Cultural Practices and Infectious Crop Diseases

The development of a crop, and therefore its health, is always the result of interplay between biological and environmental factors, as influenced by human agency. In other words, crop health is a highly complex affair. This book is concerned with only one group of agents affecting crop health, the pathogens, and not with animal pests or direct effects of physiological or weather factors. Even within this one group, however, the interaction of causal agents with environmental and biotic factors is highly complex. No less complex is the effect of cultural practices on the crop and its health. There is probably no major practice that does not affect diverse facets of crop growth, which in turn affects crop/pathogen relationships. Thus tillage se­ quentially affects depth and rate of root development, hence nutrient uptake, hence general plant size and habit as well as crop climate and crop susceptibility. Irri­ gation affects all these parameters, and facilitates crop growth under diverse macro­ climatic conditions, with all the ensuing implications for disease development. In this book an attempt is made to superimpose one set of complexities, the cul­ tural practices, on another such set, crop health. This may seem overambitious, not to say foolhardy, unless we remember that it has been done by farmers, consciously or unconsciously, ever since the beginnings of agriculture. We are here chiefly try­ ing to rationalize traditional practices, review modern research on the development of further practices, and assess the place of the latter in integrated disease control.

1 Climate, Cropping and Crop Disease.- 1.1 Agro-Ecosystems, the Cultural Practices They Have Generated, and the General Impact of Such Practices on Crop Disease.- 1.1.1 Humid Agroclimates.- 1.1.1.1 The Humid Cool Temperate Agroclimates.- 1.1.1.2 The Warm Humid Temperate Agroclimates.- 1.1.1.3 The Wet Tropics.- 1.1.2 Dry Agroclimates.- 1.1.2.1 The Cool Dry Temperate Agroclimates.- 1.1.2.2 The Warm Dry Temperate Agroclimates.- 1.1.2.3 The Semi-Arid Tropical Agroclimate.- 1.1.3 Agroclimates and Crop Disease ― Outlook for the Future.- 1.2 Microclimate and Crop Climate.- 1.2.1 The Microclimate as Affected by Topography and Soil.- 1.2.1.1 Topography.- 1.2.1.2 Soil.- 1.2.2 Crop Factors Interacting with Microclimate, and the Resultant Crop Climate.- 1.2.2.1 Density of Plant Cover (Canopy).- 1.2.2.2 Shade.- 1.2.3 When, Where and How Much Can Cultural Practices Influence the Crop Climate?.- 1.3 The Collective Approach to Disease Control: Epidemiological Considerations and the Role of Cultural Practices in Regional Management of Inoculum.- 1.3.1 The Cardinal Role of Inoculum and its Control for the Farming Community as a Whole.- 1.3.2 Various Crops Susceptible to the Same Pathogen ― Which Crop is More Valuable to the Farming Community?.- 1.3.3 Crop Varieties Differing in Susceptibility ― Dangers and Opportunities.- 1.3.4 Restricting Seasons, Locations and Growing Practices for Susceptible Crops.- 1.3.5 Minimizing Multiplication and Spread of Air- and Vector-Borne Inoculum.- 1.4 Soil, Soil Microbiota, and Soil-Borne Disease.- 1.4.1 Soil and the Growth of Underground Organs of the Crop.- 1.4.1.1 Texture and Depth.- 1.4.1.2 Soil Reaction.- 1.4.1.3 Soil Water.- 1.4.2 Soil Microbiota and Their Interaction with Soil-Borne Pathogens.- 1.4.2.1 Soil Microbiota Restricting Pathogen Development.- 1.4.2.2 Soil Microbiota Transmitting Plant Pathogens or Associated with Their Development.- 1.4.2.3 Plant Symbionts and Plant Pathogens.- 1.4.3 Suppressive or Resistant Soils.- 1.5 Stress, Strain and Predisposition.- 1.5.1 Types of Stress-Induced Strain.- 1.5.2 Temperature Strain.- 1.5.2.1 High-Temperature Strain.- 1.5.2.2 Low-Temperature Strain.- 1.5.3 Water Strain.- 1.5.3.1 Water Deficit Strain.- 1.5.3.2 Excess Water Strain.- 1.5.4 Other Strains.- 1.5.5 Combinations of Stresses and Strains.- 1.5.6 Charcoal Rot (Macrophomina phaseolina): Prototype of a Disease on Crops Under Stress.- 1.5.7 Summary of the Effects of Stress and Strain on Diseases Caused by Pathogens.- 1.6 Crop Age, Injury and Disease on Leaf and Fruit, with Special Reference to Disease in the Ageing Crop.- 1.6.1 Germination to Pre-Maturation of the Crop.- 1.6.1.1 Seedling and Early Growth Stage.- 1.6.1.2 Flowering or Full Vegetative Growth Stage.- 1.6.2 Maturation and Senescence.- 1.6.2.1 Physiological Changes.- 1.6.2.2 Changes in Crop Climate.- 1.6.2.3 Injury and Wound Parasites.- 1.6.2.4 The Time Element and the Mounting Inoculum.- 1.6.2.5 Disease in Ageing Tree Crops.- 1.6.2.6 The Ageing Crop as Source of Inoculum for its Neighbours.- 1.6.2.7 Disease Control in the Ageing Crop.- 1.6.2.8 Botrytis cinerea ― a Pathogen of Soft and Senescent Tissues.- 1.7 Weeds and Crop Disease.- 1.7.1 Which Pathogens Spread and Survive Through Weeds?.- 1.7.2 Weeds Particularly Apt to Endanger Crop Health.- 1.7.3 Effects of Cultural Practices on Weeds as Related to Disease Control.- 2 Major Cultural Practices and Their Effect on Crop Disease.- 2.1 Cost/Benefit and Risk Assessment and the Complexity of Multiple Choice in Pest Control Decisions on the Farm.- 2.1.1 Cost/Benefit Assessment.- 2.1.2 Risk Assessment.- 2.1.3 The Complexity of Multiple Choice in Pest Control Decisions.- 2.2 Sanitation.- 2.2.1 Aims and Limitations of Sanitation.- 2.2.2 Preventing the Introduction of Inoculum.- 2.2.2.1 Propagating Material.- 2.2.2.2 Irrigation and Drainage Water That Spreads Inoculum.- 2.2.2.3 Inoculum Introduced in Plant Debris, Compost and Manure.- 2.2.2.4 Inoculum Introduced and Spread by Equipment and Man.- 2.2.3 Elimination of Living Plants That Carry Pathogens.- 2.2.3.1 Additional and Alternate Hosts.- 2.2.3.2 Groundkeepers and Volunteers.- 2.2.3.3 Roguing.- 2.2.3.4 Removal of Diseased but Living Parts from Trees.- 2.2.4 Destruction or Inactivation of Inoculum Deriving from Dry Plant Matter and Debris.- 2.2.4.1 Sanitation of Diseased Trees.- 2.2.4.2 Removal of Crop Debris or its Incorporation in the Soil.- 2.2.4.3 Burning or Flaming Crop Residue.- 2.2.4.4 Flooding Fields and Orchards.- 2.2.4.5 Disinfestation of Soil by Heat.- 2.3 Crop Sequence.- 2.3.1 Aims of Crop Sequence Management.- 2.3.2 Economic Considerations.- 2.3.3 Choice of Crop Sequence in Relation to Other Farming Practices.- 2.3.4 The Benefits of Fallowing.- 2.3.5 What Are the Chances of Improving Crop Health by Management of Crop Sequence?.- 2.3.5.1 The “Heritage” of the Preceding Crop.- 2.3.5.2 Survival of Pathogens Outside Crop Debris.- 2.3.5.3 Survival and Multiplication of Inoculum by Aid of Non-Hosts.- 2.3.5.4 Use of Varieties Resistant and Seasons Unfavourable to the Pathogens.- 2.3.6 Monoculture.- 2.3.6.1 Irreversible Disease Pattern.- 2.3.6.2 Reversible Disease Pattern.- 2.3.7 Multiple Cropping.- 2.3.7.1 The Benefits of Multiple Cropping.- 2.3.7.2 Multiple Cropping of Field and Vegetable Crops.- 2.3.7.3 Intercropping in Orchards and Plantations.- 2.3.8 Decoy and Trap Crops.- 2.3.9 Crop Sequence and Crop Disease in the Future.- 2.4 Soil Amendments and Mulches.- 2.4.1 Organic Amendments.- 2.4.1.1 Effects on Soil and Water Relations.- 2.4.1.2 Effects on Pathogens.- 2.4.1.3 Practical Application of Soil Amendments.- 2.4.2 Organic Mulches.- 2.4.2.1 Effects on Soil Temperature and Retention of Precipitation.- 2.4.2.2 Stubble Mulch and Cereal Debris in Relation to Cereal Diseases.- 2.5 Tillage.- 2.5.1 The Aims of Tillage.- 2.5.2 Tillage to Prepare Land for Sowing and Planting.- 2.5.2.1 Depth of Soil Favourable to Root Growth.- 2.5.2.2 Distribution of Inoculum in the Soil Profile and Over the Field.- 2.5.2.3 The Diverse Effects of Non-Tillage.- 2.5.2.4 Tillage Practices as Affecting Cereal Diseases in England.- 2.5.3 Topsoil Management.- 2.5.3.1 Shaping the Topsoil and Earthing-Up (Hilling).- 2.5.3.2 Elimination of Soil Crusts.- 2.5.4 Tillage as a Control Practice.- 2.5.4.1 Destruction of Weeds and Volunteer Plants Between Successive Crops.- 2.5.4.2 Weed Control While the Crop Grows.- 2.5.4.3 Reduction of Inoculum by Tillage.- 2.6 Crop Nutrition.- 2.6.1 Balanced Nutrition and Nutrition Unbalanced for Economic and Crop Health Reasons.- 2.6.1.1 Size, Quality and Maturation of Yield.- 2.6.1.2 Crop Nutrition and the Pathogen.- 2.6.1.3 Manipulation of Nutrients.- 2.6.2 Fertilization with Nitrogen.- 2.6.2.1 General Effects of Nitrogen in Relation to Crop Disease.- 2.6.2.2 Nitrate Nitrogen and Ammonium Nitrogen.- 2.6.2.3 Timing of Nitrogen Fertilization.- 2.6.2.4 Toxic Effects of Nitrogen on Pathogens.- 2.6.3 Fertilization by Phosphates, Potassium and Calcium.- 2.6.3.1 Phosphates.- 2.6.3.2 Potassium.- 2.6.3.3 Calcium.- 2.6.4 Minor and Trace Elements.- 2.7 Moisture Management in Non-Irrigated Crops.- 2.7.1 Practices Affecting the Soil Moisture Potential, and Their Effects on Crop Disease.- 2.7.2 Optimization of the Use of Rainfall as Related to Crop Disease.- 2.7.3 Management of Leaf Wetness in Rain-Fed Crops.- 2.8 Irrigation.- 2.8.1 Effects of Irrigation on Soil and Foliosphere Climate.- 2.8.2 Irrigation Effects on the Host Crop.- 2.8.2.1 Extension and Manipulation of Growing Seasons.- 2.8.2.2 General Effects of Irrigation on Crops and on Stress.- 2.8.3 Irrigation and the Pathogen.- 2.8.3.1 Survival and Management of Inoculum in Irrigated Crops.- 2.8.3.2 Dispersal of Inoculum in Irrigated Crops.- 2.8.3.3 Attraction of Virus Vectors to Irrigated Crops.- 2.8.4 Techniques of Irrigation.- 2.8.4.1 Overhead Sprinkling May Promote Disease.- 2.8.4.2 Trickle Irrigation.- 2.8.5 Minimizing Disease by Irrigation Management.- 2.8.5.1 Choice of Irrigation Technique.- 2.8.5.2 Timing of Water Supply.- 2.8.6 Irrigation and Crop Disease ― Outlook.- 2.9 Rate of Sowing and Planting, and Density of Stand.- 2.9.1 Effects at Various Stages of Growth.- 2.9.2 Root and Shoot Contact in High-Density Crops.- 2.9.3 Density and Disease in Tree Crops and Vines.- 2.9.4 Crowed Stands May Mean Lower Incidence of Certain Systemic Diseases.- 2.10 Sowing and Planting Dates and Manipulation of Flowering and Fruiting Periods.- 2.10.1 Date of Sowing and Incidence of Disease.- 2.10.2 Minimizing Virus Diseases by Varying Sowing Dates.- 2.10.3 Relative Growth Rates of Crop and Pathogen, and Levels of Crop Susceptibility, at Various Sowing Dates.- 2.10.4 Seasonal Massing of Air-Borne Inoculum.- 2.10.5 Management of Periods of Bud-Burst, Flowering and Fruiting to Minimize Disease.- 2.10.6 Manipulation of Periods when Crop Meets Pathogen.- 2.11 Harvesting Dates and Practices.- 2.11.1 Timing of the Harvest.- 2.11.2 The Danger of Inoculum Spreading at Harvest.- 2.11.3 Harvesting Techniques as Related to Crop Injury and Disease.- 2.12 Planning to Minimize Influx of Air- or Vector-Borne Inoculum to Neighbouring Crops.- 2.12.1 What Makes a Neighbouring Crop a Dangerous Source of Inoculum?.- 2.12.2 Planning to Reduce Infection Risks from Neighbouring Crops.- 2.13 Pruning and Grafting.- 2.13.1 Pruning and Bark Ringing.- 2.13.2 Grafting.- 2.14 Effects of Physical Barriers on Crop Infection and of Optical Means on Virus Vector Control.- 2.14.1 Effects of Windbreaks and Tall Crops on Infection.- 2.14.2 Physical Protection of Crops from Infection by Soil-Borne Inoculum.- 2.14.3 Optical Means for Virus Vector Control.- 3 Interactions Between Cultural Practices, Resistance Breeding, and Application of Chemicals: Integrated Control.- 3.1 Keep Inoculum Out ― by Any Available Means.- 3.2 Prevent Multiplication and Spread of Inoculum.- 3.2.1 Use of Resistant Varieties to Delay Inoculum Build-up.- 3.2.2 Cultural Practices and the Timing of Pesticide Use.- 3.3 The Proper Place for Cultural Practices in Integrated Disease Control.- 3.3.1 Economic and Human Factors.- 3.3.2 Pathogen, Crop, and Environmental Factors.- 3.4 Profit in Fungicide Applications, as Related to Cultural Factors.- 3.5 Cultural Practices and the Use of Herbicides and Physiologically Active Chemicals.- 3.5.1 Herbicides and Desiccants.- 3.5.2 Chemicals Applied to Affect Crop Physiology.- 3.6 Hop Wilt in England: Success of Integrated Control.- 3.7 Some Thoughts on the Future of Integrated Disease Control and its Components in World Crop Production.- 3.7.1 Bringing New Areas into Production.- 3.7.2 Intensification of Production on Areas Already Cultivated.- 3.7.3 Widening the Geographic Range of Valuable Crops.- 3.7.4 Education of Farmers to Employ Cultural Practices for Disease Control.- French, German and Spanish Translation of Some of the English Terms Used in this Book.- References.- Pathogen Index.