Résistances aux herbicides chez les mauvaises herbes

Résumé - L'usage inconsidéré des herbicides pour un désherbage systématique des grandes cultures a conduit à l'apparition de mauvaises herbes résistantes. Huit familles d'herbicides sont concernées par ce problème. Plus de 60 espèces montrent des populations résistantes qui sont réparties dans tous les pays industrialisés. Monoculture et répétition des mêmes traitements sont à l'origine de ce phénomène. Dans certains cas, la sélection pour la résistance à un herbicide a aussi conduit à la résistance pour d'autres herbicides de modes d'action parfois différents. Des exemples sont décrits faisant le point de nos connaissances et en essayant de dégager les stratégies propres à combattre ces résistances.

Abstract - Herbicide resistances in weeds. The indiscriminate use of herbicides for selective weed control in major crops has led to the appearance of resistant weed biotypes. There are now 67 species that have evolved biotypes resistant to one or more herbicides. This includes 19 grasses and 48 broadleaf weed species. Nine herbicide families are involved in this connection. Herbicide resistance is now found in virtually all industrial countries. It is estimated that the land infested with triazine resistant weeds exceeds 2 million ha mostly in the USA, Canada and Europe. Repetition of the same crop and the same herbicide on a field is largely responsible for this phenomenon. In a few cases, selection for resistance to one herbicide has also led to resistance to other herbicides sometimes having different modes of action (cross-resistance). Control of triazine resistant weeds has been satisfactorily achieved, however increasing the cost of the weed management strategy. It is doubtful whether new resistances, especially in the case of cross resistances, can be managed as successfully as triazine resistance was in the past. As triazine resistance is the first and the most documented case of herbicide resistance, one third of this paper is devoted to its history, distribution (table I), mechanism, inheritance, physiology and fitness consequences. Other examples of herbicide resistance are described (table II) as well as discussion of strategies to combat resistance.