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Management of black sigatoka in Cameroon

De Lapeyre de Bellaire L., Essoh Ngando J., Abadie C., Carlier J., Fouré E.. 2006. In : International Congress Black Sigatoka Management in Banana and Plantain in Latin Ameria and the Caribbean, San Jose, Costa Rica, March 21-23, 2006. s.l. : s.n., 19 p.. International Congress Black Sigatoka Management in Banana and Plantain in Latin Ameria and the Caribbean, 2006-03-21/2006-03-23, San José (Costa Rica).

In Cameroon, Mycosphaerella fijiensis was reported for the first time in 1981 and the control against black leaf streak disease represents the highest production cost which can attend up to 10% of total production cost. Towards the end of the 80s, a forecasting system using biological descriptors was elaborated and applied with success, reducing the number of treatments to 12 - 14 per year. Since 1996, the development of fungicide resistance lead to the progressive abandon of this rational strategy at the expense of systematic control methods. Thus in 2005, about 40-50 treatments were done on most of the plantations and the control program was based on the ratio of 90% of contact fungicides and 10% of systemic and penetrant fungicides. This evolution has lead to an important increase of the cost of disease control, but also to an increase of negative environmental effects. Material and Methods. In those conditions, research conducted in Cameroon is aimed to: (1) Experiment fungicides having less negative environmental effects; (2) Adapt control strategies to the situation of fungicide resistance; (3) Evaluate the adaptive potential of Mycosphaerella fijiensis populations in response to the use of systemic fungicides. Results. (1) Some of the new fungicides tested enabled an acceptable control of BLSD when they were used in oil. (2) Experiments realised in 2005 have shown that chlorothalonil applied on a systematic framework, and compared with penetrants used in a forecasting strategy, enabled a very good control of the disease, even in the rainy season: strong reduction of the Stage of Evolution of the disease, increase of phytosanitary level in the banana plantations (Youngest leaf spotted). (3) Very important fluctuations in the levels of resistance to systemic fungicide have been observed in Cameroon. Some observations clearly show that management of resistance should refer to the control of the disease in nurseries, and also to nurseries location. Discussion. New fungicides should be used in water alone to enable a rapid conversion to chlorotalonil applications and to reduce negative effects of oil when used in a systematic calendar (treatments every week). New strategies where the proportion of chlorothalonil would be rationalized to a minimum will be evaluated in the next year. We make the hypothesis that the fluctuations observed in the resistance frequency to systemic fungicides could result from a lower fitness of resistant strains, which could be counter- selected in the absence of the fungicide selection pressure and/or gene-flow between the treated and the untreated areas.

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