Preemergence herbicides were applied at recommended and three times the recommended rates during 1995, 1996, and 1997 to eight established zoysiagrass (Zoysia spp.) cultivars. Oxadiazon was the only herbicide that did not significantly reduce the quality of any zoysiagrass cultivar. The zoysiagrass cultivars had intermediate tolerance to prodiamine and pendimethalin, while oryzalin, dithiopyr, and benefin plus oryzalin caused the highest injury. ‘Emerald’ and ‘Meyer’ cultivars were least affected by herbicide application. ‘Diamond,’ ‘El Toro,’ ‘Cavalier,’ and ‘Crowne’ showed moderate injury, while ‘Royal' and ‘Palisades’ had the greatest injury. When the performance of zoysiagrass cultivars was averaged across herbicides, turf quality in May was best for Meyer, El Toro, and Crowne. The quality of the majority of cultivars except for Royal improved during the summer and was similar to that of Meyer by late August both years.

During 1989 and 1990, herbicides were applied to suppress common bermudagrass in a mixed stand of common bermudagrass and ‘Emerald’ zoysiagrass. When the mixed stand was treated with fluazifop at 0.2 kg ha-1 mid-May and 0.1 kg ha-1 1 mo later for two consecutive years, the common bermudagrass cover was reduced from 35 to 7% and the zoysiagrass cover increased from 65 to 85%. Similar results were achieve when fenoxaprop was applied at 0.2 kg ha-1 mid-May and repeated at monthly intervals for a total of four applications each year for 2 yr. The quality of mixed common bermudagrass and zoysiagrass turf was reduced immediately after each treatment; however, zoysiagrass recovered and treatments did not result in permanent damage. Sethoxydim suppressed common bermudagrass during the second year of treatment, but reduced the zoysiagrass stand each year. Ethofumesate applied along or with flurprimidol severely reduced the zoysiagrass stand with an increase of common bermudagrass.