Tomatoes are one of the most beloved crops in home gardens, but they are also highly susceptible to various diseases, especially in warm and humid climates. Understanding the symptoms and applying the right treatments can make the difference between a thriving tomato patch and a disappointing harvest.

Why tomatoes are prone to diseases

Their fast growth, soft foliage, and sensitivity to moisture create ideal conditions for fungi, bacteria, and viruses. Poor air circulation, excessive humidity, and contaminated soil can accelerate the spread of infections.

Most common tomato diseases

Early blight (Alternaria)

Early blight causes brown concentric-ring lesions on older leaves. Infected foliage yellows and drops prematurely, reducing the plant’s ability to produce fruit.

Treatment: Remove affected leaves immediately, improve airflow, avoid overhead watering, and apply organic fungicides like copper-based sprays.

Late blight (Phytophthora infestans)

One of the most destructive tomato diseases. It creates dark, water-soaked spots on leaves, stems, and fruits, often spreading rapidly during cool, wet weather.

Treatment: Remove infected plants completely, avoid planting tomatoes in the same area the following season, and use preventive organic fungicides when conditions are favorable.

Powdery mildew

A white, powder-like fungus that covers leaves and reduces photosynthesis. It appears in shaded, humid areas and spreads easily.

Treatment: Increase sunlight exposure, prune crowded branches, and apply neem oil sprays regularly.

Fusarium wilt

A soil-borne fungus that causes wilting on one side of the plant. Leaves yellow from the bottom up, and the plant eventually collapses.

Treatment: There is no cure once infected. Remove the plant and avoid replanting tomatoes in the same soil. Use resistant varieties whenever possible.

Bacterial spot

Small water-soaked lesions appear on leaves and fruits, eventually turning dark and scabby. It spreads easily with rain or irrigation splash.

Treatment: Remove infected leaves, disinfect tools frequently, and apply copper-based organic bactericides.

Tomato mosaic virus (ToMV)

This viral disease causes mottled leaves, distorted growth, and reduced fruit size. It spreads through contaminated hands, tools, or infected plants.

Treatment: Remove infected plants and sterilize tools. Avoid touching healthy plants after handling diseased ones.

Prevention: your best defense

• Rotate crops: Avoid planting tomatoes in the same spot for at least 2–3 years.
• Use resistant varieties: Explore options in the tomato category for disease-tolerant seeds.
• Improve airflow: Space plants well and prune lower leaves regularly.
• Water correctly: Water at the base to keep foliage dry.
• Soil health: Add compost and organic matter to boost plant resilience. Learn how in this compost guide.
• Pest control: Whiteflies and aphids can transmit diseases—see this natural control guide for safe solutions.

When to remove a tomato plant

If more than half of the plant is infected, or if it carries soil-borne diseases like Fusarium wilt, removal is often the safest option to protect nearby crops. Dispose of infected material—don’t compost it.

Strengthening your plants

Healthy tomato plants are more resistant to disease. Use high-quality seeds like Marglobe, water deeply but infrequently, mulch to keep soil moisture stable, and feed regularly with compost tea or organic fertilizer.