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Plantwise Factsheets for Farmers

Potato late blight

Phytophthora infestans

Recognize the problem

This common disease of potato can be devastating unless controlled. It affects leaves, stems and tubers, turning them brown or black and rotten.
This disease will significantly reduce yield and make potato rot in store.
Early blight is a similar disease, but early blight has rings inside the brown spots. Late blight does not have rings in the spots.


Late blight is more common in wet weather. The disease infects leaves and will spread to the tubers. The disease can be carried in seed potatoes.


  • Inspect your crops often and act as soon as you see late blight in your potatoes.
  • As soon as you see the disease, spray with Ridomil Gold (Metalaxyl and Mancozeb) at a rate of 35 ml per 20 ltr knapsack sprayer.
  • Spray every two weeks if the weather is wet and every three weeks if the weather is dry until two weeks to harvest. Spray when the leaves are dry.
  • Use clean seed potatoes, from a source you trust.
  • After harvesting potatoes, plant a different crop the following year.
  • Moulding soil along the potatoes to protect the tubers from the disease.
  • Remove and destroy all stems and leaves at least two weeks before harvesting, so the disease does not spread from the leaves to the potatoes when harvesting.
  • Some potato varieties are somewhat resistance to late blight such as Tigoni (Kenya) and Rutuku (Uganda).

When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.

The recommendations in this factsheet are relevant to: Ghana, Kenya

Authors: Phil Taylor, Hongmei Li, Joseph Mulema

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

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