Biotypes resistant to herbicides in paddy fields in the Iberian Peninsula

A consequence of modern agriculture and its dependence on herbicides, is the appearance of resistant weed populations. The first case of resistance on the Iberian Peninsula was found in Portugal and it was in a population of Alisma plantago-aquatica, resistant to bensulfuronmethyl, an ALS-inhibitor. For the same herbicide, control problems with Cyperus difformis were found in some Spanish rice fields. In the same rice field area, tolerance was observed in some Echinochloa spp. when auxinic herbicides (quinclorac) were used and some resistant Echinochloa spp. populations were found due to the long use of PS II inhibitors herbicides (propanil). The association of active ingredients, rotation of crops and adoption of mechanical control methods are the main strategies to combat resistance to herbicides.