Effects of water management and herbicide treatments on red rice control.

Two field experiments were conducted in 1999 and 2000 at Zeme (Pavia, Italy) to determine the effects of water managements and herbicide treatments on red rice control. In the first experiment, all plots were flooded 10-13 cm deep from April 1 to May 17 in 1999 and from April 3 to May 6 in 2000. At the same time, in the second experiment, the plots were alternately drained-flooded. At the end of water management, all plots of both experiments were drained and sprayed with herbicides to control the emerged red rice plants. In both years were applied: Propaquizafop 78 g a.i.ha-1, Cycloxydim at 300 and 400 g a.i. ha-1; Dalapon at 15.300 Kg a.i. ha-1; Quizalofop-ethyl at 100 g a.i. ha-1. Six days after the chemical treatments, all field plots were flooded 10 cm deep and three days later, an early variety of rice (Loto) was sown at 150 Kg ha-1. Seedling emergence was reduced by lack of oxygen (especially from seeds covered with soil in flooded condition). In alternately drained-flooded soil, the red rice emerged and developed from seeds located in the top 4-5 cm. In flooded condition, no red rice plants emerged from seeds at more than 1 cm depth. In both experiments, the density of red rice plants increased during the season in the untreated check and in the plots where treatments were ineffective or performed poorly. The best red rice control, both in submerged and in alternately drained-flooded soil, was obtained with Quizalofop-ethyl (100 g a.i./ha), Cycloxydim (300 and 400 g a.i.ha-1) and Propaquizafop (78 g a.i.ha-1). These herbicides controlled 90-99% of red rice. Partial control of red rice resulted with the other chemical treatments. The shattered grains of red rice were reduced in both experiments by the herbicide treatments. Grain yield reflected the level of red rice control. In fact, the highest commercial grain yields were obtained with Quizalofop-ethyl, Propaquizafop, and Cycloxydim (400 g a.i.ha-1), in both years and experiments. The red rice percentages of the total yields resulted about 3.6-5.7% with all chemical treatments except Dalapon, which was not much effective.