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Plantwise Factsheets for Farmers

"Burned tip" or downy mildew in onions

Peronospora destructor

Recognize the problem

Downy mildew is a fungus that affects all stages of the onion plant. It produces burns and coffee-colored spots on the leaves, generally starting at the tips and moving downwards. At the beginning, it can be confused with injuries caused by chemicals and mechanical damage.

A severe attack may reduce the yields and the product quality almost completely.


This fungus is transmitted through spores that can survive on the soil, attacking new crops. It can be spread by the wind and contaminated seeds. This disease best develops under humid and cool conditions. During the rainy period, prevention and control measures are necessary.


  • Improve fertilization conditions with bokashi or another organic fertilizer to revive the soil and maintain good nutrition of plants
  •  Add ash or lime to the soil
  • Sow during hot and dry periods, but be careful because this type of weather is favorable for the growth of thrips, a pest that is harmful to onions
  • Preventively apply natural products that control harmful fungi such as Bacillus subtilis, Saccharomyces sp., Mimosa tenuiflora extract ("Revancha"), and Trichoderma; make applications on the soil and the leaves at 400 grams per hectare
  • Keep the crop clean, destroying the crop residues
  • Preventively apply Azoxystrobin (e.g. Amistar) at a dose of 67 grams in 200 liters of water or 10 grams per 25-liter pump, totaling up to three applications during the cycle. After applying Azoxystrobin three times, 70% Antracol (Propioneb) can be sprayed at 400 grams per 200 liters of water or 8 bayer cups per 20-liter pump every week.
  • For already infected crops, use products containing 12.8% pyraclostrobinand and 25.2% boscalib (e.g. Bellis) at one gram per liter of water or 80% fosetyl-aluminium (e.g. Aliette) at one kilogram in 200 liters of water.

The recommendations in this factsheet are relevant to: Honduras

Authors: Edgardo Arita, Julio Santos
CENOC (Centro Empresarial de Negocios de Ocotepeque)
tel: 504 97437505 email:;
©CAB International. Published under a CC-BY-SA 4.0 licence.

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