Plant Disease Guide
Identify, treat, and prevent common vegetable garden diseases
Prevention First
Most plant diseases are easier to prevent than cure. Follow these principles:
- • Good air circulation - Space plants properly, prune for airflow
- • Water at soil level - Wet leaves spread disease
- • Rotate crops - Don't plant the same family in the same spot yearly
- • Remove infected material - Don't compost diseased plants
Common Garden Diseases
Powdery Mildew
Squash, cucumbers, beans
Severity: Moderate
Blight (Early & Late)
Tomatoes, potatoes
Severity: Severe
Blossom End Rot
Tomatoes, peppers, squash
Severity: Moderate
Downy Mildew
Cucumbers, lettuce, basil
Severity: Moderate-Severe
Fusarium Wilt
Tomatoes, peppers, melons
Severity: Severe
Root Rot
All vegetables
Severity: Severe
Bacterial Leaf Spot
Peppers, tomatoes, lettuce
Severity: Moderate
Mosaic Virus
Tomatoes, cucumbers, beans
Severity: Moderate-Severe
Damping Off
All seedlings
Severity: Severe for seedlings
Anthracnose
Tomatoes, peppers, beans
Severity: Moderate
Disease Categories
Fungal Diseases
Most common. Spread by spores in air, soil, or water. Thrive in humid conditions. Examples: powdery mildew, blight, fusarium wilt.
Viral Diseases
Spread by insects, tools, or touch. No cure - prevention is key. Examples: mosaic virus, tomato spotted wilt virus.
Bacterial Diseases
Enter through wounds or stomata. Spread by water splash, insects. Examples: bacterial leaf spot, bacterial wilt.
Organic Treatment Options
Neem Oil
Effective against fungal diseases and some insects. Mix 2 tablespoons per gallon of water with a few drops of dish soap. Spray in evening to avoid leaf burn.
Baking Soda Spray
Prevents and treats powdery mildew. Mix 1 tablespoon baking soda + 1 tablespoon vegetable oil + few drops dish soap per gallon of water.
Copper Fungicide
Organic-approved for bacterial and fungal diseases. Use early in season as preventive. Follow label directions carefully - can build up in soil.
Milk Spray
Surprisingly effective against powdery mildew. Mix 40% milk to 60% water. Spray weekly as preventive or at first sign of infection.
When to Remove Plants
Sometimes the best action is to remove infected plants entirely to protect the rest of your garden. Remove when:
- • More than 50% of the plant is affected
- • The disease is spreading rapidly to other plants
- • It's a viral disease (no cure exists)
- • It's late in the season and treatment won't save the harvest
Never compost diseased plants - bag and dispose of them in trash.