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Describe the overall disease situation

Late blight is the most important disease and one of the most important limiting factors to potato production in D.R. Congo. It was recorded for the first time in the country in 1942 [1]. In D.R.Congo, potato is grown by small farmers in highland areas over 1800 m asl where weather conditions are very favorable for potato late blight epidemics; the growing season coincides with periods of intermittent rainfalls and moderate temperatures, both pre-requisites for LB development. Furthermore, farmers in these areas grow potato year round; the major consequence of this practice is a permanent high level source of inoculum in the field.

Estimate crop losses

Relying on data recorded in the Research Center of Mulungu (IDM trials, 2005), crop losses due to late blight represent ± 50%.

Describe farmer practice in disease management

In North-Kivu province, farmers in highlands over 2000 m grow potato year round, for relative humidity is high(>85%) and rainfall is spread out over year round; because of these conditions, farmers  plant potato on hillside during abundant rainfalls and go down in the bottoms(valleys) when rains become scarce. As the pressure of the disease is high on hillside areas, farmers prefer to plant in the valleys during dry season to escape the severe effects of late blight.

In South-Kivu province, there are two rainy seasons: the long one from September to January and the shorter one from March to May. Farmers some time avoid to grow potatoes during long rainy season because of the high late blight  pressure. But, they grow resistant varieties like Cruza. Those who can afford to buy fungicides grow all varieties. Some time, farmers plant towards the end of  long rainy season to escape from late blight; but this management leads to reduced yields because of scarcity of rain.

Fungicides currently being used against late blight in order of priority

Dithane M45 and Ridomil are  the two fungicides currently used ; however, Dithane is the most used because it is more cheaper than Ridomil.

Metalaxyl resistance

During the second meeting of Potato Late Blight Working Group for Eastern and Central Africa held  in Kabale, Uganda  on 28 August-2 September 2005, the laboratory practical

Varieties / land races used in the country. Give for each variety if available additional information in the spreadsheet (CPupdate.xls) on:

Relative importance of tuber blight

Late blight tuber rot is common in the farmer fields; this leads to severe losses during storage. Infected tubers left in the field after harvesting regrow as volunteers and constitute therefore  reservoirs of inoculum.

Describe on-going potato late blight research:

A research on late blight is going on to promote IDM options for control of disease in order to reduce pesticide usage and maintain biodiversity. A working group for this research is formed with representative from CIP, PRAPACE, and the national potato research programs of Burundi, D.R.Congo, Eritrea, Etiopia, Kenya, Rwanda and Uganda.

Currently, regional trials are conducting on Demonstration of IDM of late blight including Development of spraying regimes for LB. Different regimes are as follow:

1: Protectant calendar (1^st spray Dithane at 80-100% emergence, followed by spraying every 14 days till first symptoms of senescence)

2: Systemic calendar (1^st spray Ridomil at 80-100% emergence, followed by Ridomil 3 weeks and 6 weeks later)

3: Protectant rainfall (1st spray Dithane at 80-100% emergence, followed by spraying after every 100 mm accumulated rainfall till first symptoms of senescence; minimum interval of 7 days, maximum interval of 28 days)

4: One spray (Spray Ridomil at first symptoms of late blight only)

5: Two spray (1^st spray Dithane at 80-100% emergence, followed by Ridomil at first symptoms of late blight only)

6: Three spray (1^st spray Dithane at 80-100% emergence, followed by Ridomil at first symptoms of late blight, followed by Dithane three weeks later, if not yet senescing)

7: Damage threshold (Ridomil at first symptoms, followed by sprays at 5, 10 and 15% leaf area infection; minimum interval of 14 days)

8: Unsprayed control.

Publications on late blight in the country

-Bouwe, N.B.1988. Le mildiou de la pomme de terre(Phytophtora infestans) au Zaïre.In : PRAPAC. . Actes du séminaire sur le mildiou de la pomme de terre. Ruhengeri,Rwanda.

-Bouwe, N.B.1988..La sélection de la pomme de terre contre le mildiou à l’INERA-Mulungu. In : PRAPAC. Actes du séminaire sur le mildiou de la pomme de terre. Ruhengeri,Rwanda.

Contact persons 

[1] Hendrick,M.L.,1946. Le mildiou de la pomme de terre(Phytophtora infestans) au Congo Belge, Institut Royal Colonial, Bulletin des Séances, Vol XII, No 3.

aContact: Nasona, Bouwe (INERA). E-mail: bouwenasona@yahoo.fr