Late Blight on Tomatoes: Identification and Management

Brown, greasy lesions on green tomato fruit starting at the stem end and spreading downward are classic symptoms of late blight (Phytophthora infestans), a devastating oomycete disease.

Confirming Late Blight

Look for:

• Firm, brown, irregular lesions on green fruit, often with a white, fuzzy sporulation on the underside in humid conditions.
• Dark brown to black lesions on stems and petioles.
• Rapid collapse of foliage in wet weather.

Management Options

Once late blight appears, curative control is nearly impossible. Focus on prevention:

• Crop rotation: Avoid planting tomatoes, potatoes, or eggplant in the same spot for 3 years.
• Resistant varieties: Choose cultivars with late blight resistance (e.g., 'Defiant', 'Mountain Magic', 'Plum Regal').
• Fungicide program: Alternate chlorothalonil and copper fungicides weekly, starting before symptoms appear. Follow labels strictly.
• Sanitation: Remove and destroy all infected plant material; do not compost.

Photos

Tomato late blight

Tomato late blight

Tomato late blight

If you can't rotate or spray, buy tomatoes from local farmers and save garden space for less disease-prone crops.