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Evaluation of a Warning System for Early-Season Control of Grapevine Powdery Mildew
Abstract
Caffi, T., Legler, S. E., Rossi, V., and Bugiani, R. 2012. Evaluation of a warning system for early-season control of grapevine powdery mildew. Plant Dis. 96:104-110. In several grape-growing areas of the world, including northern Italy, powdery mildew epidemics, caused by Erysiphe necator, are mainly triggered by the ascospores produced in overwintered chasmothecia. Growers in northern Italy usually control the disease with fixed-interval fungicide applications. A warning system was developed for early-season powdery mildew control based on (i) short-term weather forecasts, (ii) a model that simulates the severity of each E. necator ascosporic infection, and (iii) a mobile phone short-message system. This warning system was evaluated in six vineyards in northern Italy from 2006 to 2008, between bud break of vines and early berry development; an unsprayed control was compared with "low-risk" and "high-risk" model-driven sprays and a calendar-based "grower" spray program. Use of the warning system reduced disease severity on leaves and bunches compared with the unsprayed control and resulted in the same level of control of powdery mildew as the grower's spray program, with reduced fungicide applications and costs. On average, 5.7 sprays were applied following the grower's spray program (with an average cost of 221 (sic)/ha/year); use of the warning system reduced fungicide applications by 36% (low-risk program, saving of 56 (sic)/ha/year) or 75% (high-risk program, saving of 161 (sic)/ha/year).
... Among the latter, thos based on generalized linear (mixed) models (GLM and GLMMs) and hypothesis testin are prevalent [9,36]. Among the models specifically developed for a pathogen, the mo frequently considered were the mechanistic models described by Rossi, Caffi, an collaborators [10,[37][38][39], as indicated by the number of publications and citation Screening of the literature indicated that there are different kinds of data used for model development. For instance, among the climate data, the air temperature was widely used, probably because it is easy to measure and interpret in a biological context, being highly correlated with development of PM and DM in vineyards. ...
... Among the latter, those based on generalized linear (mixed) models (GLM and GLMMs) and hypothesis testing are prevalent [9,36]. Among the models specifically developed for a pathogen, the most frequently considered were the mechanistic models described by Rossi, Caffi, and collaborators [10,[37][38][39], as indicated by the number of publications and citations. Specifically, among our literature search, Rossi V. authored 22 documents, followed by Caffi T (15). ...
... A later study [75] reported that the model tended to overpredict spore viability by 25% throughout the day and concluded that this could be an explanation for failure to detect the disease in the field in earlier studies, while Pérez-Expósito et al. [6] reported that this model, as well as the EPI model, tended to underestimate the risk of infection, estimating that at least 30 years of climatological data would be needed to provide accurate predictions. As with previous models, this one also requires validation and calibration before the model can be used in different environments [47], although the model optimized by Rossi et al. [10] in Piacenza (Italy) with a fully mechanistic approach requires no calibration or correction and provides an accurate, detailed, and dynamic simulation of the sexual phase of P. viticola [38,47,76]. Finally, the mechanistic model developed by Rossi and collaborators [77] at the Università Cattolica del Sacro Cuore (UCSC; Piacenza, Italy) estimates the whole infection process (from oospore maturation until appearance of symptoms) by breaking it down into component pieces. ...
Environmental and economic costs demand a rapid transition to more sustainable farming systems, which are still heavily dependent on chemicals for crop protection. Despite their widespread application, powdery mildew (PM) and downy mildew (DM) continue to generate serious economic penalties for grape and wine production. To reduce these losses and minimize environmental impacts, it is important to predict infections with high confidence and accuracy, allowing timely and efficient intervention. This review provides an appraisal of the predictive tools for PM and DM in a vineyard, a specialized farming system characterized by high crop protection cost and increasing adoption of precision agriculture techniques. Different methodological approaches, from traditional mechanistic or statistic models to machine and deep learning, are outlined with their main features, potential, and constraints. Our analysis indicated that strategies are being continuously developed to achieve the required goals of ease of monitoring and timely prediction of diseases. We also discuss that scientific and technological advances (e.g., in weather data, omics, digital solutions, sensing devices, data science) still need to be fully harnessed, not only for modelling plant-pathogen interaction but also to develop novel, integrated, and robust predictive systems and related applied technologies. We conclude by identifying key challenges and perspectives for predictive modelling of phytopathogenic disease in vineyards.
... Compared to the average number of treatments conducted with the farmers' strategy, the adoption of the EPI forecasting model resulted in a significant reduction of the number of treatments performed against downy mildew (14% in 2020 and 12.5% in 2021) and, more markedly, against powdery mildew (57% in 2020 and 25% in 2021). The potential reduction of treatments applied for grapevine powdery and downy mildew control is particularly important when compared to the current practises observed in Italy, where growers typically control the diseases by fixedinterval fungicide applications, or by using a calendar-based fungicide spraying program, which leads them to perform more than 10 fungicide sprayings per season against each disease [34,45]. For example, in an organic vineyard located in Veneto (North-Eastern Italy) in 2020, 12 treatments were performed to control downy mildew and 13 to manage powdery mildew [46]. ...
... It was demonstrated that the diseases could be controlled effectively with fewer fungicide applications than included in the growers' schedule by using the forecasting model. For example, the warning system developed by Caffi and co-workers [34,45] reduced fungicide applications by 36% (with a low-risk program) and 75% (with a high-risk program) for powdery mildew control and from 33 to 86% for downy mildew control, compared to standard schedules in Italian vineyards. Similar results were obtained by Pellegrini et al. [25] and Menesatti et al. [48]. ...
Downy and powdery mildews are major grapevine diseases. In organic viticulture, a few fungicides with protectant activities (copper and sulphur in particular) can be used, and their preventative application frequently leads to unneeded spraying. The adoption of an epidemiological disease forecasting model could optimise the timing of treatments and achieve a good level of disease protection. In this study, the effectiveness of the EPI (Etat Potentiel d’Infection) model in predicting infection risk for downy and powdery mildews was evaluated in nine organic vineyards located in Panzano in Chianti (FI), over a 2-year period (2020–2021). The reliability of the EPI model was investigated by comparing the disease intensities, the number of fungicide sprayings, the quantities of the fungicides (kg/ha), and the costs of the treatment achieved, with or without the use of the model, in a vineyard. The results obtained over two seasons indicated that, in most cases, the use of the EPI model accurately signalled the infection risk and allowed for a reduction in the frequency and cost of spraying, particularly for powdery mildew control (−40% sprayings, −20% costs compared to the farmer’s schedule), without compromising crop protection. The use of the EPI model can, therefore, contribute to more-sustainable disease management in organic viticulture.
... Such an intensive fungicide calendar is not economically or ecologically sound and may result in needless sprays. In the context of a more sustainable use of pesticides [19], there is an increasing interest in moving from calendar-based to infection-risk-based fungicide applications [20,21]. ...
... Because the control of ripe rot under these conditions is often ineffective and may result in fungicide residue problems [67], growers should prevent the disease through timely fungicide applications, from flowering to véraison. In this context, our model can contribute to the scheduling of fungicides based on the risk of infection rather than on the calendar; scheduling fungicides according to the risk of infection results in an effective control of the downy and powdery mildew of grapevines with less use of chemicals [20,21] and, as a consequence, in a reduced risk of resistance to fungicides in Colletotrichum populations [68][69][70][71]. ...
Ripe rot caused by Colletotrichum spp. is a serious threat in many vineyards, and its control relies mainly on the repeated use of fungicides. A mechanistic, dynamic model for the prediction of grape ripe rot epidemics was developed by using information and data from a systematic literature review. The model accounts for i) the production and maturation of the primary inoculum; ii) the infection caused by the primary inoculum; iii) the production of a secondary inoculum; and iv) the infection caused by the secondary inoculum. The model was validated in 19 epidemics (vineyard × year combinations) between 1980 and 2014 in China, Japan, and the USA. The observed disease incidence was correlated with the number of infection events predicted by the model and their severity (ρ = 0.878 and 0.533, respectively, n=37, P≤ 0.001). The model also accurately predicted the disease severity progress during the season, with a concordance correlation coefficient of 0.975 between the observed and predicted data. Overall, the model provided an accurate description of the grape ripe rot system, as well as reliable predictions of infection events and of disease progress during the season. The model increases our understanding of ripe rot epidemics in vineyards and will help guide disease control. By using the model, growers can schedule fungicides based on the risk of infection rather than on a seasonal spray calendar.
... A range of models are available to support growers with the application of fungicides to control powdery mildew (e.g. Caffi et al., 2012;Carisse et al., 2009;Gubler et al., 1999). By inference from the models and through observations (Lybbert et al., 2016;Zito et al., 2018), growers vary their fungicide programs in response to changes in environmental conditions that may affect disease pressure. ...
... A number of epidemiological models have been developed for powdery mildew; most of which aim to aid growers with decisions about the timing of fungicide applications (Caffi et al., 2012;Carisse et al., 2009;Gubler et al., 1999). Moyer et al. (2016) observed that these models often do not relate well to the severity of powdery mildew epidemics in the cool and humid climate of New York and that pan Table 4 The number of applications and the number consecutive applications of fungicide groups with single site activity per seasons, averaged across eight cultivars and fifteen Geographical Indicator regions. ...
Powdery mildew (Erysiphe necator Schwein) is a major disease of grapevines. Extensive empirical information is available on the performance of fungicide programs, but little is known about the influence of cultivar, management system and especially the climate on grape growers’ fungicide use practices. Fungicide use records were analysed from a database that covered fifteen Australian production regions, seven seasons, and eight cultivars. Sulphur was the predominant fungicide used. Differences in fungicide programs were small between cultivars relative to differences between seasons. Fungicides were applied later in the season than recommended; after fruit set. The evapotranspiration during the 30-days following the separation of the first leaf from the shoot tip was a good predictor of the number of agrochemicals applied in all but the cooler regions. Growers overwhelmingly conformed to guidelines to prevent the development of fungicide resistance. The effectiveness of fungicide programs may be further improved by increasing the proportion of applications early in the season, targeting more susceptible cultivars, and using evapotranspiration to help identify and respond to seasons with high disease pressure. A better understanding of the practices of grape-growers may allow the refinement of fungicide use recommendations.
... In the Pacific Northwest and similar growing regions, ascospore release begins with fall rains and continues throughout host dormancy and into the growing season (Caffi et al. 2011;Gee et al. 2000;Thiessen et al. 2018). Ascospores have been described as the primary inoculum, initiating the disease epidemic each season (Caffi et al. 2011Cortesi et al. 1997;Gadoury and Pearson 1988;Gee et al. 2000;Legler et al. 2012Legler et al. , 2014Pscheidt et al. 2000;Rossi et al. 2010). Several models have been developed to predict the occurrence and magnitude of ascospore release to generate management decision aids (Caffi et al. 2011;Gadoury and Pearson 1990;Moyer et al. 2014;Thomas et al. 1994); however, these models inaccurately predict ascospore release in the Willamette Valley of Oregon (Thiessen et al. 2018). ...
... In the Willamette Valley of Oregon (L. D. Thiessen, personal observation), chasmothecia have only been observed to form around the beginning of véraison, despite heavy infestations (>90% of leaf surface area) on individual leaves similar to observations in other Mediterranean climates (Legler et al. 2012). The proximity of E. necator colonies to those of the opposite mating type is suggested as an explanation for the late formation of chasmothecia in other heterothallic species (Byford and Bentley 1976;Gadoury and Pearson 1988;Smith 1970); however, the dynamic temporal distribution of mating types within a vineyard and on the leaf surface has not yet been investigated. ...
In the Pacific Northwest, chasmothecia formation is not observed in vineyards until the beginning of véraison despite heavy infestations whereby 100% of leaf tissue is covered by Erysiphe necator. Mating type proximity and distribution were sampled from individual lesions (∼71 mm2) on leaf tissue in a stratified sampling from three canopy heights at three times during the 2013, 2014, and 2015 growing seasons. Both mating types were observed at every sampling point and within the same lesions at all sampling dates and canopy heights. Effect of temperature and day length were examined by inoculating seedlings with known mating type 1 and 2 isolates and placed in incubators at different temperatures (5, 10, 15, 20, 25, and 30°C) or different day length changes (long day to long day, long day to short day, short day to short day, and short day to long day). Chasmothecia were produced at all temperatures that E. necator was able to colonize tissue, and the greatest number of chasmothecia were produced at 15 and 20°C (P ≤ 0.02). Day length shifts from short day (8 h) to long day (16 h) resulted in a significant increase in chasmothecia production (P < 0.001). End of season plant stress observed in the Pacific Northwest, such as water stress or host senescence, was assessed under naturally infested field conditions by either girdling canes or applying 150 mg·liter-1 abscisic acid solution to vines, respectively, and quantifying chasmothecia production. No differences were observed in chasmothecia production in the plant stress assessment, likely due to the high vigor and ability for plants to overcome stress treatments.
... Ideally, this system would be used to warn growers when crop conditions are favorable or unfavorable for disease development, assist growers in making rational crop protection decisions, and potentially reduce the number of fungicide applications and minimize development of fungicide resistance. Weather-driven simulation models which use microclimate data to predict disease development have been created as a first step in developing a disease warning system for powdery mildews of crops such as wheat (Cao et al. 2015;Rossi and Giosué 2003), grape (Arafat 2015; Caffi et al. 2012;Moyer et al. 2016), and apple (Xu 1999). To the authors' knowledge, no such model has been reported for powdery mildew on cucurbits. ...
... RF is a parameter that refers to the effectiveness of fungicides in reducing DS. In this model, RF is calculated according to Caffi et al. (2012) Data for model calibration, validation, and simulation. Three field studies, summarized below, were conducted to generate data for model calibration and validation (Sapak 2012). ...
A weather-based simulation model, called POMICS, was constructed to predict fungicide application scheduling to manage powdery mildew of cucurbits. The model was developed on the principle that conditions favorable for Podosphaera xanthii, a causal pathogen of this crop disease, generate a number of infection cycles in a single growing season. The model consists of two components that: (i) simulate the disease progression of P. xanthii in secondary infection cycles under natural conditions and (ii) predict the disease severity with application of fungicides at any recurrent disease cycles. The underlying environmental factors associated with P. xanthii infection were quantified from laboratory and field studies and also gathered from literature. The performance of POMICS model when validated with two datasets of uncontrolled natural infection was good (the mean difference between simulated and observed disease severity on the scale of 0 to 5 was 0.02 and 0.05). In simulations, POMICS was able to predict high- and low-risk disease alerts. Furthermore, the predicted disease severity was responsive to the number of fungicide applications. Such responsiveness indicates that the model has the potential to be used as a tool to guide the scheduling of judicious fungicide applications.
... Early in the growing season, powdery mildew incidence has a near-exponential growth, but this is coupled with little to no increase in disease severity (Gadoury et al. 1997b). The prolonged latency of existing colonies may be one explanation why epidemic development is low in the weeks immediately following vine bud break, while the low abundance and delayed release of primary inoculum might also contribute to delayed epidemic development (Caffi et al. 2011(Caffi et al. , 2012Gadoury et al. 1997a;Moyer et al. 2014;Rossi et al. 2010). However, that alone does not describe why incidence of disease is not delayed in this pathosystem; instead, severity is delayed. ...
... Day of year, where Day 1=1 January of the vine), grape growers in many viticultural regions are likely to apply protectant sprays due to the presumed high risk based upon the ontogenic susceptibility of the developing inflorescences. These protectant sprays may be timed through the use of decision support systems (Caffi et al. 2012;Kast and Bleyer 2010;Legler et al. 2012b;Peduto et al. 2013) that incorporate surrounding environmental variables, or may be based on calendar dates or vine development. However, no current decision support system considers the excessive delay in latent period induced by acute cold events (Moyer et al. 2010), beyond how the recorded variable may influence average daily temperature. ...
Erysiphe necator is an obligate biotroph capable of infecting three genera within the Vitaceae (Vitis, Parthenocissus, and Ampelopsis). The pathogen inhabits a niche unique to most powdery mildews, i.e., wholly external mycelial growth supported by haustoria within the subtending host epidermal cells. This growth habit coupled with its biotrophic reliance on the host makes E. necator sensitive to both direct effects of abiotic stresses on the pathogen and indirect abiotic effects via the host responses. Development of the pathogen during acute cold events (e.g., 1 h at 4 °C) results in death of hyphal segments and a prolonged latency, an effect further increased by the development of ontogenic resistance as epidermal tissues of leaves and berries age. Acute cold events can also stress the host prior to the arrival of the pathogen, and thereby reduce susceptibility to infection via cold Stress-Induced Disease Resistance (SIDR), a recently described phenomenon. This effect requires approximately 24 h post-cold before maximal resistance effect occurs, and is also transient in that the effect diminishes to a basal level within 48 h after exposure. Although the phenotypic responses to cold SIDR may be similar to those observed on ontogenically-resistant leaves, the effects of cold SIDR and ontogenic resistance are additive. Sufficient tools are now available for investigating the mechanistic basis of cold SIDR. While pathosystems involving obligate biotrophs complicate research on direct and indirect environmental effects on the pathogen, this requisite interaction also creates interesting systems to understand how the condition of the host may influence subsequent disease development. At the population level , the effects of repeated cold events have profound effects on the nature of epidemic progress and implications for management of grape powdery mildew. The objective in this review is to summarize our current knowledge regarding the indirect and consequential effects of low temperature on the development of grapevine powdery mildew.
... Caffi & al. (28) mentioned that in several grape-growing areas of the world, including northern Italy, powdery mildew epidemics, caused by Erysiphe necator, are mainly triggered by the ascospores produced in overwintered chasmothecia. Growers in northern Italy usually control the disease with fixed-interval fungicide applications. ...
Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit. Downy mildews affect important crops and cause severe losses in production worldwide. Accurate identification and monitoring of these plant pathogens, especially at early stages of the disease, is fundamental in achieving effective disease control.
In this research, the Biblical verses dealing the mildew are presented. So, the description, some historical data, the characteristics, the household conditions where the mildew grows, the health effects and the management are examined
The Research deals with numerous effects of mildew including spoilage of vegetable crops by bacteria and fungi, infectious diseases, respiratory diseases such as asthma, bronchitis, pneumonia, chronic rhinosinusitis, idiopathic pulmonary fibrosis, pulmonary function of school children, obstructive sleep apnea syndrome, as well as vision, and sleep, allergy, atopic diseases, sarcoidosis, occupational sensitization, vineyard sprayer's lung including carcinoma, and pesticide poisoning.
In the recent years, the diagnostic possibilities have been validated through scientific research and have shown medicinal value in the diagnostics and the management of conditions associated with the mildew.
This research has shown that the awareness of the mildew accompanied human during the long years of our existence.
... Knowledge of Erysiphe necator presence and severity in a vineyard can be used to guide management decisions (Carisse et al., 2009;Caffi et al., 2012;Thiessen et al., 2018). However, visually scouting for E. necator can be very time-consuming and have a low probability of detecting disease (Mahaffee, et al., 2022). ...
... These models also include the effects of disease management strategies and are therefore used to establish recommendations for growers. Some authors have developed decision rules to help growers determine the start of spraying and adapt the maximal time lag after the application (Caffi et al., 2012;Carisse et al., 2009). Other decision support systems aim to integrate different disease risk indicators, such as phenological stage, rainfall, shoot growth, disease or outputs from a risk model (Davy et al., 2020;Delière et al., 2015;Kuflik et al., 2009). ...
... These models also include the effects of disease management strategies and are therefore used to establish recommendations for growers. Some authors have developed decision rules to help growers determine the start of spraying and adapt the maximal time lag after the application (Caffi et al., 2012;Carisse et al., 2009). Other decision support systems aim to integrate different disease risk indicators, such as phenological stage, rainfall, shoot growth, disease or outputs from a risk model (Davy et al., 2020;Delière et al., 2015;Kuflik et al., 2009). ...
High quantities of pesticides are applied on vineyards. For example, the average treatment frequency index (TFI) for French vineyards was 13.5 in 2016, whereas the average TFI for wheat (a major annual crop in France) was 4.9 in 2017. Reducing pesticide use is a key issue to improve viticulture sustainability. The aims of this study were (i) to analyse the evolution of pesticide use in vineyard farms voluntarily participating in a pesticide reduction programme, and (ii) to understand the options winegrowers used to reduce their pesticide use. We analysed data from the DEPHY farm network, including 244 cropping systems followed over 10 years and spread across 12 winegrowing regions. We used the TFI to assess the intensity of pesticide use. Mean pesticide use within the network decreased over the 10-year period and mostly concerned fungicide use. By analysing several indicators such as the number of treatments and the mean TFI per fungicide treatment, we were able to identify some of the management options mobilised for achieving this pesticide reduction. The use of biocontrol products and the reduction of sprayed doses were often associated with a low TFI. The analysis of yield evolution showed a significant mean reduction, although it was smaller than the TFI reduction. This raised the question of the impact of pesticide reduction on productivity. Further trade-off analyses are required in the future.
... Therefore, the risk of resistance development to specific classes of these latter materials is higher. Decision Support System (DSS) based on epidemiological models have been successfully developed to help viticulturists make informed decisions about fungicide treatments against DM (Caffi et al. 2012(Caffi et al. , 2013Cola et al. 2014;Rossi et al. 2014). Cultural practices can also help to limit the potential for fungal infection and disease spread unless environmental conditions are favorable for disease development. ...
Grapevines are challenged by a range of diseases and pests, causing economic losses and requiring often costly approaches to mitigate damage. Public interest in reducing the use of chemicals is a related challenge, along with climate change. Yet, the Vitis gene pool provides vast resources for the development of genetic resistance in rootstock and scion cultivars. Traditional breeding approaches have made great strides in the development of adaptive traits, and recent access to ‘omic technologies has further facilitated the identification of useful loci along with rapid trait introgression from wild species. Moreover, marker technologies are now used to stack multiple genes for the same trait into a single genotype, a heretofore barely accessible technology. Genomic technologies are also impacting germplasm characterization, and thereby facilitating “Breeding by Design” approaches. Genetic transformation and gene-editing technologies are also applicable for both cultivar improvement as well as functional studies of genes. The landscape for acceptance of new resistant cultivars is complex and with wine grapes, subject to high degrees of regulation especially in the European Union. With rootstocks, as well as table/raisin grapes, gaining acceptance in the marketplace for new cultivars developed through either traditional or marker-assisted approaches is routine. Yet even in the highly regulated EU environment, the adoption of new wine cultivars of interspecific origins is beginning to take place in both traditional wine growing regions as well as non-traditional regions nearby.KeywordsGenotypingMolecular breedingPathogenPestPhenotypingR-lociResistance
Vitis
... In addition, some observation data from wireless sensors networks (WSNs) and satellite remote sensing can also be included in the forecasting models to indicate environmental conditions and the growing status of host plants [40,41]. For model structure, it is worth attempting to introduce some mechanism-based model (e.g., disease development model) to enhance the robustness of the forecasting [42,43]. Such efforts are important to promote the green control of orchards' diseases and pests. ...
Early warning of plant diseases and pests is critical to ensuring food safety and production for economic crops. Data sources such as the occurrence, frequency, and infection locations are crucial in forecasting plant diseases and pests. However, at present, acquiring such data relies on fixed-point observations or field experiments run by agricultural institutions. Thus, insufficient data and low rates of regional representative are among the major problems affecting the performance of forecasting models. In recent years, the development of mobile internet technology and conveniently accessible multi-source agricultural information bring new ideas to plant diseases’ and pests’ forecasting. This study proposed a forecasting model of Alternaria Leaf Spot (ALS) disease in apple that is based on mobile internet disease survey data and high resolution spatial-temporal meteorological data. Firstly, a mobile internet-based questionnaire was designed to collect disease survey data efficiently. A specific data clean procedure was proposed to mitigate the noise in the data. Next, a sensitivity analysis was performed on the temperature and humidity data, to identify disease-sensitive meteorological factors as model inputs. Finally, the disease forecasting model of the apple ALS was established using four machine learning algorithms: Logistic regression(LR); Fisher linear discriminant analysis(FLDA); Support vector machine(SVM); and K-Nearest Neighbors (KNN). The KNN algorithm is recommended in this study, which produced an overall accuracy of 88%, and Kappa of 0.53. This paper shows that through mobile internet disease survey and a proper data clean approach, it is possible to collect necessary data for disease forecasting in a short time. With the aid of high resolution spatial-temporal meteorological data and machine learning approaches, it is able to achieve disease forecast at a regional scale, which will facilitate efficient disease prevention practices.
... All in all, our study provides information for a better prediction of ascospore release in spring. Several models for predicting ascospore release and infection are available (Gubler et al. 1999;Caffi et al. 2011Caffi et al. , 2012Moyer et al. 2014;Thiessen et al. 2018), and most of them are based on either the potential or the actual ascospore release. Our data indicate that the potential ascospore release combined with the actual ascospore release can improve the data basis for developing a more accurate ascospore release model. ...
Ascospores of grape powdery mildew (Erysiphe necator Schw.) play a crucial role in the disease onset in spring in many vine-growing areas. We investigated the physiological maturation of chasmothecia and the time of the first potential ascospore release in three grape-growing areas in Austria by providing standardized conditions for ascospore release in the laboratory and excluding the environmental influence for the release itself. In the overwintering season 2017/2018, the potential ascospore release started in March 2018 in all three investigated wine-growing areas, while in 2018/19, the potential ascospore release was already possible in autumn 2018. Autumn 2018 was characterized by higher temperatures than autumn 2017. We related accumulated degree days (base 8 °C) after chasmothecia formation with the time of first potential chasmothecia dehiscence and found that more than 480 degree days are necessary to reach physiological maturity of chasmothecia. Temperature significantly influenced the dynamics of the potential of ascospore release. More than 50% of the total potential of ascospore release occurred before bud break in both years. Furthermore, weather factors affecting the actual ascospore release in the field were studied. Precipitation and leaf wetness showed a significant positive correlation with ascospore release in the vineyard. In contrast to the potential release, only a small percentage of actual release in the field occurred before bud break, while 84 and 95% of total trapped ascospores were found between bud break and flowering in 2018 and 2019, respectively. Our results reveal that the potential release and actual release have to be combined to predict ascospore release in spring.
... In addition to the phytosanitary aspect, the cost of production should be considered in works that validate or use plant disease warning systems. Caffi et al. (2012) presented a reduction of expenditure of up to 161 euros/ha/year using an alert system for grapevine powdery mildew (Erysiphe necator) when compared to grower's spray program. ...
The management of downy mildew of onion requires frequent applications of protective and systemic fungicides. In order to reduce production costs, we evaluated a control strategy that integrated the use of resistant experimental cultivar and a disease warning system. Regardless of the type of management adopted, the experimental cultivar was always more productive. In turn, management based on the applications of protective fungicide was more effective. Considering only the value of the fungicide and using the resistant experimental cultivar, we had a cost of BRL 3.5 cents/kg for management only with Antracol®; BRL 10.7 cents/kg for management based on the warning system; and BRL 14.8 cents/kg for management only with Ridomil® Gold MZ. The integration of different control strategies for downy mildew can bring greater productivity and profitability to farmers.
... Therefore, the establishment of the practical impact and market credentials of a DT is really important [123], and evidence of the relevance the DT can have on the activities of potential users and the resulting benefits must be carefully demonstrated. For instance, Caffi and colleagues [126,127] demonstrated that the use of DTs for the management of powdery and downy mildews in viticulture led to a reduction on the application of pesticides by 30%. Considering that the costs of pesticide treatments against these diseases might reach 500 €/ha per year, a DT is able to decrease these costs by 150 €/ha per year. ...
The rational control of harmful organisms for plants (pests) forms the basis of the integrated pest management (IPM), and is fundamental for ensuring agricultural productivity while maintaining economic and environmental sustainability. The high level of complexity of the decision processes linked to IPM requires careful evaluations, both economic and environmental, considering benefits and costs associated with a management action. Plant protection models and other decision tools (DTs) have assumed a key role in supporting decision-making process in pest management. The advantages of using DTs in IPM are linked to their capacity to process and analyze complex information and to provide outputs supporting the decision-making process. Nowadays, several DTs have been developed, tackling different issues, and have been applied in different climatic conditions and agricultural contexts. However, their use in crop management is restricted to only certain areas and/or to a limited group of users. In this paper, we review the current state-of-the-art related to DTs for IPM, investigate the main modelling approaches used, and the different fields of application. We also identify key drivers influencing their adoption and provide a set of critical success factors to guide the development and facilitate the adoption of DTs in crop protection.
... Historically, vineyard managers have followed a calendar-based fungicide application program or have utilized disease forecasting models, particularly the UC Davis Risk Index (Gubler et al. 1999), to time fungicide applications. There have been numerous efforts to improve existing disease forecasting models to reduce the frequency of fungicide applications (Caffi et al. 2012;Caffi et al. 2011;Calonnec et al. 2008;Calonnec et al. 2009;Moyer et al. 2010;Moyer et al. 2014;Rossi et al. 2010). However, these disease forecasting models make various assumptions about ascospore maturity (e.g., ascospores are mature at bud break) and the availability of early-season inoculum (e.g., inoculum is available whenever infection conditions are suitable) (Caffi et al. 2011;Carisse et al. 2009a;Carisse et al. 2009b;Gubler et al. 1999). ...
Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases relies on numerous fungicide applications that follow calendar or model-based application intervals, both of which assume that inoculum is always present. Quantitative molecular assays have been previously developed to initiate fungicide applications, and could be used to optimize fungicide application intervals throughout the growing season based on inoculum concentration. Airborne inoculum samplers were placed at one research and six commercial vineyards in the Willamette Valley of Oregon. Fungicide applications in all plots were initiated at the first detection of E. necator inoculum, and all subsequent fungicide application intervals were made based the grower standard calendar program or based on inoculum concentration. In adjusted-interval plots, fungicides were applied at the shortest labelled application interval when >10 spores were detected and longest labelled application interval when <10 spores were detected. Fungicide applications in control plots consisted of the grower’s standard management practice. An average of 2.3 fewer fungicide applications in 2013 and 1.6 fewer fungicide applications in 2014 were used in the adjusted fungicide application intervals treatment in grower fields without significant differences in berry or leaf disease incidence between treatments.
... Indeed, plant disease epidemics result from interactions of host and pathogen populations in a conducive environment, the so-called 'disease triangle' (Agrios, 2005). The host susceptibility on which we focused in this paper (here for the grapevine) is only one component of this triangle and other factors like climate (Williamson et al., 2007;Gadoury et al., 2012) or the amount of primary inoculum (Caffi et al., 2012) need to be taken into account. However, our results suggest opportunities to reduce fungicide use in a few years and highlight an interesting synergy for doing so with powdery mildew and grey mould, two major grapevine diseases, at the same time. ...
Reducing plant growth to limit their susceptibility to diseases has been proposed as a way to reduce pesticide use, but reducing crop growth may have detrimental effect on yield. In this paper, we test the hypothesis of a trade-off between maintaining grape yield and reducing grapevine susceptibility to powdery mildew (Erysiphe necator) and grey mould (Botrytis cinerea), two major diseases of the grapevine (Vitis vinifera L.). Grapevine susceptibility to these two diseases was measured by relevant features of grapevine vegetative development identified in previous studies: leaf biomass at flowering for powdery mildew and pruning mass for grey mould. Data were collected during a 3-year field experiment in a vineyard located in the south of France, in which pests and disease were controlled by spraying pesticides. The two pathogens studied in this paper were chosen because they differ in terms of their biology (biotroph vs necrotroph) and their interaction with the grapevine (the highest grapevine susceptibility occurs early in the cycle for powdery mildew and late in the cycle for grey mould), in order to give genericity to the results. Results confirmed the hypothesis of a trade-off between maintaining grape yield and reducing grapevine susceptibility to both pathogens through reduced vegetative growth, but provided evidence that win–win situations (high yield, low susceptibility) do exist. Moreover, we found a synergy between reducing grapevine susceptibility to powdery mildew and grey mould. These results suggest opportunities to reduce fungicide use when a win–win situation occurs as the risk of yield and quality losses may be lower in those years. Inter-annual variation in water stress at flowering was found to be a key driver of the balance between grape yield and grapevine susceptibility to both pathogens through their effect on the source–sink balance of the grapevine. Water stress at flowering appeared as a relevant indicator to inform the probability of occurrence of a win–win situation. Our results suggest that it could also be used to adapt management practices like irrigation, cover cropping or a combination of both, to reach a win–win situation. The relevance of these findings to vineyards in similar semi-arid environments is discussed.
... The former model can represent a key tool for scheduling sanitation treatments, offering a promising approach to reducing the number of overwintering chasmothecia, i.e. the main source of primary inoculum of E. necator in many grape-growing areas (Caffi et al., 2013a,b). The latter model was validated in different Italian grape-growing conditions and was successfully used to schedule fungicide application against powdery mildew in a real time warning system (Caffi et al., 2012a). The use of the model reduced fungicide applications by 36% (low-risk programme, saving 56 V/ha/year) or 75% (high-risk programme, saving 161 V/ha/year). ...
... This means that timing of the Ampelomyces treatments in autumn should be based on the monitoring of the development of chasmothecia in the targeted vineyards. Epidemiological models are helpful in timing plant protection product applications (Carisse et al. 2009;Caffi et al. 2010Caffi et al. , 2012Caffi et al. , 2013 and should be also used to assist the application of Ampelomyces as a BCA of E. necator in autumn. Recently, a model was developed to predict the time-course of development of the E. necator chasmothecia Legler et al. 2012Legler et al. , 2014. ...
To develop a new biofungicide product against grapevine powdery mildew, caused by Erysiphe necator, cultural characteristics and mycoparasitic activities of pre-selected strains of Ampelomyces spp. were compared in laboratory tests to the commercial strain AQ10. Then, a 2-year experiment was performed in five vineyards with a selected strain, RS1-a, and the AQ10 strain. This consisted of autumn sprays in vineyards as the goal was to reduce the number of chasmothecia of E. necator, and, thus, the amount of overwintering inocula, instead of targeting the conidial stage of the pathogen during spring and summer. This is a yet little explored strategy to manage E. necator in vineyards. Laboratory tests compared the growth and sporulation of colonies of a total of 33 strains in culture; among these, eight strains with superior characteristics were compared to the commercial product AQ10 Biofungicide® in terms of their intra-hyphal spread, pycnidial production, and reduction of both asexual and sexual reproduction in E. necator colonies. Mycoparasitic activities of the eight strains isolated from six different powdery mildew species, including E. necator, did not depend on their mycohost species of origin. Strain RS1-a, isolated from rose powdery mildew, showed, together with three strains from E. necator, the highest rate of parasitism of E. necator chasmothecia. In field experiments, each strain, AQ10 and RS1-a, applied twice in autumn, significantly delayed and reduced early-season development of grapevine powdery mildew in the next year. Therefore, instead of mycohost specificity of Ampelomyces presumed in some works, but not confirmed by this study, the high sporulation rate in culture and the mycoparasitic patterns became the key factors for proposing strain RS1-a for further development as a biocontrol agent of E. necator.
... Multiple disease development models exist, used to deduce risk and aid in decision making for grape powdery mildew management. Of the models currently in use by regional growers, the model by Caffi et al. (2012) has been successful in pred\icting primary infection events, thus allowing growers to more precisely time earlyseason management programs. The OiDiag 2.2 model (Kast and Bleyer 2010) focuses on predicting primary inoculum load and subsequent disease development to help determine both the timing of the initial management choice and spray interval selection. ...
Recorded severity of grape powdery mildew on berries of untreated, susceptible hybrid cultivars varied from 0.2 to 50.5% across a 30-year period in Geneva, NY; within 7 of those years, cluster disease severity ranged from 3.42 to 99.5% on Vitis vinifera ‘Chardonnay’. Although existing temperature-driven risk models could not account for this annual variation,pan evaporation (Epan
), an environmental variable influenced by the collective effects of temperature, vapor pressure deficit, solar radiation, and windspeed, did. Logistic regression analysis (LRA) was used to classify epidemics as either mild or severe. Recursive partition analysis (RPA) provided a simplified decision tree for calculation of powdery mildew risk and incorporated (i) an estimate of the relative primary inoculum levels based on temperatures in the previous late summer and (ii) the current season favorability for pathogen development during the grapevine phenological period critical
for berry infection by Erysiphe necator. Although the LRA had fewer instances of misclassification, RPA provided a rapid means for seasonal risk
classification. Both the RPA and LR
A models are able to describe disease
severity risk in real time or can be used to forecast risk, thereby allowing
growers to adjust management pr
ograms in a responsive manner
... The model can then be regarded as an improvement of the previous Botrytis models in viticulture. Utility of the model in scheduling fungicides to control Botrytis bunch rot, however, should be verified with experiments [100][101][102]. After that, this new model could be used instead of the 15-15 rule or the previous models for making decisions about fungicide application at specific vine growth stages. ...
A mechanistic model for Botrytis cinerea on grapevine was developed. The model, which accounts for conidia production on various inoculum sources and for multiple infection pathways , considers two infection periods. During the first period (" inflorescences clearly visible " to " berries groat-sized "), the model calculates: i) infection severity on inflorescences and young clusters caused by conidia (SEV1). During the second period (" majority of berries touching " to " berries ripe for harvest "), the model calculates: ii) infection severity of ripening berries by conidia (SEV2); and iii) severity of berry-to-berry infection caused by mycelium (SEV3). The model was validated in 21 epidemics (vineyard × year combinations) between 2009 and 2014 in Italy and France. A discriminant function analysis (DFA) was used to: i) evaluate the ability of the model to predict mild, intermediate, and severe epidemics; and ii) assess how SEV1, SEV2, and SEV3 contribute to epidemics. The model correctly classified the severity of 17 of 21 epidemics. Results from DFA were also used to calculate the daily probabilities that an ongoing epidemic would be mild, intermediate, or severe. SEV1 was the most influential variable in discriminating between mild and intermediate epidemics, whereas SEV2 and SEV3 were relevant for discriminating between intermediate and severe epidemics. The model represents an improvement of previous B. cinerea models in viticulture and could be useful for making decisions about Botrytis bunch rot control.
... Pscheidt et al. (2000) and Hall (2000) demonstrated that there was a delay in inoculum availability and epidemic onset in western Oregon that resulted in multiple unwarranted fungicide applications prior to inoculum availability. This asynchrony appears to result in the host escaping some or all of the overwintering inoculum through the occurrence of ascospore release prior to bud break (BBCH stages 00-07; Rossi et al., 2010;Caffi et al., 2012), delayed pathogen development compared to that of the host (Hall, 2000), or environmental stresses that impact pathogen development and rate of disease development (Moyer et al., 2010). ...
Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases often relies on calendar-based pesticide application schedules that assume the presence of inoculum. An inexpensive, loop-mediated isothermal amplification (LAMP) assay was designed to quickly detect airborne inoculum of E. necator to determine when to initiate a fungicide application program. Field efficacy was tested in 2010 and 2011 in several commercial and research vineyards in the Willamette Valley of Oregon from pre-bud break to véraison. In each vineyard, three impaction spore traps were placed adjacent to the trunk. One trap was maintained and used by the grower to conduct the LAMP assay (G-LAMP) on-site and the other two traps were used for laboratory-conducted LAMP (L-LAMP) and quantitative PCR assay (qPCR). Using the qPCR as a gold standard, L-LAMP was comparable with qPCR in both years, and G-LAMP was comparable to qPCR in 2011. Latent class analysis indicated that qPCR had a true positive proportion of 98% in 2010 and 89% in 2011 and true negative proportion of 96% in 2010 and 64% in 2011. An average of 3.3 fewer fungicide applications were used when they were initiated based on spore detection relative to the grower standard practice. There were no significant differences in berry or leaf incidence between plots with fungicides initiated at detection or grower standard practice plots, suggesting that growers utilizing LAMP to initiate fungicide applications can use fewer fungicide applications to manage powdery mildew compared to standard practices.This article is protected by copyright. All rights reserved.
... Quantification of economic benefits rising from the use of DSSs has been demonstrated in only a few cases. Caffi et al. (2010Caffi et al. ( , 2012 conservatively estimated that the use of DSSs to manage powdery and downy mildews in viticulture reduce PPP applications by 30%; given that conventional application of PPPs for control of these diseases costs about 500 € ha -1 per year, a DSS can reduce the cost by 150 € ha -1 per year. However, even when DSSs have been demonstrated to provide economic benefits, DSSs have not been widely used (Gelb, 1999;Parker, 1999). ...
The European Community Directive 128/2009 on the Sustainable Use of Pesticides establishes a strat-egy for the use of plant protection products (PPPs) in the European Community so as to reduce risks to human health and the environment. Integrated Pest Management (IPM) is a key component of this strategy, which will become mandatory in 2014. IPM is based on dynamic processes and requires decision-making at strategic, tactical, and operational levels. Relative to decision makers in conventional agricultural systems, decision makers in IPM systems require more knowledge and must deal with greater complexity. Different tools have been developed for supporting decision-making in plant disease control and include warning services, on-site devices, and decision support systems (DSSs). These decision-support tools operate at different spatial and time scales, are provided to users both by public and private sources, focus on different communication modes, and can support multiple op-tions for delivering information to farmers. Characteristics, weaknesses, and strengths of these tools are described in this review. Also described are recently developed DSSs, which are characterised by: i) holistic treatment of crop management problems (including pests, diseases, fertilisation, canopy management and irrigation); ii) conversion of complex decision processes into simple and easy-to-understand 'decision supports'; iii) easy and rapid access through the Internet; and iv) two-way communication between users and providers that make it possible to con-sider context-specific information. These DSSs are easy-to-use tools that perform complex tasks efficiently and effectively. The delivery of these DSSs via the Internet increases user accessibility, allows the DSSs to be updated easily and continuously (so that new knowledge can be rapidly and efficiently provided to farmers), and allows users to maintain close contact with providers.
... Caffi et al. have also proposed a rule-and-threshold-based DSS for managing powdery mildew that relies on the outputs of a mechanistic pathosystem model. 17 Coptimizer is another model-driven DSS 18 designed to optimise the rate of copper-based fungicide use in organic viticulture against grapevine downy mildew. ...
Background
In France, viticulture accounts for 20% of the phytochemicals sprayed in agriculture. Eighty percent of grapevine pesticides target powdery and downy mildews. European policies promote pesticide use reduction, and new methods for low-input diseases management are needed for viticulture. Here we present the assessment, in France, of Mildium®, a new decision support system for the management of grapevine mildews.ResultsA 4 years assessment trial of Mildium® has been conducted in a network of 83 plots distributed across the French vineyards. In most vineyards Mildium® has proved to be successful at protecting the crop while reducing by 30% to 50% the number of treatments required when compared to grower practices.Conclusion
Mildium®'s design results from the formalization of a common management of both powdery and downy mildews and eventually leads to a significant fungicides reduction at the plot scale. It could foster stakeholders to design customized farm-scale and low-chemical-input decision-support methods.
... Application of Ampelomyces quisqualis, a hyperparasite of powdery mildews that is known to destroy chasmothecia ((Kiss et al. 2004; Angeli et al. 2009), reduced both the number of chasmothecia dispersed from leaves to the bark and their survival on bark (Falk et al. 1995; Legler et al. 2011). For the control of ascosporic infection, a warning system was recently developed (Caffi et al. 2012) based on short-term weather forecasts, a model that simulates the severity of each E. necator ascosporic infection (Caffi et al. 2011). This warning system was evaluated in North Italy from 2006 to 2008, between bud break of vines and early berry development (most of berries touching, E-L stage 32, Coombe 1995). ...
Chasmothecia of Erysiphe necator form in one season, survive winter and discharge ascospores that cause primary infections and trigger powdery mildew epidemics in the next season. A strategy for powdery mildew control was developed based on (i) the reduction in overwintering chasmothecia and on (ii) spring fungicide applications to control ascosporic infections timed based on estimate risk (two to five sprays per season). Several fungicides, the hyperparasite Ampelomyces quisqualis, and a mineral oil product were first tested as separate applications in a greenhouse and in vineyards. In the greenhouse, A. quisqualis suppressed chasmothecia formation by 41 %; fungicides and mineral oil suppressed chasmothecia formation by 63 % and ascospore viability by 71 %. In vineyards, application of boscalid + kresoxim-methyl or meptyldinocap once after harvest, as well as application of A. quisqualis pre- and post-harvest, delayed disease onset and epidemic development in the following season by 1 to 3 weeks and lowered disease severity (up to the pea-sized berry stage) by 56 to 63 %. Risk-based applications of sulphur and of synthetic fungicides provided the same control as the grower spray program but required fewer applications (average reduction of 47 %). Sanitation strategies were then tested by combining products and application times (late-season, and/or pre-bud break, and/or spring). Adequate disease control with a reduced number of sprays was achieved with the following combination: two applications of A. quisqualis (pre- and post-harvest), one application of mineral oil before bud break, and model-based applications of sulphur fungicides between bud break and fruit set.
The increased regulation of pesticides in Europe (Directive 128/2009/EC), the public concerns about the environmental impacts of viticulture, and the consumers demand of residue-free products has leaded to an increase, in the last years, of several environmentally safe crop control methods in European vineyards. The Sustainable Use of Pesticides Directive promotes the use of integrated pest management (IPM) and of alternative approaches and techniques such as nonchemical alternatives to pesticides. The application of a combination of different tactics, as recommended in IPM, is the foundation for a sustainable vineyard management. To implement such approach, viticulturists need to access to timely and robust information that can help them to support sound decisions regarding the need of applying control methods and minimize the risk of damages in grapes. This article summarizes some of the innovations applied in viticulture, including tactics and tools that promotes a more sustainable use of pesticides, with lower environmental impacts.
Strategies for the control of grape powdery mildew, caused by Erysiphe necator, Schw., require consideration of the development of fungicide resistance. We investigated the effect of inoculum reduction by fungicides with low resistance risk (copper oxychloride, potassium bicarbonate, meptyldinocap, wettable sulphur) in the laboratory and as individual post-harvest and bud break treatments. Ascospore viability and release were analyzed after a post-harvest treatment and disease incidence and severity of grapes were determined following a bud break treatment. In the laboratory all fungicides reduced the viability (spring 2018 p = 0.008; autumn 2018 p = 0.021; spring 2019 p = 0.010; autumn 2019 p = 0.484) and the release (spring 2018 p = 0.007; autumn 2018 < 0.001; spring 2019 < 0.001) of ascospores, although the decrease was more pronounced in spring compared to autumn. At Krems, the post-harvest field application of copper oxychloride, potassium bicarbonate, meptyldinocap and wettable sulphur in autumn 2017 reduced the percentage of viable chasmothecia significantly (p < 0.001) by 56–74%. In autumn 2018, the tested fungicides had no effect on the percentage of viable chasmothecia (p = 0.129). At Andau, the percentage of viable chasmothecia was only reduced by copper oxychloride (p = 0.029). The amount of viable ascospores was significantly (p = 0.002) lowered after a post-harvest field treatment with the fungicides by 46–70%, whereas for meptyldinocap only a trend could be determined. Disease incidence and severity were not influenced by sulphur applications at bud break (p = 0.689, p = 0.224) and by different levels of chasmothecia (p = 0.104, p = 0.353). A trend in one year, that a high amount of chasmothecia increased the disease incidence, was related to the weather conditions and the duration from the time of first ascosporic infection until flowering. The data indicates the importance of an effective control with fungicides during the pre-flowering stage in years with a long time from primary infection until flowering. Furthermore, this study shows that post-harvest sprays with low risk fungicides can help to reduce the number of fungicide treatments needed for powdery mildew control at the end of the in-season spray program. This measure could be integrated into an environmentally friendly pesticide reduction program for controlling powdery mildew in viticulture.
Hop powdery mildew, caused by the ascomycete fungus Podosphaera macularis is a consistent threat to sustainable hop production. The pathogen utilizes two reproductive strategies for overwintering and perennation: (i) asexual vegetative hyphae on dormant buds that emerge the following season as infected shoots; and (ii) sexual ascocarps (chasmothecia), which are presumed to discharge ascospores during spring rain events. We demonstrate that P. macularis chasmothecia, in the absence of any asexual P. macularis growth forms, are a viable overwintering source capable of causing early season infection two to three orders of magnitude greater than that reported for perennation via asexual growth. Two epidemiological models were defined that describe (i) temperature-driven maturation of P. macularis chasmothecia; and (ii) ascosporic discharge in response to the duration of leaf wetness and prevailing temperatures. Podosphaera macularis ascospores were confirmed to be infectious at temperatures ranging from 5 to 20°C. The organism’s chasmothecia were also found to adhere tightly to the host tissue on which they formed, suggesting that these structures likely overwinter wherever hop tissue senesces within a hop yard. These observations suggest that existing early season disease management practices are especially crucial to controlling hop powdery mildew in the presence of P. macularis chasmothecia. Furthermore, these insights provide a baseline for the validation of weather driven models describing maturation and release of P. macularis ascospores that can eventually be incorporated into hop disease management programs.
Grapevine anthracnose caused by Elsinoë ampelina is a serious threat in many vineyards, and its control requires repeated application of fungicides, usually on a calendar basis. A better understanding of the pathogen life cycle would help growers to manage anthracnose more safely and effectively. After conducting a systematic literature search of grape anthracnose, we used the retrieved information and data to develop a mechanistic model based on systems analysis. The model simulates (i) production and maturation of primary inoculum; (ii) infection caused by both primary and secondary conidia; and (iii) lesion formation and production of secondary inoculum. The model was validated for its ability to predict i) first seasonal onset of anthracnose lesions by using 8 years of data collected at Auckland, New Zealand, and ii) disease progress during the season by using 3 years of data collected at Frelighsburg, Canada. Overall, the model provided accurate predictions of infection occurrence, with 0.96 accuracy, 0.91 sensitivity, and 0.97 specificity. The model also showed good accuracy for predicting disease progress, with a concordance correlation coefficient between observed and predicted disease severities of CCC=0.92, a root mean square error of RMSE=0.14, and a coefficient of residual mass of CRM=0.06. Although the model failed to predict 10 of 110 real infection periods, these missed infections led to only mild disease symptoms. We therefore conclude that the model is reliable and can be used to reduce the costs of anthracnose management by improving the timing of fungicide applications.
In a 6-year Hungarian study, ascospore density of Erysiphe necator in the air was monitored and related to three weather variables (temperature, relative humidity, and rainfall) and powdery mildew disease progress in two commercial vineyards. Temporal pattern in aerial density was also quantified. In total, 71 ascospore trapping periods were detected over the 6-year period from early April until end June. Across all years, 6.6 % of the total ascospores (0.5 % mean ascospore percent per day) were caught between the initiation of sampling in April and bud break, 62.2 % (1.6 %) from bud break to bloom, and 31.2 % (0.3 %) between bloom and the conclusion of sampling at the end of June. Hourly proportions of ascospores caught did not reveal diurnal patterns of spore release. All three weather factors (in the order of rainfall, relative humidity and temperature) correlated significantly with mean ascospore catches in each year. Mean hourly rainfall correlated best with mean hourly ascospore catches (correlation coefficient, r, ranged from 0.43 to 0.78) in both vineyards and in all years. First leaf and berry symptoms appeared between 7 and 24 May and between 25 May and 19 June, respectively, during the 6-year study. Disease started to progress slowly after the appearance of the first infected leaf followed by an exponential increase from early June. By the end of June, leaf and berry disease incidences ranged from 4.1 to 98.2 % and from 0.9 to 6.8 %, respectively, over the 6-year period. Leaf incidences showed significant relationship with corresponding cumulative numbers of trapped ascospore in five out of 6 years, which was described by three-parameter Gompertz functions in each year. Results were compared and discussed with previous observations.
The available knowledge on black-rot of grape was retrieved from literature, analyzed, and synthesized to develop a mechanistic model of the life cycle of the pathogen (Guignardia bidwelii) based on the systems analysis. Three life-cycle compartments were defined: (i) production and maturation of inoculum in overwintered sources (i.e., ascospores from pseudothecia and conidia from pycnidia in berry mummies and cane lesions); (ii) infection caused by ascospores and conidia; and (iii) disease onset and production of secondary inoculum. An analysis of published, quantitative information was conducted to develop a mechanistic model driven by weather and vine phenology; equations were developed for ascospore and conidial maturation in overwintered fruiting bodies, spore release and survival, infection occurrence and severity, incubation and latency periods, onset of lesions, production of pycnidia, and infectious periods. The model was then evaluated for its ability to represent the real system and its usefulness for understanding black-rot epidemics by using three typical epidemics. Finally, weaknesses in our knowledge are discussed. Additional research is needed concerning the influence of wetness duration and temperature on infection by ascospores, production dynamics of pycnidia and conidia in black-rot lesions, and the dynamics of conidia exudation from pycnidia.
Gestion des maladies de la vigne
The temporal evolution of the disease on leaves and damage on grape was monitored at different scales in order to study the effect of early primary contamination on epidemic development and its relationship with damage on grape. At a vine scale, on vines artificially inoculated with 12 days delay, the disease evolution on leaves was delayed. At flowering, early contaminated vines were 60% more diseased than late contaminated vines. On bunches, the progression and final disease were significantly different with, at veraison, an average severity of 99% for early contaminated vines versus 62% for late contaminated ones and 29% for uncontaminated ones. A significant difference for the Incidence-Severity relationship at the leaf scale was quantified indicating the difference in symptoms according to the date of contamination. At the plot scale (330 vines), we compared the maps of frequency of diseased leaves per vine at different scoring dates with the maps of frequency of bunches with a given level of damage. Epidemics initiated earlier were characterised by higher severity for a given level of frequency of diseased leaves (at the vine scale) and higher final diseased leaves frequency (at the plot scale). Early difference in the number of diseased leaves led to significant differences in the number of highly damaged clusters (> 25%) and in the average clusters severity. The analysis of disease maps demonstrated the spatial relationship between the frequency of diseased leaves at flowering and the frequency of severe damaged bunches.
Vitis labruscana 'Concord' is a widely planted grape cultivar grown in the United States for processing into juice and other products. Concord fruit are sporadically but sometimes severely damaged by the grape powdery mildew pathogen, Uncinula necator. The effects of powdery mildew on vine growth, yield, and quality of Concord grapes at three levels of cropping intensity commonly found in commercial grape production were determined in vineyard studies. Top-wire cordon-trained Concord vines were balance pruned, pruned to retain 80 nodes, or minimally pruned. Replicated plots of the foregoing were then either protected from powdery mildew by regular fungicide applications, or were inoculated and left unsprayed. Over a 4-year period, the effects of foliar infection on vine growth, yield, and juice quality of unsprayed vines were compared with vines that received a conventional protection program of four fungicide applications. Failure to control powdery mildew resulted in a chronic reduction in wood maturity measured as the number of nodes on canes that developed periderm. The reduction in nodes did not reduce yield, possibly due to compensation in shoots produced from the remaining nodes. Powdery mildew did not affect bud survival or vigor, measured as the number of shoots produced per node on retained canes. The most significant effects of powdery mildew were on berry sugar levels and juice color and acidity, which on the unsprayed vines were sometimes reduced below minimally acceptable thresholds for processed grapes. Significant reductions due to powdery mildew in these parameters occurred in all three pruning treatments, but were most pronounced at higher cropping levels.
Density and viability of populations of cleistothecia of Uncinula necator from bark, leaves, and soil were determined in three vineyards in the Florence and Siena provinces of Tuscany for 3 years. A higher density of cleistothecia was found on fallen leaves than on bark. However, the percentage of viable cleistothecia was higher on bark. No viable cleistothecia were recovered from soil. U. necator overwintered as mycelium in dormant infected buds, which gave rise to flag shoots, only in Santa Cristina, where 20 acid 92 flag shoots per hectare were detected before bloom in 1994 and 1995, respectively. Disease incidence and severity increased similarly at Corti, Fornace, and at Santa Cristina, although powdery mildew epidemics started from ascospores only in Cord and Fornace, whereas flag shoots were present at Santa Cristina. Cleistothecia were formed in autumn in both 1994 and 1995, and their dispersal started in late September to mid-October, with the maximum number of cleistothecia trapped in funnels during the second half of October. Cleistothecia appear to function as the sole source of primary inoculum for grape powdery mildew in some Italian vineyards and serve as additional sources of inoculum where the pathogen also overwinters in infected buds. In Australia but not in New York, the pathogen also overwinters as cleistothecia on fallen leaves.
The effects of powdery mildew (Uncinula necator) on grape yield, juice and wine quality were quantified for cultivar Cabernet Sauvignon (CSa) in 1997 and 1999, and for Sauvignon blanc (Sa) in 1999. Analyses were carried out on batches of healthy berries to which known percentages (0–50%) of diseased berries were added, and on natural clusters that were classified into four visual classes from low (C1) to high (C4) disease severity. CSa diseased berries showed an average weight reduction of 12% (1997) and 20% (1999). The direct consequence of a higher percentage of smaller, diseased berries was a reduction in yield. The accompanying loss of weight in must from C1 to C4 clusters increased from 10 to 45%. Sugar content in diseased berries was not significantly different from disease-free berries in 1997, but was 20–21% (CSa) and 14% (Sa) higher in 1999. Severely infected batches also showed a higher total acidity than healthy ones. The total anthocyanin content of CSa was decreased by 0·91% (1997) and 0·66% (1999) per percentage mildewed berries added by weight. In Sa wines the concentration of 3-mercaptohexanol, a component of varietal aroma, was decreased by powdery mildew. Multidimensional analyses, based on all the variables studied, successfully grouped batches of CSa according to disease severity. Using directional triangular tests wine experts were able to recognize CSa wines produced from berries with ≈25% of powdery mildew; the threshold for nonexperts was 50%. CSa wines obtained from samples with more than 30% of diseased berries by weight were significantly classified as the worst according to preference order criteria, but below this value the preference was not significant. Sa wines with <50% mildewed berries could not be differentiated significantly by organoleptic tests performed by nonprofessionals.
Limiting the use of fungicides is due to become an important issue in managing Erysiphe necator (Schwein) Burrill infections in vineyards. The authors determined how three fungicides currently used by vine growers could be managed to control the early stages of an E. necator-induced epidemic.
Leaf-disc bioassays and field experiments suggested that the protectant quinoxyfen induced minor disruption in E. necator development, but compounds with protectant and curative properties (tebuconazole and trifloxystrobin) caused significant, although different, disruption during E. necator-induced epidemics. Bioassays showed that each of the antifungals were most effective at different stages of fungal development, tebuconazole before sporulation and trifloxystrobin after sporulation of the colonies. Results from the bioassay also highlighted likely occurrences in the field, where several stages of fungal development are encountered simultaneously.
The present findings were complementary: leaf-disc tests showed when the fungicides were most effective at inhibiting E. necator infection cycles; the field trial provided results in terms of incidence and severity of disease on bunches without reference to the pathogenic cycle development. A protection strategy combining the different types of fungicide under study is suggested.
Growth and development of Erysiphe necator (syn. Uncinula necator) has been extensively studied under controlled conditions, primarily with a focus on development of grapevine powdery mildew within the optimal temperature range and the lethal effects of high temperatures. However, little is known of the effect of cold temperatures (above freezing but <8 degrees C) on pathogen development or host resistance. Pretreatment of susceptible Vitis vinifera leaf tissue by exposure to cold temperatures (2 to 8 degrees C for 2 to 8 h) reduced infection efficiency and colony expansion when tissues were subsequently inoculated. Furthermore, nascent colonies exposed to similar cold events exhibited hyphal mortality, reduced expansion, and increased latent periods. Historical weather data and an analysis of the radiational cooling of leaf tissues in the field indicated that early-season cold events capable of inducing the foregoing responses occur commonly and frequently across many if not most viticultural regions worldwide. These phenomena may partially explain (i) the unexpectedly slow development of powdery mildew during the first month after budbreak in some regions and (ii) the sudden increase in epidemic development once seasonal temperatures increase above the threshold for acute cold events.
ABSTRACT Plasmopara viticola populations collected from three islands in the Ionian Sea-an arm of the Mediterranean Sea to the west of Greece-were analyzed with microsatellite molecular markers in order to investigate the pathogen population structure. Downy mildew populations from mainland regions previously studied were found to have high genotypic diversity and limited clonality; however, populations under Mediterranean island conditions mostly showed limited variation and the epidemics basically were driven by the multiple clonal infections of one or a few genotypes. Populations from different islands were differentiated from each other, whereas genetic divergence also was found among subpopulations of the same plot. Polyploid individuals and individuals that overwintered in asexual form were observed in some cases. The findings obtained by this population genetics study improve our understanding of the biology of the pathogen and lead to potential alternative control measures for the disease.
ABSTRACT Berries of Vitis vinifera are reported to be susceptible to infection by Uncinula necator until soluble solids levels (brix) reach 8%, and established colonies are reported to sporulate until brix reach 15%. However, our analysis of disease progress on fruit of selected V. vinifera cultivars indicated that severity became asymptotic several weeks earlier in fruit development. When mildew-free fruit clusters of V. vinifera 'Chardonnay', 'Riesling', 'Gewürztraminer', and 'Pinot Noir' were inoculated at stages ranging from prebloom to 6 weeks postbloom, only fruit inoculated within 2 weeks of bloom developed severe powdery mildew. Substantial ontogenic resistance to infection was expressed in fruit nearly 6 weeks before fruit brix reached 8% and over 2 months before they reached 15%. Rachises of 'Chardonnay' and 'Riesling' fruit clusters developed severe powdery mildew when inoculated at bloom, and disease increased steadily over the next 60 days. The rachis of fruit clusters inoculated 31 days after bloom developed only trace levels of powdery mildew. Berry weight of all four cultivars at harvest was reduced when fruit clusters were inoculated at bloom or 16 days postbloom, primarily by splitting, rotting, and dehydration of mildewed berries, but the weight of later-inoculated berries was not reduced. Inoculation of berries just as ontogenic resistance increased markedly, approximately 3 to 4 weeks postbloom, resulted in the development of inconspicuous, diffuse, non-sporulating mildew colonies on berries, sometimes associated with a network of necrotic epidermal cells. Rather than a protracted and relatively static period of berry susceptibility lasting 3 months, fruit of V. vinifera appear to acquire ontogenic resistance rapidly after fruit set. A refocusing of disease management on this critical period of high fruit susceptibility should greatly improve the efficacy of fungicides directed against powdery mildew.
Little is known about the mode of survival and sources of primary inoculum of Uncinula necator, the causal pathogen of grapevine powdery mildew, in vineyards in the Western Cape province. A study was therefore undertaken to determine whether cleistothecia and flag shoots are formed on vines in local vineyards. Flag shoots were found shortly after budbreak in September 1997 in a Carignane vineyard near Somerset West. Cleistothecia were first observed during April to May 1996 on severely infected leaves from three vineyards in the main grapegrowing areas of Stellenbosch. This was the first report of cleistothecia and flag shoot formation in vineyards in the Western Cape province. Cleistothecia occurred in small numbers on leaves (1 - 10 per leaf) and all were immature. Cleistothecia were dispersed by late summer and autumn rains from leaves to bark of grapevines, where they overwinter. No conclusion could be made regarding the viability of cleistothecia. However, the characteristics of the first symptoms that developed on leaves, namely separate, individual lesions formed at random on first-formed leaves growing in close proximity to the bark, provided circumstantial evidence that cleistothecia are dispersed to the bark. Weather conditions suitable for release of ascospores from overwintered cleistothecia occurred frequently between budbreak and bloom in all the areas.
A software implementation of PLASMO (Plasmopara Simulation Model) model for downy mildew (Plasmopara viticola Berl. et De Toni) of grapevine (Vitis vinifera L.) development forecasting is presented in this paper. The computer program has been developed to facilitate validation and further improvements and to allow direct model use in vineyard management. The model simulates the development of downy mildew on the basis of climatic conditions. The inputs to the model are: temperature and leaf wetness for the inoculation phase, temperature and relative humidity for the incubation phase and the type of treatment applied. Numeric or graphic outputs are available. The program provides useful information for identifying fungicide application times on the basis of the actual downy mildew development. Field validation tests performed in untreated rows show a good correlation between field observed and model simulated infections. Moreover the model identifies only three treatment distribution periods, while with the traditional method six treatments were applied.
The main objectives of this study were to determine which of the two overwintering forms of Erysiphe necator (either by hyphae in grapevine buds or via cleistothecia on leaf, cane or trunk surfaces) dominate in different vine-growing regions of Hungary, and to find out their impact on initiating disease epidemics. The only evidence of mycelial overwintering of this fungal pathogen in grapevine buds in 2004 was found in a vineyard in Sióagárd where one single plant showed the typical symptoms of "flag shoot", whereas in all other cases initial infections by ascospores from overwintering cleistothecia were evident. The appearance and spread of E. necator was quite similar in the vineyards of Eger, Kecskemét and Sióagárd, the first leaf symptoms appearing about three weeks before flowermg, and by the time grape bunches became susceptible to powdery mildew attack, a significant amount of inoculum was available that resulted in up to 90-100% infection. Microscopical investigations revealed a relatively low percentage of parasitism of cleistothecia by Ampelomyces sp. in the grapevine cultivars examine.
A warning system based on (i) a model that simulates the development of all cohorts of Plasmopara viticola oospores, from oospore germination to infection; (ii) short-term weather forecasts; and (iii) a mobile phone short message system was tested in Northern Italy, from 2006 to 2008. An unsprayed control was compared with a "Warning A" treatment (WA, fungicides were applied whenever the warning system predicted an infection period), a "Warning B" treatment (WB, fungicides were applied as in the WA treatment but only when the relative dimension of any oospore cohort predicted by the model exceeded a threshold), and a "grower" treatment (fungicides were applied according to a conventional schedule). Average disease incidence on leaves was reduced by up to 90% in sprayed plots compared with unsprayed plots. On bunches, efficacy was always >90% at fruit set; when most berries were touching, efficacy was higher for the WA (96%) than for grower (89%) and WB (85%) treatments. On average, 6.8 fungicide sprays were applied following the grower's schedule; use of the warning system reduced applications by about one-half (WA treatment) or two-thirds (WB treatment). The grower's schedule had an average cost of 337 (sic)/ha; the average saving with the WA and the WB treatments was 174 and 224 (sic)/ha, respectively.
Sporulation of Uncinula necator on grapevines (Vitis vinifera Carignane' and Chardonnay') was quantified at 19, 22, 26, and 30 C by harvesting conidia at periodic intervals from individual colonies. Temperature was shown to influence the length of the infectious period. Colonies began sporulating 5 days after inoculation, except at 19 C, when sporulation was first observed after 7 days. Sporulation stopped by 35, 35, 25, and 20 days after inoculation at 19, 22, 26, and 30 C, respectively. Sporulation was greater on Carignane than Chardonnay at all temperatures except 19 C. The maximum number of conidia produced per colony was 11.450 (...)
Atmospheric concentrations of Erysiphe necator conidia were monitored for 2 years in a vineyard planted with cultivars susceptible to powdery mildew in the vine production area of Quebec, Canada. The concentrations of airborne conidia were determined and compared using two types of samplers: a Burkard volumetric sampler and a rotating-arm sampler. The coefficients of correlation between the volumetric and rotating-arm sampler placed at 45cm from the ground was r=0.81 and 0.82 in 2000 and 2001, respectively. The relationship between incidence of powdery mildew on the leaves of three cultivars (Chancellor, Geisenheim, and Frontenac) and the cumulative concentration of airborne conidia (based on 3d of sampling weekly) was then studied. This relationship was similar for the three cultivars, (R2=0.97, 0.95, 0.97, for cvs Chancellor, Geisenheim, and Frontenac respectively) and was well described using the cumulative form of the Weibull model. Based on this model, it was possible to establish the period of high risk (highest rate of increase in powdery mildew incidence) from 645 to 5614, 2437 to 2951, and 1052 to 3061conidiam−3 of air for the cvs Chancellor, Geisenheim, and Frontenac, respectively. An action threshold, for timing interval between fungicide sprays, of 50conidiam−3d−1 was evaluated under field conditions with cv Chancellor and was as good as a calendar-based program with fewer fungicide sprays under unfavourable weather conditions. Monitoring airborne inoculum could be used as a component of a risk management system for grape powdery mildew to time intervals between fungicide sprays.
During a 5-year period (1993-1997), the release of Uncinula necator (Schweiniz) Burrill ascospores was monitored under natural conditions in the Bordeaux region. Ascospore release always began after bud burst and generally ended before blossoming. The release periods of ascospores were always associated with a rainfall higher than 2 mm, a wetting duration greater than 2.5 h, an average temperature generally above 11°C and a daily mean temperature sum from November 1 to the first ascospore release above 1100°C. There was no relation between earliness, number of ascospores released, and disease severity on grapes (Vitis vinifera L. cv. Merlot). The primary infection did not appear to be important for the increase of the powdery mildew population; on the other hand, the weather conditions of April (rainfall and temperature) seemed to strongly influence disease severity on berries by enabling good growth of the pathogen on leaves. These findings could be used to determine the optimal dates of the first fungicide treatments for powdery mildew according to the weather conditions.Key words: cleistothecia, ascospores, release, weather conditions, powdery mildew, Uncinula necator, grapevine.
Grapevine downy mildew (Plasmopara viticola) is an important disease that can heavily affect the quality and quantity of vine production. In central Italy disease control is based on a regular scheduling of about 10 fungicide applications from May to August, with a cost ranging from 250 to 350 (sic)/ha just for products purchase. In this study an agrometeorological system based on the model PLASMO, which is able to simulate the appearance and progress of infections, was applied to define the timing of fungicide applications and then compared with a regular application scheduling. The two strategies were compared on the basis of their efficacy and their economic cost. For the year analysed the strategy based on the use of the model was economically convenient when the treated area was at least 6 ha.
Powdery mildew, caused by Erysiphe necator, is the most important grape disease in Quebec, Canada. Based on the premise that the production of secondary inoculum is a key factor in powdery mildew development, a model based on degree-day accumulation was developed and validated as a tool to initiate a calendar-based fungicide program. The Richard%rsquo;s model was used to describe the proportion of seasonal airborne inoculum as a function of degree-days (base 6 °C) accumulated since the Eichhorn-Lorenz grape phenological stage 7 (2%ndash;3 fully expanded leaves). The model explained 91% of the variation in proportion of seasonal airborne inoculum and 96% when validated against independent observations. Reliability of the model to time the initiation of a standard fungicide spray program was validated in experimental vineyards from 2004 to 2007. The following management schemes were compared: (1) no fungicides (control); (2) fungicides applied at fixed intervals starting at the 3%ndash;4 leaves growth stage; (3) a fungicide spray program initiated based on the degree-day model; and (4) a fungicide spray program initiated based on both the degree-day model and airborne inoculum concentration. Depending on years and cultivars, the use of the model reduced the number of fungicide sprays by 40% to 55%. The degree-day model could be used as a component of a risk management system for grape powdery mildew to estimate the need for fungicide sprays before bloom or to time the initiation of a fungicide spray program.
A new dynamic model for Erysiphe necator ascosporic infections on grapevine was developed. Between budbreak of vines and the time when the pool of ascospores is depleted, the model uses weather data for calculating, at daily intervals: curve of ascospore maturation; ascospore discharge events and relative proportion of the discharged ascospores; infection periods and their relative infection severity; and progress of latency period and time when secondary infections should begin. The model was validated over a 4-year period (2005–2008) in 26 vineyards in Italy by comparing model predictions with actual observations of the first seasonal symptoms of powdery mildew. The model showed high sensitivity, specificity and accuracy. Proportions of true and false positive predictions were TPP = 0·94 and FPP = 0·26, respectively. Because a proportion of predicted infection periods did not result in actual disease onset, confidence was higher for prediction of non-infections than for prediction of infections. Most of the false positive predictions occurred in the earlier growth stages of the host, when the surface area of susceptible tissue may be very small so that the probability that ejected ascospores land on susceptible tissue is low. An equation was then developed to describe the probability that a predicted infection period results in disease onset as a function of the growth stage of vines at the time of prediction. The new model should improve early season powdery mildew management by helping vineyard managers schedule fungicide sprays or schedule the scouting of the vineyard for detection of first disease signs.
The foregoing paper by Lorenz et al. (1995), translated into English by P. May, describes a new system for the identification of grapevine growth stages called the BBCH system. This is an adaptation, for the grapevine, of a basic scale developed to cover all monocot and dicot crops. Appraisal of this and two other systems has led to a preference for that by Eichhorn and Lorenz (1977) but with some amendments. These amendments are discussed and a new system of measurement and description of stages of the grapevine is proposed which copes with the dual needs for a simple listing of major stages and, at the same time, provides intermediate detailed stages. It is called the Modified E-L system.
¶The nonhydrostatic model LM was developed for small scale operational predictions. Advances in computer development will
give the possibility of operational models of a rather fine scale, which will cover the meso-gamma scale. The LM is currently
applied at a scale of 7 km and an increase of the operational resolution to 2.5 km is planned for the next few years. Predictions
of such high resolution require to abandon the hydrostatic assumption, which is used with most current operational weather
prediction models. The LM was designed to cover all resolutions from 50 m to 50 km with an efficiency making it suitable for
operational use. It is a fully elastic model, using second order centred finite differences. The time integration is done
using the Klemp–Wilhelmson method, treating the slow modes by a larger time step than the fast modes. The vertical propagation
of the fast waves is done implicitly.
After describing the design of the LM, this paper gives examples of model predictions at the meso-γ scale. Some results of
the current operational application at the resolution 7 km are presented. Deficiencies in the localisation of model generated
precipitation are investigated using an idealised bell shaped mountain and applying different resolutions. In this way the
convergence to the correct solution can be investigated. From these results it is concluded, that orographic filtering is
necessary and the effect of such filtering on precipitation forecasts is investigated. Finally, the prediction of a squall
line over northern Germany is shown in order to demonstrate the potential of the model in forecasting the meso-γ scale.
Dynamics of ascocarp development, ascospore maturation, and dispersal in Erysiphe necator were studied over a 4-year period, from the time of ascocarp formation to the end of the ascosporic season at the end of June in the following spring. Naturally dispersed chasmothecia were collected from mid-August to late November (when leaf fall was complete); the different collections were used to form three to five cohorts of chasmothecia per year, with each cohort containing ascocarps formed in different periods. Chasmothecia were exposed to natural conditions in a vineyard and periodically sampled. Ascocarps were categorized as containing mature or immature ascospores, or as empty; mature ascospores inside chasmothecia were enumerated starting from late February. Ascospore discharge was determined using silicone-coated slides that were placed 3 to 4 cm from sections of the vine trunk holding the chasmothecia. Before complete leaf fall, 34% of the chasmothecia had mature ascospores, 48% had immature ascospores, and 18% were empty; in the same period, the trapped ascospores represented 56% of the total ascospores trapped in an ascosporic season (i.e., from late summer until the next spring or early summer). The number of viable chasmothecia diminished over time; 11 and 5% of chasmothecia had mature ascospores between complete leaf fall and bud break and after bud break, respectively. These ascocarps discharged ≈2 and 42% of the total ascospores, respectively. All the ascocarp cohorts released ascospores in autumn, survived the winter, and discharged viable ascospores in spring; neither ascospore numbers nor their pattern of temporal release was influenced by the time when chasmothecia were collected and exposed in the vineyard. Abundance of mature ascospores in chasmothecia was expressed as a function of degree-days (DD) (base 10°C) accumulated before and after bud break through a Gompertz equation (R² = 0.92). Based on this equation, 90% of the ascospores were mature when 153 DD (confidence interval, 100 to 210 DD) had accumulated after bud break. Most ascospores were trapped in periods with >2 mm of rain; however, a few ascospores were airborne with <2 mm of rain and, occasionally, in wet periods of ≥3.5 h not initiated by rain.
Control of grapevine powdery mildew: timing of fungicide applications by use of the U C Davis Risk Assessment Model
- W D Gubler
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Managing powdery mildew
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Dispersal of the sexual stage of Erysiphe necator in northern Italy
- V Rossi
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- F Sozzani
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Principles for managing the foliage diseases of grapevine with low input of pesticides
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Protection of grapevine against powdery mildew with fungicides applied at increasing disease incidence thresholds
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grapevine against powdery mildew with fungicides applied at increasing
disease incidence thresholds. Atti Giornate Fitopatol. 2:305-310.
UC IPM Pest management guidelines: grape powdery mildew
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Gubler, W. D., Smith, R. J., Varela, L. G., Vasquez, S., Stapleton, J. J., Purcell, A. H., and Leavitt, G. M. 2006. UC IPM Pest management guidelines:
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