Botanical identification of several Echinochloa biotypes collected in Spanish rice fields with control failures of cyhalofop-butyl.

There is some disagreement about the species that constitute Echinochloa. Correct identification is agronomically and economically important because Echinochloa spp. are aggressive invaders and difficult to control. The identification of Echinochloa spp. is complicated because of the morphological diversity shown by the genus. This work was initiated because of the differential response to cyhalofop-butyl treatment shown by some populations of Echinochloa spp. Four biotypes were selected for botanical identification: two biotypes collected in the Seville area, one of them susceptible to cyhalofop-butyl (ED50 = 64 g a.i.ha(-1)) and the other one tolerant (ED50 = 560 g a.i.ha(-1)), one tolerant biotype collected in the Badajoz area (ED50 = 420 g a.i.ha(-1)) and one tolerant biotype collected in the Valencia area (ED50 = 860 g a.i.ha(-1)). Botanical identification was carried out following Carretero's Keys (1981) on plants grown at the site of origin. The main distinguishable character of the species was the length of the upper glume. The following results were obtained: the susceptible biotype collected in the Seville area and the tolerant biotype collected in the Valencia area were characterized as Echinochloa oryzoides, the tolerant biotype collected in Badajoz was characterized as E. oryzicola and the tolerant biotype collected in Seville area as E. hispidula.