Answer: Unfortunately, it's not as simple as just applying an organic herbicide. A thick, healthy lawn is the best weed prevention. There's a reason that undesirable plants are growing in your lawn - the turn can't compete properly for some reason.
It may be that the soil nutrients or pH are in need of adjustment so that the turf will outgrow the weeds. First, have a soil test done and follow the recommendations for fertilizing. (Your agricultural extension office can help you with soil testing (ph# 317/776-0854.) If the soil is gravelly and low in organic matter, I suggest adding and inch of compost over the whole area with a fertilizer spreader. If the soil is compacted, use an aerator tool (as simple as a garden fork stuck into the soil at intervals, or as complex as a mechanical aerator from a rental agency). It also may be that the turf growing in your lawn isn't the species best suited for the job. Proper mowing height and moisture will also increase the health of the grass. Finally, there is an organic product that's made of corn by-products that both inhibits seed germination and adds nutrients to the soil. Your local garden center may have it on the shelf (if not, let us know, and we'll find a source for you). This product will not kill perennial weeds or those that grow from runners, only those that propagate from seed. But proper nutrition, moisture and mowing should take care of the die-hard weeds. For detailed information about your turf type (mowing height, is it suitable for your area, etc.), submit another question to let us know what species of grass you have in your lawn, and we'll find the info for you. Best of luck!
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