This article was published originally on 6/20/1997
Byline: by Anne Larson, Department of Horticulture
One of the most important breakthroughs in organic lawn care has its roots in a fortunate accident by Iowa State University researcher Nick Christians. The natural herbicide that resulted from Christians’ research (made from corn gluten meal) is now patented, and is licensed to 15 distributors for use in turf and home gardens.
Christians discovered corn gluten meal’s herbicidal activities more than a decade ago while using leftover cornmeal to grow a pathogen found on golf course turf. While the experiment was a “failure” for its original intent, Christians found that the protein part of the corn–corn gluten meal (CGM), a corn milling byproduct–could inhibit root growth. He also discovered that the corn gluten meal contains 10% nitrogen by weight, thus making it an ideal “weed and feed” product.
CGM is labeled for use on turf, field crops, and home gardens. Among the weeds controlled with pre-emergent application of the product are crabgrass, dandelions, smart weed, redroot pigweed, purslane, lambsquarters, foxtail, and barnyard grass. Both powder and pelleted formulations are available–Christians says research shows that both forms are comparable in effectiveness.
Christians is now looking at the effect of corn gluten meal on garden seeds. While the research is still in the early phase, initial indications are that deep-seeded species such as beans and peas as well as radishes fare very well with CGM. However, shallow-seeded species such as carrots and lettuce seem to incur damage. Most labels call for the herbicide to be applied pre-emerge in spring and fall. Is CGM suitable for your garden? Christians says the best approach is to first try the product on a small area of your yard or garden.
In turf situations, the CGM is often applied at 20 lb/1000 square feet; in garden situations, the rate may vary from 20 to 60 lb/1000 square feet. Garden seed can be sown slightly deeper than usual and CGM broadcast uniformly over the area and lightly raked into the surface, then watered in well. The CGM then inhibits growth of the weed seedlings’ root tips.
Potential problems with CGM stem from the fact that extensive moisture and microbial soil activity can reduce its effectiveness. The other drawback is the higher cost of CGM as compared with other weed and feed products. For instance, one catalog offers a bag of CGM treating 5,000 square feet of lawn for $43; a conventional weed and feed product with a 27-3-6 analysis costs $15.00 to treat the same area. However, many consumers seem willing to pay the higher price because of its nontoxic nature.