Seedling mortality and submergence in Diplachne fusca: a semi-aquatic weed of rice fields

Murray-Darling Freshwater Research Centre

MDFRC item.

(1) Causes of seedling mortality in Diplachne fusca were investigated, and the flooding tolerance of seedlings was examined in field and glasshouse experiments in temperate New South Wales, Australia. (2) Seedlings growing under non-flooded conditions in rice crops sown in unflooded soils, were susceptible to water stress, with up to 65% dying. Seedlings emerging in autumn after rain also became water stressed. Those surviving were stunted by cold temperatures or killed by frost or site disturbance. (3) Under controlled flooding conditions, continuous submergence resulted in greater germination than brief irrigations. Delaying permanent flooding gave less germination but fewer deaths after the onset of flooding compared with flooding for the duration of the experiment. Significantly more seedlings established in 4 cm deep permanent floodwater than in 12 cm. (4) In the glasshouse, single-leaved seedlings could establish in 20 cm deep water with no mortality. Submerged seedlings emerged above water level by rapid elongation of the fourth and fifth leaves. (5) A strategy for the control of D. fusca in rice fields is described, using the results of this and previous studies.