Several chemical products (approved for lawn usage) contain 2,4-D to kill weeds. 2,4-D is a known carcinogen.
You can have a healthy lawn and (relatively) free of weeds without harmful chemicals by simply raising your lawn mower blade to cut at 2.5 inches. Longer grass does not allow weeds (that need light) to germinate, and yet the grass grows well (and thick). Areas that are not mowed can be planted with clover or alfalfa (these are legumes). Those plants shade germinating weed seeds plus enrich the soil naturally.
Gardeners should use black polyvinyl plastic to shade out germinating weed seeds. Mulching the area around shrubs and small trees with sawdust, bark, pine needles, limestone chips, or similar materials effectively keep unwanted plants at bay. This practice also reduces competition for soil moisture.
A highly recommended 100% natural (organic) fertilizer for the lawn is Milorganite®. One advantage is that it won't burn the lawn as easily as other fertilizers...if you apply it wrong. The bag instructions recommend three feeding cycles per year. (Note: Feedings times are on the bag... three times a year, but easy to remember: Memorial Day, Labor Day, and Thanksgiving Day.) Remember, to follow the simple directions! Also note that Milorganite®; costs seven to nine dollars for forty pounds and covers approximately 2500 square feet... very inexpensive. Milorganite® can be purchased at a varity of places... ACO, Meyers, KMart, Walmart to name a few.
Note: I have less problems with moles since I began using Milorganite®... I can't claim a relationship, but it is very real observation. I also scatter coffee grounds in bare spots... thus giving another natural source of nourishment to the grass (roses like coffee (grounds) too).
Another lawn tip is to plant grass seed in August for best results (seems strange to pant in the heat of the Summer, but it is the recommended planting time).
My lawn took about two years to recover from cutting too short (I never used chemicals since I react adversely to them). However, my grass never grew well (I have sandy soil). But, by following the advise of a greens keeper (a "Doctor of Grass" from Michigan State), my lawn is looking better than ever. Oh yes, stubborn weeds are extracted by hand.
Mow Grass Higher (set cut to 2.5 to 3.0 inches -- cutting at 4.5 inches)
Use Milorganite® as recommended on the label three times a year
Seed in August
Give the above a try... and, be patient! It may take a few years to see the results.
Kill Grass Growing Between Concrete (in the cracks)
Pour white vinegar in the cracks. The weeds and grass will die.
Golfers: Do not put your golf ball in your mouth, or even near it (as former U.S. President Clinton did on national TV). What a dumb habit! No offense to the former President). Most golf courses use horrific amounts of chemicals.
Note: A friend forwarded this site for "Safe and Natural Fertilizers": http://www.naturesafe.com/ so, you may also want to check this out.