Fungal Severity: High ⚠️ Contagious

Alternaria Leaf Spot: Urgent! How to Save Your Plant

Alternaria leaf spot is a common fungal disease caused by Alternaria solani and Alternaria alternata that affects a wide range of plants including tomatoes, potatoes, brassicas, and ornamentals. The disease thrives in warm, humid conditions and can cause significant crop damage if left untreated. Spores overwinter on plant debris and can attach to seeds, making complete elimination difficult.

Spread speed

Medium

Recovery time

28 days

🔍 Symptoms

Main Symptoms

! Small dark circular spots (0.5-0.75 inches diameter) on leaves
! Concentric rings forming target-like patterns
! Spots change from black to tan/gray with yellow halos
! Fuzzy texture develops as fungus produces spores
! Premature leaf wilting and drop
! Brown or black spots on fruits and stems
! Weakened plants and reduced vigor

Visual Signs

Small dark circular spots 0.5-0.75 inches in diameterConcentric rings spreading from infection point (target pattern)Color changes from black to tan or gray with yellow haloFuzzy texture as spores developLeaf wilting and premature dropSpots on fruits and vegetable surfaces

Affected parts: LEAVESFruitsStem

❓ Possible Causes

→ Fungal pathogens Alternaria solani and Alternaria alternata
→ Warm temperatures (60-80°F) with high humidity
→ Overhead watering creating prolonged leaf wetness
→ Dense plant spacing limiting air circulation
→ Plant stress from nutrient deficiency or drought
→ Overwintering spores on plant debris
→ Contaminated seeds carrying fungal spores

💊 Treatment

⚡

Quick Fixes

~14 days

Step 1

Remove heavily infected leaves immediately

Step 2

Apply chlorothalonil or mancozeb protectant fungicide to all plant surfaces

Step 3

Ensure thorough coverage including leaf undersides

Step 4

Reapply every 7 days or after rain

Step 5

Switch to azoxystrobin systemic fungicide after 2 applications for resistance management

Step 6

Continue treatment for 2 weeks after symptoms clear

Materials needed:

Chlorothalonil fungicide (Daconil)Mancozeb fungicideAzoxystrobin (Quadris)Garden sprayerProtective glovesPruning shears

🌿

Organic Treatment

~28 days

Step 1

Remove all visible infected leaves and plant debris, dispose in sealed bags

Step 2

Apply Bacillus subtilis biological fungicide spray, covering all leaf surfaces thoroughly

Step 3

Spray copper fungicide (organic-approved copper hydroxide or oxychloride) on remaining foliage

Step 4

Apply straw mulch around plant base to prevent soil splash

Step 5

Reapply biological spray every 5-7 days

Step 6

Reapply copper spray every 7-10 days

Step 7

Continue monitoring and treatment for 3-4 weeks

Materials needed:

Bacillus subtilis (powder or liquid)Organic copper fungicideNeem oilStraw mulchSterilized pruning shearsPlastic bagsSpray bottle

🔬

Expert Treatment

~42 days

Step 1

Conduct thorough sanitation: remove all infected plant material and debris within 3-foot radius

Step 2

Prune infected stems 6 inches below visible symptoms, sterilize tools between cuts

Step 3

Apply broad-spectrum protectant fungicide (chlorothalonil or mancozeb) as base treatment

Step 4

Follow with systemic fungicide rotation: azoxystrobin (week 1-2), then difenoconazole (week 3-4)

Step 5

Implement cultural controls: install drip irrigation, increase plant spacing if possible

Step 6

Apply straw mulch 2-3 inches thick to prevent soil splash

Step 7

Monitor plants twice weekly for new infections or resistance signs

Step 8

Adjust watering to early morning only, avoid wetting foliage

Step 9

Apply foliar nutrition (balanced NPK) to support plant recovery

Step 10

Continue fungicide rotation for 4 weeks, then switch to preventive schedule

Step by Step

1
Remove and destroy all infected leaves and plant debris
2
Apply appropriate fungicide based on chosen treatment approach
3
Reapply fungicide according to product schedule
4
Monitor plants weekly for new infection signs
5
Continue treatment for 2-3 weeks after symptoms disappear

🧪 Solutions

🌱 Natural Solutions

✓ Bacillus subtilis spray every 5-7 days
✓ Trichoderma harzianum application every 10-15 days
✓ Neem oil spray weekly as preventive
✓ Copper fungicide (copper hydroxide/oxychloride) every 7-10 days
✓ Essential oil formulations every 5-7 days

💉 Chemical Solutions

✓ Chlorothalonil fungicide every 7-10 days
✓ Mancozeb protectant fungicide every 7-10 days
✓ Azoxystrobin (strobilurin) systemic every 10-14 days
✓ Difenoconazole (triazole) systemic every 10-14 days
✓ Rotate fungicides to prevent resistance

🛡️ Prevention

✓ Remove and destroy infected plant debris immediately
✓ Practice 3-4 year crop rotation with non-host plants
✓ Space plants properly for good air circulation
✓ Water at soil level, avoid overhead irrigation
✓ Apply straw mulch immediately after planting
✓ Use certified disease-free seeds and transplants
✓ Avoid working with wet plants to prevent spore spread
✓ Maintain plant health through proper fertilization

🌿 Common in These Plants

Rose Painted Calathea

Peacock Plant

Corn Plant

African Milk Tree

Heartleaf Philodendron

Moon Orchid

Sunflower