Is chemical control of Mycosphaerella foliar diseases of banana sustainable?

Leaf spot diseases of banana caused by Mycosphaerella musicola or Mycosphaerella fijiensis are the main constraints in commercial plantations in most banana-producing countries. In humid, high-rainfall conditions, plantation production of dessert bananas for export can only be achieved through intensive chemical control. The development of chemical control strategies in Belize, Cameroon and the French West Indies (FWI) over the past 20 years is described. In all of these countries, which are representative of many banana-growing regions, there have been difficulties in terms of the efficacy, cost and environmental impact of chemical control. This is the result of three major factors: (i) the tightening of legislation governing aerial spraying, which is becoming more and more restrictive, especially in the FWI; (ii) the small number of fungicides now approved for leaf spot control; and (iii) the development of resistance to systemic fungicides. In Belize, the intensive use of systemic fungicides over the past 20 years (35-40 applications/year) has led to M. fijiensis developing fungicide resistance. Regular applications (40-45 applications/year) of contact fungicides (mancozeb, chlorothalonil) are now used to control black leaf streak. Although in Cameroon systemic fungicides (12-14 applications/year) were originally used in combination with a forecasting strategy to control black leaf streak, fungicide resistance has developed in commercial plantations, and this has led to regular application of contact fungicides (40-45 applications/year). In Guadeloupe and Martinique, M. musicola has been controlled efficiently through the use of systemic fungicides (5-7 applications/year) in a forecasting strategy for more than 30 years. Recent French legislation limiting aerial spraying and the kind of fungicides that can be used has resulted in the development of fungicide-resistant strains of the pathogen. As a consequence, the number of treatments/year has recently doubled (10-14 applications/year). New alternatives for control are needed. The introduction of fungicides that have less negative environmental effects may be a short-term solution. Organic fungicides or biofungicides applied in mixtures with contact fungicides may allow producers to reduce the amount of active ingredient applied. The possibility of reversing fungicide resistance in order to reintroduce a more sustainable forecasting strategy may be a mid-term solution. The introduction of cultivars bred for resistance is a long-term goal. (Résumé d'auteur