I've planted for several years now, and had farmers that have planted rr ready bean and corn do my plotsfor me as well....Both my farmer friends, who have done it since this seed was engineered, and myself spray at the same time the seed is drilled....don't worry about shading the seed, what you need to worry about is your weeds and other grasses taking the nutrients away...that's why you spray round up to begin with, to kill out anything that's harmful, that will choke out the seed and take it nutrients away...you need to spray as soon as you can...Your seed will grow no matter what as long as the weeds and grasses are dead, by the time your seed would be up enough for shade to matter, they would done be robbed, and that's what would hurt them and that's what makes the difference...