If the herbicide is atrazine, then yes, absolutely. The USDA just published that about atrazine. The more often you use it, the less effective it is. Nevermind that, weed and feed almost always has no effect on weeds. It is just about the worst product made for lawns. Why? Because weeds die best when they are well fertilized. If you apply herbicide and fertilizer at the same time, the weed killer goes to work right away on the unhealthy weeds and fertilizer takes 2 weeks to kick in. So by the time the weeds are healthy enough to uptake the herbicide, it's dissipated. Not only that but you probably don't need fertilizer at the beginning of spring. It is much better to apply fertilizer after you are mowing the grass and even into May. Then apply 2/3 to 3/4 of your annual fertilizer in the fall. But if you want to kill weeds, fertilize now (I know I just said not to) then come back in 2 weeks with Weed-B-Gone spray and spot treat the weeds that are left. Or, if you already used the weed n feed, then wait 2 weeks and spray with Weed-B-Gone.

Sara is right about the grass needing to be wet before you apply wnf products. This is counter intuitive because no other products go onto wet grass. It's also a pain in the butt because the grass you watered will often dry enough before you get to it that the wnf again goes onto dry grass. You almost need two people to do it right. Your grass seeding plan is almost certainly doomed. It is too late for even a spring seeding. Spring seeded lawns typically end up being weedy with crabgrass by July. The new grass plants cannot compete in the heat against crabgrass, so the crabgrass wins. Fall is the time to seed. Furthermore you should not rototill prior an area for a lawn. Scott's recommends rototilling, but it is our contention that they do it so they can sell more products later on when you try to fix your lawn. Rototilling destroys the soil structure and kills off much of the soil microbes. It can take months to restore the biology and years to restore the structure. Once the structure is repaired, the surface is left bumpy. Still further, don't add more topsoil unless you have low spots that need to be raised to correct poor drainage. Adding topsoil always changes your drainage. At worst it can redirect water into your basement. At best it will correct low spots. Adding topsoil simply because you're seeding is not a good reason. Mother Nature does not add topsoil when She seeds. Yes, lots of newbies screw up their lawns, but so do lots of experience lawn folks. I had been taking care of my lawns incorrectly for 40 years before I found this forum. I had 40 years of experience to unlearn before I got things turned around. The Scott's approach is expensive because you are applying fertilizer at the wrong time of year and end up applying extra later to fix the damage caused by the original poor timing. It also makes the blanket assumption that all yards need to be treated for weeds and insects. This is not true and is a waste of insecticide and herbicide. These products do harm the soil microbes. Lastly (at least all I can think of for now), Scott's fertilizer program does not address the primary issues with lawns of improper watering and mowing. Fertilizer is last on the list of importance in the elements of lawn care. If you're watering and mowing right, you likely will not need either herbicide or insecticide. Oh one more thing. Scott's advertising would have everyone seeding in the spring. I can't remember seeing seed advertising in the fall. Spring seeding sells a LOT more herbicide as people try to stop crabgrass from its inevitable domination of the spring seeded lawn. When lawns are seeded in the fall there should be no crabgrass the following year.

Weed and feed is a broadleaf weed killer and will have no effect on grassy weeds. To post a picture, upload it to a photo sharing site like photobucket.com or imageshack.us, then use the img html tag to post it here (don't use the bbs tag that the photo hosting site provides. GW doesn't use bbbcode). If they don't provide a copy/paste link, the code is: <img src=http://www.site.com/imagename.jpg> Change www.site.com to the url of the site where it is hosted and imagename.jpg to the name of your picture.

If you are watering only once per week, then you have a shot at fixing this. The least harmful non-organic approach (after pulling the weeds) is to spot spray individual weeds with something like weed-b-gone. The idea of sprays is to moisten the leaves (ONLY) with the spray. That way you are doing the least harm to the soil and soil microbes. Crabgrass is easily killed in St Augustine. Crabgrass is very sensitive to salt and St Augustine is nearly impervious to salt. Thus you can dust baking soda onto wet crabgrass and it will die in a day or two. It turns a nice color of black almost immediately. When you wet the crabgrass, use a little detergent in the water or even molasses so the water does not simply ball up and roll off the crabgrass blades. Then dust the baking soda from a sock. That makes a very fine powder that will stick to the leaves. You might try that on the other weeds, too. I never thought of trying it on dollar weed. Two weeks after you use the baking soda, dust some compost onto the area to reinvigorate the soil fungi. Baking soda is very hard on fungi.