B. Jack Johnson (1933-2025) was a professor of crop and soil sciences at the University of Georgia at Griffin. He grew up on a cotton farm in Georgia, and early in his academic career he worked in sorghum, soybeans and sunflowers. After his service in the U.S. Army, he changed his focus to turfgrass weed control and management.
Among turf weed scientists, he was known as a prolific researcher and writer, with a lengthy record of publications in Weed Science, Weed Technology and other journals. Let’s take a look at one of his studies involving a unique interaction with verticutting and herbicides.
Vertical mowing or verticutting utilizes a putting green mower fitted with thin, tightly spaced blades that cut vertically into the turf. The depth of the blades is adjusted below the mowing height so that the blades penetrate the turf canopy. With bermudagrass, verticutting removes excess thatch and leaf growth that reduces “puffy” or “spongy” surface conditions. By slicing through stolons (above ground stems) and rhizomes (below ground stems), this process promotes an upright growth habit to form a dense, healthier and more resilient turf. The open grooves formed by those verticutting blades are useful for the incorporation of sand topdressing. Verticutting is also used for the physical removal of annual bluegrass (Poa annua) seedheads. The overall goal with verticutting for both cool- and warm-season turf is to improve mowing quality and surface smoothness. The equipment, method and frequency of verticutting is best determined by the turf conditions combined with the experience and judgment of the turf manager.
Two field studies were conducted over four consecutive years from 1974-1977 in a replicated field trial format. One study was conducted on Tifway bermudagrass on a sandy clay loam root zone with 1.0% organic matter. The second study was conducted on Tifgreen bermudagrass on sandy clay loam with 3.75% organic matter. With both studies, turf was maintained at 1.0 inch (2.5 centimeter) height-of-cut with clippings removed, fertilized with 1 pound nitrogen per 1,000 square feet (49 kilograms nitrogen per hectare) each month from March through September and irrigated as needed. With both studies, vertical mower blades were spaced 1.5 inch (3.8 centimeters) apart and at a depth to the soil surface, and thatch and loose debris were removed after each verticutting event.
In the first study on Tifway bermudagrass, plots were verticut zero, one (February), two (February + June), three (February + June + July) or six (February + May + early June + late June + early July + late July) times per year. Also, herbicides were applied to control weeds in the entire test area. As expected, the accumulation of thatch was lower in the verticut-treated plots compared to untreated plots. No differences in thatch accumulation were measured among plots verticut at one, two, three or six times per year. Bermudgrass quality was acceptable in plots verticut two or more times per year, but best overall quality was observed with six verticut events per year. All verticut plots displayed faster spring green-up compared to untreated plots.
In the second study on Tifgreen bermudagrass, plots were verticut zero, one (February), two (February + July) or three (February + June + July) times per year. A preemergence crabgrass herbicide was included in this study. Dacthal (active ingredient = DCPA) was a common preemergence herbicide labeled for turf during the 1970s. The herbicide was applied at various rates (low and high label rate) and timings: (once in March, twice in March + October, three times in March + June + October, four times in March + May + July + October).
Successful weed control was achieved in all herbicide-treated plots, as none of the verticutting timings or events interfered with the herbicide. Regardless of verticutting timings or events in the absence of a herbicide, weed populations increased, with observations of large crabgrass (Digitaria sanguinalis) in the summer, and chickweed (Stellaria media), henbit (Lamium amplexiaule) and bromegrass (Bromus sp.) in the winter.
Professor Johnson received the USGA Green Section Award and other accolades recognizing his professional accomplishments. He was known in his community as a master rose gardener. Thank you, Professor Johnson, for your contribution to turfgrass weed science and for your friendship to many in academia and the turf industry.
Source: Johnson, B.J. 1979. Vertical mowing and herbicide treatments on thatch in bermudagrass (Cynodon dactylon) turf. Weed Science 27(1):14-17
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 25-year member of GCSAA.