Growth of Murdannia keisak as affected by water management and timing and rate of several herbicides

Murdannia keisak (Hassk.) Handel-Mazz. is a member of the Commelinaceae family and it is reported in the spontaneous vegetation of Italy since 1974, while first significant infestations in paddy fields are dated from the end of 1990’s. Despite the importance of M. keisak in several rice growing areas, only few information on biological and ecological traits related to the agronomical management of this weed are available in the literature. The aim of this paper was to study the effect on M. keisak of different water management strategies and to investigate the sensitivity of the weed to widely used rice herbicides applied at different growth stage. M. keisak and rice plants were grown in pot in greenhouse under different water management conditions: saturation (A), intermittent irrigation (B), and continuous flooding (C). Aboveground fresh weight of both species were measured 50 days after seeding. M. keisak plants grown in pots at 3- or 7-leaf leaf stage were sprayed with one of the following herbicides: azimsulfuron, bensulfuron-methyl, cinosulfuron, bispyribac-sodium, bentazone, ethoxysulfuron, glyphosate and triclopyr. The herbicides were applied at the rates of 0 (untreated check), 0.5, 1 or 2 times the recommended field rate. Herbicide efficacy was determined by measuring aboveground fresh weight 15 days after spraying. Plants of M. keisak grown under continuous flooding conditions showed the lowest values of aboveground fresh weight (9.6% of that recorded in saturation conditions). Bispyribac-sodium, bentazone, triclopyr and glyphosate effectively controlled M. keisak already at 0.5x field rate, either when sprayed at 3- or 7-leaf stage plants. Bispyribac-sodium, triclopyr and glyphosate were more effective against older plants. A successful control strategy of this weed can be achieved with a correct choice of water management, herbicide and stage of application.