Verdure: Bermudagrass triangle

How do you selectively remove one warm-season grass species from another?


Warm-season turfgrass being watered by a sprinkler

Common bermudagrass (Cynodon dactylon) is a warm-season grass but is considered an invasive weed and unwanted guest in a desired stand of seashore paspalum (Paspalum vaginatum), which incidentally is also a warm-season grass. Bermudagrass infestation or encroachment into seashore paspalum is common since both species grow and thrive in similar environments and are maintained under similar conditions. So, how do you selectively remove one warm-season grass species from another warm-season grass species?

First let’s take a historical look at how herbicides might help answer this question. The ability to selectively control broadleaf weeds in turfgrass lawns was first documented in 1944 with the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The 2,4-D chemical composition causes severe injury to broadleaf weeds, but turfgrasses are not affected. Controlling broadleaf weeds in grasses is one thing, but controlling grassy weeds without injury to the desired grass species is another. Then in the 1980s, fenoxaprop-p-ethyl was first used to control grassy weeds in barley and wheat, both grass crops. In the early 1990s, it became one of the first herbicides labeled for selective postemergence control of crabgrass (Digitaria sp.) in turfgrass. Also in the 1990s, postemergence applications of ethofumesate + atrazine (tank-mix) was first used to control common bermudagrass in St. Augustinegrass (Stenotaphrum secundatum) sod in Florida.

Back to the question of removing common bermudagrass from seashore paspalum. Research was conducted on a golf course on Oahu in Hawaii. The purpose of this field study was to evaluate herbicides for their potential to control or suppress common bermudagrass without damaging the seashore paspalum. The test site was a putting green consisting of Salam seashore paspalum and a population of unwanted common bermudagrass. The putting green was maintained on a native silty clay root zone and topdressed regularly with sand.

The herbicide active ingredients of ethofumesate, mesotrione, metribuzin and topramezone were evaluated in various tank mixtures for their potential to control the common bermudagrass and for their ability to cause any injury to the seashore paspalum.  Commercial product label application rates were used. Individual plot size was 3 feet × 15 feet (0.9 meters × 4.6 meters) with a 1-foot (0.3-meter) buffer between all plots, and treatments were applied through an air induction nozzle from a CO2-powered backpack sprayer in 44-gallon water-carrier per acre (412 liters per hectare). All treatments were arranged in four replications within the experimental design. The study was conducted in 2017 as two separate trials within the same test site. In the first trial, herbicide treatments were applied on Feb. 14, with a second series of treatments applied five weeks later on March 23. In the second trial, treatments were applied on March 7, and a second series of applications five weeks later on April 20.

The best bermudagrass injury was observed from treatments of topramezone + metribuzin + ethofumesate (with another ethofumesate application two weeks later), topramezone + metribuzin + ethofumesate, or ethofumesate (with mesotrione + mestribuzin + ethofumesate two weeks later). However, three weeks after the second series of treatment applications, the bermudagrass was recovering and thus indicates a need for continuing to re-apply those herbicide treatments.

What about the seashore paspalum? All herbicide treatments caused a minimal loss of green color; however, the seashore paspalum’s visual color was considered acceptable. Also of note, the foliar bleaching associated with applications of mesotrione or topramezone was reduced with the tank-mix addition of metribuzin and/or ethofumesate.

Overall, selectively removing or controlling or suppressing the growth of one warm-season grass (common bermudagrass) from within the population of another warm-season grass (seashore paspalum) is not easily or automatically achieved with herbicides. This research demonstrated that herbicides repeatedly applied over time can be helpful with weakening the bermudagrass with minimal-to-acceptable injury to the desired seashore paspalum. A herbicide program along with optimum cultural practices to promote healthy turf would be the best long-term strategy to keep common bermudagrass from “taking-over” and thus ensure that seashore paspalum is the right warm-season grass to thrive and dominate the site.

Source: Lindsey, A.J., J. DeFrank and Z. Cheng. 2020. Bermudagrass suppression and goosegrass control in seashore paspalum turf. Journal of Applied Horticulture 22(2):92-96 (

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.