I actually did mow right before I seeded. I sprayed because I wanted a real clean brassica plot. I think it was the right move because I had a strip of the oats/peas/ clover that I missed somehow with spray. In this strip that was just mowed,not sprayed, there were some weeds,some thick clover, the oats had started growing again, causing the brassicas didn't germinate as well. This is the first time I tried this rotation so its a little trial and error. I was really happy the way it turned out, the only thing that I think I will do next year is run the disk over the plot a few more times before I seed. It was a night and day difference as far as growth and germination, although if some didn't want to disk the germination was good enough to have a nice plot.