How to Handle Tomato Blight (Early & Late Blight ID and Treatment)
Identify early and late blight, remove infected foliage, spray fungicide, and prevent next year's infection.
TL;DR
- Time: 30 minutes
- Cost: $
- Yield: Save the fruit, prevent spread
- Difficulty: Beginner
Supplies
- Loppers or hand pruners (sharp, sterilized)
- Fungicide: sulfur dust OR Bacillus subtilis (organic) OR chlorothalonil (conventional)
- Spray bottle or pump sprayer
- 10% bleach solution (for sterilizing pruners)
- Trash bag (for removing infected foliage—don't compost it)
Tools
- Gloves
- Eye protection (when spraying)
- Pruners
Steps
Identify the blight type
Early blight: brown spots with concentric rings, starts on lower leaves in mid-July. Late blight: water-soaked spots, white fungal growth on leaf underside, more aggressive. If you're not sure, take a photo and email your county Extension office. They'll confirm.
Remove infected leaves immediately
Don't wait. Cut off all leaves with spots using sharp, sterilized pruners. Go at least 6 inches below the lowest spot—you want to remove the visible infection plus buffer zone. Dip pruners in 10% bleach between cuts to avoid spreading spores. Bag and trash the foliage. Don't compost it—spores will survive winter in compost and re-infect next year.
Improve air circulation
Remove lower foliage (bottom 12 inches) on healthy plants so air moves through. Blight fungi love humid, stagnant air. Thin out dense growth. If plants are crowded, space them further apart next year.
Water at soil level only
Never water foliage. Wet leaves are blight's playground. Use drip irrigation or soaker hoses. Water in early morning so any splash dries quickly.
Spray fungicide if infection is spreading
If you're removing new infected leaves every few days, spray. Options: (1) Sulfur dust, applied weekly. (2) Bacillus subtilis (organic, kills spores). (3) Chlorothalonil (conventional, highly effective). Follow label directions. Spray early morning or evening, not midday heat. Reapply after rain.
Monitor and remove new infected growth
Check plants daily. At the first sign of new spots, remove those leaves. Quick action stops spread. Don't let it fester.
Pro Tips
Plant resistant varieties: 'Mountain Magic', 'Mountain Red', 'Mountain Marvel' are blight-resistant hybrids that perform well in Utah.
Space plants 3+ feet apart. Crowded plants never have good air circulation, and blight thrives in humidity.
Water only at soil level. Overhead watering is the fastest way to spread blight.
After harvest, remove the entire plant and bag or burn the foliage. Don't leave dead plants standing—that's a disease factory for next year.
Early blight is less aggressive than late blight. You can often save an early-blight plant with leaf removal alone. Late blight is meaner and spreads fast.
Mulch under plants to prevent soil splash. Blight spores live in soil; rain splash spreads them to lower leaves.
Warnings
Never touch a blight-infected plant and then touch a healthy one. Wash your hands or change gloves.
Don't compost infected foliage. Burn it or bag it for trash. Blight spores are survivors.
Research & Sources
- Tomato Diseases in Utah
Dr. Dan Drost, USU Extension Plant Pathology (2024) - Early and Late Blight Management
Dr. Heidi Kratsch, USU Extension (2023) - Fungicide Options for Organic and Conventional Growers
Utah State University Extension (2024) - Sevier County Disease Prevention
Sevier County Extension (2023)
Frequently Asked Questions
Can I save a plant that's heavily infected?
If less than 50% of the plant is infected, yes. Remove all infected foliage, spray fungicide, and monitor. If more than 50% is gone, the plant won't fruit well. Pull it and start fresh next year.
Is it safe to eat tomatoes from a blighted plant?
Yes. Blight doesn't infect the fruit (unless it's late blight and spots appear on fruit). Wash the fruit and eat normally. The disease affects foliage, not the inside of the tomato.
Why do my tomatoes keep getting blight every year?
Possible reasons: (1) You're planting susceptible varieties. (2) You're leaving diseased foliage on the ground year to year. (3) Your spacing is too tight. (4) You're watering foliage. Fix those, and blight usually disappears.
What fungicide should I use?
Organic: Bacillus subtilis or sulfur (both safe, slower acting). Conventional: Chlorothalonil (fast, highly effective). Copper fungicides work but aren't ideal in Utah's alkaline soil. Start with removal and better practices; spray only if it's spreading fast.
