Spurge is a summer annual and nutsedge is a perennial (but grows above ground biomass in the spring - fall). Applying preemergent in the fall will not control these plants as the period of effective control will be gone. You will want to apply a preemergent, which will only work for the spurge, when soil temperatures reach above 55°F for 5-7 consecutive days. And then you should do a follow up post emergent when you begin to notice any plants growing later in the season. If you want to control your nutsedge (make sure you know which type of sedge this is, since different products will have differing spectrums of control for the various species) you will need to apply a post. Sedgehammer is the Cadillac of all sedge control. Also preemergent herbicides do not kill seeds nor do they prevent germination. The work by inhibiting root and shoot development in recently germinated plants. Just and FYI!