Plant Disease Identification Guide
Complete reference to identify, treat, and prevent 20+ common plant diseases
Updated: May 2026 | By Garden with Serge
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Powdery Mildew
Symptoms:
- White, powdery coating on leaves and stems
- Leaves curl, deform, or turn yellowish
- Appears in warm, dry conditions with poor air circulation
- Mainly affects tops of leaves
Treatment:
- Spray with neem oil or sulfur fungicide every 7-10 days
- Remove infected leaves
- Increase air circulation (fan, prune crowded foliage)
- Avoid overhead watering
- Reduce humidity and maintain 50°F-85°F temperature
Leaf Spot Disease
Symptoms:
- Brown, black, or red circular spots on leaves
- Spots may have yellow halos
- Spots enlarge and merge over time
- Affected leaves eventually yellow and drop
Treatment:
- Remove infected leaves immediately
- Avoid overhead watering (keeps leaves dry)
- Apply copper fungicide or sulfur spray
- Improve air circulation and reduce humidity
- Sterilize tools between cuts to prevent spread
Rust
Symptoms:
- Orange, red, or brown pustules (bumps) on leaf undersides
- Yellow spots on upper leaf surface
- Affected leaves wither and drop
- More common in cool, wet weather
Treatment:
- Remove infected leaves immediately
- Apply sulfur or copper fungicide
- Avoid wetting foliage when watering
- Increase air circulation
- Isolate infected plants from others
Bacterial Plant Diseases
Bacterial Leaf Spot
Symptoms:
- Small, water-soaked spots on leaves
- Spots often have yellow halos
- Can affect stems and fruit
- Spreads rapidly in warm, wet conditions
Treatment:
- Remove infected leaves and branches
- Apply copper bactericide spray
- Avoid overhead watering
- Sterilize tools between cuts
- Discard heavily infected plants
Bacterial Wilt
Symptoms:
- Sudden wilting of leaves and stems
- Yellow discoloration spreading through plant
- Plant collapses even with adequate water
- Often no spots or visible lesions
Treatment:
- No cure - remove and discard infected plant
- Sterilize soil before replanting
- Control insects that spread bacteria (beetles, grasshoppers)
- Choose resistant plant varieties
Root & Soil Diseases
Root Rot
Symptoms:
- Wilting despite moist soil
- Roots are mushy, dark, and foul-smelling
- Stunted growth
- Yellow or brown leaves that drop easily
Treatment:
- Remove plant from pot
- Cut away rotted roots with sterile knife
- Repot in fresh, well-draining soil
- Improve drainage by adding perlite or bark
- Let soil dry out between waterings
- Use fungicide-treated soil for severe cases
Damping Off (Seedling Disease)
Symptoms:
- Seedlings collapse at soil line
- Stems become dark and thin
- Affects newly sprouted seedlings
- More common in cool, wet conditions
Treatment:
- Use sterile seed-starting mix
- Ensure good air circulation with small fan
- Water from below to keep foliage dry
- Do not overwater
- Apply fungicide preventatively if planting in old soil
- Keep temperature between 65°F-75°F
Pest-Related Issues
Insects (Aphids, Whiteflies)
Symptoms:
- Tiny green, black, or yellow bugs clustered on new leaf growth
- Sticky honeydew residue on leaves and stems
- Black sooty mold growing on the sticky honeydew
Treatment:
- Spray foliage with insecticidal soap or neem oil every 5-7 days
- Blast pests off physically with a strong stream of water
- Introduce beneficial predators like ladybugs or lacewings
Spider Mites
Symptoms:
- Very fine webbing on leaf undersides, joints, and stems
- Tiny yellow or white speckling on upper leaf surfaces
- Leaves turn bronze, dry out, and fall off prematurely
Treatment:
- Increase humidity around plants as mites thrive in dry air
- Wash foliage undersides thoroughly with insecticidal soap
- Apply neem oil or miticide for severe infestations
Scale Insects
Symptoms:
- Small, hard, brown or white bumps stuck to stems and leaf veins
- Sticky residue (honeydew) and stunted plant growth
Treatment:
- Scrape scales off gently using an old toothbrush or fingernail
- Dab individual pests with a cotton swab dipped in rubbing alcohol
- Spray horticultural oil or systemic insecticide for severe cases
How to Diagnose Plant Diseases
- Examine the entire plant - Check both sides of leaves, stems, soil, and roots
- Look for patterns - Is damage on new growth, lower leaves, or random?
- Check environmental conditions - Note humidity, temperature, watering habits, and air circulation
- Take clear photos - Close-up shots of affected areas help with identification
- Use the Plant Doctor - Upload photos to our AI for instant diagnosis
- Compare to guides - Match your observations to disease descriptions above
- Act quickly - Early treatment prevents disease spread
General Treatment Strategies
Prevention is Key
- Choose disease-resistant plant varieties
- Provide proper air circulation
- Water at soil level (avoid wetting foliage)
- Maintain proper humidity (40-60% ideal)
- Use sterilized tools and pots
- Quarantine new plants for 2 weeks
- Keep plants healthy with proper light and nutrients
Treatment Options
- Organic: Neem oil, sulfur, copper fungicide, insecticidal soap
- Chemical: Systemic fungicides, bactericides (follow label instructions)
- Cultural: Remove infected leaves, improve conditions, isolate plants
- Integration: Combine organic + cultural methods for best results
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