Alternaria solani

Early blight is a persistent fungal disease that targets tomatoes and potatoes, often making its first appearance as dark, concentric-ring lesions on older leaves. As it spreads, it causes leaf drop, weakens the plant, and exposes fruit to sunburn and other stressors. It thrives in warm, wet conditions and often rears its head after prolonged leaf wetness or overhead watering. The fungus survives in soil and plant debris, making it a repeat offender if not properly managed.

Controlling early blight after infection is difficult, and damage can escalate quickly. It leads to lower yields, poor fruit quality and increased stress on plants. Relying solely on treatment is time-consuming and often expensive. Preventative approaches are far more effective and allow gardeners to grow healthier crops without having to constantly react to disease outbreaks.

Early blight can be seed-borne in tomatoes, particularly in saved or untreated seed. The fungus may survive on the surface or in seed debris and can contribute to early infections if conditions are favourable. This is less of a concern with professionally processed seed, but gardeners saving their own should follow best practices like fermentation, proper drying and optional hot water treatment. In potatoes, early blight is not seed-borne but can carry over in infected tubers or persist in soil from previous crops.

Prevention starts with sound cultural practices. Space plants well to ensure good airflow and stake them early to keep foliage off the ground. Avoid watering from above and apply mulch to reduce splash-back of soil-borne spores. Remove infected leaves as soon as symptoms appear. For tomatoes and potatoes in blight-prone areas, a preventative foliar program is the most effective defence.

• Organics

  • Biogrow Copper Soap
    A certified organic fungicide with preventative action against early blight and other fungal infections. Forms a protective barrier that stops spores from establishing. Spray every 2–3 weeks during high-risk periods. Can be combined with other Biogrow products for enhanced effectiveness.

  • Biogrow Phyta
    A foliar tonic that enhances plant resistance to stress and disease. Helps maintain plant health in high-pressure periods and works well alongside Copper Soap.