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Late blight of tomato

Phytophthora infestans
  • Do not cultivate tomato in the same field the year after potato or tomato cultivation because tomato blight fungus remains in the soil for several years
  • Volunteer plants (e.g. potato and chilli) should be removed from the garden prior to planting
  • Recommended spacing should be maintained.
  • Avoid overhead watering to prevent splashing so that the leaves do not remain wet.
  • Symptoms often first appear on the lower, older leaves as light-green water-soaked spots or as dark brown patches without a yellow border.
  • Very soon after this, white fungal growth forms around the edges of the patches on the undersides of leaves. This is the most characteristic feature of Late Blight.
  • Stems develop dark brown patches without yellow edges; the plant does not wilt initially.
  • Fruit remains hard and develops brown patches but the skin of the fruit is not damaged.
  • Remove and destroy affected crops at the end of the season
  • If only one or two leaves are seen with the disease, carefully remove them with a knife and seal in a plastic bag. This will not prevent the spread but it will slow it down.
  • Stop irrigation in the infected field.
  • You should spray as soon as the disease is seen.
  • Use protective clothes and mask during spraying
  • Spray a fungicide containing mancozeb (eg. Indofil, Ditane M-45) @ 2g/L of water as preventive measure.
  • Mancozeb: WHO class U, unlikely to present acute hazard in normal use; FRAC M 03.
  • Spray a fungicide containing Fenamidone + Mancozeb (e.g. Secure), Metalaxyl (e.g. Ridomil gold), Dimethomorph or Cymoxanil, along with Mancozeb or Maneb, at the first sign of blight, then at 7-10 day intervals or after rain.
  • Fenamidone: WHO class III, FRAC 11; Mancozeb: WHO class U, FRAC M 03; Metalaxyl: WHO class II, FRAC 4; Dimethomorph: WHO class III, FRAC 40; Cymoxanil: WHO class II, FRAC 27; Maneb: WHO class U, FRAC M 03.
AUTHOR(S): Dr. M. Monirul Islam (BARI), Dr. Aziza (BADC), Md Masud Reza (DAE), Samir Kumar Goswami (DAE)

CREATED/UPDATED: April 2016; updated October 2020
PRODUCED BY: Plantwise

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