Mildew Of Grape Research Articles

Behaviour of trifloxystrobin and tebuconazole on grapes under semi‐arid tropical climatic conditions

A mixture of trifloxystrobin and tebuconazole is excellent in controlling both powdery and downy mildew of grapes. The objective of the present work was to study the behaviour of trifloxystrobin and tebuconazole on grape berries and soil following treatment with Nativo 75 WG, a formulation containing both fungicides (trifloxystrobin 250 + tebuconazole 500 g kg(-1)). This study was carried out for planned registration of this mixture for use on grapes in India. Initial residue deposits of trifloxystrobin and tebuconazole on grapes were below their maximum residue limit (MRL) of 0.5 and 2 mg kg(-1), respectively, when Nativo 75 WG was applied at the recommended dose of 175 g product ha(-1). The residues dissipated gradually to 0.02 and 0.05 mg kg(-1) by 30 days, and were below the quantifiable limit of 0.01 mg kg(-1) at the time of harvest (60 days after the last treatment). Trifloxystrobin and tebuconazole dissipated at a pre-harvest interval (PHI) of 36 and 34 days, respectively, from the recommended treatment dose. The acid metabolite of trifloxystrobin, CGA 321 113, was not detected in grape berries at any point in time. Soil at harvest was free of any pesticide residues. Residue levels of both trifloxystrobin and tebuconazole were below MRLs when grapes were harvested 30 days after the last of four applications of 175 g product ha(-1) (trifloxystrobin 44 g AI ha(-1), tebuconazole 88 g AI ha(-1)) under the semi-arid tropical climatic conditions of India.

Relação entre doses de calda bordalesa e de fosfito potássico na intensidade do míldio e na produtividade da videira cv. 'Goethe'

O míldio da videira, é uma das principais doenças dessa cultura no Sul do Brasil e provoca grandes perdas caso não sejam adotadas medidas de controle. Trabalhos envolvendo diferentes aspectos do patossistema são importantes para redução das perdas provocadas pela doença. O objetivo deste trabalho foi avaliar a influência de doses da calda bordalesa e do fosfito potássico no controle do míldio e na produtividade da videira cv. "Goethe" sob condições do Litoral Sul Catarinense, Brasil. Foram testadas as concentrações de 0,0, 0,1, 0,2, 0,4 e 0,8% do fungicida e do adubo foliar em um esquema fatorial de blocos ao acaso com três repetições. As variáveis de área abaixo da curva de progresso da doença (AACPD), porcentagem de cachos doentes (PCD) e produtividade foram submetidas à análise de variância e de regressão. Diferenças para AACPD e PCD foram verificadas nas doses dos tratamentos. Por outro lado, não houve diferenças na comparação da calda bordalesa com fosfito, nem para as interações entre doses e tratamentos. Doses de 0,4% de calda bordalesa e 0,3% de fosfito controlaram a doença, pois reduziram em 98 e 94% a AACPD, bem como diminuíram em 46 e 76% a incidência nos cachos, respectivamente. Sintomas de fitotoxidez nas plantas foram observados nas doses de 0,8% de calda bordalesa e 0,4% de fosfito. Não foram verificadas diferenças de produtividade para nenhum dos fatores estudados. A calda bordalesa na dose de 0,4% e o fosfito potássico a 0,2% proporcionaram controle adequado do míldio na cv. 'Goethe'.

Activity of a microencapsulated mixture of constituents of essential oils against grey mould and powdery mildew in grapes and vegetables

In an effort to fend off microbial invaders, plants have evolved biosynthetic pathways to produce a variety of products, such as essential oils, that act as natural pesticides. In the current study, the in vivo activity of a microencapsulated mixture of eugenol, thymol and geraniol that are constituents of essential oils against grey mould (Botrytis cinerea) and powdery mildew (Uncinula necator, Sphaerotheca fuliginea) in grape and vegetables was investigated. Wine grape (cv. Agiorgitiko) field trials showed that the mixture, applied curatively close to harvest, was significantly (P=0.05) more effective in reducing B. cinerea bunch rot (43% reduction) than the fungicide iprodione (26%). Preventive spray applications of the mixture to greenhouse grown tomato (cv. Kalisti) had an overall efficacy of 30% under conditions of high grey mould pressure (max 74% infected leaf area on control). However, when the mixture of essential oils was applied curatively the gray mould severity on treated tomato (cv. Optima) plants did not differ significantly (P=0.05) from that of the control. Preliminary studies showed that the mixture did not affect the must/wine quality or the concentration of antioxidants in tomato fruit. In in vitro bioassays, B. cinerea mycelial growth was inhibited by 95% at the concentration of 0.14µg ml-1 (EC95 value) of the mixture. Although the mixture was less effective than wettable sulphur against powdery mildew (U. necator) on wine grape (cvs Merlot, Syrah) leaves, it reduced disease severity on bunches at the same level as sulphur. In greenhouse trials, the mixture had no effect against powdery mildew (S. fuliginea) in potted zucchini (cv. Pepo) plants.

Control of powdery mildew of grape in Greece using Sporodex® L and Milsana®

Six field trials were conducted in Greece to study the efficacy of two formulations of Reynoutria sachalinensis extract (Milsana® Vp 1999 & 2001) and a formulation of Pseudozyma flocculosa (Sporodex® L) against powdery mildew (Uncinula necator) of grapes. In three trials where Milsana® was tested alone it was found that a) both formulations significantly reduced disease severity on berries, b) its efficacy was moderate to low but within the range of sulphur treatment alone and c) significant increase in yield was obtained in one out of two trials where yield was measured. In two field trials where Sporodex® L was tested it was found that a) it was effective on moderate to high disease pressure on bunches, but its efficacy declined when disease severity was extremely high and b) its efficacy was similar or inferior to that of sulphur alone. Alternated applications of Milsana® and Sporodex® L tested in one trial improved the efficacy of Milsana®, but not that of Sporodex® L. Alternation of Milsana® and Sporodex® L with sulphur did not result in significantly better efficacy than the stand alone applications of the control agents (one trial). The potential use of Milsana® or Sporodex® L in low input systems in grapes is discussed.

Extracts of Inula viscosa Control Downy Mildew of Grapes Caused by Plasmopara viticola

ABSTRACT The oily paste extracts of Inula viscosa leaves made with organic solvents were effective in controlling downy mildew caused by Plasmopara viticola in detached leaf tissues of grapes in growth chambers. Thin-layer chromatography of such extracts revealed the presence of 11 Rf regions of which four contained highly effective compounds against the disease. Two major inhibitory compounds, each comprising 10.6% of the total paste weight, were identified as tomentosin and costic acid. An emulsified concentrate formulation of the oily paste extracts provided excellent activity against the disease in the field. The effective dose (concentration) required for 90% control of the disease in treated shoots in the field was below 0.125% (paste in water). No seasonal fluctuations were observed in the control efficacy of six extracts made from I. viscosa leaves harvested during the period of May to July. In whole vines, treated and artificially inoculated, the paste concentration required for 90% control of the disease ranged between 0.30 to 0.37%, whereas in naturally infected vines it was 0.58%. It appears that I. viscosa is a valuable source for fungicidal preparations against downy mildew of grapes. This is the first report on the control of a disease with I. viscosa extracts under field conditions.

Microsatellite DNA markers for Plasmopara viticola, the causal agent of downy mildew of grapes

AbstractMicrosatellite loci were isolated from Plasmopara viticola (Oomycetes), the causal agent of downy mildew of grape, one of the most damaging fungal diseases of grapevine worldwide. Seven polymorphic loci were obtained from an enriched partial genomic library. A low genetic diversity was observed at all loci, with a mean observed allele number of 3.75 and an observed heterozygosity ranging from 0.074 to 0.547. Cross‐amplification tests on three closely related taxa indicated that two loci could be used in other Oomycetes species. These microsatellite loci were proved to be useful for population genetic analysis.

Effects of Timing of Powdery Mildew Infection on Carbon Assimilation and Subsequent Seasonal Growth of Potted Chardonnay Grapevines

Potted Chardonnay (<i>Vitis vinifera</i> L.) grapevines were inoculated with conidial suspensions of <i>Uncinula necator</i> (Schw.) Burr., the causal agent of powdery mildew of grape, just prior to bloom (early), just after the estimated 5-mm berry stage (late), or they were not inoculated but were treated with myclobutanil fungicide to maintain foliage free of the disease (control). The effects of the timing of initial infection on net carbon assimilation (<i>A</i>), carbon partitioning, stomatal conductance (g_s), internal CO₂ concentration (C_<i>i</i>), and transpiration (<i>E</i>) were studied over two seasons. Early vines had reduced <i>A</i> relative to late and control vines until the estimated preveraison period, when late vines also showed reduced <i>A</i>. Early vines had reduced fresh and dry weights compared to other treatments. Leaves on both early and late vines senesced earlier than those on control vines. During the following growing season, shoot lengths and fresh and dry weights were negatively correlated with the length of the disease development period in the previous growing season.

Absence of Oospores of Downy Mildew of Grape Caused by Plasmopara viticola as the Source of Primary Inoculum in Most Western Australian Vineyards.

Grapevine downy mildew, caused by the obligate, oomycete pathogen, Plasmopara viticola, was first recorded in Western Australia (W.A.) in 1998 (2) and has subsequently been observed in most viticultural regions of the state. Heterothallism in P. viticola was established by Wong et al. (3), whereby more than one mating type of the pathogen is required for sexual reproduction to occur. Oospores are considered to be the source of primary inoculum for this disease with further, secondary infection being advanced by asexual inoculum. However, recent research in European vineyards suggests that the majority of infection throughout the growing season arises via sexually derived (oosporic) inoculum (1). Since downy mildew is relatively new to W.A., few surveys have been conducted to study populations of the pathogen within the state. It is also noteworthy that the incidence of oospores in Australian vineyards has not been reported. The objective of this research was to assess the occurrence and type of inoculum of P. viticola in W.A. vineyards. A total of 1,266 P. viticola-infected leaf discs (LD) from eight wine-grape (775 LD), five table-grape (450 LD), and seven unknown (41 LD) cultivars grown in 16 vineyards in 10 geographically separate regions of W.A. were collected in the growing seasons of 2001-2003. These regions range from Chittering in the north to Albany in the south and received 700 to 1,200 mm annual rainfall, mostly in winter. Each LD was cleared in 1 M KOH at 60°C for 12 to 24 h and then was assessed for the presence of oospores with light microscopy. Leaves showing "mosaic"-type lesions (older infection) late in the season were collected where possible to ensure colony maturity and an increased likelihood of oospore formation. All LD from all regions were negative for the presence of oospores except for samples from a single vineyard (approximately 1,200 mm annual rainfall), where all 140 LD from six wine-grape cultivars contained oospores. The discovery that oospores were present in only one of 16 sampled vineyards provides a rare opportunity to study gene flow in field populations of the pathogen with time and to determine sources of primary inoculum where overwintering of P. viticola may not involve oospores.

Effects of Powdery Mildew of Grape on Carbon Assimilation Mechanisms of Potted `Chardonnay' Grapevines

Potted grapevines (Vitis vinifera L. `Chardonnay') were inoculated with conidial suspensions of the grapevine pathogen causing powdery mildew of grape (GPM) (Uncinula necator (Schw.) Burr.). Leaves of inoculated and noninoculated vines were studied for the effects of varying light (PAR) and CO2 concentrations on factors affecting carbon assimilation. GPM reduced carboxylation efficiency (k), net CO2 assimilation rate (A), stomatal conductance (gs), and internal CO2 concentration (Ci) under ambient CO2, Amax at &gt;900 ppm CO2, stomatal limitations to A (lg), and photochemical efficiency (Φ) on diseased leaves, while having no effect on the CO2 compensation point (Γ) or the light compensation point (cp). GPM had no significant effect on chlorophyll fluorescence (Fv/Fm).

Evaluation of a Disease Warning System for Downy Mildew of Grapes.

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.

Downy mildew of grape.

Downy mildew of grape.

Leaf Hairs as a Basic Protective Barrier against Downy Mildew of Grape

Leaf Hairs as a Basic Protective Barrier against Downy Mildew of Grape

Leaf Hairs as a Basic Protective Barrier against Downy Mildew of Grape

AbstractThe influence of hairs during the interaction of Plasmopara viticola with leaves of four Vitis species was studied both under natural conditions and upon treatment with the detergent Tween 20. The hydrophobic felt consisting of hairs on the adaxial leaf sides repels water from the leaf surface preventing a successful penetration of the host via fungal germ tubes. Treatment with a detergent solution led to an enhanced attachment of water droplets. As a consequence of the detergent treatment, infection structures of P. viticola were formed on the field‐resistant hosts Vitis doaniana and Vitis davidii as in the susceptible Vitis vinifera hosts. It can be concluded that covering the leaf surface with hydrophobic hairs represents a major defence strategy and that the infection process is dependent on wetness. Although in Vitis cinerea and Vitis labrusca primary infection structures can be monitored after detergent treatment, the growth of the fungus was found to be restricted in these species indicating the action of additional or different defence strategies.

Spatial Heterogeneity of the Incidence of Grape Downy Mildew

Heterogeneity of the incidence of downy mildew of grape, caused by Plasmopara viticola, was quantified in an experimental Ohio vineyard. The proportion of diseased leaves on each of 15 shoots (sampling units) per plot was determined for 18 separate plots at two times (generally August and September) during each of 3 yr. The binary data analogue of Taylor's power law, in which the logarithm of the observed variance is regressed on the logarithm of the theoretical variance for a binomial (random) distribution, provided strong and consistent evidence that diseased leaves were aggregated. Year and assessment time did not affect power law parameters. The estimate of the regression slope (b), an overall measure of heterogeneity, was 1.30 (SE = 0.04). Heterogeneity in individual plots was measured with variance ratio and C(α) tests and with the aggregation parameter (θ) of the beta-binomial distribution fitted to the data. Except for mean incidence less than 0.05, the majority of the plots had significant heterogeneity, and the data were better described by the beta-binomial than by the binomial distribution. Estimates of θ were variable but were highest in the middle range of disease incidence. Using the modified power law, sampling curves were generated to precisely estimate disease incidence

Soluble Silicon Sprays Inhibit Powdery Mildew Development on Grape Leaves

The effect of root or leaf applications of soluble Si on severity of grape (Vitis vinifera L.) powdery mildew [Uncinula necator (Schwein) Burrill] was determined. On potted plants, root-feeding at 1.7 mm Si had no effect on disease severity, but foliar sprays at 17 mm Si substantially reduced the number of mildew colonies that developed on inoculated leaves. Scanning electron micrographs showed that, on Si-sprayed leaves, hyphae did not develop in areas where thick Si deposits were present on the leaf surface; and where surface deposits were not present, Si was translocated laterally through the leaf and surrounded the appressoria. Leaves on plants that were fed Si via roots showed a similar deposition of Si surrounding the appressoria. On water-sprayed leaves and leaves from untreated plants, internal deposition of Si was more variable and generally less than on Si-sprayed or root-fed plants. Conidia germination and germtube development on agar media were weakly promoted by the presence of Si. Reduced severity of grape mildew by Si sprays may be partly due to a physical barrier to hyphal penetration and to a resistance response involving the lateral movement of Si and its deposition within the leaf at fungal penetration sites.

Effects of Foliar Diseases on Gas Exchange Processes: A Comparative Study

The effects of 10 different foliar diseases on the photosynthetic and transpirational activities of five annual and three perennial crops were examined under field conditions. The following pathosystems were investigated: leaf rust, powdery mildew, and Septoria tritici blotch of wheat; rust of corn; downy mildew of cucumber; Alternaria leaf spot of cotton; powdery mildew of pepper; Pestalotia of mango; powdery mildew of peach; and powdery mildew of grapes. Visual estimates of infection do not always indicate adequately the effect of a pathogen on these physiological processes (...)

Control of powdery mildew of grapes with plant extracts

Control of powdery mildew of grapes with plant extracts

Climatic Zoning and Plant Disease Potential – Examples from the Near and Middle East1

Actual plant disease and pest occurrence depends on many genetic and environmental factors, and frequently obscures the basic suitability of a given location to support or prevent epidemic development. In order to allow the demarcation of climatic zones related to the potential of disease or pest occurrence, we have used long‐term average climatic data, especially monthly average temperatures and monthly average rainfall. If applied to sugar beet leaf pathogens such as Cercospora beticola and Erysiphe betae in the Near and Middle Eastern region, some interesting zoning became possible, which could be verified by extended field studies. Other examples that have been analysed in the region are apple scab, Venturia inaequalis, and downy mildew of grapes, Plasmopara viticola. A recent and ongoing analysis of the factors controlling chickpea anthracnose caused by Ascochyta rabiei indicates that the same principle may be applied for very different pathogens. Large‐scale planning and control strategies as tried by the International Agricultural Research Centers should therefore be based on careful climatic zoning for plant pest and disease potential, to avoid waste of the limited genetic and financial resources available.

Control of powdery mildew in grapes

Control of powdery mildew in grapes

Control of grape mildew by combined treatment with fungicides

Control of grape mildew by combined treatment with fungicides