3 Types of Plant Diseases
Fungal
85% of all plant diseases
Most common. Caused by fungi thriving in warm, humid conditions. Spread by spores through air, water, and soil.
Bacterial
10% of all plant diseases Enter through wounds or natural openings. Spread rapidly in wet conditions. Harder to treat than fungal diseases.
Viral
5% of all plant diseases
Transmitted by insects (aphids, whiteflies). No cure exists — prevention and removal are the only options.
Source: FAO estimates. Exact ratios vary by region and crop type.
How to Spot the Difference
Leaf spots Circular, defined edges Irregular, water-soaked Mosaic/mottled patterns
Texture Powdery or fuzzy growth
Slimy or wet lesions
No surface growth
Spread speed
Moderate (days-weeks)
Fast (hours-days) Slow, systemic
Smell
Musty/earthy
Foul, rotting odor
No distinct smell
Color change
White, brown, rust
Brown, black, yellow
Yellow, light green streaks
Fungal Diseases: Deep Dive
Disease Cause Treatment
Powdery Mildew
High humidity, poor airflow
Neem oil, baking soda spray, improve ventilation
Downy Mildew
Cool, wet conditions
Copper fungicide, remove affected leaves
Botrytis (Gray Mold)
Overwatering, poor drainage
Reduce moisture, prune affected areas, fungicide
Rust
Warm temps + leaf wetness
Sulfur spray, remove debris, resistant varieties
Fusarium Wilt
Soil-borne fungus, warm soil
Remove plant, solarize soil, crop rotation
Environmental Triggers to Watch
Excess Moisture
Overwatering and poor drainage create breeding grounds for fungi and bacteria. Always check soil before watering.
Poor Air Flow
Temperature Stress
Sudden temperature changes weaken plant immunity. Protect plants during cold snaps and heatwaves.
Crowded plants trap humidity around leaves. Space plants properly and prune dense foliage regularly.
Contaminated Tools
Pruning tools spread pathogens between plants. Sterilize with rubbing alcohol between each plant.
Quick Diagnosis Flowchart
