In general, it tends to work best on common weeds like crabgrass. Corn gluten is also a good source of slow releasing nitrogen fertilizer (9-0-0) for your lawn. Using a fertilizer spreader, apply it at a rate of 20lbs per 1000 sq ft. of turf and scratch it into the topsoil. Follow with a light watering so that it sprouts seeds. Don't worry; these seeds will not develop roots.
The trick is in the timing. You need to time application in the spring prior to the weed seeds developing roots, but avoiding rainfall, so that the corn gluten has time to do its thing before being eaten by microbes. Once the weeds establish roots, the corn gluten loses its effectiveness as an herbicide. However, it will still act as a fertilizer and grow you a healthy crop of weeds. Don't plant seeds where you've applied corn gluten for at least 60 days following application. You can find corn gluten at feed mills or grain elevators.
I am looking for a recipe for a weed killer/lawn fertilizer combination. I think it has vinegar, dish soap, and two other ingredients. The recipe was given to me years ago and I can't find it.
I know a vinegar mix will kill off weeds, but it will also kill the grass. So be very careful of what you spray. For weeds in cracks and crevasses I use 4 cups white vinegar, 1/4 cup salt and 2 teaspoons of dish detergent. Spray plants especially at root level.