Tomato blight is a common fungal disease that can devastate plants if not recognized and managed early. This article explains how to identify blight, cultural controls, and treatment options to protect your crop.
Practical guidance for identifying tomato blight, preventive cultural practices, and effective chemical and biological treatments for home gardeners and small growers.
What is Tomato Blight?
Tomato blight refers primarily to two fungal diseases: early blight (caused by Alternaria spp.) and late blight (caused by Phytophthora infestans). Early blight typically produces concentric rings on older leaves, while late blight causes water-soaked lesions that rapidly turn brown and can affect leaves, stems, and fruit. Both diseases thrive in warm, humid conditions but have different seasonal patterns and management approaches.
Identifying Symptoms
Look for small, dark spots on lower leaves that enlarge into larger lesions with concentric rings (early blight) or irregular, dark, water-soaked patches that spread quickly under cool, wet conditions (late blight). Fruit may develop sunken, firm lesions that rot. Check stems for lesions and note rapid collapse of foliage in severe late blight outbreaks. Accurate identification is important because management timing differs.
Cultural Control Measures
Reduce disease pressure by planting resistant varieties when available, rotating crops (avoid planting tomatoes or other solanaceous crops in the same area for at least two years), improving air circulation with proper spacing and pruning, and avoiding overhead irrigation to keep foliage dry. Remove and destroy infected plant debris and volunteer tomato plants. Mulching and staking plants to keep fruit off the soil can also lower infection risk.
Chemical and Biological Treatments
Fungicides can be used preventively or at the first sign of disease. Common options include protectant fungicides (copper formulations, chlorothalonil) and, for severe outbreaks, systemic products labeled for home or commercial use—always follow label instructions and local regulations. Biological products containing Bacillus subtilis or other antagonists may reduce disease severity when used as part of an integrated program. Rotate modes of action to reduce resistance development and combine chemical, biological, and cultural practices for best results.