importance of intraday meteorological variation in the development of STB in winter wheat fields. Furthermore, the FTM approach has potential for identifying microclimatic conditions prevailing at given sites and could help in improving the prediction of disease forecast models used in regional warning systems. [less ▲]

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See detailA threshold-based weather model for predicting stripe rust infection in winter wheat
El Jarroudi, Moussa ULiege; Kouadio, Louis; Bock, Clive et al

in Plant Disease (2017), 101(693-703),

Wheat stripe rust (caused by Puccinia striiformis f. sp. tritici) is a major threat in most wheat growing regions worldwide, which potentially causes substantial yield losses when environmental conditions ... [more ▼]

Wheat stripe rust (caused by Puccinia striiformis f. sp. tritici) is a major threat in most wheat growing regions worldwide, which potentially causes substantial yield losses when environmental conditions are favorable. Data from 1999-2015 for three representative wheat-growing sites in Luxembourg were used to develop a threshold-based weather model for predicting wheat stripe rust. First, the range of favorable weather conditions using a Monte Carlo simulation method based on the Dennis model were characterized. Then, the optimum combined favorable weather variables (air temperature, relative humidity, and rainfall) during the most critical infection period (May-June) was identified and was used to develop the model. Uninterrupted hours with such favorable weather conditions over each dekad (i.e., 10-day period) during May-June were also considered when building the model. Results showed that a combination of relative humidity > 92% and 4°C < temperature < 16°C for a minimum of 4 continuous hours, associated with rainfall ≤ 0.1 mm (with the dekad having these conditions for 5-20% of the time), were optimum to the development of a wheat stripe rust epidemic. The model accurately predicted infection events: probabilities of detection were ≥ 0.90 and false alarm ratios were ≤ 0.38 on average, and critical success indexes ranged from 0.63 to 1. The method is potentially applicable to studies of other economically important fungal diseases of other crops or in different geographical locations. If weather forecasts are available, the threshold-based weather model can be integrated into an operational warning system to guide fungicide applications. [less ▲]

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See detailEffects of rater bias and assessment method on disease severity estimation with regard to hypothesis testing
Chiang, Kuo-Szu; Bock, Clive; El Jarroudi, Moussa ULiege et al

in Plant Pathology (2016)

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See detailDo single, double or triple fungicide sprays differentially affect the grain quality in winter wheat?
El Jarroudi, Moussa ULiege; kOUADIO, Louis; Junk et al

in Field Crops Research (2015), 183(257-266),

Foliar fungicides in wheat are typically used to safeguard against economic losses from diseases. In this study, we assessed the effects of three fungicide spray regimes [single, double, and triple ... [more ▼]

Foliar fungicides in wheat are typically used to safeguard against economic losses from diseases. In this study, we assessed the effects of three fungicide spray regimes [single, double, and triple treatments] on four different grain quality parameters [thousand grain weight (TGW), test weight (TW), grain protein content (GPC), and Zeleny sedimentation volume (ZSV)] during the 2006–2009 period at two sites in Luxembourg. The fungicides used were generally a mix of chlorothalonil and triazoles. At Burmerange, (cultivar Cubus), the values of TGW, TW, GPC and ZSV ranged from 38 to 62 g, 67 to 83 kg hl−1, 12.0% to 14.7% dry matter (DM), and 27 to 54 ml, respectively. Whereas, at Everlange (cultivar Achat), the ranges of TGW, TW, GPC and ZSV were 42 to 65 g, 65 to 81 kg hl−1, 11.0% to 15.0% DM, and 21 to 66 ml, respectively. In more than 75% cases, the results indicate that fungicides did not significantly affect TW or ZSV at either sites (P > 0.05). However, there was a significant and positive fungicide effect on GPC in 2006 and 2009 at Burmerange, and only in 2006 at Everlange (P < 0.05). On the contrary, TGW was significantly affected at Burmerange in all years, except 2008 when a positive increase was observed compared to control plots; and in 2006 and 2007 at Everlange. Interestingly, when there was an effect of fungicides on a quality parameter, there was no difference among different fungicide treatments. Thus under conditions prevailing in Luxembourg, a single fungicide treatment applied with judicious timing generally resulted in statistically similar grain quality parameters when compared with a double or triple fungicide treatment. [less ▲]

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See detailDisease Severity Estimates – Effects of Rater Accuracy and Assessment Methods for Comparing Treatments
Bock, Clive; El Jarroudi, Moussa ULiege; Kouadio, Louis et al

in Plant Disease (2015), 99(1104-1112),

Assessment of disease severity is required for several purposes in plant pathology; most often the estimates are made visually. It is established that visual estimates can be inaccurate and unreliable ... [more ▼]

Assessment of disease severity is required for several purposes in plant pathology; most often the estimates are made visually. It is established that visual estimates can be inaccurate and unreliable. The ramifications of biased or imprecise estimates by raters have not been fully explored using empirical data; partly because of the logistical difficulties involved in different raters assessing the same leaves for which actual disease has been measured in a replicated experiment with multiple treatments. In this study nearest percent estimates (NPEs) of Septoria leaf blotch (SLB) on leaves of winter wheat from non-treated and fungicide treated plots were assessed in both 2006 and 2007 by four raters and compared to assumed true values measured using image analysis. Lin’s concordance correlation (LCC, ρc) was used to assess agreement between the two approaches. NPEs were converted to Horsfall-Barratt (HB) mid-points and again compared for agreement with true values. The estimates of SLB severity from fungicide-treated and non-treated plots were analyzed using generalized linear mixed modeling to ascertain effects of rater using both the NPE and HB values. Rater 1 showed good agreement with image analysis (ρc = 0.986 to 0.999), while raters 3 and 4 had less good agreement (ρc = 0.205 to 0.936). Conversion to the HB scale had little effect on bias or accuracy, but reduced both precision and agreement for most raters on most assessment dates (precision, r = -0.001 to -0.132; and agreement, ρc = -0.003 to -0.468). Inter-rater reliability was also reduced slightly by conversion of estimates to HB midpoint values. Estimates of mean SLB severity were significantly different between image analysis and raters 2, 3 and 4, and there were frequently significant differences among raters (F=151 to 1260, P=0.001 to <0.0001). Conversion to the HB scale changed the means separation ranking of rater estimates on 26 June 2007. Nonetheless, image analysis and all raters were able to differentiate control and treated plots treatments (F=116 to 1952, P=0.002 to <0.0001, depending on date and rater). Conversion of NPEs to the HB scale tended to reduce F-values slightly (2006: NPEs, F=116 to 276, P=0.002 to 0.0005, and for the HB converted values F=101 to 270, P=0.002 to 0.0005, and in 2007, NPEs, F=164 to 1952 P=0.001 to <0.0001, and for HB converted values F=126 to 1633 P=0.002 to <0.0001). The results demonstrated the need for accurate and reliable disease assessment to minimize over or underestimates compared to actual disease, and where multiple raters are deployed, they should be assigned in a manner to reduce any potential effect of rater differences on the analysis. [less ▲]

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See detailEconomics of a decision-support system for managing the main fungal diseases of winter wheat in the Grand-Duchy of Luxembourg
El Jarroudi, Moussa ULiege; Kouadio, Louis; Beyer, Marco et al

in Field Crops Research (2015), 172(2), 32-41

We evaluated the cost effectiveness of a decision-support system (DSS) developed for assessing in real time the risk of progression of the main fungal diseases (i.e., Septoria leaf blotch, powdery mildew ... [more ▼]

We evaluated the cost effectiveness of a decision-support system (DSS) developed for assessing in real time the risk of progression of the main fungal diseases (i.e., Septoria leaf blotch, powdery mildew, leaf rusts and Fusarium head blight) of winter wheat in the Grand-Duchy of Luxembourg (GDL). The study was conducted in replicated field experiments located in four agricultural locations (representative of the main agro-ecological regions of the country) over a 10-year period (2003-2012). Three fungicide spray strategies were compared: a single DSS-based system and two commonly used spray practices in the GDL, a double- (2T)- and a triple- spray (3T) spray treatment; there was also a non-treated control. In years with a high disease pressure, the DSS-based recommendation resulted in protection of the three upper leaves comparable to that achieved with the 2T and 3T treatments, with significant grain yield increases (P > 0.05) compared to the control (a 4 to 42% increase, depending on the site and year). Overall, the financial gain in treated plots compared with the control ranged from 3 to 16% at the study sites. Furthermore, in seasons when dry weather conditions precluded epidemic development, no the DSS-basedDSS recommended no fungicide spray was recommended, reducing use of fungicide, and thus saving the cost of the product. The gain in yield for the 2T and 3T plots (compared with control) did not necessarily result in a financial gain during the duration of the experiment. This study demonstrates the potential advantages and profitability of using a DSS -based approach for disease management. [less ▲]

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See detailA comparison between visual estimates and image analysis measurements to determine Septoria leaf blotch severity in winter wheat
El Jarroudi, Moussa ULiege; Kouadio, Louis; Mackels, Christophe et al

in Plant Pathology (2015)

Methods to estimate disease severity vary in accuracy, reliability, ease of use and cost. Severity of Septoria leaf blotch (SLB, caused by Zymoseptoria graminicola) was estimated by four raters and by ... [more ▼]

Methods to estimate disease severity vary in accuracy, reliability, ease of use and cost. Severity of Septoria leaf blotch (SLB, caused by Zymoseptoria graminicola) was estimated by four raters and by image analysis (assumed actual values) on individual leaves of winter wheat in order to explore accuracy and reliability of estimates, and to ascertain whether there were any general characteristics of error. Specifically, (i) we determined the accuracy and reliability of visual assessments of SLB over the full range of severity from 0 to 100%, and we investigated (ii) whether certain 10% ranges in actual disease severity between 0 and 100% were more prone to estimation error compared with others, and (iii) whether leaf position affected accuracy within those ranges. Lin's concordance correlation analysis of all severities (0 to 100%) demonstrated that all raters had estimates close to the actual values (agreement: ρc = 0.92-0.99). However, agreement between actual SLB severities and estimates by raters was less good when compared over short 10% subdivisions within the 0-100% range (ρc = -0.12 to 0.99). Despite common rater imprecision at estimating low and high SLB severities, individual raters differed considerably in their accuracy over the short 10% subdivisions. There was no effect of leaf position on accuracy or precision of severity estimate on separate leaves (L1-L3). Pursuing efforts in understanding error in disease estimation should aid in improving the accuracy of assessments, making visual estimates of disease severity more useful for research and applied purposes. [less ▲]

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See detailDisease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat.
El Jarroudi, Moussa ULiege; Kouadio, Louis; Mackels, Christophe et al

in Phytopathology (2014), 104(11), 37

The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard ... [more ▼]

The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard area diagrams and DISTRAIN) was determined by comparison with assumed actual values obtained by digital image analysis. Initially analyses were performed using SLB severity over the full 0-100% range; then, to explore error over short ranges of the 0-100% scale, the scale was divided into sequential 10%-increments based on the actual values. Lin’s concordance correlation (LCC) analysis demonstrated that all raters were accurate when compared over the whole severity range (LCC coefficient (ρc)= 0.92-0.99). However, agreement between actual and visual SLB severities was less good when compared over the short intervals of the 10×10% classes (ρc= -0.12-0.99), demonstrating that agreement will vary depending on the actual disease range over which it is compared. Inter-rater reliability between each pair of raters over the full 0-100% range (correlation analysis r= 0.970-0.992, P<0.0001), and inter-class correlation coefficient (ρ≥ 0.927) were very high. This study provides new insight into using a full range of actual disease severity vs limited ranges to ensure a realistic measure of rater accuracy and reliability, in addition to contributing to the ongoing debate on the use of visual disease estimates based on the 0-100% ratio scale for epidemiological research. [less ▲]

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See detailThe effects of rater bias on hypothesis testing when using different assessment methods for estimating disease severity.
CHIANG, KUO-SZU; Bock, Clive; El Jarroudi, Moussa ULiege et al

in Phytopathology (2014), 104(11), 26

Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales was explored. Nearest percent estimates (NPE), the ... [more ▼]

Bias (over and underestimates) in estimates of disease severity, and the impact of that inaccuracy on hypothesis testing using different disease scales was explored. Nearest percent estimates (NPE), the Horsfall-Barratt (H-B) scale and four different linear category scales (5% and 10% increments, with and without additional grades at low severity) were compared. Actual values and estimates by 4 different raters of the severity (0 to 100%) of Septoria leaf blotch on leaves of winter wheat were used to develop distributions for a simulation model. The simulations were based on i) all the 4 raters data combined, ii) only the most accurate rater estimates, and iii) only the most biased rater. Regardless of the effect of rater ability, we found that, there were lower type II error rates with NPEs as compared with the other category scales at severities of 80 to 100%. On the other hand, with lower severities (0 to 20%), the 5% and 10% scales with additional grades had type II error rates comparable to those for the NPEs. Raters who overestimated severity and used the H-B scale had the highest risk of a type II error when the mean disease severity was low. Knowledge of how rater ability and scale type can affect hypothesis testing can be used to improve disease assessment as well as to provide a logical framework for developing standard area diagrams. [less ▲]

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See detailA comparison of raters and disease assessment methods for estimating disease severity for purposes of hypothesis testing.
Bock, Clive; El Jarroudi, Moussa ULiege; Kouadio, Louis et al

in Phytopathology (2014), 104(11), 26

Assessment of disease severity is most often made visually, and estimates can be inaccurate. Nearest percent estimates (NPEs) of Septoria leaf blotch on leaves of winter wheat by four raters (R1-R4 ... [more ▼]

Assessment of disease severity is most often made visually, and estimates can be inaccurate. Nearest percent estimates (NPEs) of Septoria leaf blotch on leaves of winter wheat by four raters (R1-R4) assessing non-treated (NT) and fungicide-treated (FT) plots were compared to true values using Lin’s concordance correlation coefficient (ρc) on two dates in 2006 and 2007. Estimates were converted to Horsfall-Barratt (HB) mid-points and again compared for accuracy and precision. Estimates of severity from FT and NT plots were analyzed to ascertain effects of rater using both the NPE and HB values. Regardless of method, all raters showed a range of agreement with true values on FT and NT plots (ρc = 0 to 1). Use of the HB scale most often reduced agreement (84.4% of the time), and did not improve rater-associated bias of treatment mean severity estimates. Consequently, estimates of mean severity differed significantly among raters and from true values (F=126 to 1260, P=0.002 to<0.0001). However, a comparison of treatment effects showed that the true values and R1 to R4 all demonstrated significant effects of fungicide (F=101 to 1952, P=0.002 to <0.00001). Ranking of raters differed on one occasion when HB values were used. These results demonstrate the effect of the HB scale, and the need for accurate disease assessment to minimize over or underestimates compared to true severity so as to minimize the potential for type II errors. [less ▲]

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