Fungicides in Crop Protection (2nd Revised edition) by H.G. Hewitt and Richard P. Oliver


1658ba7ba6d7a43-261x361.jpg Author H.G. Hewitt and Richard P. Oliver
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Year 2014
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Fungicides in Crop Protection 2nd Edition This page intentionally left blank Fungicides in Crop ­Protection 2nd Edition Richard P. Oliver Curtin University, Australia and H. Geoffrey Hewitt Formerly School of Plant Sciences, University of Reading, UK CABI is a trading name of CAB International CABICABI Nosworthy Way 38 Chauncy Street Wallingford Suite 1002 Oxfordshire OX10 8DE Boston, MA 02111 UKUSA Tel: +44 (0)1491 832111 Fax: +44 (0)1491 833508 E-mail: [email protected] Website: www.cabi.org Tel: +1 800 552 3083 (toll free) E-mail: [email protected] © R.P. Oliver and H.G. Hewitt 2014. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data Oliver, R. P.   Fungicides in crop protection / by Richard P. Oliver, Curtin University, Australia, and H. Geoffrey Hewitt, formerly School of Plant Sciences, University of Reading, UK. -- 2nd edition.    pages cm   Includes bibliographical references and index.  ISBN 978-1-78064-166-9 (hardback : alk. paper) -- ISBN 978-1-78064-167-6 (pbk. : alk. paper) 1. Fungicides. I. Hewitt, H. G. II. Title.   SB951.3.O45 2014  632'.952--dc23 2014002482 ISBN-13: 978 1 78064 166 9 (hbk) 978 1 78064 167 6 (pbk) Commissioning editor: Rachel Cutts Editorial assistant: Alexandra Lainsbury Production editors: Lauren Povey and Tracy Head Typeset by SPi, Pondicherry, India. Printed and bound by Gutenberg Press Ltd, Tarxien, Malta. Contents Preface to the First Editionvii Preface to the Second Editionix 1 Introduction 1 2  Plant Pathology and Plant Pathogens 11 3  The Fungicides Market 21 4  Fungicide Discovery 38 5  Fungicide Performance 71 6  Fungicide Resistance 123 7  Strategy and Tactics in the Use of Fungicides 150 8  Legislation and Regulation 162 9  The Future Prospects for Fungicides and Fungal Disease Control 177 Index 183 v This page intentionally left blank Preface to the First Edition Fungal diseases of crops limit our ability to produce food safely in sufficient quantity and of an acceptable quality to satisfy a rapidly expanding and discerning world population. The discovery and development of effective chemical control emerged only in the mid-19th century and did not become a significant part of crop production until comparatively recently. Current methods of agriculture and horticulture rely heavily upon the use of fungicides to the extent that some crops cannot be grown in their absence. All crops are host to a range of fungal pathogens, many of which cause severe economic damage under suitable conditions. However, fungicide development is driven not by the occasional or regional fungal problems of crops, but by their global value to the manufacturing industry. The need to return sufficient profit from a research investment is becoming more difficult to fulfil under ever increasing legislative stringency and spiralling costs of product development. More and more, the potential benefits of fungicides to growers are being challenged as the levels of economic return to the industry hasten their withdrawal from low-value crops. This book approaches the subject of fungicide use from an economic standpoint. Discovery and development are shown to be dependent firstly upon the capacity of new products to support further research investment, and secondly upon biology. Much of the text describes the chemistry and biochemical mode of action of a wide range of fungicides, but the emphasis is predominantly biological and demonstrates that growers do not purchase clever chemistry but practical performance. Other important features are described which highlight the continuing diversification of an industry seeking to integrate the opportunities available in the use of natural products and their derivatives with biological control systems and in the application of biotechnology to crop protection. Because of the weakening reliance on traditional fungicide use, the industry is now more correctly called a crop protection business. Inevitably there have been casualties in the number of companies trading in chemical control. The drive to continue to fund the discovery and development of new products urges companies to acquire or form partnerships with others in order to gain market size and hence to fund research and registration expenditure. It is from this background of proven benefit, economic constraint, industry change and new technical opportunity that the text launches a description of fungicide use in crop protection. Little weight is placed on application technology or on those aspects of the fungicide industry that are common to herbicides and insecticides, although comparisons are made between the value of each agrochemical sector. Acknowledgements I gratefully acknowledge the encouragement and guidance given to me by colleagues from the agrochemicals industry and academia, especially Dr Mike Smith, Research vii and Development Manager, Novartis (UK) and Professor Peter Ayres, Department of Biological Sciences, Lancaster University. It is also appropriate to thank everyone who, over the last 20 years, has played a key role in showing me that plant science and its application to crop protection is exciting and worthwhile. In that respect, I single out Dr Len Copping for his unfailing support and wit. There were times when I was tempted to abandon the effort and if, in reading the book, you find it useful in any way, then your thanks must go to my wife and family for persuading me to do otherwise. The contribution of Zeneca Agrochemicals in providing the cover illustration of Azoxystrobin (© ZENECA Limited) is gratefully acknowledged. H. Geoffrey Hewitt viii H.G. Hewitt Preface to the Second Edition It is 15 years since the first edition of Fungicides in Crop Protection was published. These 15 years have seen very significant changes in the world of crop protection in general and in fungicides in particular that more than justify the need for an update of this book. The most significant of these changes is the growth in demand for food crops. The world’s population has risen from about 6 billion to 7 billion in that period. Many people eat more meat than before and hence the demand for grain is growing even faster than the population. In clear contrast to the 1990s, we no longer hear about food surpluses. There is an undoubted and urgent need to grow more food, on less land, using less water, fertilizer and other resources and it is clear that fungicides have a major role to play in this. Fungicide utilization has grown significantly in the last decades. In 1998, fungicide use was dominated by Europe and Japan but is now much more widespread. Fungicides are widely used in Asia, Australia, New Zealand and the Americas. Use is particularly heavy in regions producing vulnerable crops such as grape vines and bananas. In some countries, regulations limiting the use of fungicides are becoming ever more rigorous. This is particularly true of the European Union. As a result, about 50% of the pesticides available in 1990 have now been withdrawn. While many of the fungicide classes in use in 1998 are still providing good value, several new classes, especially the quinone outside inhibitor (QoI) and succinate dehydrogenase inhibitor (SDHI) groups, have been introduced. There is a strong pipeline of new compounds especially to combat Oomycota and powdery mildews. The underlying sciences have advanced in important ways. We now have a firm understanding of the evolution of the major groups of target organisms. Oomycota have been clearly differentiated from the true Fungi and we no longer talk about Deuteromycota or the Fungi Imperfecti. Fifteen years ago, it was widely predicted that many crop cultivars would carry transgenes conveying disease resistance. While the area grown to genetically modified (GM) crops has expanded rapidly, these crops generally carry only two GM traits, herbicide resistance and insect tolerance. The failure to develop and release GM disease resistance traits is partly due to the inherent difficulty of developing useful genes, but also due to the widespread public antipathy to GM technology. As a result the regulations are very stringent and so the costs associated with developing GM traits are very high. It remains to be seen whether the next 15 years will witness the widespread introduction of GM disease resistance. The major challenges for the fungicide industry in 2014 are interlinked. It is increasingly more difficult to discover new fungicides and especially new modes of action and to bring such compounds to market. Resistance to fungicides is now a major concern. Genomics is now central to the discovery of new fungicides, determining modes of action and in resistance management. This new edition is designed to introduce this exciting and critical world of fungicide use in crop protection. ix Acknowledgements I gratefully acknowledge the cooperation of Geoff Hewitt, the author of the first edition. This edition has been prepared with the help of many people in the fungicide industry who have provided me with insight into the world of fungicides over the last 15 years. These include Andy Leadbeater, Derek Hollomon, Craig White, Craig Ruchs, Craig Pensini, Jenny Davidson, Doug Wilson, Fran Lopez, Frank van den Bosch, Gavin Heard, Geoff Robertson, Gerd Stammler, Hans Cools, Ian Dry, Kithsiri Jayasena, Ken McKee, Kevin Bodnaruk, Lise Nystrup Jørgensen, Michael Csukai, Naomi Pain, Neil Paveley, Nick Poole, Paul Chatfield, Peter Hobbelen, Rick Horbury, Scott Paton, Geoff Thomas, John Lucas, Bart Fraaije, Andy Corran, James Brown and many others. I am grateful to Rothamsted Research for help in selecting images for the front cover. Thanks also go to Kasia Rybak, Wesley Mair and Fran Lopez for supplying photographs and tables. Research in the author’s laboratory is funded mainly by the Australian Grains Research and Development Corporation and the Grape and Wine Research and Development Corporation. Richard P. Oliver x R.P. Oliver 1 Introduction Fungicides are agents, of natural or synthetic origin, which act to protect plants against invasion by fungi and/or to eradicate established fungal infection. With herbicides, insecticides and plant growth regulators, they form the battery of agrochemicals (also known as pesticides) that is available to protect crops and maintain their yield potential, measured as the quantity or quality of produce. Diseases of crops are caused by a vast range of organisms that include the true fungi (e.g. Ascomycota and Basidiomycota), fungal-like but unrelated Oomycota (e.g. Phytophthora and Pythium), Plasmodiophora, bacteria, viruses and nematodes. The term fungicide is conventionally taken to mean compounds that control the true fungi, Plasmodiophora and the Oomycota. It does not include chemicals that control bacteria (these compounds are conventionally called antibiotics), viruses (mainly controlled by insecticides) or nematodes (mainly controlled by genetic and cultural methods). Since the discovery of the various types of pesticide, several factors have ensured their continued use and the growth of the pesticide businesses. They include an increasing world population, higher incomes and direct benefits both to the grower, such as lower labour costs, higher yields and greater profit, and to the consumer, such as a higher consistency of food quality, increased variety of produce and lower prices. Population Growth and Food Production For most of recorded history, the global population growth rate has been below 0.2% per annum. However, the early 19th century witnessed the beginning of an accelerating advance in the control of human disease and in the consistent ability of growers to produce cheaper, higher quality food and a varied diet, which initiated a reduction in mortality rates. In industrialized countries birth rates remained high initially, resulting in a rapid increase in population growth. What we know as the ‘developed’ world passed through that initial phase and has a low growth rate once again. However, the population of the ‘developing’ world is still expanding rapidly. The world population is currently estimated at 7 billion, having increased from 6 billion just 15 years ago (http://esa.un.org/wpp/unpp/panel_population.htm). There is clearly a need for more food to be produced and delivered to the world’s population; currently an estimated 25,000 persons die from malnutrition each day (Skamnioti and Gurr, 2009). Conservative estimates predict a world population of 10 billion by 2060. An increasing proportion of the world’s population is demanding a diet that is higher in dairy and meat produce. The animals are increasingly fed on grain. The area of land available to grow all these crops is under threat from urbanization, pollution and climate change. There is a clear and urgent need to produce © R.P. Oliver and H.G. Hewitt 2014. Fungicides in Crop Protection, 2nd Edition (R.P. Oliver and H.G. Hewitt) 1 more food that is nutritious and safe on less land, using less water and fertilizers. And the evidence is convincing that fungicides have had and will increasingly have a major role to play. Historically, the world’s demand for food has been met largely through an expansion of the area under cropping and by improvements in the food distribution network. The increased food needs of Western Europe in the 19th century, for example, were supplied by the expansion of production in the Americas and Australasia. The 20th century introduced a technological revolution into agriculture which has made possible a rapid rate of growth of food production to feed a historically unprecedented growth of world population. Central to the growth in food production was the development of artificial fertilizers and high-yielding crop varieties – the Green Revolution (Evenson and Gollin, 2003). The high yields increased disease levels. This both increased the need for fungicides and justified their costs. Agriculture makes a significant impact on global warming (Berry et al., 2010). About a seventh of all greenhouse gas (GHG) emissions can be ascribed to agriculture. These include direct use of fossil fuels for transport and tillage, indirect use of fossil fuels for nitrogen fertilizer production, and GHG emission due to soil microbe release of methane and nitrogen oxides. It is therefore possible to quantify food production not just on a tonne per hectare basis but also on a tonne per GHG emission basis. Such studies consistently show that the disease control and green leaf area d ­ uration promoted by appropriate use of fungicides maximizes both food production per hectare and per GHG equivalent (Berry et al., 2008). It is therefore somewhat ­ provocatively argued that fungicide-based agriculture is the most ‘ecological’. Recent studies of disease losses and fungicide use have been made in Australia (Murray and Brennan, 2009, 2010). Australia has a generally low rainfall and poor soils, giving average cereal yields in the range of 1–2 t/ha. These are conditions in which disease levels would be expected to be low by world standards. It is sobering that even under these close-to-ideal conditions, pathogens still cause percentage losses in major, highly researched crops of up to 30% (Table 1.1). Table 1.2 details the absolute actual loss in Australian dollars in comparison to the loss expected if no control methods (genetics, cultural or fungicide) were applied. The difference between the potential loss and the actual has been apportioned to each of the major control methods. It is clear that fungicides have a very significant role in protecting yield. This varies between disease, crop, variety and season, but overall the annual AUS$250 million expenditure on fungicides in Australia generates a return of AUS$2000 million; an 8 to 1 ratio. Table 1.1.  Current estimates of losses due to disease in major crops in Australia. (Modified from Murray and Brennan, 2009, 2010.) Crop Wheat Barley Field pea 2 % yield lost to diseases 18.0 13.5 29.6 Chapter 1 Table 1.2.  Breakdown of losses to disease and gains to genetic, cultural and chemical disease control in selected grain crop diseases in Australia; all figures are in AUS$ million. The ‘potential loss’ is the loss incurred if no control measures were in place; the ‘actual loss’ is the current estimate. The difference between potential and actual is assigned to either genetic control, cultural practices or fungicide control. It is clear even in low-input, sustainable agriculture situations like Australia that fungicides contribute heavily to disease control. (From Murray and Brennan, 2009, 2010.) Disease Tan spot Stripe rust Septoria nodorum Barley mildew Potential loss Actual loss Genetic control Cultural control Fungicide control 676 868 230 103 212 127 108 39 200 431 36 10 155 78 51 3 108 359 35 52 Agricultural Technology and the Impact of Fungicide Use Crop production is a process governed by a series of limiting factors which interrelate. These are crop variety (i.e. the varying degree of genetic disease resistance), nutrition, water supply and crop management (pest, weed and disease control, cultivation). Each factor may assume a dominant, yield-limiting role, depending upon the crop, husbandry practices and the region. For example, water availability is the major factor governing plant distribution and in crops it is often the determining factor in yield production. Historically, the combined action of early improvements in irrigation and the introduction of new varieties with higher genetic potential for yield resulted in dramatic yield increases. Later, the use of fertilizers relieved the limitations to yield dictated by nutrient deficiency and allowed the inherent yield capacity of the crop to be realized to a point that was limited by weed populations, insect infestation and disease. In the 20th century, intensive breeding programmes have further improved the genetic potential for yield in many crops and their capability to respond to other inputs such as fertilizers and agrochemicals. One of the consequences of increased fertilizer use is more frequent and damaging attacks by fungi, and in intensively grown crops their control is a significant factor in yield determination. However, to a large extent the development and use of pesticides have permitted an even greater use of fertilizer and further increases in yield. Since the 1940s, the search for new fungicides has intensified and the total value of the crop protection business, as fungicide sales, now stands at US$13 billion, compared with US$6 billion in 1995 (http://www.amisglobal.com/). The economics of pesticide use vary from crop to crop, between targets and according to the levels of weed, insect or disease infestation. Recent studies in Australia document the gain of AUS$8 for every AUS$1 spent on fungicides (Murray and Brennan, 2009, 2010). This figure is driven by the sharp reductions in the cost to farmers for some fungicides in the last 10–15 years. The cost of off-patent fungicides has fallen to less than AUS$5/ha and so disease gains need only be small to justify the costs. The value gained from the use of small amounts of fungicide to control seed-borne diseases is very large. More modest but still significant gains are obtained when controlling foliar diseases. The use of cereal fungicides in Western Introduction 3 Europe probably accounts for an extra 2–3 million t of grain annually, equal to US$400–600 million. In some cases the benefit gained through fungicide use is more critical to the extent that certain crops cannot be cultivated in the absence of disease control. By the late 1800s coffee rust epidemics were a serious and frequent problem in India, Sri Lanka and Africa. Eventually, production levels became uneconomic and stimulated a change in cropping from coffee to tea. The recovery of the coffee industry was, and remains, totally dependent on the use of fungicides. The impact of fungicide use on wheat in the UK is illustrated in Fig. 1.1. The average yield of wheat in the UK increased from about 4 to 8 t/ha from 1960 to 2004. During this period, first methyl benzimidazole carbamate (MBC), then demethylation inhibitor (DMI) and finally quinone outside inhibitor (QoI) fungicides were introduced. Each introduction coincided with a further increase in yield. The History of Fungicide Use The devastating social effects of plant disease are a common feature of history, extending into Biblical times and beyond with references to ‘blasting and mildew’ in the books of Deuteronomy and Amos (Large, 1940/2003). Wheat rusts were known 9 100 8 90 80 7 Yield (t/ha) 60 5 50 4 40 3 30 2 20 1 0 1960 % of crops sprayed 70 6 10 0 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 Year MBCs DMIs Qols Fig. 1.1.  Average wheat yields in the UK, 1960 to 2004 ( ; original data source: Cereal Production Surveys, Defra), introduction of the main fungicide groups (arrowed; MBCs, methyl benzimidazole carbamates; DMIs, demethylation inhibitors; QoIs, quinone outside inhibitors) and percentage of crops sprayed with fungicides ( ▲ ; original data source: Polley and Thomas, 1991; Crop Monitor, Defra/CSL). (From Lucas, 2006 with permission from HGCA.) 4 Chapter 1 at least from Roman times and were considered so important that their occurrence was attributed to divine action. Regular festivals to appease the gods Robigus and Robigo were held in the hope that cereal rust disease could be prevented. However, the gods were clearly not to be trusted and some rudimentary chemical disease control was also practised, the therapeutic but mysterious nature of sulfur being passed down from the ancient Greeks. Other than crop failure, fungal disease can have a dramatic and direct effect upon human welfare. In 943, a European chronicler described the ‘wailing and writhing’ of men in the street suffering from a disease which came to be known as ‘St Anthony’s fire’, named after the behaviour of people who, in hope of a cure, visited the shrine of St Anthony in France. The cause is now known to be rye grain contaminated with the alkaloids present in the ergot fungus Claviceps purpurea. By 1750, cereal diseases had attained such a significant economic status in Europe that the French Academy of Arts and Sciences volunteered a prize for the best treatise describing the cause and control of wheat bunt. The solution was not forthcoming and 10 years later up to half of the French wheat crop failed because of bunt and smut (Ustilago nuda) diseases. Mathieu Tillet eventually characterized the causal organism of bunt, which carries his name, Tilletia tritici, and went on to describe the life cycle of the fungus. Of equal importance was the work, based on a series of field experiments, which examined the efficacy of various treatments against T. tritici. It was demonstrated that crops treated with various materials mixed with lime or putrefied urine could be maintained relatively free from bunt disease and these treatments came to be of major economic importance in France. The catalogue of incidents of fungal disease during the 19th century is extensive (Table 1.3). However, the social impact of plant disease was at its greatest where potatoes were the staple diet. In those regions threats of famine were common and in Eastern Europe and Ireland reached dramatic reality. In Ireland alone, in the 15 years from 1845, over 1 million people died and 1.5 million were forced to emigrate as a direct result, mainly to the USA. Table 1.3.  Major outbreaks of fungal disease in the 19th century. Crop Pathogen Cereals Hops Potatoes Vines Vines Vines Vines Coffee Vines Cereals Cereals Cereals Cereals Claviceps purpurea (ergot) Sphaerotheca humuli (powdery mildew) Phytophthora infestans (late blight) Uncinula necator (powdery mildew) U. necator (powdery mildew) U. necator (powdery mildew) Plasmopara viticola (downy mildew) Hemileia vastatrix (coffee rust) Guignardia bidwellii (black rot) Puccinia spp. (rust) Puccinia spp. (rust) Puccinia spp. (rust) Puccinia spp. (rust) Year reported 1816 1840 1845 1845 1848 1851 1865 1869 1880 1889 1892 1894 1916 Region France England Europe England France Europe France Sri Lanka France Austria Prussia USA Canada, Denmark, Russia, Argentina, South Africa, India Introduction 5 Commercially, plant disease was a critical factor in the survival of some industries. The vine industry, for example, was under continual attack; first from grape powdery mildew (UNCNEC – see Chapter 2 for pathogen abbreviations), initially observed in England in 1845, and then followed in the late 1860s by grape downy mildew (PLASVIT). Out of necessity, this period also witnessed the beginnings of modern fungicide use. Observations by the gardener who first reported UNCNEC in England suggested that applications of sulfur could be used to control the disease. Although his findings were confirmed by Professor Duchartre of the Institut Agronomique, Versailles, the challenge to produce a product that could be applied easily to an extensive area of vineyards was not successful until 1855, when Bequerel produced a fine form of sulfur that could be used to achieve effective plant coverage. Similar advances were made in 1885 with Millardet’s invention of Bordeaux mixture, copper sulfate and lime, for the control of PLASVIT, later shown to be effective against late blight in potatoes (PHYTIN). Several versions of the treatment were explored but the mixture is still in use today for the control of fungal diseases on a wide range of crops. The technology developed in France in response to the frequency and severity of crop disease, especially in vines, became the stimulus for other international investigations. This led, in 1886, to a large programme of trials in the USA to evaluate all the leading French fungicides against black rot, Guignardia bidwellii, on vines; apple scab, VENTIN; gooseberry mildew, Sphaerotheca fuliginea; and several vegetable pathogens. This collaboration between the US Department of Agriculture (USDA) and French experts was one of the first to examine the relationship of dose–response, cost of spray per hectare, optimum timing and phytotoxicity. However, the problem of cereal rust disease that had persisted throughout this period of fungicide development evaded similar attempts at control. Farmers resorted to the use of resistant varieties and altered crop management practices to combat the disease. Little success was achieved and by the turn of the 19th century, world wheat production could be severely limited by rust infection, a situation destined to remain until the advent of systemic fungicides in the mid-1960s. Other crops also suffered from rust diseases. In 1869, coffee rust was reported in what became Sri Lanka, and in 10 years reduced average yields by over 50% to 251 kg/ha. The effective destruction of the coffee industry led to investment in a replacement crop, tea. Henceforth, the cultivation of coffee in India and Sri Lanka was totally dependent on the use of fungicides to control rust disease. An excellent and lively introduction to the social history of plant pathology can be found in Money (2006). The use of complex organic chemistry began with the introduction of new seed treatments designed for the control of wheat bunt. Studies in the pharmaceutical industry which developed medicinal compounds made from arsenic and various dyestuff intermediates stimulated similar research by German plant pathologists, and resulted in the synthesis of several phenolic fungicides containing metallic elements such as mercury, copper and tin. The discovery by the Bayer Company of a compound containing mercury and chlorinated phenol, active against wheat bunt, prompted the intensive development of organomercury seed treatments; the first, Uspulam, being introduced in 1915 by Bayer, followed by Ceresan from ICI (1929) and Agrosan G, also from ICI (1933). The efficacy of these products ensured their widespread popularity in the farming community and they led the cereal seed-treatment 6 Chapter 1 market until mercury-based products were banned in the 1970s and 1980s on the grounds of adverse toxicology. The establishment of the commercial organizations that would become the major companies in the agrochemicals industry began in the late 1850s, but significant development did not occur until the late 1940s. During the First World War (1914–1918) in Europe agriculture had responded to the need for self-sufficiency, but after the crisis the incentives were reduced and agriculture retreated into its former uncertainty fuelled by poor wages and fluctuating prices. It was not until after the Second World War (1939–1945) that the potential of fungicide use in crop protection and the maintenance of yield were realized, and it is generally accepted that this marks the real beginning of crop fungicide technology. The early fungicides business was founded on the control of crop diseases that previously had been unchecked and competition between companies was relatively light. Most of the products that were introduced were in response to clear needs of growers and they created new markets by exploiting latent demand. Later products improved on existing control and were established at the expense of their lesser competitors. This is particularly true of the introduction of fungicides that were able to move within plants and throughout crops, the so-called systemic or mobile materials, which captured a significant part of the market previously held by surface-bound non-systemic (immobile) products such as sulfur and copper-based materials. Fungi infect plants through wounds or directly via stomata or penetration of the surface layers. In leaves this barrier is further enhanced by the presence of a sometimes thick and waxy cuticle. Before the development of systemics in the late 1960s, all fungicide compounds were non-systemic protectants, effecting disease control only through their activity on the plant surface. Characteristically, after application to foliage these compounds control disease either by killing superficial mycelium, as for example in the powdery mildews that penetrate only the topmost cellular layer, or more commonly by preventing the germination of fungal spores already present on the leaf or impacting on the leaf after application. Non-systemics cannot penetrate the leaf and hence cannot control pathogens already established within the plant tissue. Therefore foliage must be treated before the pathogen has colonized the plant. Subsequent development of the plant exposes new tissues to fungal attack and may rupture protective fungicide deposits. Hence, such products have to be applied frequently during the growing season to maintain acceptable disease control levels. Although the lack of mobility of early fungicides limited their flexibility of use, their inability to penetrate plant tissue allowed them to exploit the control spectrum inherent in their non-specific biochemical mode of action (MOA). This remains a valuable feature in their current uses against minor pathogens and in strategies to control resistance to systemic fungicides. The introduction of systemic compounds caused a revolution in farmer practice and in fungicide discovery and development. New opportunities for fungicides were immediately identified, as in intensive cereal production in Western Europe. Fungal diseases of wheat and barley had been a disturbing feature of cereal production for at least 2000 years but the use of resistant varieties, stimulated in part by the failure of early products to control pathogens such as mildew and rust, enabled infection to remain at what was considered to be an acceptable level. The associated yield losses were estimated to be insignificant until systemic fungicides were discovered and tested, beginning with ethirimol and tridemorph. Introduction 7 Field trials demonstrated that the yield benefits that could be achieved using the new fungicides were on average about 10%. Yields increased further as the limits of varietal potential were explored using combinations of higher fertilizer inputs and fungicides. European Community legislation encouraged high-output production systems, and inputs such as the use of high levels of fertilizers and pest control chemicals increased to maximize yields. The rate of discovery of new and more effective fungicides also increased and in 20 years the range of foliar and ear diseases for which some control could be claimed had expanded from a few seed-borne pathogens and mildews to include PUCCRT, LEPTNO, SEPTRI, Fusarium, Pyrenophora, Pseudocercosporella, Cochliobolus and Rhynchosporium. The new products afforded better levels and duration of control and allowed the grower more flexibility in application. However, even they failed to provide complete disease control, and the search for more effective materials and technology continues. The appearance of systemic fungicides and the increasing variety of products available to the grower corresponded with the requirement of the fungicides industry to adopt new and higher standards of performance. The most important was, and remains, safety to the manufacturer, the user, the consumer of treated crops and all aspects of the environment. The industry and government registration authorities became responsible for the development of only those materials proven to be safe and environmentally acceptable. In addition, in order to compete successfully, product attributes other than biological activity assumed major roles (Table 1.4). The number of products and mixtures grew to meet the new market standards of disease control. In the triazole family alone there are on average about ten products (different formulations of solo active ingredients and mixtures) per compound. Many fungicides appear to increase yield beyond that attributable to the reduction of disease. Late-season treatment with benomyl, an early systemic fungicide, was shown to delay senescence and increase yield by up to 10% through a combination of fungicidal action and plant growth regulator effects. Similar activity is reported for QoI Table 1.4.  General targets for new fungicidal products. Attribute Type of product improvement Safety Safe to users Environmentally acceptable Safe to consumers of the treated product Broader disease-control spectrum Extended control period Increased reliability Anti-resistance activity Improved crop safety Compatibility with other products Easy-to-use formulations Safe application Lower cost per treatment through the use of:   cheaper fungicides   lower use rates   fewer treatments per season   lower application costs Performance Use Cost 8 Chapter 1 and succinate dehydrogenase inhibitor (SDHI) fungicides and is associated with the control of phylloplane organisms and, more likely, a direct effect on the maintenance of photosynthetic ability. Devastating crop diseases and their social impact can now be avoided by the careful use of fungicides. Yet, as in any living system, the threat posed by fungal disease is dynamic and we cannot afford to be complacent. If any one crop can be identified as having stimulated the growth of the fungicide business and been the subject of intensive fungicide use, then it must grapevine. But it appears that even in vines new problems can emerge. In 1977, Eutypa armeniacae was identified in France and by 1996 an estimated 50% of all vines in the Cognac region were infected, causing a total loss of about 10%. Once again, the official advice is to destroy affected vines while waiting for new fungicidal treatments to be developed or for the arrival of genetically engineered resistant varieties. There is little doubt that the intensive agricultural systems that are needed to provide the growing population with food also encourage fungal disease epidemics, and the removal of fungicides from agriculture does not appear to be a realistic option. The emergence of fungicide resistance and the need for more cost-effective products encourage the search for better remedies, whether they be synthetic products or materials derived from natural sources or through the introduction of genetic modification of target crops. The Growth of the Agrochemicals Industry Pesticides, synonymous with agrochemicals or crop protection agents, comprise mainly herbicides, insecticides, fungicides and plant growth regulators. Further definition can be confusing. A pesticide is strictly an agent that kills a pest and it can be either synthetic or natural. However, the definition omits plant growth regulators, which are designed to enhance the growth and development of crops directly. In addition, the term pesticide is often applied only to insecticides. Pesticides are better classified as agents that maintain the yield potential of crops under adverse growing conditions, most commonly caused by the presence of weeds, fungi or insects. In other words, pesticides combat biotic stresses. Agrochemicals companies developed as a diversification of those chemical industries specializing in the manufacture of organic dyestuffs. Originally including the fertilizer industry, the agrochemicals business is now distinct and comprises a large, high-value, high-technology industry that survives upon innovation and the discovery and development of synthetic and natural pesticidal products. Despite the success of the pesticides business, the industry is shrinking. The conflicting forces of price competition, affecting margins and profitability, and the increasing costs of discovery and development of potential products and the maintenance of established pesticides have resulted in a phase of consolidation. The situation was made more acute through the increased political and social recognition of the environmental issues associated with pesticide use and the subsequent demand for more extensive product examination. This led to spiralling increases in the costs of safety testing, the prolongation of development time and a subsequent reduction in effective patent life. A shorter product lifespan and the need to generate a return on a rapidly increasing research and development investment have stimulated the search for economies of scale such that the Introduction 9

Author H.G. Hewitt and Richard P. Oliver Isbn 1780641664 File size 4MB Year 2014 Pages 192 Language English File format PDF Category Biology Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare Plant pathogenic fungi cause devastating damage to crop production worldwide. The growing global population necessitates reduced crop losses to improve food security, and the control of fungal plant pathogens is vital to help maintain food production. Providing a concise and balanced review of fungicides used in crop protection, this book describes the science of fungicide use, selection and resistance within the context of farming situations. Major updates and additions reflecting the emergence of two new classes of fungicides (strobilurins and SDHI) and the increased incidence of fungicide resistance are included in this new edition, which also discusses legislative requirements to reduce fungicide applications, and current trends in fungicide use.     Download (4MB) Plant Breeding Reviews, Volume 40 Silicon in Plants: Advances and Future Prospects Growth And Mineral Nutrition Of Field Crops, Third Edition World Economic Plants: A Standard Reference, Second Edition Nitrogen Management in Crop Production Load more posts

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