Plant disease control PDF
Preview Plant disease control
PLANT DISEASE CONTROL PLANT DISEASE CONTROL Eric G. Sharvelle, Ph.D. Professor Emeritus Purdue University Lafayette, Indiana avi AVI PUBLISHING COMPANY, INC. Westport, Connecticut © Copyright 1979 by THE AVI PUBUSHING COMPANY, INC. Westport, Connecticut All rights reserved. No part of this work covered by the copyright hereon may be re - produced or used in any form or by any means- graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems—without written permission of the publisher. Library of Congress Cataloging in Publication Data Sharvelle, Eric George. Plant disease control. Includes index. 1. Fungous diseases of plants. 2. Fungi, Phyto- pathogenic—Control. 3. Fungicides. I. Title. [DNLM: 1. Fungicides, Industrial. SB951.3 S532p] SB733.S46 632 79 -16417 ISBN 0 -87055 -335 -6 Printed in the United States of America by Eastern Graphics, Inc., Old Saybrook, Connecticut Preface In this world of energy crises, oil spillage, nuclear proliferation, compu¬ terized technology, social change, and continuing international contro¬ versy, it is difficult to realize that man is still a guest of the plant king¬ dom on this orbiting satellite known as EARTH. Many representatives of Homo sapiens, either in ignorance or in over¬ fed complacency, take flowering plants for granted and have little con¬ cern for, or understanding of, their significance for the welfare of man¬ kind. Even though astronauts from different nations can ride their juggernauts of outer space to meet and exchange greetings hundreds of miles above the surface of the earth, most common people must eat to survive. DAVID FAIRCHILD, the renowned American explorer, once declared, “Agriculture is the source of that element which Plato declared was the most important of them all in the building of a state—FOOD.” Despite our vaunted technological progress in industry and agriculture, the provision of sufficient food for ourselves and for others in the im¬ mediate future is a cause for grave concern for agricultural scientists and for the governments of developing nations with exploding popula¬ tions. The future provision of our daily bread will be no easy task and few people appreciate the technology that is required to provide the thou¬ sands of processed food items displayed in the average supermarket. There are many factors that may and do limit world food production. Among these, the “Crop Robbers,” plant diseases, must be considered as important saboteurs of essential crop yields. For the commercial grower of wheat, rice, soybeans, maize (corn), and fruits, and vegetables—the farmer—a crop failure or a significant reduc¬ tion in productivity may mean the difference between profit and loss. Many farmers in the major corn-producing regions of the world still re¬ member the losses caused by southern corn leaf blight (Helminthospori- um maydis) in 1970-1971 that devastated fields of corn in the U.S. Corn Belt and other regions. Many people who once admired the stately vi PLANT DISEASE CONTROL beauty of the native American elm have mourned its virtual destruction by the Dutch elm disease, and regret the almost complete elimination in the U.S.A. of chestnut trees as a consequence of chestnut blight disease (.Endothia parasitica). These are well known examples of the destructive potential of plant diseases that may attack and destroy many plants both large and small. In agriculturally developed countries crop losses caused by plant dis¬ eases may be tolerated in times of plenty, but in less well developed countries, or following years of low crop yields, these losses become a source of concern for those involved in the task of providing adequate food supplies for the six billion people who will populate the earth at the dawn of the 21st Century. For the grower of plants for pleasure, it is always a source of frustra¬ tion and disillusionment to discover, with experience, that most plants in the home garden rarely look like they are pictured in the seed cata¬ log, and often fall victim to numerous pests and adverse growing condi¬ tions. Only infrequently will garden plants grow to maturity without suffering from environmental hazards that conspire to mar their beauty, reduce their productivity, and sometimes even threaten their existence. When this happens, the Green Thumb Enthusiast is puzzled and con¬ cerned by the parade of ragged roses, puny petunias, tattered tulips, tired turf, spotted strawberries, scabby apples, and other problems that frequently afflict the dwellers of the backyard garden. To prevent plant diseases effectively, a knowledge of their nature and cause is fundamental to successful control. Once the causal agents have been correctly diagnosed, then it is possible to prescribe effective meth¬ ods for their prevention. However, there are no miracle cures for most plant diseases, and, in fact, most plant diseases cannot be cured once they are well established. However, they usually may be prevented by a combination of plant protection principles that are usually necessary for effective protection against the several agencies that may incite plant diseases. Chemicals for plant disease control, the fungicides, are just one of the weapons in our arsenal of defense against unwanted and frequently destructive blights of growing plants. Only infrequently will fungicides work alone to prevent plant disease outbreaks, but when used in combi¬ nation with other methods they are safe and effective remedies for many plant ills. In recent years, usage of chemicals in agriculture, and in the home gar¬ den, has become subject to a veritable barrage of adverse criticism by organic gardeners, some governmental agencies, radio and television performers, a few politicians, and publicity-seeking journalists. Agricul¬ tural chemicals, including fungicides, have become victims of stringent PREFACE vii federal and state regulations under the provisions of the Federal In¬ secticide, Fungicide and Rodenticide Act (FIFRA). Very recently, still further restrictions have been placed on the manufacture and dis¬ tribution of agricultural pesticides under the authority of a process known as “Rebuttable Presumption Against Registration” (RPAR) which requires a detailed assessment of risks and benefits of all pesti¬ cides for which there is some evidence that they may cause unreason¬ able risk to man or the environment. There are now very few commercial products subject to the restrictive regulations governing agricultural pesticides, including fungicides. Fungicides, chemicals for plant disease prevention, are included by a large segment of the public in the same category as those insecticides known to be toxic to humans. Fungicides have been branded along with insecticides by an uninformed public as “Poisons on the American Dining Table.” The controversy on the desirability of using chemicals on essential crop plants will doubtless continue and this textbook will inevitably become a target for criticism by those opposed to the use of any chemical on crop plants that are grown for human or animal con¬ sumption. Ever since the publication of the late Rachel Carson’s “Silent Spring” in 1962, there has been a public plethora of fiction and a paucity of facts printed on the nature and safe uses of chemicals for plant disease con¬ trol. In the minds of many of the laypublic the word “fungicide” is either synonymous with “insecticide” or they have never heard of the word. In fact, fungicides, the plant disease protectants, are usually to be found in the “Insecticide Department” of most department and garden supply stores. Despite the unfavorable publicity and lack of general knowledge con¬ cerning the necessity for plant disease control chemicals, professional fruit and vegetable growers, the commercial florists, and the informed home gardener have accepted and successfully used fungicides as use¬ ful tools in the annual Battle of the Blights on the farm and in the sub¬ urban garden. As early as 1939 the author was working with the distinguished fun¬ gicide expert, Dr. James G. Horsfall, at the Geneva, New York and the New Haven, Connecticut experiment stations in the search for safer and more effective organic chemicals for plant disease control. As a result of this research the first organic fungicide, a derivative of quinone named “Spergon,” was introduced by the U.S. Rubber Company (now known as Uniroyal Chemical Co.). The introduction of this organic, non-mercurial seed protectant was credited with opening the door for further discov¬ ery and introduction of organic chemicals of low mammalian toxicity for the control of plant diseases. Since 1939 virtually all of the modern fungicides have been organic compounds. viii PLANT DISEASE CONTROL In this book an attempt has been made to organize the available in¬ formation on modern tools for the prevention of losses caused by plant diseases. It is hoped that this compilation of fungicide facts will help to draw aside the curtain of confusion and misinformation generated by overzealous environmentalists and misinformed conservationists that has cast a stigma of unfounded belief that chemicals for plant disease control, like some other pesticides of established mammalian toxicity, are poisons on the dining table of the American homeowner, and therefore should be barred from use by professional growers of edible plant products. For more than a quarter of a century the author served as the “Hoosier Plant Doctor” at Purdue University with the major responsibility for preparing plant disease control recommendations for Hoosier farms and backyard gardens. This reference was prepared with the assistance of many professional friends in land-grant universities and the agricultural chemical industry. Their help and contributions are recognized in the Acknowledgements. Appreciation is expressed also to Dr. Norman W. Desrosier and Ms. Karen L. Carter of the AVI Publishing Company for their encouragement and assistance in bringing this book into being. The writer is the author of two other textbooks on plant disease control published in 1960 and 1969, and hopes that this modern reference on plant disease control will constitute a useful reference for professional agriculturalists, university and vocational agriculture teachers, county agricultural agents, representatives of the agricultural chemical indus¬ tries, and for those who enjoy the pastime of growing plants for pleasure. Eric G. Sharvelle Lafayette, Indiana March 1979 Acknowledgements Three difficulties often are incurred in authorship: to write a concise, informative manuscript; to locate an effective publisher; and to encour¬ age wise people to read the final results. With the help of those listed below, I have attempted to surmount the first two problems, and hope that the last difficulty will be resolved. To Purdue University, I am grateful for the privilege of over thirty years’ membership in its distinguished family of “people helpers.” I am also indebted to the following plant pathologists for their con¬ tributions of specific information on plant disease control: Dr. Einar Palm, University of Missouri, Columbia, Missouri Dr. Walter Stevenson, Purdue University, Lafayette, Indiana Dr. Donald Scott, Purdue University, Lafayette, Indiana Dr. Arthur McCain, University of California, Berkeley, California Dr. David Quinn, West Virginia University, Morgantown, West Virginia. To Dr. Donald K. Tressler and Dr. Norman W. Desrosier and their associates in the AVI Publishing Company, my sincere thanks for their acceptance of the manuscript for publication. The professional compe¬ tence and patience of Ms. Karen L. Carter, AVI Publishing Company, in editing and correcting the original manuscript has made this difficult task a much improved and pleasant undertaking. Finally, to “Glib,” my partner of many years in many places, a long deferred acknowledgement for her patience, tolerance, and encourage¬ ment, without which this project could never have been completed. IX
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