scholarly journals Distribution of Baseline Sensitivities to Azoxystrobin Among Isolates of Plasmopara viticola

Plant Disease ◽  
2000 ◽  
Vol 84 (3) ◽  
pp. 275-281 ◽  
Author(s):  
Francis P. Wong ◽  
Wayne F. Wilcox
Keyword(s):  
New York ◽  
Disease Severity ◽  
Disease Incidence ◽  
Leaf Disc ◽  
Plasmopara Viticola ◽  
Grapevine Downy Mildew ◽  
Coefficients Of Variation ◽  
Control Versus ◽  
Strobilurin Fungicide ◽  
Effective Doses

An excised leaf disc assay was developed for determining the sensitivity of isolates of Plasmopara viticola (causal agent of grapevine downy mildew) to the strobilurin fungicide azoxystrobin. Five repeated assays with the same five single-sporangiophore isolates showed that the technique yielded reproducible results; that is, coefficients of variation ranged from 4.0 to 20% (mean 12%) for effective doses for 50% control (ED50 values) based on disease incidence and from 4.4 to 14% (mean 8.1%) for ED50 values based on disease severity. Then, the assay was applied to 81 single-sporangiophore isolates of P. viticola collected from 10 geographically distinct vineyards in western New York, providing a baseline distribution of sensitivities within this population. For disease incidence, individual ED50 values ranged from 0.05 to 0.94 μg/ml (mean 0.40 μg/ml), whereas for disease severity they ranged from 0.04 to 0.78 μg/ml (mean 0.24 μg/ml). When 61 of these isolates were similarly tested at a single discriminatory dose of 0.50 μg/ml, azoxystrobin provided 61% control of disease incidence versus 41 and 1.1% control for trifloxystrobin and kresoximmethyl, respectively; for disease severity (colony diameter), azoxystrobin provided 80% control versus 57 and 1.1% control for trifloxystrobin and kresoximmethyl, respectively. These results provide information that can be utilized in future monitoring of P. viticola resistance to azoxystrobin and indicate differences in the intrinsic activities of the three strobilurin fungicides against this pathogen.

scholarly journals Effect of Detergent on the Quantification of Grapevine Downy Mildew Sporangia from Leaf Discs

HortScience ◽  
2015 ◽  
Vol 50 (5) ◽  
pp. 656-660 ◽  
Author(s):  
Atsushi Kono ◽  
Akihiko Sato ◽  
Bruce Reisch ◽  
Lance Cadle-Davidson
Keyword(s):  
Downy Mildew ◽  
Leaf Disc ◽  
Plasmopara Viticola ◽  
Inhibitory Effect ◽  
Tween 20 ◽  
Infected Leaf ◽  
Grapevine Downy Mildew ◽  
Visual Rating ◽  
Leaf Discs ◽  
Highly Correlated

Grapevine downy mildew (DM), caused by the oomycete Plasmopara viticola (Berk. & Curt.) Berlese & de Toni, is a major disease, especially in humid viticultural areas. Development of resistant cultivars is an important objective for grapevine breeding. To establish a reliable and inexpensive quantitative method to aid in breeding for DM resistance, we improved the method for counting the number of sporangia on leaf discs, and developed a method for counting the number of sporangia in solution. To prevent the loss of DM sporangia from adhesion onto plastic ware, we found as little as 0.01% Tween 20 was effective. On the other hand, this detergent was shown to have a severe inhibitory effect upon DM infection of leaves. We developed a sporangia counting method using dried droplets of DM suspensions, and the method was highly correlated with counting by hemacytometer (R2 > 0.96). The nonparametric Spearman’s rank correlations between visual rating and the number of the sporangia were as high as ρ = 0.82 to 0.91, suggesting that evaluation by the visual rating could provide a good estimate of the sporangia numbers on leaf discs. We established a high-throughput and inexpensive method with acceptable accuracy for DM resistance evaluation based on a leaf disc assay, and our results suggested that visual ratings of infected leaf discs provide a good estimate of sporangia numbers.

Addressing the Gaps in our Knowledge of Grapevine Downy Mildew for Improved Forecasting and Management

2007 ◽  
Vol 8 (1) ◽  
pp. 66 ◽  
Author(s):  
Megan M. Kennelly ◽  
David M. Gadoury ◽  
Wayne F. Wilcox ◽  
Peter A. Magarey ◽  
Robert C. Seem
Keyword(s):  
New York ◽  
Downy Mildew ◽  
Primary Infection ◽  
Weather Conditions ◽  
Plasmopara Viticola ◽  
Disease Forecasting ◽  
Knowledge Gaps ◽  
Grapevine Downy Mildew ◽  
Complex Interactions ◽  
High Viability

The complex interactions of Plasmopara viticola with environment and host make grapevine downy mildew an ideal candidate for disease forecasting. However, a forecasting model is only as good as the knowledge used to build it, and DMCast is no exception. We addressed some knowledge gaps concerning this disease: (i) initial timing and span of primary infection; (ii) survival of the lesions and sporangia; and (iii) critical period of fruit susceptibility. Experiments revealed that, though emerging shoots are susceptible earlier than previously thought, primary infection frequently occurs near the confluence of a specific host phenological stage and certain weather conditions. Primary infection also may trigger new epidemics later in the season than was traditionally hypothesized. Lesions declined with repeated sporulation cycles but, contrary to prior reports, not age alone. Sporangia died within 8 h on dry, warm days but retained high viability on cooler days. With controlled inoculations, we determined that in the New York climate, fruit of several cultivars (Chardonnay, Riesling, Concord, and Niagara) become resistant to infection by 2 to 3 weeks post-bloom. These studies have clarified several knowledge gaps and long-held assumptions that have direct implications for improving disease forecasting and disease management. Accepted for publication 14 March 2007. Published 26 July 2007.

scholarly journals An IPM Program for Managing Fungal Leaf Blight Diseases of Carrot in New York

Plant Disease ◽  
2007 ◽  
Vol 91 (1) ◽  
pp. 59-65 ◽  
Author(s):  
B. K. Gugino ◽  
J. E. Carroll ◽  
T. L. Widmer ◽  
P. Chen ◽  
G. S. Abawi
Keyword(s):  
New York ◽  
Disease Severity ◽  
Crop Rotation ◽  
Disease Incidence ◽  
Leaf Blight ◽  
Yield Reduction ◽  
Weather Forecasts ◽  
Alternaria Dauci ◽  
Leaf Blights ◽  
Cultivar Susceptibility

Fungal leaf blight diseases caused by Cercospora carotae and Alternaria dauci occur annually on processing carrot in New York, with growers applying up to eight fungicide sprays to manage these diseases. An integrated pest management (IPM) program involving the use of a 25% disease incidence threshold to prompt the first fungicide application and timing subsequent sprays by monitoring for increases in disease severity and weather forecasts in conjunction with a 10- to 14-day spray interval was evaluated in grower fields in 1997 and 1998. The IPM plots, compared with the grower plots, required two to six fewer fungicide applications but showed no yield reduction. From 1999 to 2004, the IPM program was validated and the effect of crop rotation and carrot cultivar susceptibility also were assessed. Carrot plants growing in fields with 2-year or longer crop rotation intervals reached the 25% disease incidence threshold later in the season and required fewer fungicide applications. The less-susceptible carrot cultivars also reached the 25% disease incidence threshold later, required fewer fungicide applications, and were less severely diseased than more susceptible cultivars. Validation of the IPM program in New York showed that both fungal leaf blights can be managed effectively using a 25% incidence threshold to prompt the first fungicide spray and making the subsequent fungicide applications based on increases in disease severity, weather forecasts, and a 10- to 14-day spray interval.

scholarly journals Salvia officinalis Extract Can Protect Grapevine Against Plasmopara viticola

Plant Disease ◽  
2010 ◽  
Vol 94 (5) ◽  
pp. 575-580 ◽  
Author(s):  
Silvia Dagostin ◽  
Tiziano Formolo ◽  
Oscar Giovannini ◽  
Ilaria Pertot ◽  
Annegret Schmitt
Keyword(s):  
Disease Control ◽  
Downy Mildew ◽  
Disease Incidence ◽  
Plasmopara Viticola ◽  
Salvia Officinalis ◽  
Promising Alternative ◽  
Rainy Period ◽  
Grapevine Downy Mildew ◽  
Progress Curve ◽  
High Level

The ability of sage (Salvia officinalis) extract to control grapevine downy mildew under greenhouse and field conditions was tested. The persistence and rainfastness of sage extract were also investigated. Sage extract provided a high level of sustained disease control in artificially inoculated, potted grapevine under greenhouse conditions. However, even small amounts of simulated rainfall (10 mm) significantly reduced efficacy of sage extract. In a field experiment in 2006, sage extract provided 94% reduction in disease incidence and 63% reduction in area under the disease progress curve for disease severity on berries and leaves, respectively, reaching a level of disease control not significantly different from that provided by copper hydroxide. In 2007, the sage extract provided only a partial reduction (less than 30%) of downy mildew on leaves, probably as a result of a long rainy period between two of the consecutive treatments. Overall, sage extract effectively controlled grapevine downy mildew and could be a promising alternative to copper in organic viticulture. However, the low rainfastness of this treatment adversely affected its efficacy.

Fungicide Sensitivity Survey of Plasmopara viticola Populations in Georgia Vineyards

2020 ◽  
Vol 21 (4) ◽  
pp. 256-261
Author(s):  
Sarah E. Campbell ◽  
Phillip M. Brannen ◽  
Harald Scherm ◽  
Marin T. Brewer
Keyword(s):  
Downy Mildew ◽  
Acid Amide ◽  
Leaf Disc ◽  
Plasmopara Viticola ◽  
Survey Period ◽  
Resistance Development ◽  
Grapevine Downy Mildew ◽  
Quinone Outside Inhibitor ◽  
History Of ◽  
Qoi Resistance

Grapevine downy mildew, caused by Plasmopara viticola, is among the most damaging diseases of grapes globally and in the viticultural regions of Georgia (U.S.A.). Although management of this disease typically involves fungicide applications, resistance development in P. viticola can render chemical management ineffective. The objective of this study was to survey fungicide sensitivities of P. viticola populations in vineyards across three regions in Georgia. Samples were collected from eight vineyards in 2017 and four in 2018 and tested phenotypically for sensitivity to quinone outside inhibitor (QoI), carboxylic acid amide (CAA), and phenylamide (PA) fungicides using leaf disc bioassays. In addition, DNA was extracted from P. viticola samples collected from 2015 through 2018 in these 12 vineyards and six others for a total of 18 vineyards sampled. All available DNA samples were tested for the presence of the known resistance-causing mutations G143A (QoI) and G1105S (CAA) using polymerase chain reaction (PCR). This study documented widespread occurrence of QoI resistance in P. viticola in Georgia, with 83.0% of isolates collected in 2017 and 2018 testing positive for QoI resistance based on bioassay and 82.9% of isolates collected from 2015 to 2018 testing positive for QoI resistance through PCR testing. In total, 94.4% (17/18) of surveyed vineyards had confirmed QoI resistance by the conclusion of the survey period. No reduced sensitivity to CAA or PA fungicides was identified. Due to widespread QoI resistance, these fungicides should not be relied upon for downy mildew management in Georgia vineyards with a long history of their use.

scholarly journals Seasonal Development of Ontogenic Resistance to Downy Mildew in Grape Berries and Rachises

2005 ◽  
Vol 95 (12) ◽  
pp. 1445-1452 ◽  
Author(s):  
Megan M. Kennelly ◽  
David M. Gadoury ◽  
Wayne F. Wilcox ◽  
Peter A. Magarey ◽  
Robert C. Seem
Keyword(s):  
New York ◽  
Downy Mildew ◽  
Early Stage ◽  
South Australia ◽  
Plasmopara Viticola ◽  
Seasonal Development ◽  
Berry Development ◽  
Critical Periods ◽  
Grapevine Downy Mildew ◽  
Ontogenic Resistance

Clusters of Vitis vinifera and V. labrusca are reported to become resistant to Plasmopara viticola at stages of development ranging from 1 to 6 weeks postbloom. It has been suggested that resistance is associated with loss of the infection court as stomata are converted to lenticels, but the time of onset, cultivar variation, and seasonal variation in ontogenic resistance has remained uncertain, as has the comparative susceptibility of stem tissue within the fruit cluster. In New York, we inoculated clusters of V. vinifera cvs. Chardonnay and Riesling and V. labrusca cvs. Concord and Niagara at stages from prebloom until 5 to 6 weeks postbloom. Berries were infected and supported profuse sporulation until 2 weeks postbloom, and pedicel tissue remained susceptible until 4 weeks postbloom. Although berries on later-inoculated clusters failed to support sporulation, discoloration and necrosis of berry tissues was often noted, and necrosis of the pedicel within such clusters often led to further discoloration, shriveling, reduced size, or loss of berries. When the epidermis of discolored berries that initially failed to support sporulation was cut, the pathogen emerged and sporulated through incisions, indicating that lack of sporulation on older symptomatic berries was due to infection at an early stage of berry development followed by conversion of functional stomata to lenticels during latency. We repeated the study on Chardonnay and Riesling vines in South Australia and found that the period of berry and rachis susceptibility was greatly increased. The protracted susceptibility of the host was related to the increased duration and phenological heterogeneity of bloom and berry development in the warmer climate of South Australia. The time of onset and subsequent expression of ontogenic resistance to P. viticola may thus be modified by climate and should be weighed in transposing results from one climatic area to another. Our results can be used to refine forecast models for grapevine downy mildew to account for changes in berry and rachis susceptibility, and to focus fungicide application schedules upon the most critical periods for protection of fruit.

scholarly journals High-Throughput Phenotyping of Leaf Discs Infected with Grapevine Downy Mildew Using Shallow Convolutional Neural Networks

Agronomy ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1768
Author(s):  
Daniel Zendler ◽  
Nagarjun Malagol ◽  
Anna Schwandner ◽  
Reinhard Töpfer ◽  
Ludger Hausmann ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Disease Severity ◽  
High Throughput ◽  
Imaging System ◽  
Leaf Disc ◽  
Ground Truth Data ◽  
Breeding Lines ◽  
Grapevine Downy Mildew ◽  
Leaf Discs ◽  
Efficient Detection

Objective and standardized recording of disease severity in mapping crosses and breeding lines is a crucial step in characterizing resistance traits utilized in breeding programs and to conduct QTL or GWAS studies. Here we report a system for automated high-throughput scoring of disease severity on inoculated leaf discs. As proof of concept, we used leaf discs inoculated with Plasmopara viticola ((Berk. and Curt.) Berl. and de Toni) causing grapevine downy mildew (DM). This oomycete is one of the major grapevine pathogens and has the potential to reduce grape yield dramatically if environmental conditions are favorable. Breeding of DM resistant grapevine cultivars is an approach for a novel and more sustainable viticulture. This involves the evaluation of several thousand inoculated leaf discs from mapping crosses and breeding lines every year. Therefore, we trained a shallow convolutional neural-network (SCNN) for efficient detection of leaf disc segments showing P. viticola sporangiophores. We could illustrate a high and significant correlation with manually scored disease severity used as ground truth data for evaluation of the SCNN performance. Combined with an automated imaging system, this leaf disc-scoring pipeline has the potential to considerably reduce the amount of time during leaf disc phenotyping. The pipeline with all necessary documentation for adaptation to other pathogens is freely available.

scholarly journals Comparative Physical Modes of Action of Azoxystrobin, Mancozeb, and Metalaxyl Against Plasmopara viticola (Grapevine Downy Mildew)

Plant Disease ◽  
2001 ◽  
Vol 85 (6) ◽  
pp. 649-656 ◽  
Author(s):  
Francis P. Wong ◽  
Wayne F. Wilcox
Keyword(s):  
Disease Control ◽  
Leaf Surface ◽  
Disease Incidence ◽  
Plasmopara Viticola ◽  
Lower Leaf Surface ◽  
Complete Control ◽  
Grapevine Downy Mildew ◽  
Modes Of Action ◽  
Vapor Activity ◽  
Colony Area

The physical modes of action of azoxystrobin, mancozeb, and metalaxyl were evaluated on grapevine seedlings using Plasmopara viticola as a model pathogen. The protectant, postinfection, postsymptom, translaminar, and vapor activities of azoxystrobin were evaluated at a rate of 250 μg/ml. Azoxystrobin provided 100% disease control when applied 1 to 5 days before inoculation. Postinfection applications of azoxystrobin had little effect on the incidence of disease, but colony area and sporulation from the resultant lesions was reduced by 47 and 96%, respectively, relative to the check treatment when applied up to 5 days after inoculation. Postsymptom applications (6 days after inoculation) of azoxystrobin resulted in an 85% mean reduction of resporulation from diseased tissue relative to the check when seedlings were evaluated 1 to 14 days after treatment. Translaminar activity was greatest when the upper surface of the leaf was treated 7 days before inoculation of the lower leaf surface (94% disease control). In contrast, control was <50% when leaves were similarly inoculated 1 and 3 days after treatment. Vapor activity was not pronounced, providing maximum reductions of 5, 11, and 37%, with regard to incidence, colony area, and sporulation, relative to the check when seedlings were treated 1 to 7 days before inoculating adjacent, untreated leaves. Comparatively, mancozeb (1,790 μg/ml) provided complete control of the disease when applied 1 to 5 days before inoculation, but showed little postinfection activity in reducing disease incidence, although it exhibited moderate to high antisporulant activity when applied in postinfection and postsymptom modes (mean reductions of 38 and 89%, respectively, compared with the check treatments). Metalaxyl (260 μg/ml) also provided complete control of the disease when used in protectant mode, and also when applied 1 day after inoculation. Applications at 3 to 5 days after inoculation provided substantial reductions in disease severity and sporulation (mean reductions of 46 and 94%, respectively, compared with the check treatments), and postsymptom applications resulted in a mean 84% reduction in resporulation. Collectively, the results of this study illustrate the unique physical modes of action for azoxystrobin in comparison to that of two traditional protectant and systemic fungicides, and provide information on how azoxystrobin and other strobilurin fungicides with similar physical modes of action should be best used in disease management programs.

scholarly journals High-throughput phenotyping of leaf discs infected with grapevine downy mildew using shallow convolutional neural networks

2021 ◽  
Author(s):  
Daniel Zendler ◽  
Nagarjun Malagol ◽  
Anna Schwandner ◽  
Reinhard Töpfer ◽  
Ludger Hausmann ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Disease Severity ◽  
High Throughput ◽  
Imaging System ◽  
Leaf Disc ◽  
Ground Truth Data ◽  
Breeding Lines ◽  
Grapevine Downy Mildew ◽  
Leaf Discs ◽  
Efficient Detection

Objective and standardized recording of disease severity in mapping crosses and breeding lines is a crucial step in characterizing resistance traits utilized in breeding programs and to conduct QTL or GWAS studies. Here we report a system for automated high-throughput scoring of disease severity on inoculated leaf discs. As proof of concept, we used leaf discs inoculated with Plasmopara viticola causing grapevine downy mildew (DM). This oomycete is one of the major grapevine pathogens and has the potential to reduce grape yield dramatically if environmental conditions are favorable. Breeding of DM resistant grapevine cultivars is an approach for a novel and more sustainable viticulture. This involves the evaluation of several thousand inoculated leaf discs from mapping crosses and breeding lines every year. Therefore, we trained a shallow convolutional neural-network (SCNN) for efficient detection of leaf disc segments showing P. viticola sporangiophores. We could illustrate a high and significant correlation with manually scored disease severity used as ground truth data for evaluation of the SCNN performance. Combined with an automated imaging system, this leaf disc-scoring pipeline has the potential to reduce the amount of time during leaf disc phenotyping considerably. The pipeline with all necessary documentation for adaptation to other pathogens is freely available.

scholarly journals Evaluation of a Warning System for Controlling Primary Infections of Grapevine Downy Mildew

Plant Disease ◽  
2010 ◽  
Vol 94 (6) ◽  
pp. 709-716 ◽  
Author(s):  
T. Caffi ◽  
V. Rossi ◽  
R. Bugiani
Keyword(s):  
Disease Incidence ◽  
Warning System ◽  
Plasmopara Viticola ◽  
Short Message ◽  
Short Term ◽  
Infection Period ◽  
Grapevine Downy Mildew ◽  
Weather Forecasts ◽  
Short Message System ◽  
Message System

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 €/ha; the average saving with the WA and the WB treatments was 174 and 224 €/ha, respectively.

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