Verdure: Pythium to preemergence crabgrass control

A historical look at how pythium blight may have unintentionally helped create a crabgrass control product.



The first Verdure column of the year is traditionally dedicated to turfgrass science history. So, “back-in-the-day” to the 1980s, some fortuitous research occurred at Iowa State University in Ames, Iowa. I had to look up the definition of fortuitous: happening by accident or chance rather than design.

The fungus that causes Pythium blight on turfgrass was cultured in the laboratory and grown onto corn gluten meal. This would serve as the carrier to then inoculate test plots with the fungus. The goal was to uniformly establish Pythium blight within the turf plots and then evaluate various fungicides for control of the disease. A funny thing happened on the way to the “Pythium forum”: The inoculated plots had noticeably less crabgrass emergence later in the summer. So, perhaps in an unintentional or indirect way, Pythium blight was responsible for the discovery of corn gluten meal as a preemergence crabgrass control product.

By definition, gluten meal is the protein fraction of the corn (Zea mays; referred to as maize globally) extracted from the wet-milling process. This corn gluten meal byproduct is typically used for animal feed, and it contains 10% nitrogen by weight. Incidentally, Iowa farmers produce the most corn in the U.S., with an estimated 2.5 billion bushels (roughly 63.5 million metric tonnes) harvested in 2022.

Nick Christians, Ph.D., translated those observations into research. A series of greenhouse and field studies were conducted during the late 1980s and early 1990s. The first study evaluated the various components of corn (i.e., corn starch, corn gluten meal, corn germ, corn seed fiber, corn meal) on the establishment of creeping bentgrass seedlings. In that greenhouse trial, only corn gluten meal inhibited creeping bentgrass establishment, with an 86% reduction in emergence from 140 pounds applied per 1,000 square feet (680 grams per square meter) and a 100% reduction at higher application rates.

A second study compared corn gluten meal with Milorganite (6% nitrogen-2% phosphorus-0% potassium; a natural organic fertilizer) on creeping bentgrass seeded with large crabgrass (Digitaria sanguinalis). In that greenhouse trial, corn gluten meal provided 63% to 95% preemergence control of crabgrass from 40 to 120 pounds applied per 1,000 square feet (194 to 582 grams per square meter) and 100% control at higher application rates. Turf treated with Milorganite was associated with a reduction in crabgrass emergence attributed to a mulching effect and not inhibition as observed with corn gluten meal.

A third study evaluated various rates of corn gluten meal applied in the spring to Kentucky bluegrass for preemergence crabgrass control. In one replicated field trial, crabgrass control of 50% to 92% corresponded to a range of 40 to 200 pounds corn gluten meal per 1,000 square feet (198 to 990 grams per square meter). In a second replicated field trial, crabgrass control of 58% to 97% corresponded to a range of 20 to 120 pounds corn gluten meal per 1,000 square feet (99 to 594 grams per square meter). Thus, about 60% crabgrass control was achieved from 20 pounds corn gluten meal applied per 1,000 square feet (99 grams per square meter); that rate of corn gluten meal also delivered 2 pounds nitrogen per 1,000 square feet (10 grams nitrogen per square meter).

As a result of this early research and several follow-up studies, Christians was awarded U.S. patent No. 5,030,268 in July 1991 on the use of corn gluten meal as a preemergence herbicide when applied to the soil surface. Further research identified the specific chemical compounds in corn gluten meal that inhibit root formation of germinated seedlings. Today, many corn gluten meal products are commercially available for lawns and landscapes. Always refer to product label instructions for proper application rate and timing, particularly regarding preemergence crabgrass control and accompanying amount of nitrogen.

Christians recently retired after a 44-year career as a professor at Iowa State University. Of note, he co-authored “The Mathematics of Turfgrass Maintenance” with Michael Agnew, Ph.D., and together they taught those popular “turf math” seminars for GCSAA for many years. Christians also authored “Fundamentals of Turfgrass Management,” a textbook now in its fifth edition. Congratulations, Dr. Nick Christians, and best wishes!

Source:  Christians, N.E. 1993. The use of corn gluten meal as a natural preemergence weed control in turf. International Turfgrass Society Research Journal 7:284-290.

Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 22-year member of GCSAA.