Use of Corn Gluten Meal to Inhibit Weeds and Other Benefits
Concerns for the potential health and environmental risks associated with conventional fertilizers and pesticides resulted in our switch from a conventionally managed lawn to one that uses natural or organic lawn care products and practices beginning in 2006. Our goal was first, a safer environmentally friendly lawn and secondly, one that was aesthetically pleasing even to those who did not understand the value and significance of what we were doing.
Corn gluten meal as a natural pre-emergent herbicide and source of nitrogen is one of the products we have used. It meets our safety criteria because according to the Environmental Protection Agency (EPA) Corn Gluten Meal (100137) Fact Sheet the active ingredient corn gluten is common in both food and feed products for humans and animals. As listed on the factsheet, “it is not harmful to humans, to other non-target organisms, or to the environment… Furthermore, it provides a safer alternative to toxic chemicals commonly used for weed control on lawns.”
The corn wet milling industry produces many products and by-products by the separation of corn into its different components. Products and by-products include starches, corn oil, high fructose corn syrup, corn syrup, sugar, alcohol, ethanol and a number of feed ingredients including corn gluten meal (CGM). Dr. Nick Christians of Iowa State University found that corn gluten meal that is a 60% corn protein material and approximately 10% nitrogen by weight inhibited root formation of germinating plants, when other conditions were right. After finding the natural pre-emergent weed control properties of corn gluten it was patented (U.S. Patent 5,030,268) for pre-emergent weed control in 1991. In 1993 additional related patents were issued expanding corn gluten meal use on home gardens and crop fields. (Iowa State Horticulture Research). In the research at Iowa State corn gluten meal was used to reduce crabgrass by 60% in the first year and 85% in the second year at the application rates below. In addition to inhibiting crabgrass they also found the meal inhibited root formation at the time of germination of other grasses and broadleaf species including creeping bent grass, foxtail, barnyard grass, Bermuda grass, dandelions, lamb’s quarter, redroot pigweed, smart weed, and purslane. Use of the product should include consideration and adjustments in your grass overseeding practices since the corn gluten will also inhibit desirable grasses too. That topic is discussed further in the article. Plants that germinated and produced a root before application and activation of the product were not negatively impacted.
Some have been unable to achieve the pre-emergent weed suppression levels reported in Christians’ research. From our personal experience we are unable to validate one way or another as to its effectiveness as a natural pre-emergent herbicide. We are able to attest to the fact that after applying the corn gluten meal followed by adequate moisture, the grass grows vigorously and turns an aesthetically pleasing green that garners attention from family and neighbors.
During the years 2002 – 2005, Robert J. Mugaas, Brian P. Horgan and Andrew B. Hollman of the University of Minnesota evaluated the pre-emergent weed suppression properties of corn gluten at Umore Park as part of the Master Gardener Education Research and Display Garden. At the conclusion of the four year study at the prescribed level of 20 pounds per 1000 sq., ft., and a variety of replications dandelion control was determined to be at an unacceptable level for home lawns for all replications. It may be relevant to note that the replications were not irrigated and it was unclear from the report about the amount and timing of rainfall over the period. Considering some of the vital factors of Christians’ research relating to timing of application in relationship to the flowering of key plants followed by moisture and then dry it would have been helpful if the report contained more information about these and related specifics. In an effort to understand the specifics of what may have contributed to the different results, key persons in the study were called or emailed, but no response was received. A search of the University of Minnesota website for more details referenced the study, but indicated the information had been sidelined.
Researchers at Cornell University conducted trials with corn gluten and found that lawn grasses grew better than unfertilized plots and grab-grass was reduced, but not significantly different than the results of using chemical or natural fertilizer, which also helped the lawn grasses better compete. (Rossi).
The timing of application coincides with the flowering phenology of key plants. “For crabgrass in the North, that date can vary from early April to early May, whenever the forsythias and daffodils begin to bloom. For crabgrass in the South, the product should be applied around mid-March, when flowers open on dogwood trees.” (Turkey, Paul p 179). Moisture is needed initially following application and then a dry period after germination to be effective. If after applying corn gluten it does not rain for 5 days, approximately .25 inch of water followed by a dry period is recommended. (Christians). Too much moisture without a dry period may allow the seeds to germinate and form a root. Excess moisture may also limit the effectiveness of synthetic pre-emergence herbicides. Under the right conditions it is reported that corn gluten may inhibit pre-emergent seed germination for 4 to 6 weeks. Application timing is vital for success. With corn gluten meal the weed and other seeds actually germinate, but then the meal inhibits the expansion of the plants’ roots. (Tukey). The spring application is to help inhibit most annual and perennial weed seeds which sprout in spring and early summer and the second application is to inhibit winter annuals that may sprout in spring or fall. The recommended application rate is 20 lbs. of corn gluten 9-0-0 per 1000 sq., ft., in the spring followed by a second application in mid-August.
Other benefits of corn gluten meal are that it is an excellent source of nitrogen. Corn gluten applied at 20 pounds per 1000 sq. ft. will provide approximately 2 lbs. of nitrogen per 1000 sq. ft. The nitrogen will be available to the plants including weeds that germinated and developed a root prior to activation of the corn gluten, for 3 to 4 weeks following application. As a plant food it has an N-P-K ratio of 9-0-0. According to the University of Minnesota Extension Service corn gluten meal is a very good source of nitrogen and recommends applying corn gluten meal in April or early May in the upper Midwest and a second time in mid-August. Unless other soil amendments are needed the use of corn gluten meal would replace the need for other fertilizer during that period. Applying 20 pounds per 1000 sq. ft., of corn gluten in April/May and then again in August results in applying a total of 4 pounds of nitrogen per 1000 sq., ft., annually. They also suggest that if the timing and rates are accurate that the effectiveness inhibiting weeds should improve each year. They also point out that corn gluten meal does not supply phosphorus or potassium which would be advantageous in applications where phosphorus is not needed, especially where the potential for water pollution is a concern. Use of corn gluten meal to inhibit weed seed germination and add nitrogen without supplying phosphorus may be especially beneficial in lawns where phosphorus, often associated with off-site pollution in water bodies, is not needed.
Corn gluten meal can also be used in the garden to inhibit weeds and provide nitrogen. Be aware that if you are planting vegetable seeds they may also be inhibited. An interview with a gardener who tried the product said she used corn gluten meal between the beds to inhibit weeds with mixed results.
On our lawns when we have used corn gluten meal we applied one application in the spring at a rate of 10 lbs., per 1000 sq. ft. when the forsythia first blooms in the spring. This rate is half of what is recommended for the spring pre-emergent weed control, but consistent with our goal of not applying more than 1 lb. of slow release N at any given period so the excess N does not runoff as pollution. The amount is within our budget and does not exceed grass maintenance needs. Applying excessive amounts of N early in the spring could result in pollution from N runoff and if the growing conditions are favorable will make it hard to keep up with the mowing.
When the forsythias and daffodils bloom we more closely monitor the weather with the purpose of planning the application to be followed by a brief period of moisture (.25 inch) and followed by a dry period. If it doesn’t appear that we are going to get the right combination within a week of the beginning of forsythia bloom and it is dry we will apply the corn gluten meal and then irrigate the lawn with about .25 inch of water using catch cans as a guide and then stop the irrigation and allow the lawn to turn dry. If heavy reoccurring rains are in the forecast when the forsythia bloom occurs we will wait, monitor the weather forecast and try and catch the last rain. In that scenario we realize we may miss the germination and root development period, but are more comfortable with that than the potential for nitrogen to run off site as pollution. Following application of any soil amendment a leaf blower or broom is used to move any material that landed on impervious surfaces like sidewalks, driveways and streets back to the lawn.
A second application of corn gluten meal is not applied in mid-August because if conditions are right in addition to inhibiting weeds it may inhibit the germination of cool season grasses that are over seeded in the fall as part of our plan.
At these lower rates of application we would not expect to see as effective of pre-emergent weed control as achieved in some of the studies. We use a number of other natural lawn care products and practices to increase the effectiveness of weed control including: soil testing every 3 years; applying soil amendments according to soil tests and grass growth needs; maintaining at least a 3 inch grass height for our grass variety; removing no more than 1/3 of the grass height at any mowing; annual fall aeration; mechanical removal of weeds when soil moisture supports complete removal; solarization; spot burning and compost tea to name a few. Due to the variability in the effectiveness of corn gluten meal as a pre-emergent weed control we are currently moving towards relying on other organic nitrogen sources and more emphasis on a fall soil disturbance followed by over seeding with grass varieties adapted to the site along with other companion practices as part of our weed control.
The cost and availability of corn gluten meal may be a factor in your decision to use the product. We are unable to purchase the product locally and in 2012, we purchased corn gluten meal labeled for lawn use for $56.50 per 50 pound bag and drove 76 miles to pick it up at a Feed and Supply. Not including transportation at $56.50 per 50 lbs., an average 5000 sq., ft., yard treated with one application of 20lbs., per 1000 sq., ft., cost $113.00. A spring and fall application at the recommended level of 20lbs., per 1000 sq., ft. on a 5000 sq. ft. lawn would cost $226.00. At the time of researching information for this article much of the nation including the Midwest was in the midst of one of the worst droughts on record. Estimated corn yields were declining with no end to the drought in sight and corn prices were at record levels and climbing. All indications are that corn gluten may be harder to come by and more expensive this year.
Corn gluten may seem expensive, but there are other factors that warrant consideration. Many fertilizers contain industrial wastes some of which are beneficial to plants and others may pose health and environmental risks. Corn gluten fertilizer product information contained on the Washington State Department of Agriculture product information site shows metals in the products were not found at or above the minimum detection limit. Most states’ fertilizer labeling laws only require beneficial nutrients to be listed and as a result knowledgeable consumers are unable to make informed decisions. If you review the fertilizer product information on their website for the fertilizer you are currently using, likely you will be surprised and concerned. Corn gluten may begin to look better. Access the site at: http://agr.wa.gov/PestFert/Fertilizers/FertDB/prodinfo. If you are interested in more information about industrial wastes in fertilizers visit: www.pirg.org/toxics/reports/wastelands/.
One final point is that corn gluten meal may come from GMO sources. Before using corn gluten meal check to ensure it is approved for the intended use in your state.
Corn gluten meal is believed to be a safer alternative, but typically will not be as effective as synthetic herbicides in controlling weeds and may even seem like it costs more unless you consider the difficulty to quantify potential health and environmental costs of other alternatives.
An Update on the Corn Gluten Meal Fertilizers/Weed Control Study at UMORE Park. Robert J. Mugaas, Brian P. Horgan, and Andrew B. Hollman, University of Minnesota.
Barbara Bingham and Nick E. Christians. “Greenhouse Screening of Corn Gluten Meal as a Natural Control Product for Broadleaf and Grass Weeds. Hortscience 30 (6): 1256-1259. October. 1995.
Christians, Nick., PhD. “A Natural Product for the control of Annual Weeds”.
Christians, Nick, Iowa State University. How to Use Corn Gluten Meal.
Christians, Nick., PhD. “A Natural Product for the Control of Annual Weeds. “Golf Course Management, October 1993, pp.74-76.
Rossi, Frank. Lawn Care Without Pesticides. Information Bulletin 248. New York. Cornell University, 2005.
Tukey, Paul. The Organic Lawn Care Manual. Storey Publishing, 2007
Earth Friendly Land Care, Inc.