Herbicide resistance in rice in Italy: is its evolution associated with agronomic and environmental conditions?

In North West Italy 200,000 ha are cropped with rice following two different systems: in the NW of the area (Piedmont region), monoculture and water seeding are traditional , while in the SE part (Lombardy region) dry seeding technique and rotation are normal practices. Over 95% of the area is treated with ALS (acetolactate synthase) and ACCase (Acetyl CoA Carboxylase) inhibiting herbicides at least once per year. In this study, all weed species affected by herbicide resistance were considered: Echinochloa spp., Oryza sativa (weedy or red rice), Alisma plantago-aquatica, Cyperus difformis and Schoenoplectus mucronatus. A map of all the resistance cases was generated through the dynamic mapping system of the Italian Herbicide Resistance Working Group (GIRE) (Fig. 1) as well as a second map with only Echinochloa spp. resistance cases (Fig. 2), as this weed genus is the most troublesome in the Italian rice system. Resistance cases were confirmed after greenhouse tests following complaint monitoring.