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PEST MANAGEMENT DECISION GUIDE: GREEN AND YELLOW LIST

Late Blight on Potato and Tomato

Phytophthora infestans In Sinhala “Paschimaangamaraya” Tamil: Pitkootuveliral
Sri Lanka
  • Select fields free of crop residues or volunteer potato or tomato plants
  • Prepare land to improve drainage
  • Avoid starting cultivation during heavy rains
  • In case of potato, use disease-free seeds and resistant varieties (e.g. Hill Star)
  • Follow recommended spacing (do not overcrowd plants)
  • Do not overuse fertilisers, especially Nitrogen fertilisers
  • Observe plants regularly from the early stage of crop
  • Look for symptoms such as: Blackish water soaked lesions occur on the leaves; Whitish sporulation of the pathogen can be seen around the margin of the lesions, particularly on the underside of the leaf.; On stems, late blight causes brown to black lesions; The lesions commonly occur at the junction of the leaf and stem where water may accumulate or on clusters of leaves at the top of the stem.
  • The disease spread very quickly over the entire field killing all foliage and causing the death of the entire plant
  • Since the disease can cause huge crop losses, it is advisable to use protective fungicides when the disease symptom first appear to reduce the disease spread
  • In wet weather conditions, application of systemic fungicides at 21 day intervals is a necessity
  • Take appropriate personal and environmental precautions when applying pesticides
  • Propineb WP; mix 2 g/L and apply 5-7 days intervals
  • WHO hazard class IV; Contact fungicide; Alternate with systemic fungicide
  • Mancozeb WP; Contact fungicide, mix 2 g/L and apply 5-7 days intervals
  • WHO hazard class IV; Alternate with systemic fungicide
  • Fluazinam SC; Contact fungicide, mix 0.5-1 ml/L and apply 5-7 days intervals
  • WHO hazard class III
  • Metalaxyl+ mancozeb; Systemic fungicide, miz 2.5 g/L and apply 14-21 days intervals
  • WHO hazard class IV; Alternate with contact fungicide
  • Dimethomorph + mancozeb (WP)l mix 2.5 g/L and apply 14-21 days intervals
  • Systemic fungicide; WHO hazard class III
  • Chlorothalonil WP; mix 3 ml/L and apply 5-7 days intervals
  • Contact fungicide; WHO hazard class IV
AUTHOR(S): K.P. Somachandra (Department of Agriculture)

CREATED/UPDATED: March 2014
PRODUCED BY: Plantwise

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