advid technical notes 5 grapevine powdery mildew · the disease development. an analysis performed...

ADVIDTechnical Notes

GrapevinePowdery Mildew

5

Series: ADVID Technical Notes

Technical Note 5 - “Grapevine Powdery Mildew”

PUBLISHING DETAILS

Publisher: ADVID - Associação para o Desenvolvimento da Viticultura DurienseText: Maria do Carmo ValPhotographs: ADVID and www.apsnet.orgCoordinator: Fernando Alves, Cristina CarlosYear: 2013

Print run: 100 copiesDistribution: ADVID - Associação para o Desenvolvimento da Viticultura DurienseISBN: 978-989-98368-1-5

Reproduction is authorised provided the source is acknowledged.

Graphic Design: www.hldesign.pt

Contents

m Introductionm Symptomatologym Damages and Losses m Systematics and Taxonomy Description

. Name and Classification

. Descriptionm Biology and Epidemiologym Risk Estimationm Means of Protectionm Decision Makingm Protection Strategy


3GRAPEVINE POWDERY MILDEW

Introduction

Grapevine powdery mildew (PM) caused by Erysiphe necator Schwein (syn. Uncinula necator) is the main disease of grapevines in the Douro Demarcated Region (DDR). The disease originated on the east coast of the USA (1834) and arrived in England in 1845, subsequently invading the rest of Europe between 1847 and 1851. PM quickly became the most important grapevine disease in the world. In 1852, strong attacks caused the loss of 50 to 70% of the production in France, which was the year in which the disease was also detected for the first time in Portugal.In the DDR, this disease manifests with increased aggression, making it demanding in terms of protection and contribu-ting significantly to the consumption of fungicides by the grapevine.Until the 1950s, sulfur was the only means of protection. The appearance of the first synthetic molecules in the mid-1980s allowed for the introduction of new strategies to combat powdery mildew.The losses caused by this disease are significant in terms of both quantity and quality because its presence interferes with the organoleptic characteristics of the wine obtained from the affected grapes.Thus, the objective of this study was to prepare a summary of the identification, biology, control methods, and ade-quate protection strategies for the control of powdery mildew in the DDR.

Symptomatology

PM attacks all organs of the grapevine (i.e., the leaves, petioles, twigs, tendrils, inflorescences, and green berries).A grayish-white powder develops on the upper leaf surface (photo 1) and causes brown spots on the lower leaf surface (photo 2). When the disease manifests at an early stage, the leaves have a crisp and undeveloped appearance. The vine shoots may also be affected, acquiring a whitish or grayish hue. This effect results in dried shoots that are commonly called “flag shoots” (photo 3), which are uncommon in the region.In the vines, the symptoms are manifested by diffuse dark green spots (photo 4) that become brownish and remain throughout the winter. In extremely severe attacks, the vines may become black, compromising their normal propaga-tion.The inflorescences and berries are covered with a grayish white powder (photo 5), with subsequent desiccation of the flower buds. During the initial development phase of the grape cluster, the initial attack of the pedicel, which extends posteriorly to the berry, is noteworthy and typical. Moreover, the development of the fungus only on the pedicels or rachis is also observed (photo 6).If the attacks are severe, then the berries may not develop and eventually dry. When the clusters are more developed and the fruits are larger, the mycelium of the fungus can colonize all or part of the cluster, covering it with an abundant powdery layer (photo 7), which may paralyze growth of the epidermis in the attacked zone and cause cracking of the berries (photo 8).

Photo 1 – Powdery mildew spots on the upper surface of the leaf.

Photo 2 – Brown patches on the lower surface of the leaf.

Photo 3 – “Flag shoots” of powdery mildew.


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Damages and losses

Severe attacks of PM can cause necrosis and death of the leaves, clusters, berries, and even tendrils. The severity of the attack depends on the developmental stage during which the infection occurs, reducing the growth and diminishing the vigor and fertility of the plants with a consequent low yield, potentially leading to the destruction of 80 to 100% in the most severe cases.In turn, when the attacks are localized, they not only allow for the onset of grey rot but also may result in a decreased production potential caused by weight loss due to the percentage of smaller berries and reduction in their number per cluster; in relation to the wine quality, the disease alters the accumulation of sugars, the acidity, the color intensity, and the sensory characteristics.The continuous presence of the disease over several years may contribute to reduce the vigor and fertility of the strains, with a consequent lower yield.

Photo 4 – Diffuse patches of powdery mildew on the vines.

Photo 5 – Inflorescences with powdery mildew (mycelium).

Photo 6 – Pedicel and berries with powdery mildew (mycelium).

Photo 7 – Grape cluster covered with mildew. Photo 8 – Cracking of the fruit caused by powdery mildew.



Systematics and description

a. Name and classification

The fungus that causes grapevine powdery mildew is an obligatory ectoparasite, represented in its perfect form by Erysiphe necator Schwein (syn. Uncinula necator) and its imperfect form by Oidium tuckery (Berk). Identified in 1834 by Schweinitz in North America, the pathogen was classified as Oidium tukeri in 1947.The mycelium of the PM fungus develops on all green organs of the plant and penetrates the epidermal cells through their haustoria, which absorb nutrients. In the asexual or imperfect form, it is known as Oidium tuckeri Berk, and in its sexual or perfect form, it has long been known as Uncinula necator, but was recently classified as Erysiphe necator (Schw.). Based on the morphological and cytological characteristics and its mode of reproduction, this organismo is currently described as the causal agent of powdery mildew and belongs to the kingdom of fung, phylum Ascomycota, class Leotiomycetes, order Erysiphaceae, and genus Erysiphe.

b. Description

The perfect form of PM is characterized by sexual fruit bodies known as cleistothecia, which are spherical bodies (devoid of ostioles) that exhibit a dark color at maturation (photo 9) and are found on the surface of infected organs. Cleistothecia are surrounded by fulcrums (photo 9), which are cylindrical and hyaline when newly formed and contain four to six asci (50-60 μm x 25-40 μm) arranged in a “bouquet.” Each ascus has four to eight unicellular ascospores (photo 9) that are hyaline and ovoid shaped (10-14 μm x 15-25 μm).Cleistothecia are initially yellowish to colorless; the color intensifies with growth of the ascospore diameter, changing from yellow to orange and dark brown during the final phase of maturation.These organs are found from July to August, in temperate climates, on leaves, canes, and berries or on the bark of old wood, where the organs remain trapped by fulcrums (ramifications).

The imperfect form, Oidium tuckeri Berk., develops a hyaline mycelium and ramifications on the surface of organs to be contaminated, thereby developing appressoria, in which the stylets are formed as haustoria that penetrate the interior of the epidermal cells. Asexual reproduction occurs because of the conidiophores, which are found perpendicular to and in a chain on the already formed hyphae (Photo 10).

Photo 9 – Cleistothecia of powdery mildew (various states of maturation); cleistothecia surrounded by fulcrums and ascospores, respectively.


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Biology and Epidemiology

PM may cause two types of symptoms (isolated patches or “flag shoots”) at the time of the first contaminations. During the spring, when the weather conditions are favorable (temperature above 15ºC and relative humidity exceeding 25%), development of the fungus begins. This development may be caused by the germination of the mycelium hibernating in buds, which spore and produce conidia, giving rise to the emergence of “flag shoots”; it can also be caused by the con-tamination of ascospores resulting from cleistothecia, which is considered the main source of the inoculum for primary infections in the DDR. After germination, the ascospores result in the formation of conidiophores and conidia (photo 10), resulting in primary infections and secondary infection cycles (powdery appearance).

Photo 10 – Conidiophores and conidia of powdery mildew and its respective detail (www.apsnet.org).

Days with high relative humidity (40-100%) contribute to the formation of haustoria. In turn, the presence and incidence of strong and direct light inhibits the germination of conidia, which is favored by a diffuse light (days of fog).Wind also contributes to the release and dissemination of conidia and powders by the mechanical effect of the droplets and projected air, the occurrence of rain and any other crop production operation, giving rise to vibrations that favor the release of conidia.Hibernation of the fungus occurs in the form of dormant mycelium on the buds (asexual form) and cleistothecia (sexual form), which, when entrained by the wind and rain, remain lodged in the rhytidome of the strains, in fallen leaves on the ground, and even in the soil itself (figure 1). Cleistothecia, which remain in the soil, appear to have little significance in relation to powdery mildew attacks during the spring, and it is assumed that they are destroyed by hyperparasitism.Throughout the growing season, the disease reproduces and spreads via the conidia, conserving its multiple and diffe-rent forms, depending on the various regions and varieties.



Figure 1- Biological cycle of powdery mildew (Erysiphe necator).

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8

Risk estimation

The estimation of disease risk is based on the knowledge of its biology and epidemiology. A fundamental approach for the protection of the vineyard is to annually adjust the risk strategy so that the objectives in terms of quality and quantity are achieved with as few interventions as possible. To complement this task, in addition to direct observations in the field, infor-mation broadcasted by the Douro Advisory Station (Estação de Avisos do Douro) is extremely important, taking into account all characteristics at the parcel level that are analyzed by the farmer. Monitoring the disease cycle and observation of the first symptoms can be used to predict the risk, with consideration of the key factors in decision support (photo 11 and table 1).These factors may favorably or unfavorably influence the development, proliferation, and harmful effects of the disease (table 1).

Table 1: Harmful factors in assessing the estimate of risk for powdery mildew.

Photo 11 – Control of growth and vigor.

H

arm

ful f

acto

rs

Abiotic • Monitor the evolution of meteorological conditions (temperature, relative humidity, precipitation, and radiation).

Biotic • Development stage of the pathogen• Resistance of the pathogen to fungicides• Inoculum present in the vines

Cultural • Sensitivity of the grape variety (Tinta Roriz, Tinta Amarela, Malvasias, Gouveio…)• Phenological stage (visible clusters and the period between pre-flowering and closing of the clusters) • System of conducting the vine• Control of growth and vigor• Exposure of the vineyard• Soil drainage• Type of plot systematization (level, hillside, and traditional vineyards)

Economic • Hillside vineyards (slopes of the plots)• Fragmentation of the plants and intervention capacity (equipment)



Means of protection

The protection strategy should be essentially preventive, thereby promoting and applying cultural measures that hinder the disease development. An analysis performed each year on the potential aggressiveness of the disease allows the application of cultural measures and other levels of protection to be adjusted according to the following strategies.Selecting the means of protection must involve respecting the principles of integrated protection. Because chemical control is essential for combating powdery mildew, it should be given greater priority than cultural control to improve the effectiveness of the treatments (table 2).

Table 2 – Protective measure for controlling grape powdery mildew.

MEANS OF PROTECTION

Cultu

ral c

ontro

l

Dire

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• Location of the plot, certified plant material selection, and opting for less sensitive varieties that are locally adapted.• Systematization of the land, giving preference to high or terrace vineyards of a bard (one line) that allows access to both sides of the vine and vegetation control on the slope.• Control the plant vigor, rationalizing the fertilization, and watering.• Opt for a system that allows good aeration to the cluster and proper exposure to light.

Indi

rect

met

hods

• Destroy (remove from the plot and burn) pruned canes, leaves, and branches that have spots.• During periods of greater sensitivity, monitor the visible clusters until closing of the clusters.• Detection and evaluation of the intensity of primary infections.• Promote correct orientation of the plant to promote aeration of the clusters (pruning, defoliation, etc.).• Preventive treatments.

Chem

ical

con

trol

• The chemical control should be performed preventively, systematically, and continuously during periods of greater sensitivity – during visible clusters, and between pre-flowering and closing of the cluster.• Give preference to sulfur powder for early applications and during flowering (as long as the weather conditions permit) due to its beneficial effects on fruit ripening. The powder should not be applied at temperatures below 16-18 °C (due to reduced efficacy) or at temperatures above 32 °C (risk of causing phytotoxicity or burning).• During an earlier stage of the plant cycle or when weather conditions limit the action of sulfur, other strategies may be preferred, such as using IBE, QoI, or benzophenone.• Correct use of the approved doses prevents overdoses that favor the development of resistant fungal populations.• Treatment programs in which the families of active substances must be alternated improve the efficacy and prevent the development of resistance.


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Decision Making

The decision to treat requires the selection of fungicides, which must be supported by knowledge of their characteristics so that fungicide application is rational and safe. In terms of methods of action, the chemical substances employed are divided into several families, which should be applied during different stages of the plant cycle due to the limitation under the rules of Integrated Protection (IP) (Table 3).

Table 3 – Anti-powdery mildew fungicides for vineyard approved in IP.

Chemical Families Active substance (form.) Persistence of Action (days)

Characteristics Toxicological Classification

Observations

Contact Sulfur powder (DP)Sulfur (WP)Sulfur (WG)Sulfur (CS)Meptyldinocap

8 - 10 Preventive and curative action, with side effects on mi-tes and phomopsis.

ExXi, IsXi, ExXi, ExXh, H

Do not perform more than three treatments and alternate its use with fungicides that have different modes of action. Maximum of 25 kg/ha per treatment (DP)

IBE (DMI) Fenbuconazole (CE) Myclobutanil (CE, EW)Penconazole (CE)Tebuconazole (CE, ME, WG, EO, WP, EW)Tetraconazole (CE)

14 Penetrating, with preventive and curative action.

Xh, HXh, HXi, HXh, H

H

Limited to two applications/yearLimited to three applications/yearLimited to three applications/yearLimited to two applications/yearLimited to two applications/year

IBE (non DMI) Myclobutanil (CE, EW) 14 Systemic with pre-ventive and curative action

Xh, H Limited to three applications/year

Strobilurin (QoI) Penconazole (CE) 12 -14 Penetrating, with preventive and curative action, acts as an inhibitor of respiration. Due to its characteristic of osmotic diffusion, is not washed by rain.

HXh, HXh, HXi, H

Limited to two applications/yearLimited to three applications/yearLimited to two applications/yearLimited to three applications/yearDo not perform consecutive applications

Fenoxyquinolines Quinazolinones

Tebuconazole (CE, ME, WG, EO, WP, EW)

14 Systemic with local redistribution by the effect of vapor. Preventive action and little healing, inhibits germination of conidia.

DXi, HXh, H

Limited to two applications/yearLimited to four applications/year

Carboxamides Tetraconazole (CE) 14 Preventive, curative and eradicative action. High resis-tance to washing by its binding capacity to the waxy cuticle layer of plant tissues.

Xn, H Limited to three applications/year

Benzophenones Metrafenone (SC) 10 -14 Preventive and healing action in the early phase of infection and anti--sporulating action.

H Limited to two applications/yearAlternate use with fungicides that have different modes of action

Legend: Formulation: CS – concentrated suspension | CE – concentration for emulsion | WP – wettable powder | WG – water dispersible granules | ME – microemulsion EO – emulsion in water and oil | EW – oil emulsion in water | SE – suspo-emulsion | DP – dustable powder (a)– mildew and powdery mildew, simultaneously Toxicological classification: Ex – Exempt | Xi – Irritant | Xh, H – Harmful



Protection strategies

A historical analysis of phytosanitary protection performed in the region, according to the interpretation of the pam-phlets issued by the Douro Advisory Station (DAS) between 1965 and 2012, reveals the evolution of the recommended strategies. There was an increase in the treatments advised after flowering, beginning in the late 1980s (figure 2), which may be associated with climate change due to the appearance of new dams in the region and the introduction of new synthetic fungicides.

Considering that the main source of the inoculum in the region comes from cleistothecia and that the models studied to date still do not allow the occurrence of infections to be accurately predicted, the strategy to combat powdery mildew should be strictly preventive and based on periods of greater sensitivity (i.e., the beginning of flowering until closing of the clusters). For more sensitive plots and grape varieties, this period of the growing cycle should be protected conti-nuously. In cases where the disease remains at closure of the cluster, treatments must be performed until the beginning of color change (figure 3).Additionally, an early treatment may be performed (visible clusters) to limit the initial infection of the leaves and inflo-rescences; this treatment is traditionally performed in the region under the designation “sulfuring the vine shoot” (or “enxofra ao pâmpano”) (figure 3).The interest in early treatment has been studied by several authors during the early phase of primary infections (flag shoots or cleistothecia) with different efficiency gains over the treatment plan throughout the cycle. Several authors found that, in vineyards with a strong presence of “flag shoots”, a combined method of treatments beginning just after sprouting and prompt elimination of the “flag shoots” is the best way to gradually reduce the presence of powdery mildew (Ypema & Gubler, 2000; Speich et al., 2001). In situations of vineyards for which the inoculum source is cleis-tothecia, treatments before flowering present variations in efficiency gains (Collet et al., 1998; Steva et al. 1997; Speich et al. 2001) (Figure 4).The effectiveness of the treatment strategy is strongly linked to the quality of the spraying, the modes of action of the various fungicides, and the timing of the application. Furthermore, the treatment must be applied on both sides, res-pecting the periods of persistence of action of each product. In cases of reported attacks, one should shorten the time interval between the treatments and opt for spraying techniques that allow for preferential treatment directed toward the cluster.Sustainable viticultural practices should be implemented to promote the rational use of pesticides to reduce negative environmental and economic impacts.

0

2

4

6

8

10

65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 01 03 05 07 09 11

before fruit set after fruit set

Number of agricultural warnings.

Anos

Figure 2 – Evolution of the number of agricultural warnings recommending treatments to powdery mildew (source: DAS).


12

Trea

tmen

t per

iod

Plots of greatest sensitivity Period of greatest sensitivity

Vine shoot with visible clusters

Surveillance Pre-flowering Small/hard grapes Closing of the cluster

Figure 3 – Strategy for positioning of treatments.

Figure 4 – Analysis of efficiency gains with early treatment strategies.

Sulfur/IBE/DMI Benzophenone

Quinolones, Strobilurin, Spiroxamine, Benzophenone

2,3% Gain Collect et al, 1998

50% Gain Steva et al, 1997

20-40% Gain Steva et al, 1997

Ypema e Gubler, 2001

Speich et al, 2001

Sulfur powder



References

Alves, F., Almeida, F. (2003) – Contributo para a discussão de estratégias de combate ao oídio da videira Uncinula necator (Schw.) Burr na Região Demarcada do Douro [Contribution to the discussion of strategies to combat powdery mildew on the grapevine Uncinula necator (Schw.) Burr in the Douro Region].Amaro, P. (ed.) (2001) – A proteção Integrada da Vinha na Região Norte [Integrated protection of the grapevine in the northern region]. Projeto PAMAF 6077. ISA/PRESS. Porto, p: 148.Amaro, P. (ed.) (2003) - A Proteção Integrada [Integrated protection]. ISA/Press, p: 446.Calonnec A, Cartolaro P, Deliere L, Chadoeuf J, (2006) - Powdery mildew on grapevine: the date of primary contamina-tion affects disease development on leaves and damage on grape. IOBC/WPRS.Bulletin 29 (11), pp: 67-73.Clerjeau, M. (1999) - Typologie épidémique de lóïdium - Rôle du climat et du végétal. Colloque Européen Oïdium - SOPRA, Toulouse, 7 Janvier. p: 1.Clerjeau, M., Blancard, D., Launes, S., Jailloux, F. (1998) - Facteurs influençant les attaques dóïdiumsur les grappes. PHYTOMA, no. 507 pp: 28-31.Collet L., Magnein C., Boyer J., Muckensturm N., Doublet B., Martinet C., Guery B., Le Gall D., Retaud P., Toussaint P., Bertrand P., Defaut K. (1998) - Raisonnement de la lutte contre lóïdium de la vigne. Quelles périodes protéger en priorité?. Phytoma – La Défense des Végétaux, no. 504, Avril, pp: 50-55.Collet L. (1999) - Lóïdium dans la vigne: 150 ans de lutte chimique. Colloque européen Oïdium - SOPRA,Toulouse, 7 Janvier.Costet, M. F. Corio, Délye, C., Stievenard, C., Douence L., Ronchi, V. (2000) – Biodiversité et résistance aux fongicides de lÒïdium de la vigne. Proc. Meet. Work. Grp. Integrated Control in Viticulture, Florence Mars 99. Bulletin IOBC/SROP. 23 (4).pp: 33-36.Costet, M. F. Corio (2007). Erysiphe necator. Monographies de microbiologie. p: 132Dubos, B., (1999) - Les maladies et les parasites de la vigne. Paisan du Midi. Vol. 1, p: 871.Freitas, J., Val, M. (2005) – Captura de ascósporos de oídio da videira na Região do Douro [Capture of ascospores from powdery mildew of the grapevine in the Douro Region]. Actas VII Encontro Nacional de Protecção Integrada. Instituto Politécnico de Coimbra. December: pp: 145-153.Galet P. (1995) – Précis de Pathologie Viticole. 2ème Edition revue et corrigée, p: 263.Galet, P. (1977) - Les maladies et les parasites de la vigne. Paisan du Midi. Vol. 1, p: 871.Gadoury M., Seem R., Pearson R. C.,Wilcox W., Dunst R. M., (2001)-Effects of powdery mildew on vinegrowth, yield, and quality of Concord grapes. Plant Disease (85): pp: 137-140.MAAPR (Ministère de Làgriculture de Làlimentation de la Pêche et la Ruralité) (2005)- Guide pour une protection durable de la vigne. p: 32.Pearson R. C., Goheen A.C. (1988) - Compendium of Grape Disease. APS Press, St Paul, MN, USA. p: 93.Pearson, R. C., Goheen, A. (2001). Plagas y enfermidades de la vid. The America Phytopathological Society. Ed. Mundi--Prensa. pp: 91.Dubuis, P.H., Bloesch B., Fabre, A. L., Mittaz C., Viret. O. (2011). Situation de l’oïdium en 2010: bonnes pratiques et stra-tégies de lutte. Revue Suisse de Viticulture Arboriculture Horticulture. Vol. 43, no. 1. pp: 78. Speich P., Bourgouin B., Blanc M., (2001) - Raisonner les interventions et gérer les spécialités disponibles. Phytoma - La Défense des Végétaux, no. 535. pp: 24-27.Steva H. Gomes da Silva M.T., Mauranx P., Novoa. (1997) - Lutte contre l´ oïdium de la vigne. Quandfaut-il traiter pour protéger les grappes?. Phytoma – La Défense des Végétaux, no. 490, Janvier, pp: 42:48.Legler S. E., Caffi T., Venuzzi M., Ladurner E., Rossi V. (2011) – New perspectives for the use of Ampelomyces- Based Biofungicides for Effective Control of Powdery Mildew on Grapevine. AFPP-Fourth International Conference on non--Chemical Crop Protection Methods – 8, 9 and 10 March 2011. LilleWillocquet L., Colombet D., Rougier M., Fargues J., Clerjeau M., (1996) - Effects of radiation, especially ultraviolet B, on conidial germination and mycelial growth of grape powdery mildew. European Journal of Plant Pathology, 102, (5): pp: 441-449.Kast W. K., Bleyer K. (2011) – Efficacy of Sprays Applied Against Powdery Mildew (Erysiphe nector) During a Critical Period for Infections of Clusters of Grapevines (Vitis Vinifera). Journal of Plant Pathology, 93 (1), Supplement. pp: 29-32.


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ADVID is a non-profit association set up in 1982 by companies associated with the production and marketing of wine in the Demarcated Douro Region.

Following the change in its statutes in 1997, winegrowing enterprises with different organisational levels, from companies to individual winegrowers, could also join as full or associate members.Its purpose is the study, experimentation, demonstration and dissemination of viticultural techniques suited to the specific characteristics of the Demarcated Douro Region, with a view to the competitiveness and quality of its wines.

Recognised since 2009 as the management entity of the Demarcated Douro Region Wine Cluster, its mission is to contribute to a dynamic and consolidated wine production sector in the Douro Region, through a sustainable technology strategy applied to all its stakeholders.

The following companies are full members:

Adriano Ramos Pinto - Vinhos, S.A.C.ª Geral da Agricultura das Vinhas do Alto DouroChurchill Graham, Lda.Niepoort (Vinhos), S.A.Quinta do Noval - Vinhos, S.A.Rozès, S.A.Sociedade Vinícola Terras de Valdigem, S.A.Sogevinus Fine Wines, S.A.Sogrape Vinhos, S.A.W. & J. Graham & C.ª, S.A.



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Quinta de Sta. Maria, Apartado 137, 5050 - 106 GODIM (PESO DA RÉGUA)

Phone: +351 254 312 940 | Fax: +351 254 321 350

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advid technical notes 5 grapevine powdery mildew · the disease development. an analysis performed...

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