2. Causal Organism:

Phytophthora infestans (fungus like oomycete)

3. Affecting Stage:

Can affect potato plants at any growth stage, but most severe during the vegetative and tuber formation stages.

4. Symptoms:

 Leaf Symptoms: 

• Initially, small, water-soaked spots appear on leaf tips or edges, often surrounded by light green halos.
• Spots enlarge, becoming brown to purplish black, and cause blighting of the leaf.
• During humid conditions, a whitish fungal growth can be seen on the underside of leaves near the lesion edges.
• Severely infected plants exhibit rapid wilting and drying of foliage.

 Stem Symptoms: 

Dark brown or black lesions develop on stems and petioles, leading to tissue collapse.

 Tuber Symptoms: 

• Tubers show brownish to purplish sunken lesions on the surface.
• On cutting, infected tubers reveal brown, granular, or corky rot extending into the flesh.
• Secondary infections by bacteria can lead to tuber soft rot.

5. Favourable Conditions:

• Cool and humid weather with temperatures between 10-25°C and high humidity (90% or more).
• Frequent rainfall, dew, or irrigation during susceptible growth stages.
• Dense planting and poor airflow in the crop canopy.

6. Cultural Control:

• Plant resistant varieties such as Kufri Jyoti, Kufri Himalini, or Kufri Bahar.
• Use certified disease-free seed potatoes to prevent initial inoculum.
• Avoid excessive irrigation and ensure proper field drainage to prevent waterlogging.
• Practice crop rotation with nonhost crops (e.g., cereals or legumes) to break the disease cycle.
• Remove and destroy infected plant debris and volunteers from previous crops.
• Apply mulches to reduce soil moisture fluctuations and protect tubers from infection.

7. Organic Control:

• Spray with neem oil or garlic based biopesticides as a preventive measure.
• Use of Trichoderma viride as a soil application or foliar spray to suppress the pathogen.
• Application of compost tea to boost plant immunity against infections.

8. Chemical Control:

• Mancozeb 75% WP @ 2.5g/liter of water (protective fungicide).
• Chlorothalonil 75% WP @ 2g/liter of water (contact fungicide with protective action).
• Metalaxyl 8% + Mancozeb 64% WP @ 2g/liter of water (systemic + contact action).
• Cymoxanil 8% + Mancozeb 64% WP @ 2g/liter of water (curative and protective fungicide).
• Propamocarb hydrochloride 722 SL @ 2.5 ml/liter of water (systemic fungicide).

9. Trade Names of Chemicals:

• Dithane M-45 (Mancozeb 75% WP) – Indofil.
• Kavach (Chlorothalonil 75% WP) – Indofil.
• Ridomil Gold (Metalaxyl 8% + Mancozeb 64% WP) – Syngenta.
• Curzate (Cymoxanil 8% + Mancozeb 64% WP) – DuPont.
• Previcur Energy (Propamocarb hydrochloride 722 SL) – Bayer.

By adopting these integrated management strategies, Late Blight in potato can be effectively controlled, ensuring higher yields and quality tubers.