History of Corn Gluten as a pre-emergent
Just in case anyone is interested in the background of corn gluten as a herbicide: The preemergent qualities of corn gluten were actually discovered by accident by Dr. Nick Christians, Professor of Horticulture, Iowa State University. He was working on a project using corn gluten when he began noticing its affect on germinating seeds. Quoting Dr. Christians, "It was found that a byproduct of the corn (Zea mays L.) wet-milling process, corn gluten meal, has potential as a natural preemergence herbicide." He later filed for the patent, the first one in 1991. Two other patents were filed later. He has never claimed any weed control qualities except as a preemergent, regardless of what some others claim.
It works by depleting essential moisture once seeds germinate. It works or 5 to 6 weeks after it is applied. If used in a wet area with frequent rains, it is not as effective. It also contains 10% N by weight.
The other two patents were issued in 1993. From Dr. Christians, "The first is on the use of hydrolyzed proteins from corn and other grains that were shown to have higher levels of herbicidal activity than the corn gluten meal. These materials are water soluble and can be sprayed on the soils surface. The second patent was on 5 dipeptides extracted from the hydrolyzed corn gluten meal. These dipeptides were shown to have the same type of biological activity observed when the corn gluten meal and the hydrolyzed meal are applied to the soil. The sprayable materials have been found to be less stable than the corn gluten meal in field studies. Current research is being directed at methods of stabilizing these soluble materials to improve their efficacy."
I live on a farm, but corn is not a major crop here. Many corn processing plants make corn gluten and it has been said that if you can sometimes get it directly from the plant, but I haven't look into it.