Environmental Effects on Development of Infectious Plant Disease

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1 Environmental Effects on Development of Infectious Plant Disease Environment can Determine whether Disease will Occur Temperature Moisture Light Soil Nutrients & ph Botrytis on raspberries Environmental Factors Influence Growth & Susceptibility of Host Multiplication & Activity of Pathogen Interaction Between Host & Pathogen Thermographic visualization of the local resistance response of tobacco to tobacco mosaic (TMV) infection as spots of higher temperature on an attached leaf. users.ugent.be Optimums for Plants & Pathogens T near Optimum for Host, or not Optimum for Pathogen = Slower Disease Cycle Stem Rust of Wheat Infection Cycle at 5 C = 22 Days at 10 C = 15 Days at 23 C = 5-6 Days If Plant & Pathogen Have Equal Minimum, Optimum & Maximum Temperatures, Pathogen Gets Upper Hand Optimum Temp for Disease maybe Different from Optimum Temp for Pathogen or Plant Effect on Viruses Unpredictable T + Light Intensity may Determine Seasonal Appearance of Symptoms Viruses Producing Yellows or Leaf-Roll Symptoms most Severe in Summer Viruses Causing Mosaic or Ringspot Symptoms most Pronounced in Spring 1

2 Resistant Varieties Native Plants Plant at Proper Time Plant on South Side Tree Wrap or Paint Avoid Lowlands Water Plants during Extended Dry Conditions Fire Blight Warm & Wet Fungal Leaf Spot Cool & Wet Soil-Inhabiting Fungi Some Trends Cool & Wet Canker Diseases Worse in Older, Drought-Stressed Plants Plant Diseases More Common & Severe in Humid to Wet Areas of World Number Rainfalls/Season Determines Number of Infection Cycles/Season for Many Fungal Diseases How Moisture Favors Pathogens Spore Germination & Germ Tube Penetration Activation of Bacteria Swimming Medium for Nematodes How Moisture Favors Plants Adequate Water Helps Ensure Healthier Plant Turgidity Results in Cell Elongation Splashing Droplets onto Plant Increased Succulence of Plants Soil Pathogens often More Virulent when Soil Near Saturation Point 2

3 Select Plants Tolerant of Site Conditions Resistant Varieties Space Plants to Allow Good Air Flow Leaves Dry more Quickly Raised Beds Mulch Ground Cover Fungicide Seed Treatments Proper Pruning Air Flow Sunlight Penetration Removing Infected Leaves or Branches Water Plants during Extended Dry Conditions Wind & Epidemics Most Disease Epidemics Are Caused by Pathogens Spread Directly by the Wind or Indirectly by Insect Vectors that can Be Carried Long Distances by the Wind Causes Wounds Direct Wind Damage Wind-Blown Sand Plants Rubbing Dries Plant Surface Effects of Wind Wind + Rain Devastating Combo Releases Spores & Bacteria from Infected Tissue Windbreaks Border Crops Trap Crops 3

4 Low Light Etiolation usually > Susceptibility of Plants to Nonobligate Parasites Etiolation usually < Susceptibility to Obligate Parasites Usually Favors Susceptibility to Viral Infections Control: Right Plant in Right Place Usually Affects Pathogens more than Plants Plasmodiophora brassicae (Clubroot of Crucifers) Optimum at ph 5.7, Inhibited at ph 7.8 Streptomyces scabies (Potato Scab) Optimum ph 5.2 to 8.0, Inhibited below 5.2 ph-caused Nutrient Imbalance Weakens Plant Control Periodic Soil Tests Proper Soil Amendments 4

5 Nutritional Status Affects Plant s Rate of Growth & Ability to Defend against Pathogens Plants Fertilized Heavily with N Attacked more Severely by some Pathogens Excess N Causes Prolonged Vegetative Period Greater Susceptibility to Pathogens that normally Attack Succulent Tissues Erwinia amylovora (Fire Blight) on Pears Puccinia (Rust) on Wheat Erysiphe (Powdery Mildew) on Wheat N Deficiency Causes Weaker, Slower Growth, Faster Aging Greater Susceptibility to Pathogens that Attack Weak, Slow-Growing Plants Fusarium Wilt on Tomato Alternaria solani (Early Blight) in Solanaceae Pseudomonas solanacearum (Wilt) in Solanaceae Sclerotium rolfsii on Sugar Beets Pythium Damping-off on most Seedlings P When P Increases Resistance, It either Improves Nutrient Balance in Plant or Accelerates Maturity of Crop Allows It to Escape Infection K Reduces Severity of numerous Diseases Stem Rust of Wheat Early Blight of Tomato Stalk Rot of Corn Excess K Increases Severity of some Diseases Magnaporthe grisea (Rice Blast) Meloidogyne incognita (Root Knot Nematode) K Promotes Wound Healing Increases Resistance to Frost Injury Delays Maturity & Senescence in some Crops 5

6 Ca Composition of Plant Cell Walls & their Resistance to Penetration Reduces Severity of some Root & Stem Pathogens Increases Severity of a few Diseases Micros Applications can Reduce many Diseases but Increase a few Regular Soil Tests Proper Fertilization Increase Organic Matter Herbicides Increase Severity of some Diseases Decrease some Diseases Stimulate or Retard Growth of the Pathogen Increase or Decrease Plant Susceptibility Alter Microclimate of Plant Canopy Follow Label Instructions Avoid Drift 6