Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor,
Puyallup Research and Extension Center, Washington State University
The Myth of Weed-Killing Gluten:
"Corn meal gluten is an effective organic herbicide"
The Myth
In terms of a holy grail, a safe and effective weed-and-feed product is what every landscape manager
continually seeks. In the 1990's, such a product was reported and patented by researchers at Iowa State
University. Corn gluten meal (CGM), the protein by-product of corn milling, is a high (10%) nitrogen,
natural compound with documented success in reducing seed germination of many species. A preemergent
herbicide, CGM inhibits root development during seed germination, at least partially by
desiccating the soil and reducing water uptake.
Usage of CGM as a pre-plant herbicide and as a weed inhibitor in existing landscapes has exploded,
especially within the organic gardening and farming communities. Corn gluten meal can be incorporated
into the soil as a pre-plant treatment or broadcast over existing landscapes. Current recommendations for
use include turf grass landscapes and commercial as well as residential small fruits and vegetable
production. Though the drawbacks of the product are occasionally mentioned (specifically its cost and
lack of control over existing weeds), they are overshadowed by the promise of an all-natural magic bullet.
The Reality
The principal researcher and patent-holder of CGM, Dr. Nick Christians, is cautious in his
recommendation of CGM for weed control. He and his students and staff have published a number of
papers in the scientific and popular literature. These researchers are careful to point out that CGM does
not affect existing weeds, and that the nitrogen in CGM will benefit existing weeds as well as desirable
plants. Therefore, inadequate weed removal prior to treatment can actually result in an increased weed
problem.
CGM is not a selective product, nor is it effective on all weed types. Several species of weeds, flowers,
and vegetables are inhibited by CGM, while others are not. Effectiveness in greenhouse trials generally
increases with application rate (as does the cost).
While greenhouse trials in other parts of the country have demonstrated that CGM application can inhibit
seed germination of a number of both weed and desirable species, field trials in these same locations often
have not. Researchers in California studying weed control of containerized plantings report that CGM
had little effect on either broadleaf or grass weed species. Use of mulch was more effective, and subirrigation
was the best weed control strategy of all. Similarly, control of turf grass weeds was not affected
by CGM, though the turf responded well to the addition of this high nitrogen fertilizer.
Washington State University researchers at the Mt. Vernon station found no differences in weed control
on field-grown strawberries, though yield was slightly improved. The Iowa State group had similar
disappointing results in their strawberry trials, with no significant differences in either weed control or
strawberry yield even after multiple treatments with CGM.
https://s3.wp.wsu.edu/uploads/...
Corn gluten contains Nitrogen and is a fertilizer which existing weeds will love.
