Spraying Tomatoes for Blight
Tomato blight is one of the most frustrating diseases a gardener can encounter. It can strike quickly and devastate an otherwise healthy crop, turning lush green leaves into shriveled, brown patches almost overnight. Blight is caused by fungal pathogens—early blight by Alternaria solani and late blight by Phytophthora infestans. Both thrive in moist, warm environments and spread through water, wind, and contaminated soil or tools. Fortunately, spraying tomatoes for blight can prevent or slow its spread if done correctly.
Know Your Enemy
Before reaching for a spray, it’s important to understand which type of blight you’re dealing with. Early blight usually begins with concentric brown spots on older, lower leaves. Late blight appears as water-soaked lesions that quickly turn dark and oily, spreading to stems and fruit. Identifying the type helps you choose the most effective treatment.
When to Start Spraying
Prevention is key. Start spraying when plants are 6–12 inches tall or when weather conditions—high humidity and rainfall—favor disease development. Don’t wait until symptoms appear. Once blight is visible, it can spread rapidly, and many treatments become less effective.
Types of Sprays
There are two main categories of sprays for blight: organic and synthetic.
Organic Options
- Copper Fungicides – Widely used and OMRI-listed, copper sprays help prevent blight by creating a protective barrier on plant surfaces. However, excessive use can lead to copper buildup in the soil.
- Bacillus subtilis – This naturally occurring bacterium fights fungal diseases by colonizing the leaf surface and outcompeting harmful pathogens.
- Neem Oil – While not a fungicide per se, neem oil has antifungal properties and can help reduce fungal spread when used preventively.
Synthetic Fungicides
- Chlorothalonil – A broad-spectrum fungicide effective against both early and late blight. It’s best used as a preventative treatment.
- Mancozeb – Another powerful fungicide that targets fungal spores before they infect the plant.
Always follow the label instructions, including dilution rates and application intervals. Rotate fungicides with different modes of action to prevent resistance.
Proper Application Techniques
- Timing: Apply early in the morning or late in the afternoon to avoid leaf burn and ensure better absorption.
- Coverage: Spray both the tops and undersides of leaves, as well as stems. Pathogens can hide in hard-to-reach spots.
- Frequency: Reapply every 7–10 days or after heavy rain, which can wash off the protective layer.
Cultural Practices to Support Spraying
Even the best spray regimen won’t help if plants are overcrowded or poorly maintained. Combine spraying with these cultural controls:
- Space plants adequately for airflow.
- Water at the base to avoid wetting foliage.
- Mulch to reduce soil splash.
- Remove infected leaves immediately.
Final Thoughts
Spraying tomatoes for blight is an essential part of maintaining a healthy garden, especially in humid or rainy climates. By understanding the disease, choosing the right treatment, and practicing good garden hygiene, you can protect your tomatoes and enjoy a thriving harvest. Early prevention and consistent care are your best defenses against this common and destructive problem.
