COMMUNAUTE FRANCAISE DE BELGIQUE ACADEMIE UNIVERSITAIRE WALLONIE-EUROPE UNIVERSITE DE LIEGE − GEMBLOUX AGRO-BIO TECH Innovative strategies for the control of apple scab ( Venturia inaequalis [Cke.] Wint.) in organic apple production Laurent JAMAR Dissertation originale présentée en vue de l’obtention du grade de Docteur en sciences agronomiques et ingénierie biologique Thesis submitted for the Doctorate in Agricultural Sciences and Biological Engineering Promoteurs (Supervisors): Mr Philippe Lepoivre Mr Marc Lateur - 2011 - © Copyright. Under the terms of the Belgian Copyright and Fees Act of 30 June 1994 only the author has the right to reproduce this work in part or in full in any way and form whatsoever or to authorise its partial or full reproduction in any way and in any form whatsoever. Photocopying or reproducing this work in another form is therefore a breach of that Act and subsequent amendments thereto. Summary / Résumé JAMAR Laurent (2011) −−− Innovative strategies for the control of apple scab ( Venturia inaequalis [Cke.] Wint.) in organic apple production (Thèse de doctorat). University of Liege −−− Gembloux Agro-Bio Tech, Belgium. 188 pages, 21 tables, 34 figures. The aim of this thesis, conducted over six growing seasons (2003 −2008), is to define new measures for reducing the use of fungicides and in particular, copper fungicides, for the control of apple scab ( V. inaequalis ) in organic apple production. Special emphasis is put on primary scab infection control during spring season. An original approach is proposed for defining a specific spray timing involving spraying during the infection processes, especially before fungal penetration, determined by the RIMpro software warning system. This ‘during-infection’ spray strategy allows reducing from 30 to 50% the amount of fungicide usually used for effective apple scab control, on high scab-susceptible cultivars. The field study shows that six alternative products (e.g., potassium bicarbonate and lime sulphur), among 60 products tested, have the potential to reduce copper use. However, copper use, even with low doses, seems to be still necessary in presence of scab-susceptible cultivars. The results obtained in these experiments could not be attributed to the specific technical performances of the tunnel sprayer used, which however, offer valuable environmental benefits. On the basis of the present study, the organic management system seems a good farming approach for maintaining soil quality with regard to biological indicators. This work shows and draws attention to the fact that (i) planting cultivars with polygenic scab- resistance traits, (ii) increasing emphasis on sanitation practices aimed at reducing initial inoculum in autumn, and (iii) applying an accurate spray strategy in spring, as defined in the present study, are the three most promising approaches for substantial further reductions in protection products fully compliant with international organic crop production standards. JAMAR Laurent (2011) −−− Stratégies innovantes de protection vis-à-vis de la tavelure du pommier (Venturia inaequalis [Cke.] Wint.) en production biologique. (Thèse de doctorat). Université de Liège −−− Gembloux Agro-Bio Tech, Belgique. 188 pages, 21 tableaux, 34 figures. L’objectif de cette thèse, conduite durant six saisons de croissance (2003-2008), est de définir des nouvelles mesures de réduction d’usage de fongicides, en particulier du cuivre, pour se protéger de la tavelure du pommier ( V. inaequalis ) en production biologique. L’accent est mis sur la protection des arbres lors des infections primaires au printemps. Une approche originale est proposée pour définir les moments d’application des traitements, spécifiquement durant les processus d’infection, avant pénétration du champignon, déterminés à l’aide du logiciel d’avertissement RIMpro. Cette stratégie dite «durant- infection », permet de réduire de 30 à 50% la quantité de fongicide habituellement utilisée pour assurer une protection efficace, sur variétés sensibles. L’étude en verger montre que six produits alternatifs (par ex., bicarbonate de potassium et bouillie sulfocalcique), parmi 60 produits expérimentés, ont le potentiel de réduire l’usage du cuivre. Cependant, le cuivre, même à faibles doses, semble être encore nécessaire en présence de variétés sensibles à la tavelure. Les résultats obtenus dans ces expérimentations ne peuvent pas être attribués aux performances techniques du pulvérisateur tunnel utilisé, qui cependant, offre de précieux avantages sur le plan environnemental. Sur base de cette étude, le système de production biologique semble une bonne approche pour maintenir la qualité du sol du point de vue de ses indicateurs biologiques. Ce travail montre et porte l’attention sur le fait que (i) planter des variétés à composante polygénique de résistance, dites tolérantes à la tavelure (ii) accroitre l’accent sur les pratiques sanitaires visant à réduire l’inoculum initial, et (iii) appliquer une stratégie de traitement adéquate au printemps, telle que celle décrite dans cette étude, sont les trois approches les plus prometteuses pour réduire l’usage futur de fongicides à un niveau plus cohérent avec le règlement international de production biologique. Acknowledgments Over 8 years, while working on the apple scab disease, I have learned a lot in the field of science and I owe this learning to many people. This work could not have been achieved without the help and support of a great number of people to whom I would like to express my gratitude. First, I would like to express my sincere gratitude to Dr Marc Lateur, Life Sciences Unit, Walloon Agricultural Research Centre (CRA-W), co-promoter of this thesis, whose expertise, precision and patience added considerably to my scientific experience. I appreciate his passion, enthusiasm and generosity, as well as his vast theoretical and technical knowledge about fruits and cultivars. I am also grateful to him for trusting me and for his assistance in writing reports and publications. Special thanks go out to Prof. Haïssam Jijakli and Philippe Lepoivre, Phytopathology Unit, ULG −Gembloux Agro-Bio Tech, co-promoters of this thesis, for their guidance and contributions throughout the process of the study and writing this paper. I would like to thank Prof. Hugo Magein (CRA-W) and Dr. Luciana Parisi (INRA-UERI Gotheron) for taking time out from their schedule to be my external readers. My acknowledgments also go to Prof. Hugo Magein and his technical team for the many practical way they helped in the experimental orchard and for sharing materials and tractors. I want to express special thanks to Marc Cavelier, ex-director of the Biocontrol & Plant Genetic Resources Department of the CRA-W, as well as Bruno Lefrancq and Isabelle Villette, my colleagues, for their valuable co-operation within the Department. It was a real pleasure to collaborate with them. Special thanks to those who assisted, reviewed and commented on this work, including: O. Mostade, B. Huyghebaert, O. Pigeon, S. Pekel, G. Dubois, C. Fassotte and H. Magein (CRA-W, Gembloux) and M. Aubinet, M. Culot, M. Yernaux and T. Fievez (ULG −Gembloux Agro-Bio Tech). I would like to thank Dr R. Oger and Dr.V. Planchon (CRA-W, Gembloux) for their valuable help in the statistical analysis. Special thanks to P. Marc (Horpi Systems s.a., Visé), P. Thiry (GAWI asbl, Visé), P. Creemers and C. De Schaetsen (PCF-KOG, St-Truiden) and R. Stiévenard (CRRG, ENR, Villeneuve d’Ascq) for stimulating discussions during this study. Thanks to the Fruit Tree Genetic Resources & Breeding technical team, mainly Bertrand Pahaut, Pascal Dupont, Laurent Delpierre, Alain Rondia, Johana Pestana, David Dantinne, Christophe Poirson, Thibaut Donis, Pascale Bacquet, Marie-Laure Decraemer and Nicole Demory, for their technical support and excellent co-operation during the whole research project. This research would not have been possible without the financial support and assistance, over 8 years, of the Head Office of the Agriculture-Ministry of the Walloon Regional Government, General Department of Agriculture, Research Direction, or without the technical support provided by the Walloon Agricultural Research Centre. Finally, I would like to thank my whole family for their support and patience over these years. In particular, I wish to thank my wife, Lidia, as well as my three children, Aïda, Nicolas and Naomé. TABLE OF CONTENTS GENERAL INTRODUCTION ......................................................................................................................... 1 I CHAPTER I : LITERATURE REVIEW............................................................................................... 11 I.1. APPLE SCAB (VENTURIA INAEQUALIS ) ........................................................................................................ 11 I.1.1. Biology ....................................................................................................................................... 11 I.1.2. Epidemiology.............................................................................................................................. 15 I. 2. SCAB CONTROL STRATEGIES .................................................................................................................... 19 I.1.3. Resistance to scab in Malus ....................................................................................................... 19 I.1.4. Cultural practices and prophylactic measures affecting scab epidemics..................................