Management of Late Blight

• Infected tubers and cull piles stocked near cold stores serve as primary source of inoculum and should therefore, be destroyed or buried deep in the soil.
• By doing this a large quantity of initial inoculum from such sources can be reduced.

• Since the fungus responsible for causing late blight survives in the infected seed tubers kept in cold stores during summer, visible blighted tubers from all seed stocks should be carefully sorted out and destroyed after storage.
• It is advisable to pile up harvested tubers for few days (7-15) in the field before storing in cold stores.
• Only disease free certified seed should be used.
• At the time of harvesting, grading and picking seed tubers should be properly examined and infected seed tubers should be sorted out and burnt or buried deep in the soil.

• In the potato fields, exposed tubers and those poorly covered with soil area easily get infected by sporangia which are washed down from foliage by rain.
• To reduce the tuber infection, proper hilling and earthing up should be practiced. About 2-3 weeks before harvest, foliage of late blight affected crop, from which seed is to be obtained, should be cut and destroyed. This will reduce the chances of tuber infection.
• The planting dates may be advanced to avoid the epidemic build up as the disease does not appear on early sown crop in Punjab.
• Wider intra-row and inter-row spacings are useful as these create unfavourable conditions for disease development. Wide spacings also help adequate earthing up of plants. Rows facing sun also discourage infection.
• Digging of potatoes should be done after 2-3 weeks of dehaulming by which time the tuber skin hardens while soil infection diminishes.

• Kufri Ashoka, kufri Chandramukhi, Kufri Bahar and Kufri Pukhraj varieties of potato are highly susceptible to late blight.
• Kufri Jyoti, Kufri Sutluj and Kufri Badshah are moderately resistant.
• Central Potato Research Institute, Shimla has released potato varieties like, Kufri Chipsona-1 and Kufri Chipsona-2 for cultivation in northern plains of the country. These varieties are also moderately resistant to late blight and are suitable for processing.
• Planting of unknown varieties should be avoided.

• It has been observed that late blight of potato generally makes its appearance on Kufri Chandramukhi and Kufri Pukhraj in first or second week of November in some areas of Hoshiarpur district from where it then spreads to the adjoining fields. Therefore, it is advisable to spray the crop at this time with protectant fungicides such as mancozeb (Indofil M-45/Mass M-45/Markzeb) or cholorothalonil (Kavach) or propineb (Antracol) each @ 500-700 gm/acre or Blitox-50/Markcopper @ 750-1000 gm/acre. However, these fungicides have to be applied as preventive measures and the spray is to be repeated after 7 days. Once the infection has established and symptoms developed, these fungicides prove ineffective.
• Successful control of the disease depends on both efficacy of the fungicide and good foliage coverage with the spray solution. The neighboring farmers should also be advised to spray crops with fungicides so that inoculum of the disease is minimized.
• Under more favourable weather conditions (highly humid due to rains, foggy, cloudy weather), late blight is likely to develop in an epidemic form.
• Under these conditions, sprays of systemic fungicides in pre-packed mixture with protectants such as Ridomil Gold (8 % mefanoxam + 64 % mancozeb) or Curzate M-8 (8% cymoxanil + 64% mancozeb),  Sectin (10% fenamidon+50% mancozeb) @ 700 g/acre or Revus (mandipropamid 250SC) or Equation pro (16.6% famoxadone+22.1% cymoxanil) @ 200ml/acre should be given and repeated once at 10 days interval.

• Under low to moderate disease risk situation, spray Indofil M-45/Mass M-45/Markzeb or Kavach or Antracol each @ 500-700 g/acre or Blitox-50/Markcopper @ 750-1000 gm/acre (starting from first week of November) before disease appearance. Give five more sprays at weekly intervals depending on disease situation and weather conditions.
• In high disease risk situation, due to favorable weather conditions (high relative humidity due to rainy spells) 3rd and 4th spray may be given with Ridomil Gold or Curzate M-8 or Sectin @ 700 g/acre or Revus or Equation pro @ 200ml/acre  at 10 days interval. Give one more spray of Indofil M-45 or Kavach or Antracol subsequently.
• On successive late sown crops and spring crop, if the preceding crop is already attacked by late blight and the inoculum is abundantly present, first spray may be given with Ridomil Gold, followed by Indofil M-45 sprays at weekly interval.
• Caution: Do not use under dose of Ridomil Gold or self prepared tank mixtures of metalaxyl and mancozeb as this may lead to development of resistant strains of the pathogen.

In high disease risk situation, due to favorable weather conditions (high relative humidity due to rainy spells) 3rd and 4th spray may be given with Ridomil Gold or Curzate M-8 or Sectin @ 700 g/acre or Revus or Equation pro @ 200ml/acre A at 10 days interval. Give one more spray of Indofil M-45 or Kavach or Antracol subsequently.