Kill the newly seeded areas? It might. It will definitely hurt the new seedlings. Directions on weed b gone and similar products usually say not to use within 3 weeks of seeding or on new grass plants until the third mowing. Just hold off until you have cut the actual blades of grass a few time. I know its ugly but give the grass a chance to establish before hitting the lawn with weed killers. Fertilize well. Bill Hill Here is a link that might be useful: Dandelions and Broadleaf Weeds

I used a [fill in the brand] weed and feed in April and it did a good job getting rid of the weeds. In all my years reading lawn forums I've never seen anyone report success with a WnF product. I'm chalking this one up to luck, but I will remember it. If anyone reading this has had success, it would be good to hear from you. Anyway, with my experience in mind, no, now would not be a good time to apply WnF. In fact, the global answer is "never" is a good time to use it. And I'm smiling at this because you have made it work. Nobody else has any good advice on using it. I agree with jdo. Spot spray individual weeds with Weed-B-Gone. Weeds should not be a problem if you are watering and mowing right? What kind of grass do you have? How high/low do you mow? How often do you water? How long do you water? How often do you fertilize and with what? Do you spray any herbicides, fungicides, or insecticides?

rhizo 1 is quite correct about soils - my compost pile, highly organic and loosely textured, is presently sporting a great crop of henbit. When it comes to henbit re-seeding itself, if you see purple you are probably too late. From experience I can tell you that even if the fall germination is eradicated more seed will continue to germinate in early spring. The way to eradicate it is to get after it and stay after it while never allowing it to reach bloom stage. hortster

I suggest seeding in late August or early September. Do a soil test now and get recommendations on lime and any other nutrients your soil needs. You can make amendments this spring and summer to help prepare. Lime, if it's still needed, can be applied every 90 days during the growing season. You could work on killing weeds now or wait until July if you want to kill everything for a fall renovation. You may just want to do an overseeding. If you want to work on weeds now, use a pre-emergent when the forsythia blooms. Use an amount that will wear off by the time you want to seed (read the directions). Use a broadleaf weed killer later in the spring when the weeds are actively growing. If you want to work on weeds later, just mow them this spring and then use Roundup to kill everything in July. Water lightly each day to encourage weed seeds to germinate and a few weeks later kill them again. If you don't want to kill everything but just want to overseed, use selective weed killers this spring and summer as needed and pay attention to how long you must wait until you can seed (read the directions). Sow seeds and water lightly and frequently, gradually decreasing frequency and increasing the amount as the grass comes in. As far as fertilizer, you could do an application in late May, then an application at seeding in August/September (starter fertilizer), then another application (normal fertilizer) in October, and a high nitrogen one after the grass stops growing but before the ground freezes (maybe around Thanksgiving). Do not fertilize in early spring. Keep any lime applications two weeks from any fertilizer. Straw would go on top of the seeds when you seed. All this is assuming you have a cool season grass. What kind of seed will you be using? Are you using good lawn practices for mowing and watering? Don't cut off more than 1/3 at a mowing. Water deeply and infrequently. When you seed, do not use a weed and feed fertilizer as it will keep grass seeds from germinating. In general, use weed killers for weeds and plain fertilizer for fertilization instead of a combination product.