EVALUATION OF THE OF EARLY POWDERY MILDEW CONTROL AND THE
ASCOSPORES RELEASE IN VINEYARDS AT DOURO REGION
ÉVALUATION DU CONTROLE DE L'OÏDIUM PRECOCE ET LIBERATION DES ASCOSPORES
DANS LES VIGNOBLES DE LA REGION DU DOURO
Carmo VAL1, *, Fernando ALVES 1, António SILVESTRE2 & Isabel CORTEZ2
1
-ADVID – Associação para o Desenvolvimento da Viticultura Duriense, Quinta de Santa Maria, Apt. 137, 5050-106 Godim, Portugal
(email: [email protected], [email protected]).
2
-CITAB - UTAD Universidade de Trás-os-Montes e Alto Douro, Apartado 1013; 5001-801 Vila Real, Portugal
*Corresponding author: Val, +351 254312940, Fax, +351 254321350 Email: [email protected]
ABSTRACT
Powdery mildew is the most harmful disease of grapevines in Douro region. To control this disease the use of fungicides takes a greater
importance in different strategies. However there are not a consensus about the start and efficiency of the fungicide applications at the
ascospores release, which occurs usually in February-March and the development of the disease during the season. The main objective of this
work was to evaluate different treatment strategies in early phenological stages (stage 14 until stage 57) where the release of ascospores is
greater. Also have the goal to contribute for the rationalizing the interventions in a steep slope vineyard, reducing treatments.
The experiment was conducted in the Douro Wine Region, in a vineyard located at Cima Corgo, with the cv Tinta Roriz (Tempranillo)
during two seasons. The monitoring of the ascospores release started at the phenological stage “dormant bud”, using glass microscope slides.
The experimental design consisted in four modalities with four replicates: 1T - control; 2T - three sprays with sulfour were applied starting at
budbreak; 3T - sprays started at inflorescence fully developed (BBCH 57), which is the common practice in Douro, and the second spray was
at pre-blooming and 4T - the spraying started only at pre-blooming with a DMI. After blooming all the treatments, with exception of the
control, were sprayed at the same time with the same product. The severity of powdery mildew was assessed in grapes and leaves, based on
the scale of OEPP (1981) in three different periods. At harvest proceeded to the evaluation of the percentage of powdery mildew (%), yield
and fruit composition. Although the early release of ascospores, the disease development only begins near the flowering. The preliminary
results reveal significant differences to the control, but no difference between the treatments 2T, 3T and 4T which move strategies to reduce
the interest of the earliest sprays saving interventions in the vineyard.
Keywords: powdery mildew, vineyard management.
RESUME
L'oïdium est la maladie la plus dangereuse de la vigne dans la région du Douro. Pour lutter contre cette maladie l'utilisation de fongicides
prend une plus grande importance dans les stratégies différentes. Cependant, il n’y a pas de consensus sur le lancement et l'efficacité des
applications de fongicides à la libération des ascospores, qui survient généralement en Février-Mars et le développement de la maladie au
cours de la saison. L'objectif principal de ce travail était d'évaluer différentes stratégies de traitement dans les premiers stades phénologique
(débourrement jusqu'à la préfloraison) où la libération des ascospores est plus grande. Ont également pour but de contribuer pour les
traitements de rationaliser les interventions dans un vignoble pente raide, réduisant. L’expérience a été menée dans la région viticole du
Douro, dans un vignoble situé à Cima Corgo, avec le Roriz cv Tinta (Tempranillo) pendant deux saisons. Le suivi de la libération des
ascospores commencé au stade "bourgeon dormant" phénologique, en utilisant des lames de microscope en verre. Le dispositif expérimental
a consisté en quatre modalités avec quatre répétitions: 1T - contrôle; 2T - trois pulvérisations ont été appliquées avec sulfour à partir de
débourrement; 3T - pulvérisations ont commencé à inflorescence complètement développée (BBCH 57), qui est la pratique courante dans le
Douro, et la deuxième pulvérisation était à préfloraison et 4T - la pulvérisation a commencé seulement au stage 57 avec un DMI. Après la
floraison tous les traitements, à l'exception de la commande, ont été pulvérisés en même temps avec le même produit. La gravité de l'oïdium
a été évaluée dans les raisins et les feuilles, en fonction de l'ampleur des OEPP (1981) en trois périodes différentes. A la récolte, a procédé à
l'évaluation du pourcentage de l'oïdium (%), le rendement et la composition du fruit. Bien que la libération anticipée des ascospores, le
développement de la maladie commence seulement à proximité de la floraison. Les résultats préliminaires révèlent des différences
significatives au contrôle, mais aucune différence entre les traitements 2T, 3T et 4T qui se déplacent stratégies visant à réduire l'intérêt des
premiers jets d'épargne interventions dans le vignoble.
Mots-clés: oïdium, la conduite du vignoble.
INTRODUTION
The causal fungus of grapevine powdery mildew is an obligatory ectoparasite shown in its perfect form by
Erysiphe necator Schwein (syn. Uncinula necator) and its imperfect form by Oidium tuckery (Berk) (Pearson
and Goheen, 2001).
In the Douro Region (RDD) the overwinter occurs mainly in the form of chasmothecia the "drapeaux" (flag
shots) are rarely seen, and it is assumed that the first infections were caused by ascospores (Freitas et al 2005).
This disease manifests itself more aggressively, becoming demanding in terms of protection and contributing
significantly to the consumption of fungicides (Calonnec A., et al. 2006). The level of fungicides utilization is
considered undesirable, both for toxicological and ecotoxicological as the risk of development of resistance to
the fungal applied products (Legler, S., et al. 2011).
The damages caused by powdery mildew remains important both in terms of quantity as of quality, since their
presence interferes with the organoleptic characteristics of the wine grapes. By other side there aren`t efficient
method`s for forecasting epidemics development by ascospores and to predict the timing and severity of primary
infections (Calonnec A., et al. 2008).
Thus, the aim of this study was to evaluate and discuss various treatment strategies, positioning applications at
an earlier stage in the early growth stages (exit leaves to pre-flowering), and try to relate the development of
disease symptoms with earliness and intensity of release of ascospores.
MATERIALS AND1 METHODS
The experiment was conducted in the Douro Wine Region, in a vineyard located at Cima Corgo, with the cv
Tinta Roriz (Tempranillo) during two consecutive seasons. The monitoring of the ascospores release started at
the phenological stage “dormant bud”, using glass microscope slides. The experimental design consisted in four
modalities with four replicates (fully randomized blocks): 1T - control; 2T - three sprays with sulfur were
applied starting at bud break; 3T - sprays started at inflorescence fully developed (BBCH 57), which is the
common practice in Douro, and the second spray was at pre-blooming and 4T - the spraying started only at stage
57 with a DMI. After blooming all the treatments, with exception of the control, were sprayed at the same time
with the same product. The severity of powdery mildew was assessed in grapes and leaves, based on the scale of
OEPP (1981) in three different periods. At harvest proceeded to the evaluation of the percentage of powdery
mildew (%), yield and fruit composition. Although the early release of ascospores, the disease development only
begins near the flowering.
The field trial was conducted a (latitude 41 º N 0910.55, 3658.24 The 7 º longitude, altitude 235m), located in
the municipality in the Adorigo (Tabuaço), at the sub region’s Cima Corgo of the Douro Region.
Monitoring for catching ascospores of powdery mildew was made only in 2011 In experimental plot still being
dormant, were placed randomly on March 11, three metal brackets U-shaped with blades which contained a thin
layer of lanolin the inner face facing the strain to capture and sequestration of ascospores designed. This
accounted for an exposed area of 72cm2 as a whole and was replaced each time after the occurrence of
precipitation. Later they were transported to the laboratory where they were previously blue stained cotton,
covered with plates (24x55mm) and observed under the microscope (magnification 125x) for display, counting
and recording the number of ascospores captured (figure I).
The treatments used in the plot are shown in the table I as well as the respective dates, active substances applied
dose and the growth stages (the data was examined through Anova followed by means separation (Tukey test),
done with SPSS 19.0 for Windows (SPSS Inc., Chicago, IL, USA).
A sampling of clusters was made in three different seasons in the year 2011. The first on 23 May, when the
vineyard was in the process of ripening, the second a14 June, when the vineyard was in pea berry phenological
state and the third on July 7, when the vineyard was in full closure bunch. In 2012, due to the delay of the season
at the initial stage, only two samples were taken. The first on June 13, when the vineyard was in lead grain of
Monday July 5, when the vineyard was at the closing of the bunch.
At harvest was performed on 10 vines per replication (5 bard on the inside and 5 outside the bard) a final
evaluation where there was the percentage of powdery mildew on bunches, because at this stage the leaves
already have many types impairing visualization of spots of powdery mildew, the average yield of bunches
(AYB), the number of bunches per vine (NB) and the weight per vine production (WVP (kg)).
The vintage vines selected for the test was done at the place where they also held the records of production /
vine, with the aid of a scale type dynamometer (pictured), proceeding at the same time to record the number of
clusters corresponding to each vine.
RESULTS AND DISCUSSION
The ascospores release began at least on March 18th and occurred till June 2nd with coincidence among the
release picks and the episodes of rain, except on two dates (on May 5th it rained and there was not a strong
ascospores release and on May 23rd it did not rain and there was a ascospores pick discharge) (Figure 1).
The efficacy of the first spraying on the development of the disease and its effect was evaluated by determination
of the percentage of infected clusters, the yield (kg) per vine (WPV), the number of bunches per vine (NB) and
the average weight of bunches (AYB) on the treatments.
In 2011, the disease presented with high expression in the demarcated Douro region due to heavy rainfall
occurred in the months of April and May associated with high temperatures recorded during the same period. In
2012, despite the different weather conditions are with less precipitation occurred, the disease was also present
but with less intensity. For the strategy used found that the percentages of attack of the disease, in two
consecutive years, in different modalities (T2, T3 and T4) showed good results when compared with the control
(T1 - without treatments). With regard to the effectiveness of different positions of treatments, we found that
during the test there were no significant differences between T2, T3 and T4, only the control (T1 - no treatment)
has been a strong development of disease throughout the year indicating a strong attack intensity, severity of
powdery mildew was greater (P <0.05) compared to previous methods. In T1 and T3, the number of clusters
(NB) / vine was very similar, with an average of 15 clusters. The modality with the highest number of bunches /
vine was T4. With regard to the yield per vine, in all modalities, the results were different, with T1 with the
lowest yield per vine, due the lowest average bunch weight value. In the evaluations, the evolution of the
intensity powdery mildew, at three different times (stage 71, 77 and 89 (BBCH Scale)) always found a greater
attack in T1 mode (statistically different P <0.05) when compared with T2, T3 and T4 (Figure 2). Among T2, T3
and T4 there were no significant differences in the intensity of the attack of the disease. We can observe that in
the modality T4 (early treatments to pre-flowering), in assessing the stage 71 and stage 89, the intensity of the
disease was recorded slightly lower in the T2 and T3 modalities.
CONCLUSIONS
The results of this work show strongly the importance of treatment in pre-flowering period when the first spots
usually appear. In the absence of flags, as in the Douro region a disease control strategy aimed at controlling the
ascosporic infections early in the season maintained the disease at a very low level during flowering and early
berry formation, which is the period when bunches are most susceptible to the disease, could be controlled
effectively with fewer fungicide applications in the early season.
The early treatments don´t show a significantly increase in the control efficacy of the disease, as also stated by
Alves et al, 2003. Some authors have studied the interest of early treatment in the early phase of primary
infections (flags or cleistotecas) with different efficiencies on the treatment plan throughout the cycle. Already
(Ypema and Gubler, 2000; Speich et al. 2001) found that in vineyards with a strong presence of "flags", a
combined method of treatment, beginning soon after sprouting, and expeditious elimination of "flags" are the
best means for gradually reducing the presence of powdery mildew. On one hand, in case of vines whose source
of inoculum is from cleistotecas, treatments before flowering, exhibit variations in efficiencies (Collet et al.
1998; Steva et al. 1997; Speich et al. 2001).
Given the importance, growing, to reduce the use of fungicides may likely result in less chemical waste in
products consumed by a public-health, also considering environmental benefits. Each treatment represents a
quantity (l / ha) in fuel consumption which is reflected in the reduction of CO2 emissions (Caffi, T. et al; 2012).
ACKNOWLEDGEMENTS
The authors thanks to the Sogevinus farm in the person of Eng. Manso, for having made available the plot, and
for the help done to this trial.
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