While herbicide advertising often talks about full-season weed control, we really only need herbicides to control weeds until the canopy has developed sufficiently to suppress any late-emerging weeds. Iowa State University research found that less than 1 percent of the waterhemp emerging at the V8 corn stage survived. While there was higher survival at earlier emergence dates, biomass and seed production of waterhemp emerging at the V5 corn stage was suppressed more than 90 percent compared to plants emerging with corn.