I live in Montreal, Quebec, Canada. Several years ago the provincial government (Similar to a statein the USA) enacted a law banning pesticides and herbicides on lawns. This was done with the future health of its' young citizens in mind. You can still buy spray bottles to kill offensive weeds or bugs, but the large scale-large bags of pesticides or herbicides are gone. I could cross the border into Ontario, a province within 1 hour of Quebec, but I don't!
I thought trying to keep weeds out of my lawn would be problematic, but with weekly efforts, you can manage quite well. Of course, you have to have the time, and make the effort to "control" the weeds. If you do so, then the effort will pay off. I live on a lot of 7900 square feet, with I guess the lawn occupying about 5000 square feet. Larger-sized lots might prove to be too hard to manage, and even my lawn size might be hard for some.
So what do I do to control the weeds?
1. Don't cut your grass too short. The taller the grass, the harder it is for the weed seeds to hit the earth and sprout. Also, the grass will be healthier and "battle" the weeds for earth. You may have to mow your lawn every 4-5 days instead of once a week. To keep the grass taller, you adjust the wheels of your lawn mover to a higher level. Be sure to do all lawn mover adjustments when the mover is off!
2. Use those weed diggers to pull out long-rooted weeds such as dandelions, and be sure to pick those weeds out before they flower and go to seed. Weed roots such as dandelions can be up to 5 inches (10.5 cm) in depth.
3. Divided your lawn into sections. By doing this, you can spread out the work over several days, rather than exhaust yourself in 1 day.
4. Wear sunglasses, a hat, and sunscreen, and drink water from time to time. Also take a rest and stand up. Most of the time, you'll be down on your knees to see those "varments". Depending on where you live, you might have to apply bug-repellant to avoid being bitten by mosquitoes and black flies.
5. Check out the acidity/alkalinity of your soil. Some weeds like acididity, so if your soil is acidic, you can add lime to the soil. Lime is slow to dissolve into the soil, so this will take time. Lime is not too expensive.
6. How do you know the difference between a weed and grass? I might be wrong, but grass has long and thin blades, whereas weeds have leaves, spread out and have flowers.
7. I also have a problem with clover, which may or may not be a "pest" to some. Clover absorbs nitrogen from the air, and can be beneficial to the soil. I prefer to try and remove it. By the way, clover also likes acidic soil.
8. I have seen an environmentally-friendly weed maintenance company. For now, however, since I have the time, I'll take care of the lawn myself.
9. I recently had a bout with sod worms. These are moth-type pests (adult stage) that lay eggs in soils). These eggs develop into larvae and eat the shoot root/stem parts in the soil. This then causes the grass to die and yellow. The results resemble the effect of urine on grass or over-fertilizing in 1 spot. The solution is interesting. You purchase live nematodes on the internet and then use water to spray them over your lawn. Water the lawn heavily, so the nematodes can burrow into the soil and kill the larvae.
Remember, that you won't eliminate all of the weeds, but you will be keeping be keeping them in check. I get lots of positive feedback from all my neighbours, who all have gardeners. They admire my perseverence and nice 95%C weed-free lawn. However, my neighbours either don't have the time, or don't care to weed their lawns. Their gardeners only mow their lawns and trim their hedges. Everything else, such as weeding is extra, and I've never seen a gardener do any weeding.
I hope this helps you out with your lawns,