scholarly journals Timing of Grape Downy Mildew Onset in Bordeaux Vineyards

2019 ◽  
Vol 109 (5) ◽  
pp. 787-795 ◽  
Author(s):  
Mathilde Chen ◽  
François Brun ◽  
Marc Raynal ◽  
David Makowski
Keyword(s):  
Downy Mildew ◽  
Severe Disease ◽  
Survival Analyses ◽  
Fungicide Treatment ◽  
Grapevine Downy Mildew ◽  
Local Characteristics ◽  
South West ◽  
Disease Surveys ◽  
Grape Downy Mildew ◽  
Regional Disease

Grapevine downy mildew (GDM) is a severe disease of grapevines. Because of the lack of reliable information about the dates of GDM symptom onset, many vine growers begin fungicide treatments early in the season. We evaluate the extent to which such preventive treatments are justified. Observational data for 266 untreated sites for the years between 2010 and 2017 were used to estimate the timing of GDM onset on vines and bunches of grapes in South West France (Bordeaux region) through survival analyses. The onset of GDM was not apparent on vines and bunches before early to mid-May, and the rate of GDM symptom appearance was highly variable across years. Depending on the year, 50% of the plots displayed symptoms between mid-May and late June for vines. For several years, our statistical analysis revealed that the proportion of plots with no symptoms was high in early August on vines (27.5 and 43.7% in 2013 and 2016) and on bunches (between 23 and 79% in 2011, 2013, and 2016). We found a significant effect of the amount of rainfall in spring on the date of symptom appearance. These results indicate that preventive fungicide application is unjustified in many vineyards, and that regional disease surveys should be used to adjust fungicide treatment dates according to local characteristics, in particular according to rainfall conditions in spring.

scholarly journals First Report of Carboxylic Acid Amide Fungicide Resistance in Plasmopara viticola (Grapevine Downy Mildew) in North America

2018 ◽  
Vol 19 (2) ◽  
pp. 139-139 ◽  
Author(s):  
Xuewen Feng ◽  
Anton Baudoin
Keyword(s):  
North Carolina ◽  
Carboxylic Acid ◽  
North America ◽  
Downy Mildew ◽  
Acid Amide ◽  
Plasmopara Viticola ◽  
Carboxylic Acid Amide ◽  
Grapevine Downy Mildew ◽  
Grape Downy Mildew ◽  
Caa Fungicides

This report documents the first known occurrence in North America of resistance in grape downy mildew (Plasmopara viticola) to the carboxylic acid amide (CAA) fungicides mandipropamid and dimethomorph. These fungicides (FRAC group 40) have been an important component of downy mildew management programs for the past decade. Resistant isolates were obtained at three locations in Virginia and one in North Carolina, at considerable distances from each other. Resistance was documented by bioassay and the presence of the G1105S mutation, which has been associated with CAA resistance of P. viticola in other areas. Further survey is needed to determine the geographic extent of this resistance.

scholarly journals Integrated Management of Downy Mildew on Slicing Cucumber With Fungicides and Host Resistance But Not Trellising

Plant Disease ◽  
2019 ◽  
Vol 103 (10) ◽  
pp. 2592-2598
Author(s):  
Anthony P. Keinath
Keyword(s):  
Downy Mildew ◽  
Host Resistance ◽  
Management Practices ◽  
Integrated Management ◽  
Cultivar Resistance ◽  
Fall Season ◽  
Fungicide Treatment ◽  
Progress Curve ◽  
Management Techniques ◽  
The Mean

The objective of this study was to evaluate fungicide applications, host resistance, and trellising, alone and in combination, as management practices for downy mildew on slicing cucumber. A split-split plot experimental design was used with three and four replications in spring and fall 2017, respectively. The whole-plot treatment was fungicide, four applications of chlorothalonil (Bravo Weather Stik 6SC) alternated with three applications of cyazofamid (Ranman 400SC), or water. Split plots were nontrellised or trellised with four strings supported by stakes. Split-split plots were cultivar Bristol, which is intermediately resistant to downy mildew, or cultivar Speedway, which is susceptible to downy mildew with similar parentage as Bristol. In both seasons, area under the disease progress curve (AUDPC) values were lower with fungicides than water for both cultivars. In the spring, AUDPC for Bristol was lower than for Speedway regardless of fungicide treatment. In the fall, Bristol had a lower AUDPC than Speedway with fungicides, but the AUDPC did not differ between the two cultivars with water. The mean AUDPC for trellised plants (376.2) was lower than for nontrellised plants (434.0; P = 0.007). Fungicide applications increased marketable and total fruit weights in both seasons (P ≤ 0.0002). Marketable weight with fungicides was almost double (93% greater) the marketable weight with water. Marketable weight was 55% greater for Bristol than for Speedway in spring, but yields did not differ between cultivars in fall (season-by-cultivar interaction, P ≤ 0.0003). Because trellising had no effect on marketable yields (P = 0.11), trellising is not recommended for managing downy mildew on slicing cucumber. Of the three management techniques examined, fungicides had the largest effects on disease and yields, followed by cultivar resistance.

scholarly journals A High-Quality Grapevine Downy Mildew Genome Assembly Reveals Rapidly Evolving and Lineage-Specific Putative Host Adaptation Genes

2019 ◽  
Vol 11 (3) ◽  
pp. 954-969 ◽  
Author(s):  
Yann Dussert ◽  
Isabelle D Mazet ◽  
Carole Couture ◽  
Jérôme Gouzy ◽  
Marie-Christine Piron ◽  
...  
Keyword(s):  
Downy Mildew ◽  
Genome Assembly ◽  
Population Genomics ◽  
Plasmopara Viticola ◽  
Plant Diseases ◽  
Host Specialization ◽  
Grapevine Downy Mildew ◽  
Downy Mildews ◽  
Genes Encoding ◽  
High Level

Abstract Downy mildews are obligate biotrophic oomycete pathogens that cause devastating plant diseases on economically important crops. Plasmopara viticola is the causal agent of grapevine downy mildew, a major disease in vineyards worldwide. We sequenced the genome of Pl. viticola with PacBio long reads and obtained a new 92.94 Mb assembly with high contiguity (359 scaffolds for a N50 of 706.5 kb) due to a better resolution of repeat regions. This assembly presented a high level of gene completeness, recovering 1,592 genes encoding secreted proteins involved in plant–pathogen interactions. Plasmopara viticola had a two-speed genome architecture, with secreted protein-encoding genes preferentially located in gene-sparse, repeat-rich regions and evolving rapidly, as indicated by pairwise dN/dS values. We also used short reads to assemble the genome of Plasmopara muralis, a closely related species infecting grape ivy (Parthenocissus tricuspidata). The lineage-specific proteins identified by comparative genomics analysis included a large proportion of RxLR cytoplasmic effectors and, more generally, genes with high dN/dS values. We identified 270 candidate genes under positive selection, including several genes encoding transporters and components of the RNA machinery potentially involved in host specialization. Finally, the Pl. viticola genome assembly generated here will allow the development of robust population genomics approaches for investigating the mechanisms involved in adaptation to biotic and abiotic selective pressures in this species.

scholarly journals Climate change and the occurrence of downy mildew in Brazilian grapevines

2017 ◽  
Vol 52 (6) ◽  
pp. 426-434 ◽  
Author(s):  
Francislene Angelotti ◽  
Emília Hamada ◽  
Edineide Elisa Magalhães ◽  
Raquel Ghini ◽  
Lucas da Ressureição Garrido ◽  
...  
Keyword(s):  
Climate Change ◽  
Latent Period ◽  
Downy Mildew ◽  
Temporal Distribution ◽  
Gas Emission ◽  
Grapevine Downy Mildew ◽  
Diseased Leaf Area ◽  
The Mean ◽  
Potential Impact ◽  
Logic Functions

Abstract: The objective of this work was to evaluate the potential impact of climate change on the occurrence of grapevine downy mildew in Brazil. Seedlings containing four to six leaves were sprayed with a sporangia suspension containing 105 sporangia per milliliter. After spraying, the seedlings were subjected to temperatures of 26, 28, 29.1, 30.4, and 31.8°C for 24 hours. The percentage of diseased leaf area and the latent period were evaluated. Maps of the geographic and temporal distribution of the disease were made considering the monthly average of the mean air temperature and leaf wetness duration for the reference climate or climate normal (1961-1990) and the future climates (2011-2040, 2041-2070, and 2071-2100), considering the A2 and B1 gas emission scenarios, designed by the Intergovernamental Panel on Climate Change (IPCC). Favorability ranges were set and used in logic functions of the geografical information system (GIS) to generate monthly maps for grapevine downy mildew. Rising temperatures interfered with the grapevine downy mildew infections, reduced the disease severity, and increased the latent period. Future climate scenarios indicate a reduction of favorability of downy mildew in Brazil, with variability in the different grape producing regions.

scholarly journals Evaluation of a Disease Warning System for Downy Mildew of Grapes

Plant Disease ◽  
2000 ◽  
Vol 84 (5) ◽  
pp. 549-554 ◽  
Author(s):  
L. V. Madden ◽  
M. A. Ellis ◽  
N. Lalancette ◽  
G. Hughes ◽  
L. L. Wilson
Keyword(s):  
Linear Model ◽  
Downy Mildew ◽  
Environmental Conditions ◽  
Generalized Linear Model ◽  
Disease Incidence ◽  
Warning System ◽  
Plasmopara Viticola ◽  
Effective Control ◽  
Subsequent Infection ◽  
Grape Downy Mildew

An electronic warning system for grape downy mildew— based on models for the infection of leaves of Vitis lambrusca, production of sporangia by Plasmopara viticola in lesions, and sporangial survival—was tested over 7 years in Ohio. Grapevines were sprayed with metalaxyl plus mancozeb (Ridomil MZ58) when the warning system indicated that environmental conditions were favorable for sporulation and subsequent infection. Over the 7 years, plots were sprayed from one to four times according to the warning system, and from four to 10 times according to the standard calendar-based schedule (depending on the date of the initiation of the experiment). The warning system resulted in yearly reductions of one to six sprays (with median of three sprays). Disease incidence (i.e., proportion of leaves with symptoms) in unsprayed plots at the end of the season ranged from 0 to 86%, with a median of 68%. Incidence generally was very similar for the warning-system and standard-schedule treatments (median of 7% of the leaves with symptoms), and both of these incidence values were significantly lower (P < 0.05) than that found for the unsprayed control, based on a generalized-linear-model analysis. Simplifications of the disease warning system, where sprays were applied based only on the infection or sporulation components of the system, were also effective in controlling the disease, although more fungicide applications sometimes were applied. Effective control of downy mildew, therefore, can be achieved with the use of the warning system with fewer sprays than a with a standard schedule.

Temporal Dynamics and Severity of Cucurbit Downy Mildew Epidemics as Affected by Chemical Control and Cucurbit Host Type

Plant Disease ◽  
2021 ◽  
Author(s):  
Isaack Kikway ◽  
Anthony P. Keinath ◽  
Peter S. Ojiambo
Keyword(s):  
Downy Mildew ◽  
Disease Severity ◽  
Temporal Dynamics ◽  
Parameter Estimates ◽  
Spring Season ◽  
Fall Season ◽  
Fungicide Treatment ◽  
Cucurbit Downy Mildew ◽  
Disease Progress ◽  
Host Type

Cucurbit downy mildew caused by the oomycete Pseudoperonospora cubensis is an important disease that affects members of Cucurbitaceae family globally. However, temporal dynamics of the disease have not been characterized at the field scale to understand how control strategies influence disease epidemics. Disease severity was assessed visually on cucumber and summer squash treated with weekly alternation of chlorothalonil with either cymoxanil, fluopicolide or propamocarb, during the 2018 spring season and 2019 and 2020 fall seasons in North Carolina, and the 2018 and 2020 fall seasons in South Carolina. Disease onset was observed around mid-June during the spring season and early September during the fall season, followed by a rapid increase in severity until mid-July in the spring season and late September or mid-October in the fall season, typical of polycyclic epidemics. The Gompertz, logistic and monomolecular growth models were fitted to disease severity using linear regression and parameter estimates used to compare the effects of fungicide treatment and cucurbit host type on disease progress. The Gompertz and logistic models were more appropriate than the monomolecular model in describing temporal dynamics of cucurbit downy mildew, with the Gompertz model providing the best description for 34 of the 44 epidemics examined. Fungicide treatment and host type significantly (P < 0.0001) affected standardized area under disease progress curve (sAUDPC), final disease severity (Final DS) and weighted mean absolute rates of disease progress (ρ), with these variables, in most cases, being significantly (P < 0.05) lower in fungicide treated plots than in untreated control plots. Except in a few cases, sAUDPC, Final DS and ρ were lower in cases where chlorothalonil was alternated with fluopicolide or propamocarb than in cases where chlorothalonil alternated with cymoxanil or when chlorothalonil was applied alone. These results characterized the temporal progress of cucurbit downy mildew and provided an improved understanding of the dynamics of the disease at the field level. Parameters of disease progress obtained from this study could serve as inputs in simulation studies to assess the efficacy of fungicide alternation in managing fungicide resistance in this pathosystem.

Use of probabilistic expert elicitation for assessing risk of appearance of grape downy mildew

2019 ◽  
Vol 126 ◽  
pp. 104926
Author(s):  
M. Chen ◽  
F. Brun ◽  
M. Raynal ◽  
C. Debord ◽  
D. Makowski
Keyword(s):  
Downy Mildew ◽  
Expert Elicitation ◽  
Grape Downy Mildew
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