AGRONOMIC RESPONSE OF WINTER RAPESEED TO RATE AND DATE OF SEEDING

In northern Idaho, winter rapeseed (Brassica napus L.) usually is seed ed on summer fallow in early to mid-August at 4.5 to 13.5 kg seed ha(- 1). A 2-yr study was conducted at Moscow, ID, to quantify crop perform ance as influenced by date of seeding and seeding rate. In the 1991-19 92 and 1992-1993 growing seasons, high-erueic-acid winter rapeseed cul tivars, 'Dwarf Essex' and 'Bridger', were seeded on four dates at 2-wk intervals from early August to mid-September at four seeding rates fr om 0.9 to 2.7 x 10(6) seeds ha(-1). Greatest yield for the four dates ranged from 1974 to 2675 kg ha(-1). Optimum spring plant stands for at taining those yields were between 61 and 112 plants m(-2), obtained at different seeding rates, depending on the date of seeding. The lowest seeding rates (0.9 and 1.5 x 10(6) seeds ha(-1)) produced optimum spr ing plant stands for the mid-August and early September seeding. Highe r seeding rates in early August and mid-September were necessary to ac hieve optimum spring plant stands.