Potato Blight Epidemics
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POTATO BLIGHT EPIDEMICS Throughout the World Agriculture Handbook No.174 UNITED STATES DEPARTMENT OF AGRICULTURE POTATO BLIGHT EPIDEMICS Throughout the World By A. E. COX and E. C. LARGE Plant Pathology Laboratory Ministry of Agriculture, Fisheries, and Food Harpenden, England Agriculture Handbook No. 174 Published by Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE Washington,^ ' D. C:^" JanuaryT^ I960ir»/n For sale by the Superintendent of Documents, Government Printing Office, Washington 25, D. C. Price $ FOREWORD Among the important diseases of miajor food crops the late blight of potato is one of the most difficult for us to understand and combat. Despite the intensive studies that have been devoted to it, the conditions for blight occurrence are still not thoroughly known. Frequently, a severe unexplained outbreak of the disease, or its appearance in a region where it was previously unknown, revives problems that had been considered already solved or raises new questions. Observations wherever the disease appears throughout the world contribute knowledge for better understanding and solution of these problems. This worldwide account of recent epidemics of potato late blight provides a useful background of epidemiological information. This Handbook is the first review of conditions as- sociated with late blight outbreaks throughout the world. Its length is due to the inclusion of the detailed information that is necessary to permit comparison between regions and correlation with climatic data. The detail cannot be omitted without lessening the precision and therefore the usefulness of the data. We gladly acknowledge our indebtedness to the authors who undertook this arduous task, and to others of the Plant Pathology Laboratory, Ministry of Agri- culture, Fisheries, and Food, Harpenden, England, who made this study possible. The inception of this collaborative effort was a joint consideration between the Crop Plant Disease Forecasting Project of the Crops Research Division, Agri- cultural Research Service, United States Department of Agriculture, and the De- partment of Plant Pathology, University of Wisconsin, Madison. The program was administered by the Wisconsin Alunrini Research Foundation with funds for conduct of the work provided by the United States Government. The results of this extensive study should be useful to plant pathologists throughout the world and especially to the many plant pathologists of the Crop Plant Disease Forecasting Project. It is hopedthatthe review will provide a basis for additional studies on the impact that plant diseases have on crops and the sub- sequent economic conditions in various parts of the world. ^'^X "Z^X O^^^C^^^^fy^Cd^'.(¿.^>Ly Crops Research Division Agricultural Research Service U. S. Department of Agriculture n PREFACE This study was made possible by the Wisconsin Alumni Research Fovindation, U.S.A., which administered funds for the purpose. Through the efforts of A. J. Riker, University of Wisconsin, who was especially interested in assembling world data about important epidemic plant diseases, the authors were able to undertake a comprehensive review of recent epidemics of potato blight throughout the world. A. E. Cox, agriculturist, and E. C. Large, plant pathologist. Plant Pathology Laboratory, Ministry of Agriculture, Fisheries, and Food, Harpenden, England, under the direc- tion of W. C. Moore, of that Laboratory, worked jointly in making contacts with specialists, in assembling the data, and in preparing the report. The maps and diagrams were prepared by V. J. Pearson, of the above-mentioned Laboratory. The material on which this world study of potato blight has been based was derived in part from published literature, but to a far greater extent it has been based upon unpublished infor- mation generously provided by leading workers in different countries and from England and Wales, verbally or in correspondence with the author s. The help sought by the authors has always been most readily given and has varied greatly in kind. Special acknowledgments are nnade to the library of the U. S. Department of Agriculture and to the following specialists: A. Angus, Northern Rhodesia W. G. Hoyman, U. S. A. G. R. Bates, Southern Rhodesia H. Johannes, Germany F. Beran, Austria P. Journet, France W. Black, Scotland M. A. Keay, Uganda R. Bonde, U. S. A. W. E. Kerr, Southern Rhodesia P. M. A. Bourke, Irish Republic D. Lihnell, Sweden C. J. Briejer, Netherlands M. M. de Lint, Netherlands L. C. Callbeck, Canada T. P. Mclntosh, Scotland L. Caudri, European Plant R. McKay, Irish Republic Protection Organization C. J. Magee, Australia H. T. Cook, U. S. A. P. R. Miller, U. S. A. J. C. CuUen, England A. E. Muskett, Northern Ireland H. M. Darling. U. S. A. R. M. Nattrass, Kenya H. Darpoux, France J. S. Niederhauser, Mexico D. Delaney, Irish Republic L. C. Peterson, U. S. A. R. W. Dickey, U. S. A. J. E. van der Plank, South Africa CM. Driver, New Zealand I. Polykov, U. S. S. R. H. Dubniak, Poland H. N. Racicot, Canada P. Dumas, France H. Richter, Germany A. H. Eddins, U. S. A. E. A. Riley, Tanganyika C. J. Eide, U. S. A. K. Scheibe, Germany S. Fish, Australia C. Bazan de Segura, Peru C. E. Foister, Scotland J. H. Simmonds, Australia E. F^rsund, Norway P. W. Smallfield, New Zealand S, Fridriksson, Iceland J. D. Tallantire, Cameroons G. P. Georghiou, Cyprus H. J. Toxopeus, Netherlands J. Grainger, Scotland J. Ullrich, Germany P. Grainger, Canada R. W. Vasudeva, India E. Gram, Denmark E. Ventura, France E. G. Gray, Scotland G. C. Wade, Australia M. Guntz, France R. W. Wallace, Northern Ireland J. M. Hirst, England J. R. Wallin, U. S. A. D. Hoctor, Irish Republic J. M. Waterston, Cameroons J. C. F. Hopkins, England W. Welvaert, Belgium J. G. ten Houten, Netherlands V. E. Wilkins, European Plant J. L. Howatt, Canada Protection Organization m CONTENTS Page Page INTRODUCTION 1 ASIA- - - 181 Potatoes as a World Crop 3 India - 181 Some Factors Affecting Potato Yields 5 Life History of the Fungus on Po- AUSTRALASIA 185 tatoes 7 **Blight Weather'' -- 9 New Zealand - -- 185 Australia - 191 THE BRITISH ISLES 10 England and Wales - 10 CONCLUSIONS - 196 Scotland 36 Northern Ireland 4-3 The Definition of Climatic Conditions 196 Republic of Ireland 48 Effect of Mean Temperature on Po- tato Cropping 196 CONTINENTAL EUROPE 60 Effect of Rainfall on Potato Growing - I96 Definition of Blight Epidemics I96 France 60 Determination of the Effects of Blight Belgium 67 Epidemics on Yield I97 The Netherlands 71 Frequency of **Blight Years" in Dif- Denmark 85 ferent Regions I97 Iceland 89 Incidence of Blight and Weather Con- Norway 92 ditions 198 Sweden 95 The Duality of the Disease 199 Western Germany 99 The Disease in the Tubers 199 Austria 107 Compensatory Effects on Yield of Poland 109 Blight Epidemics and Rainfall 199 Union of Soviet Socialist Republics - - m Economic Effects of Blight Losses: Cyprus 115 Tropical and Subtropical Regions - - 200 Economic Effects of Blight: Main NORTH AMERICA 118 Potato-Growing Countries 200 Course of Establishment of Blight in United States of America 118 New Areas 201 Canada 140 Carryover of Blight From Season to Mexico 151 Season 201 Effect of Varietal Resistance in Modi- SOUTH AMERICA - 155 fying Blight Epidemics 202 Potato Blight Forecasting 202 Peru -- 155 Protective Spraying: Materials 203 Chile 160 Protective Spraying: Extent of Use- - 203 Protective Spraying: Effect on Control AFRICA 166 of Blight in Tubers 204 Haulm Destruction 204 Union of South Africa 166 Control by *'Disease-Escape'* Meth- Southern Rhodesia 170 ods 205 East Africa 171 Indications of Subjects for Further Kenya - 172 Inquiry 205 Uganda 175 Tanganyika 177 LITERATURE CITED 207 Northern Rhodesia 177 West Africa 178 INDEX 220 IV INTRODUCTION Over a century has now passed since the It would be idle ^:o attempt to de s cribe potato potato late blight fungus, Phytophthora in- blight epidemics except against the background festan s (Mont.) de Bary, found its way from of the distribution and climatic requirements the New World to the Old, and first ravaged of the potato cultivations in which they occur. the potato crops of Europe. Since 1845 the To do this for all countries, and for all the fungus has been the subject of innumerable differing regions in countries extending across studies: The commonly occurring stages of its whole continents, could not be profitably at- life history and the phases of its parasitism tennpted in a couple of years. This study is upon its solanaceous hosts are now well known; therefore confined to a limited number of but, like the true cryptogam that it is, it still countries, and regions within those countries, contrives to conceal much from human scru- which among them probably experience most tiny. After more than a century of search its of the types of epidemic that occur in the world. sexual reproduction by means of oo spore s For each country studied a fairly full section has only recently been found occurring on po- or case study was compiled, after first setting tato plants in the field--in Mexico. The means forth some very brief general observations on by which it succeeds in producing new races the potato as a world crop, and on the life or strains elsewhere in tíie apparent absence history of the fungus, for the assistance of in- of a sexual phase remains a subject of dis- terested readers who maybe neither profes- putation. The relations between sporulation sional agronomists nor plant pathologists. and spread of the fungus and the microclimatic An indication of the world distribution of conditions within potato crops are now under potato growing is given in figure 1. In general, active investigation but are still very im- principal areas of production were chosen for perfectly known; real progress in blight fore- the closest study.