Late blight is the most destructive potato disease in the world. It affects all potato producers (small-scale, commercial, seed producers, even urban producers) and the annual losses in developing countries are estimated at EUR 10 billion. Late blight can attack many varieties of potatoes and most farmers use large quantities of fungicides to control this disease. The fungicides can cause environmental damage as well as human health problems when they are misused, since many farmers do not use protective gear that would prevent contact with this type of pesticide. So any technology that optimizes fungicide use to control late blight represents significant progress for potato producers.  

Yungay potato field severely affected by late blight in Chota (Cajamarca, Peru). Photo: Willmer Pérez


Farmers without protective gear apply fungicides to control late blight in Huasahuasi (Junín, Peru). Photo: Willmer Pérez.


Toward this end, the International Potato Center (CIP), in partnership with research and development institutions in Ecuador and Peru, has developed a low-tech tool to help farmers optimize fungicide use. Development of the tool was based on three questions farmers need to answer when they are considering using fungicides:  

  • When do I start to apply the fungicide 
  • Which fungicide should I use? 
  • How often should I apply it?
Answering these questions is more complicated than it appears. Multiple factors are at play. Many farmers in developed countries address these questions with the help of decision-making support systems, which use environmental data from weather stations. The data is uploaded through the Internet to then be analyzed. Alerts can be issued and sent via text message to farmers who should initiate application of fungicides. However, due to the low coverage of the Internet and cell phones in the Andes as well as extreme environmental variation, these systems are impractical there and in other tropical zones.


The CIP tool is called disc tool for potato late blight management. Unlike the systems used in developed countries, the CIP tool is printed on cardboard and does not need the Internet or batteries. Yet it enables integration of the most important factors in the decision on whether to use fungicides: How resistant is the potato variety of concern? Number of days of rain in last week? Number of days since last fungicide application? Taking these three factors into consideration, the tool helps farmers decide when to initiate fungicide application, which fungicide to use, and how often to apply it.

Continue reading on the CIP website.