Accompagner les réseaux DEPHY-FERME et DEPHY EXPE dans la caractérisation de l’effet des systèmes de culture sur la flore adventice

National audience ; To characterize weed pressure in agricultural fields of the DEPHY Ecophyto networks, the "weeds" working group of the CASIMIR project, helped by crop and weed experts working for the french crop institutes, developed two methods (CASIMIR DEPHY­FARM and CASIMIR DEPHY­EXPE) to survey weeds in main crops. The objectives of these methods are: (i) with short­term concern, assess the efficacy of farming practices to manage weeds within the crop season, (ii) with long­term concern, assess the effect of cropping system (farming practices and crop sequence) on the dynamic of the weed communities. The CASIMIR DEPHY­FARM method is based on walk away surveys made within a 2000­m² reference plot where the trained person walks across the survey area (“W” path). The weeds are identified and their density is visually assessed using a "Barralis" modified scale. Their dominant phenological stages are also recorded. This simple and quick method intends to be used in the DEPHY FARM network. The CASIMIR DEPHY­EXPE method is based on surveys performed on eight 16­m² plots with one quadrat in each. Weed species are identified. The density of each species is visually estimated with a "Barralis" modified scale within the 16­m² plots and precisely counted in the quadrats. On both, the dominant phenological stage of each species is recorded. At the end of the second surveys, the above ground biomass of each weed and crop species is yield to assess the crop­weed competition. This method which is more complex and time­consuming intends to be used in the DEPHY EXPE network. Surveys are performed twice a year: firstly before winter weedings (in winter crops) or before post­emergence weeding (in spring crops) to observe emerging flora; then before the closed­canopy occurred to assess the flora competed crop. To design these methods, the CASIMIR project benefited from the expertise of the RMT Florad. To assess their feasibility, methods were performed in the RotAB and Rés0Pest networks. They are also discussed and criticized ...