Potato Health Management, Second Edition

Front cover photograph by William J. Schaefer, used by permission Back cover photograph (left) by Dennis A. Johnson

Mention of various pesticides is made throughout this book. To the best knowledge of the editor, these pesticides were registered for use on potatoes in the United States or Canada at the time of this writing.

Pesticide labels are constantly changing, and thus current labels must be in hand at the time of pesticide use, and applications must be made in strict accordance with these labels. Mention of specific pesticides in this book is to be construed not as a recommendation or endorsement of their use but rather as information for readers of this book to consider when devising their own potato health management plans.

Reference in this publication to a trademark, proprietary product, or company name by personnel of the U.S. Department of Agriculture or anyone else is intended for explicit description only and does not imply approval or recommendation to the exclusion of others that may be suitable.

Library of Congress Control Number: 2007935822 International Standard Book Number: 978-0-89054-353-5 © 1993, 2008 by The American Phytopathological Society First edition published 1993 Second edition published 2008 All rights reserved.

No portion of this book may be reproduced in any form, including photocopy, microfilm, information storage and retrieval system, computer database, or software, or by any means, including electronic or mechanical, without written permission from the publisher.

Copyright is not claimed in any portion of this work written by U.S. government employees as a part of their official duties.

Printed in the United States of America on acid-free paper The American Phytopathological Society 3340 Pilot Knob Road St. Paul, Minnesota 55121, USA

Dedication

The Land-Grant Mission The Morrill Land-Grant College Act of 1862, which established a state university or land-grant college in every state, was possible only because of foresight and persistence.

It initiated a series of legislation that revolutionized higher education and extended research-based knowledge and technology to agriculture and industry nationwide. In the midst of the Civil War, which preoccupied the nation from 1861 to 1865, as the young republic fought for survival, the Morrill Act was passed by Congress and signed by Abraham Lincoln, setting a course for true change—extending higher education to the “common people” and enabling agricultural and industrial production to achieve levels never before envisioned.

The passage of the bill was the culmination of a long and often bitter fight. The land-grant idea was championed throughout the North by farm organizations, labor unions, educators, preachers, newspapers, and public-spirited reformers. One of the first supporters was Jonathan Baldwin Turner, of Illinois, who espoused the creation of “industrial universities” financed with land endowments to each state.

Later, Horace Greeley’s New York Tribune advocated a system of people’s colleges. Hard-driving New York businessman Ezra Cornell threw himself into the educational reform movement, with the belief that higher education should be a democratic possession. Thomas Clemson, son-in-law of John C. Calhoun, added support from the South. Justin Morrill, of Vermont, authored the legislation (Nevins, 1962).

Land-grant institutions replaced the old-style classical curriculum with one that championed science and included agriculture and mechanical arts. Higher education, which had been accessible primarily to the sons of the leisure class, government leaders, and members of the professions, was opened to the common people. It has been said that no true university existed in the United States before the land-grant system was created (Nevins, 1962). The land-grant philosophy evolved further through legislation to fund scientific and agricultural research at state agricultural experiment stations (the Hatch Act of 1887) and to extend new knowledge to farmers and industry through the Cooperative Extension Service (the Smith-Lever Act of 1914). A second Morrill Act, in 1890, provided college access to blacks, and legisla-

tion in 1994 established Native American tribal colleges and funded universities serving Hispanic students.

Greater educational access and equality of opportunity were the primary goals of the land-grant movement. The principal motivation for change was the belief that every person should have the opportunity to complete an education as his or her tastes and abilities warranted. Education is not just for aristocrats and the wealthy; it is for all people. At the heart of the land-grant movement was the idea that liberty and equality could not survive unless all people had the opportunity to pursue all occupations at the highest practicable level (Nevins, 1962).

As a result of the land-grant college acts, there is at least one land-grant institution in every state and territory of the United States and the District of Columbia. Out of nearly 100 major state universities and colleges in the United States, about 70 are land-grant institutions. They enroll the majority of students and award the majority of all graduate degrees in the United States (Nevins, 1962). Agricultural experiment stations and extension programs in every state have played major roles in promoting scientific knowledge and increasing agricultural production. The land-grant system, along with favorable soils, water, and climate, a free-market system, and a hard-working people, has been a major factor in the development of America’s tremendous agricultural strength.

Society and agriculture have changed greatly since the land-grant system was created. The United States is now mostly urban, with less than 2% of the population involved in farming. Educational and employment opportunities are vastly more diverse. Agriculture has become a major business, rather than a way of life. Research is focused on basic rather than applied topics. Diminishing proportions of federal and state money currently support the land-grant system. For example, less than 27% of budgeted funds at Washington State University in 2005 was provided by state appropriations. Students pay a relatively high percentage of the cost of education, and private sources and federal grants are required to fund research and to extend new technologies and information. Less financial support from federal and state sources is projected for the future. Land-grant universities iii

iv • DEDICATION are becoming privatized, in a reversion to the pre-land-grant era. The land-grant system may all be history in the near future.

Commitment is needed for the land-grant mission to continue and to build on its success—commitment from landgrant institutions and those who work there to continue to pursue research that yields economic and social returns while maintaining environmental quality, along with commitment from state and federal decision makers to provide adequate and consistent funding for university instruction, agricultural

and natural resource research, and the extension of technology to agriculture and business.

This book is dedicated to the future and continued success of the land-grant mission and American agriculture.

Reference Nevins, Allan. 1962. The Origins of the Land-Grant Colleges and State Universities: A Brief Account of the Morrill Act of 1862 and Its Results. Civil War Centennial Commission, Washington, DC.

Preface tenths of the potato crop in Ireland was destroyed, and the epidemic spread across Europe. Additional crop failures in following years further extended the devastation. One million Irish died, and another 1.5 million emigrated to North America as a result of the famine. More recently, migrations of the A2 mating type likely occurred in the late 1970s into Europe and in the 1990s into North America (Fry and Goodwin, 1997).

In contrast to the early agricultural system in the highlands of Peru, where several staple crops and multiple potato cultivars were grown, the Irish relied on a single, genetically uniform staple crop. Crop uniformity and a lack of understanding of the potato plant, the pathogen, and how both are affected by the environment intensified the Irish late blight epidemic.

Modern agriculture has made great strides since the Irish Potato Famine. However, late blight and many other diseases and pests are still not adequately managed. Many problems challenge modern agriculture. Today, not only are satisfactory yields, quality, and markets needed, but also human health and the environment must be protected. North American agriculture competes in a global market, with fierce competition from areas of the world with inexpensive labor. Energy inputs in agriculture are high and expensive. Markets are sometimes restricted because of political decisions. Environmental conditions and legal decisions dictate that production practices be modified to protect human health and the environment. All these factors are pushing modern agriculture toward more management-intensive systems.

Potato production is no exception. To thrive, production management strategies must be improved at all levels. A better understanding of both the potato plant and the underlying principles of modern pest and disease management is needed, along with an appreciation of how various factors interact to affect the overall health of the potato crop. A comprehensive, integrated strategy for potato health management must be implemented that results in a high-quality product, reasonable profit, and environmental health. This is holistic health management, as explained in Chapter 1.

A holistic approach to potato health management is emphasized throughout this book. Our goals are twofold: first,

Potatoes have been cultivated in the Andean highlands of South America for at least 8,000 years and were a staple crop of the native peoples of Peru when the Spanish explorers arrived in the mid-1500s. The agriculture of the Incas and their predecessors was sustained by planting a diversity of crop species and multiple potato cultivars; practicing fallowing, crop rotation, and multiple cropping; adding organic amendments to the soil; planting on raised beds; using sanitation practices and tillage; and altering the time of planting to avoid pest outbreaks (Thurston, 1994). These practices were discovered through trial and error and intentionally integrated over time to support a sustained food supply for human survival (Thurston, 1994). Today, successful agriculture requires more uniform products and energy-intensive inputs. The fundamental goals of both past and present production strategies, however, are similar: stability, resilience, productivity, and efficiency. Agricultural systems of the past are much different and cannot feed the millions of people that modern agriculture currently does, except we are now beginning to recognize the value of sound, sustainable practices, similar to those of the Andean people thousands of years ago.

The potato has hundreds of pests (weeds, deleterious insects, and rodents) and pathogens (disease-causing agents, including nematodes, fungi, oomycetes, bacteria, phytoplasmas, and viruses). Many pest and disease problems have followed potatoes to wherever they are grown, because the potato is vegetatively propagated from tubers, which easily carry some pathogens and pests. Some pathogens and pests were transported to new locations as the potato was moved from South America throughout the world.

The late blight pathogen migrated on seed tubers throughout the world on several different occasions. Evidence indicates that the causal organism originated in central Mexico, and the A1 mating type was carried to the eastern United States, eastern Canada, and northern Europe in the early 1840s. Late blight was unknown in Europe until it devastated the Irish potato crop in 1845, causing the infamous Irish Potato Famine. The moist, mild weather typical of Ireland favored the development of late blight, which spread like wildfire first in the latter part of the 1845 growing season and then in full force during much of the 1846 season. Ninev

vi • PREFACE to provide the most current information on potato production practices, with an emphasis on pest and disease management, and, second, to provide a knowledge base so that these practices can be integrated into a comprehensive management scheme in the context of today’s agriculture.

Some constraints encountered in culturing and storing potatoes are still not adequately addressed, because of insufficient knowledge. A lack of scientific knowledge contributed to the Irish late blight epidemic; likewise, it is a contributing factor for the crop constraints we must currently manage.

Research funded through the land-grant system and other sources has greatly enhanced agricultural production, but additional research is warranted if a stable agriculture system is to meet today’s needs. For example, cultivars resistant to many insect pests and diseases are needed. Relatively few resistant potato cultivars are available, in comparison to small grains, in which extensive breeding efforts have produced a wealth of resistant cultivars that are widely grown. The relatively small number of resistant potato cultivars is not due to a lack of genetic resources in potato but rather is due to past decisions to manage potato pests and diseases with what were then relatively inexpensive pesticides with broad-spectrum activity. Profits from potatoes, per unit of area, are greater than profits from small grains, and thus pesticides have gen-

erally been more affordable for potato production, allowing breeders to focus their efforts on quality factors. Today, pesticides are more expensive, and society has come to realize that there are environmental benefits from utilizing host resistance. As a result, research is ongoing to develop potato cultivars with durable resistance to disease and insect pests and to learn how to culture, process, and market these new cultivars. Research is also needed in many other areas, such as soil health and how to promote it. The challenge today is to keep potato production viable and strong through research and to apply the new knowledge in a holistic approach in managing potato health.

Dennis A. Johnson and Randall C. Rowe

References Fry, W. E., and Goodwin, S. B. 1997. Re-emergence of potato and tomato late blight in the United States. Plant Disease 81:1349– 1357.

Thurston, H. D. 1994. Andean potato culture: 5,000 years of experience with sustainable agriculture. Pages 6–13 in: Advances in Potato Pest Biology and Management. G. W. Zehnder, M. L. Powelson, R. K. Jansson, and K. V. Raman, eds. American Phytopathological Society, St. Paul, MN.

Acknowledgments This book is the result of the dedicated efforts of many people. Planning began in the summer of 2004, when Rose Gergerich, Editor-in-Chief of APS Press, requested that the first edition of Potato Health Management be revised. The first edition was a tremendous success, with over 7,000 copies sold. However, new research had been conducted and several diseases and pests had emerged since the printing of the first edition, and it was time to include this information in a revision of the book. Randy Rowe edited the first edition, and it served as a solid foundation for this revision. I thank him for that publication.

The best decision I made as editor was in selecting the steering committee: Mary Powelson, Randy Rowe, Walt Stevenson, and Bob Thornton. These four are dedicated plant scientists with solid backgrounds in potato research and the potato industry, and each has keen editorial skills that helped me greatly. We initially met for a day-long meeting at the headquarters of the American Phytopathological Society (APS), in St. Paul, Minnesota, in October 2004. There we decided on the organization of the book, the contents, chapter topics, and the principal author of each chapter. Subsequently, we met various times in groups of two or three, and

each member of the committee additionally met or corresponded with me on several occasions and offered extremely valuable counsel. Each member of the steering committee thoroughly reviewed and edited each chapter and then reread either portions of the book or the entire book as the manuscript was submitted for peer review. I greatly appreciate the advice and editorial suggestions given me by each of them.

For each chapter, a scientist knowledgeable about the topic was invited to be the principal author, and that person then selected co-authors when desired. I thank the authors for their contributions and most authors for meeting timelines. Tim Paulitz served as APS Press Senior Editor, reviewed the entire manuscript, and organized a peer review by two anonymous scientists. I appreciate their help and contributions. I thank Ryan Johnson and Brenda Schroeder for suggestions on specific chapters. I also thank Maegan Davis for drawing several of the illustrations and Erin and Frank Jones for clerical and technical help. The APS headquarters staff handled the production of the book, and I thank them for their dedicated service.

Dennis A. Johnson

Contents Chapter 1

1

Potato Health Management: A Holistic Approach

Randall C. Rowe and Mary L. Powelson Chapter 2

7

Checklist for a Holistic Potato Health Management Plan Jeffrey S. Miller and Bryan G. Hopkins

Chapter 3

11

Soil Health: Managing the Soil Microora to Enhance Potato Health

Linda Kinkel Chapter 4

15

Economics of Potato Plant Health

Joseph F. Guenthner and R. Thomas Schotzko Chapter 5

23

Selecting and Preparing the Planting Site

Mike Thornton, Jeff Stark, Bryan G. Hopkins, and Robert E. Thornton Chapter 6

31

Quality Seed: Seed Improvement, Cultivar and Seed Lot Selection, and CertiďŹ cation

Jonathan L. Whitworth and Robert D. Davidson Chapter 7

43

Seed Tuber Health Before and During Planting

Gary A. Secor and Steven B. Johnson Chapter 8

55

Managing Potato Fertility

Jeff Stark and Dale Westermann Chapter 9

67

Potato Health from Sprouting to Harvest

Neil C. Gudmestad Chapter 10

79

Maintaining Tuber Health During Harvest, Storage, and Post-Storage Handling

N. Richard Knowles and Edwin S. Plissey

vii

viii • CONTENTS Chapter 11

101

Organic Potato Production

Bryan G. Hopkins and Ronda E. Hirnyck Chapter 12

109

Managing Potatoes in the Home Garden

Thomas F. Cummings and Robert E. Thornton Chapter 13

113

Applying Pesticides

Philip B. Hamm, Rick A. Boydston, Casey W. Hoy, Walter R. Stevenson, and Pamela J. S. Hutchinson Chapter 14

123

Managing Pesticide Resistance

Philip B. Hamm, Casey W. Hoy, Pamela J. S. Hutchinson, Walter R. Stevenson, Rick A. Boydston, Juan Manuel Alvarez, Andrei Alyokhin, Galen Dively, Neil C. Gudmestad, and William W. Kirk Chapter 15

133

Managing Insect and Mite Pests

Casey W. Hoy, Gilles Boiteau, Andrei Alyokhin, Galen Dively, and Juan Manuel Alvarez Chapter 16

149

Managing Aphids and Leafhoppers

David W. Ragsdale, Edward B. Radcliffe, and Kathy L. Flanders Chapter 17

161

Managing Diseases Caused by Viruses, Viroids, and Phytoplasmas

James M. Crosslin, Philip B. Hamm, Keith S. Pike, Thomas M. Mowry, Phillip Nolte, and Hassan Mojtahedi Chapter 18

171

Managing Soft Rot and Ring Rot

Solke H. De Boer Chapter 19

183

Managing Diseases Caused by Seedborne and Soilborne Fungi and Fungus-Like Pathogens

Mary L. Powelson and Randall C. Rowe Chapter 20

197

Managing Diseases Caused by Nematodes

Ann E. MacGuidwin Chapter 21

209

Managing Foliar Diseases: Early Blight, Late Blight, and White Mold

Walter R. Stevenson, William W. Kirk, and Zahi K. Atallah Chapter 22

223

Managing Weeds

Rick A. Boydston, Pamela J. S. Hutchinson, and Robin R. Bellinder Chapter 23

235

Managing Physiological Disorders

Larry K. Hiller and Robert E. Thornton

247

Glossary

253

Sources of Additional Information

255

Index

POTATO HEALTH MANAGEMENT

CHAPTER 1

Randall C. Rowe Department of Plant Pathology Ohio State University, Wooster

Mary L. Powelson Department of Botany and Plant Pathology Oregon State University, Corvallis

Potato Health Management: A Holistic Approach health must include economic considerations. Many decisions are made when growing a crop, and each has a cost attached, which will affect the total profit from the crop. Total freedom from biological and physical constraints in potato production is not achievable. Nor is that really the issue, because there is some tolerance for these constraints before economic loss occurs. The foundation of effective potato health management is understanding how each constraint affects the economics of production and when it is appropriate to take action. Thus, from a practical standpoint, a healthy potato crop is one in which biological and physical constraints are managed in such a way that economic gain can be maximized.

There is no single correct way to raise potatoes. Not only do local conditions and market requirements vary greatly, but biological constraints on production often differ considerably among fields and across geographic regions. Despite this variability, all potato producers face the challenge of developing and implementing management practices by which the health of the potato crop can be maximized in the face of threats from diseases, insects, and weeds.

This book is written for those involved in managing the health of potato crops—producers of commercial and seed potatoes, extension specialists, farm advisors, consultants, home gardeners, students, and anyone interested in growing healthy potatoes. The information presented here pertains directly to potato production in the United States and Canada, but much of it will be of value worldwide.

Holistic Management of Potato Health

What Is Potato Health?

Holistic is a word that is not commonly used in discussing the management of potato crops. Implicit in a holistic viewpoint is that choices among management strategies cannot be made in isolation—the big picture must be considered. Each management practice must be evaluated not only for its direct effects on a particular biological or physical constraint but also for its potential indirect and unintended effects on the overall agricultural enterprise and on surrounding farms, communities, and natural resources. A holistic approach addresses the reality facing today’s agriculture, where emphasis has shifted from maximizing total yield to maximizing total economic return with due regard for environmental protection and social responsibility.

Holistic management can be visualized as a pyramid in which the four sides represent the criteria that any production practice must satisfy: production efficiency, economic viability, environmental compatibility, and social responsibility (Fig. 1.1). Each practice must be effective and efficient in managing an identified constraint. Production practices must also be economically viable components of the total production system. Beyond being effective and affordable, each practice must not pose a threat to local or regional environments; must not jeopardize the health of workers,

As a preliminary to a discussion of potato health management, an understanding of the concept of health is needed.

In human terms, health means freedom from biological, environmental, and genetic factors that adversely affect bodily functions, daily activities, and personal well-being. If this concept is applied to potatoes, a healthy potato crop would be defined as one that is free of biological constraints (insects, diseases, and weeds) and physical limitations (nutrition, water, and chemical and environmental stresses) that prevent the plants from achieving their full genetic potential.

This definition is not adequate from a practical standpoint, since perfect potato health is seldom if ever achieved in the real world. Furthermore, although humans are valued as individuals, plants are usually valued only as a population (a crop) for the yield it produces. Since potatoes are grown to produce tubers, a healthy potato crop could be defined as one free from any constraints that limit tuber yield or quality.

This definition of potato health focuses on the final product, the tubers, but it is still unsatisfactory as a basis for management. A potato crop is grown for the economic benefit that is returned to the producer. Thus, a valid concept of potato 1

2 • CHAPTER 1 neighbors, and consumers; and must be acceptable to the local community. If all four criteria are satisfied, the pyramid will stand firm, whereas if even one is not met, the stability of the system is threatened.

Holistic potato health management is the application of a totally integrated set of production practices that results in a quality crop produced in a manner that optimizes economic return and minimizes environmental impacts and undesirable societal effects. A thorough understanding of the biology of the potato plant and the underlying principles of modern pest and disease management, together with an appreciation of how these factors interact to affect the overall health of the potato crop, is central to holistic management. With this knowledge, various production options can be evaluated and then assembled into an effective and appropriate holistic management plan.

Principles of Holistic Potato Health Management

Fig. 1.1. Holistic potato health management visualized as a pyramid in which the four sides represent the criteria that any production practice must satisfy. When all four are satisfied, the pyramid will stand firm, whereas if even one is not met, the stability of the system will be threatened. (Adapted from a logo of the College of Food, Agricultural, and Environmental Sciences, Ohio State University)

Production of a healthy potato crop is a constantly moving target. Factors that affect potato health are continually changing, and effective management requires that production systems be continually adjusted to improve the management of existing constraints and to address emerging threats.

Thus, practices must be selected that are effective in multiple ways and interlink appropriately, like pieces of a jigsaw puzzle (Fig. 1.2). Because of the biological complexity of a potato production system, changes in one management practice may cause rebound effects (Chapter 3) throughout the system and may even result in the emergence of a new and unanticipated problem. Recognizing that management practices are all interlinked is key to understanding holistic potato health management.

Effective management of potato health requires that production factors be manipulated to provide conditions

Fig. 1.2. Practices selected for a holistic potato health management plan must be effective in multiple ways and must interlink appropriately, like pieces of a jigsaw puzzle. Recognizing that management practices are all interlinked is key to understanding the concept of holistic health management. (Drawing by Maegan Davis)

HOLISTIC POTATO HEALTH MANAGEMENT • 3

that both optimize the crop environment and minimize the effects of pests and diseases. Once the requirements of the crop and the production limitations of the planting site are fully understood, management options can be selected and implemented to minimize stresses throughout the production cycle. A holistic health management plan includes decisions about crop rotation, site selection and land preparation, tillage, seeding practices, water and fertility management, and harvest and postharvest procedures. After these have been addressed, specific pest and disease management decisions are made and implemented before and as the crop develops.

Three concepts can be considered in pest and disease management decision making: the damage level, the economic loss level, and the action threshold.

The damage level is the pest population or disease level that is of sufficient magnitude to limit crop yield or quality. One Colorado potato beetle chewing on a potato leaf will not affect the yield of a crop, but a larger population can cause severe damage. The level at which a pest population becomes large enough to affect the yield or quality of the crop is the damage level for that pest.

Given that the most practical definition of potato health is one that is linked to maximizing economic gain from the crop, a second, more useful management concept is the economic loss level (often referred to as the economic injury level in insect pest management). This is the pest population or disease level, usually somewhat beyond the damage level, at which the potential financial loss due to the pest or disease exceeds the cost of management. Thus, to avoid a net financial loss, corrective action must be taken sometime before the economic loss level is reached. The pest population or disease level at which action should be taken is called the action threshold (often referred to as the economic threshold in insect pest management).

Fig. 1.3 illustrates the relationship between the economic

Fig. 1.3. Implementation of pest and disease management practices based on the concept of the economic loss level. The economic loss level is the pest population or disease level at which the potential financial loss due to the pest or disease exceeds the cost of management. The action threshold is the pest population or disease level at which corrective action should be implemented to avoid reaching the economic loss level. (Adapted from C. S. Hollingsworth, D. N. Ferro, and W. M. Coli, eds., 1986, Potato Production in the Northeast: A Guide to Integrated Pest Management, Publ. C-178, Massachusetts Cooperative Extension Service, Amherst)

loss level and the action threshold. As the crop develops, the population of a particular pest or the amount of a particular disease may go up or down. Beginning treatment too early results in an unnecessary production expense, whereas applying a treatment when the action threshold is reached prevents the potential loss from exceeding the cost of the treatment.

Building a Holistic Health Management Plan An effective holistic health management plan will contain multiple integrated components selected on the basis of strategies that work together to protect the crop. Pest outbreaks and disease epidemics originate from small populations of organisms that increase into larger populations capable of causing economic loss. The population that begins the process may be introduced on seed tubers or equipment or by natural means, or it may already be present in a production field. This reservoir of pest and disease organisms is referred to as the initial population in the case of insects or weeds and as the initial inoculum (or primary inoculum) in the case of microbes that cause disease.

The first strategy for protecting potato health is to exclude or evade pests and disease organisms (Box 1.1). The goal is to avoid contact between the crop and organisms that might cause damage. Exclusionary practices are particularly effective in avoiding the introduction of pests and disease organisms that might be carried on or in seed tubers. Planting seed tubers produced under strict certification procedures is an important foundation of any health management plan. Other exclusionary practices include sanitary precautions to prevent the introduction of soilborne pests and disease organisms into uninfested lands (such as cleaning and sanitizing field equipment before moving it to a new production field), governmental regulations (such as quarantine and inspection of seed shipments), planting in uninfested production sites, and selection of appropriate planting and harvest times.

In many cases it is not possible to avoid contact with some organisms that may damage the crop. Thus, a second strategy for protecting potato health is to target the initial populations of pests or the initial inoculum of disease organisms. The goal is to reduce initial populations or limit the effectiveness of initial populations of pests and disease organisms that cannot be avoided (Box 1.1). Practices that reduce initial populations of weeds, insects, and disease organisms include crop rotation, soil fumigation, removal of long-term survival sites, prevention of weeds from going to seed, deep plowing of crop residues, and sanitation of equipment and facilities.

Practices that limit the effectiveness of the initial inoculum of disease organisms include the selection of cultivars with some types of disease resistance, selection and preparation of planting sites to ensure satisfactory soil drainage, use of chemical seed piece treatments and other soil-applied fungicides, adjustment of soil pH, incorporation of soil amendments and green manure crops, early- and late-season irrigation management, planting at an appropriate seeding depth, adjustment of the planting date to avoid planting in cold soil, and harvest timing. Treatment with soil-applied insecticides, selection of cultivars resistant to insect feeding, and application of pheromones to disrupt mating can reduce the activity of initial populations of insects. Application of

4 • CHAPTER 1

Box 1.1

Health Protection Practices That Can Be Integrated into a Holistic Health Management System Practices that EXCLUDE or EVADE pests and disease organisms

Planting certified seed tubers Federal inspection of seed tubers Sanitation of field equipment between cropping sites Quarantines Site selection Timing of planting and harvest dates

Practices that REDUCE INITIAL POPULATIONS of pests and disease organisms Crop rotation Soil fumigation Removal of long-term survival sites Preventing weeds from going to seed Deep plowing of crop residues Sanitation of equipment and facilities

Practices that LIMIT THE EFFECTIVENESS OF INITIAL POPULATIONS of pests and disease organisms

Selection and preparation of planting sites to ensure satisfactory soil drainage Use of chemical seed piece treatments Use of soil-applied pesticides Selection of cultivars resistant to certain diseases or insects Pre- and postemergence herbicide application Adjustment of soil acidity (pH) Incorporation of soil amendments or green manure crop residues Planting at an appropriate seeding depth Cultivation Early- and late-season irrigation management Adjustment of the planting date to avoid planting in cold soil Pheromone treatment to disrupt insect mating Timing of harvest

pre- and postemergence herbicides and cultivation can reduce competition from initial populations of weeds.

Once an insect or weed population is expanding or a disease epidemic has begun, management practices that minimize the rate of population growth of pests and disease organisms come into play (Box 1.1). Practices in this category include selection of cultivars with some types of resistance to insects or diseases, most foliar pesticide applications, cultural practices such as row spacing and orientation, management of fertility and irrigation, harvesting and handling practices that minimize mechanical damage, and management of the storage environment.

The challenge is to select an appropriate set of management practices and integrate them into a holistic health management plan that results in a quality crop and maximizes total economic return. Because all management options have associated costs, economic loss levels and action thresholds must be considered before implementation. The successful manager understands the genetic potential of the crop and the limitations of the production site and then makes a series of decisions that take into account the changing weather, pest populations, and disease levels. Economic, legal, and societal constraints also must be considered as they affect management options (Fig. 1.1).

Devising a holistic potato health management plan that will be effective in a specific production situation can best be approached in a systematic fashion (Fig. 1.4): Step 1: Identify and prioritize the potato health problems at the production site. What problems have historically affected the crop at this site, and what new problems

Practices that MINIMIZE THE RATE OF POPULATION GROWTH of pests and disease organisms

Selection of cultivars resistant to certain diseases or insects Foliar pesticide treatment Row spacing and orientation Nutrition management Irrigation management Harvest management to minimize mechanical damage Storage environmental management

Fig. 1.4. A systematic approach for devising a holistic potato health management plan.

HOLISTIC POTATO HEALTH MANAGEMENT • 5

are likely to develop? Of these potential problems, which are most likely to limit the quantity and quality of potato tubers produced? Which ones are of major importance, and which are tolerable?

Step 2: Identify the problems that are manageable in the production process. Some problems may not be manageable in certain situations, because of physical, economic, environmental, or legal limitations.

Step 3: Select a set of practices capable of managing the high-priority problems and integrate them into a holistic health management plan.

Individual management practices must be compatible and must not be implemented without consideration of their effects on the entire agricultural enterprise. In most cases, various trade-offs must be evaluated. Certain options aimed at managing one problem may aggravate another, and the priorities established in Step 1 must be reevaluated. The economics of various management options must be considered in terms of input costs and effects on the profitability of the

production enterprise. Legal constraints and concerns for environmental stewardship also affect choices among management options.

Throughout this book, a holistic approach to potato health management is emphasized. Chapter 2 contains a checklist of important health management practices. Chapters 3 through 14 discuss various aspects of potato production and present a generalized, comprehensive plan for producing a healthy potato crop, starting before planting and proceeding through production, harvest, and storage.

Chapters 15 through 23 provide information on management strategies for specific problems affecting potato health—insect pests, diseases, weeds, and environmental stresses. A holistic health management plan can be devised for any potato production situation by selecting relevant management practices from Chapters 15 through 23 and then integrating them into the overall production plan presented in Chapters 1 through 14. A glossary and a list of relevant resource materials and Web sites are included at the end of the book.