Symptoms:

1. Foliage Symptoms:
   • Dark, water-soaked lesions on leaves, initially appearing as small, greenish spots that quickly enlarge and turn brown or black.
   • Lesions may appear greasy in wet conditions and develop a white mold-like growth on the undersides of leaves during humid weather.
   • Infected leaves may curl, wither, and die, leading to rapid defoliation.
2. Tuber Symptoms:
   • Dark, sunken lesions on potato tubers, often starting at the stem end or wounds.
   • Lesions may be firm or mushy, with a granular appearance.
   • Infected tubers are prone to rotting, which can lead to storage losses and spread of the disease.

Recommendations:

1. Cultural Practices:
   • Crop rotation: Rotate potato crops with non-host crops to break the disease cycle and reduce inoculum levels in the soil.
   • Proper spacing: Maintain adequate spacing between potato plants to promote air circulation and reduce humidity around plants, which can help minimize disease development.
   • Timely planting: Plant early-maturing potato varieties to avoid late blight epidemics later in the season.
2. Chemical Control:
   • Apply fungicides labeled for late blight control according to recommended schedules, particularly during periods of high disease pressure.
   • Rotate between fungicide groups with different modes of action to reduce the risk of resistance development in Phytophthora infestans populations.

Causes:

1. Fungal Pathogen: Late blight of potatoes is caused by the oomycete (water mold) pathogen Phytophthora infestans.
2. Environmental Conditions: Late blight thrives in cool, wet conditions. Rain, dew, and high humidity create favorable conditions for spore germination and disease development.
3. Infection Sources: Phytophthora infestans can survive between growing seasons on infected potato tubers or as spores in plant debris, soil, or on volunteer potato plants.

Preventive Measures:

1. Sanitation: Remove and destroy infected plant debris, including leaves, stems, and tubers, to reduce the source of inoculum for future infections.
2. Resistant Varieties: Select potato varieties that are bred for resistance or tolerance to late blight to minimize disease incidence and severity.
3. Monitoring: Regularly scout potato plants for symptoms of late blight, such as lesions on foliage and tubers, and take prompt action if detected.
4. Integrated Pest Management (IPM): Incorporate cultural practices, fungicidal control, and resistant varieties into an integrated pest management program to effectively manage late blight while minimizing environmental impact and pesticide use.

By implementing these preventive measures and adopting an integrated approach to disease management, potato growers can mitigate the impact of late blight and sustain healthy potato production.