Phytophthora infestans

Late blight is a devastating disease that targets tomatoes and potatoes, often wiping out entire crops in just a few days under the right conditions. It thrives in cool, wet weather, spreading rapidly through windborne spores and water splash. The first signs are water-soaked patches on leaves, quickly turning brown with pale halos. As the disease progresses, stems darken and fruit begins to rot, often while still green and on the plant.

Once symptoms appear, treatment becomes increasingly difficult and often ineffective. Late blight progresses rapidly, leaving little time to recover affected plants. It reduces yields, spoils fruit and compromises storage quality. For home gardeners, prevention is not just more effective, it's essential. It allows for confident crop planning without the stress of chasing symptoms through the season.

Unlike some diseases, late blight is not seed-borne in tomatoes. Properly processed and dried seed poses no risk of carrying the pathogen. In potatoes, however, the disease can persist in infected seed tubers. These tubers act as reservoirs, reintroducing late blight into the soil and future crops. Always select certified, disease-free seed potatoes, and never save tubers from infected plants or store bought "free" potatoes for replanting.

Late blight prevention relies on clean planting material, wide plant spacing, and consistent airflow around crops. Stake or trellis tomatoes early and avoid overhead watering. Mulch generously to prevent splash-up from the soil, and remove all infected material from the garden immediately. In wet seasons or areas with past infections, start a preventative spray program before symptoms develop.

• Organics

  • Biogrow Copper Soap
    An OMRI-certified organic fungicide that forms a protective barrier on leaves, preventing fungal spores from germinating. Use every 7 to 14 days, especially during rainy periods. Highly effective when used preventatively. Can be combined with other Biogrow products for greater efficacy.

  • Biogrow Phyta
    A foliar tonic that boosts plant defences and improves resilience to stress. Apply regularly during growth to support plant health and strengthen resistance, especially when used alongside Copper Soap.