Late blight

Late blight is a devastating plant disease caused by the oomycete Phytophthora infestans. Classified within the kingdom Chromista, this pathogen is infamous for causing the Irish Potato Famine and remains one of the most significant threats to potato and tomato production worldwide.

Symptoms of the disease initially appear as small, dark, water-soaked spots on the leaves. As the infection progresses, these lesions expand rapidly, turning brown or black. Under high humidity, a characteristic white fuzzy growth, containing millions of spores, appears on the underside of infected leaves.

The biology of P. infestans is highly adapted to cool, wet conditions. The pathogen spreads via sporangia that can travel long distances through wind or rain splash. Once they land on a host plant, they release motile zoospores that penetrate the plant tissue and initiate a new infection cycle.

The development of the disease is strictly dependent on environmental factors. The pathogen thrives in temperatures between 15°C and 20°C combined with high relative humidity or leaf wetness. These conditions can lead to rapid systemic infection, resulting in the decay of the entire foliage and rot of the tubers.

Integrated pest management (IPM) is essential for effective control and protection against this pathogen:

• Planting resistant cultivars and certified disease-free seeds.
• Implementing strict crop rotation and removing cull piles.
• Applying protective and systemic fungicides according to disease forecasting models.
• Destroying infected vines before harvesting to prevent tuber contamination.