answer:Your best bet is to prevent the crabgrass with pre-emergent application of Scott’s or another brand. In So Cal, you’d need to apply the prevention products in December. Since you already have the crabgrass, you’ll need to use post-emergent killer. You can do that anytime, but you’ll need to be mindful of drought/heat. Do not use any lawn weed herbicide product when the temperature is above 85 degrees. Ideally, you’d apply either early AM or close to sunset. You could use a pre-emergent product now to prevent the crabgrass that has yet to sprout. Pre-emergent products work best at helping you completely rid yourself of the crabgrass overtime (meaning you’ll see more results next year and the following year, not ASAP). Since you have fescue, you’ll need to read the bags of Crabgrass Killers (these will most likely need to be applied seperately from a Weed & Feed product…they’re rarely an all-in-one application) to be certain the product you choose isn’t going to harm your lawn. I looked up the organic products…all of them say they’ll damage Bluegrass & Fescue. It looks like you’ll need to go with Scott’s or a local brand. Some of our landscape companies have their own brands that work just as well as the name brands but for a fraction of the cost. You may want to talk to a local nursery to see what they recommend. Overall, I’d recommend you build up the turf you have to inch out weeds. A healthy turf will take care of itself. Don’t cut your lawn too short, feed it, water it and you should notice you’ll naturally have less weeds.