PEST MANAGEMENT DECISION GUIDE: GREEN AND YELLOW LIST
Late blight of tomato
- 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.
CREATED/UPDATED: April 2016; updated October 2020
PRODUCED BY: Plantwise
©CAB International. Published under a CC-BY-SA 4.0 licence.