INFLUENCE OF SOWING TIME ON WINTER WILD OAT (ARENA-LUDOVICIANA) CONTROL IN WHEAT (TRITICUM-AESTIVUM) WITH ISOPROTURON

Field experiments were conducted during the winters of 1987-88 and 198 8-89 at Haryana Agricultural University, Hisar, India to evaluate the response of winter wild oat to sowing date and isoproturon application time in wheat. In another experiment, the effect of sowing time on em ergence and growth of winter wild oat and wheat sown separately was st udied. The treatments that provided more than 75% control of winter wi ld oat were: isoproturon at 0.75 kg ha(-1) applied at the 2-1eaf stage of winter wild oat; isoproturon 1 kg ha(-1) applied at the 4-leaf sta ge of winter wild oat in the November 30 planting; and isoproturon 0.5 0 kg ha(-1) applied at the 1- to 2-leaf stage of winter mild oat in th e December 20 sowing. Isoproturon did not provide more than 50% contro l of winter wild oat in the November 10 sowing. Mortality of winter wi ld oat increased from 38 to 72 to 87% in November 10, November 30, and December 20 sowings, respectively. Mortality of winter wild oat was s imilar in November 30 and December 20 sowings but higher grain yield w as recorded in November 30 sowing. Due to vigorous growth of winter wi ld oat in the November 10 sowing, isoproturon did not provide good con trol. December 20 sowing favored wheat growth due to lower density and late emergence of winter wild oat but reduction in wheat grain yield was greater. When averaged over isoproturon treatments, the grain yiel d of wheat was 4607, 5297, and 4457 kg ha(-1) in the November 10, Nove mber 30, and December 20 sowings, respectively.