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PEST MANAGEMENT DECISION GUIDE: GREEN AND YELLOW LIST

Citrus scab fungal disease in lemon and tangerine

Elsinoë fawcettii
Zambia
  • Plant resistant varieties such as sweet or navel orange
  • Intercrop citrus with non-citrus trees that are not prone to infection, such as avocado, guava, papaya
  • Grow young plants under a cover
  • Do not allow tall weeds to grow around young citrus tree plantings as they increase the dampness in the citrus tree canopy, which favours disease development.
  • Keep the orchard clean as the pathogen survives on diseased leaves, twigs, and fruits within the tree canopy and in citrus plant debris
  • Prune trees once in 3 months to increase air circulation. Free the tree from deadwood which harbours the fungus. Foliage will dry more rapidly after a rainfall and fungicide sprays can penetrate the canopy more efficiently after pruning.
  • Check for symptoms of this fungal disease once a week
  • Look for small slightly raised spot or rounded swelling on leaves and young fruits. They are pink to light brown and may progress to yellowish brown and then to a dirty grey
  • Later the small elevated spots become warty and crack.
  • Consider taking action before flowering starts, and when first symptoms are found on leaves of several trees.
  • Also consider action if heavy scab infections had been experienced the previous cropping season.
  • Action is too late, when scab symptoms are found all over the orchard. This is because most actions are preventive not curative.
  • During early symptom detection remove infected leaves and fruits and destroy by burying deeply
  • Prevention is the most powerful measure because symptoms are difficult to see in young trees, and by the time you see them the damage has already been done.
  • When using a pesticide or botanical, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, pre-harvest interval, max number of sprays, restricted re-entry interval. Do not empty into drains and water sources.
  • WHO toxicity class II pesticides might not be allowed in local IPM schemes.
  • Always consult recent list of registered pesticides of ZEMA
  • Protective (not curative) Captan –based products (such as Merpan, Orthocide, SR-406, Vancide 89 and others). Usually at 2 level tablespoon per 5 litres water, but double-check product label. Protective preventive fungicide of phthalimide group.
  • WHO toxicity class U (unlikely to present acute hazard in normal use). Do not use close to fruit maturation. Pre-harvest interval p.h.i 14 days, restricted re-entry interval 4 days. Max 5 sprays per season, with no less than 10 day intervals. Toxic to aquatic organisms
AUTHOR(S): Mooya Nzila, Zambia Agriculture Research Institute ZARI, Mt Makulu, Zambia, email: mooyanzila@yahoo.com

CREATED/UPDATED: July 2015
PRODUCED BY: Plantwise

©CAB International. Published under a CC-BY-SA 4.0 licence.