Effects of Herbicide Treatments on Suppression of Seashore Paspalum (Paspalum vaginatum) in Bermudagrass (Cynodon spp.)

The adaptation of herbicides to control the encroachment of one warm-season grass into another species is an important management practice. A field study was conducted in Georgia to determine the rates and frequency of herbicide applications needed to suppress three seashore paspalum cultivars and determine what effects these treatments will have on three bermudagrass cultivars. MSMA plus triclopyr plus clopyralid applied at a total of 2.7 kg/ha in each of three applications for a cumulative total of 8.1 kg/ha effectively suppressed (> 70%) 'Sea Isle 1' and 'Sea Isle 2000' for 13 wk during 1998 and 1999 and 'K-3' during 1998. The suppression of K-3 in 1999 was 56%. The suppression was higher in all instances when MSMA was applied with triclopyr plus clopyralid than when it was not included (< 45%). Four-way combinations of MSMA plus 2,4-D plus mecoprop plus dicamba applied at a total of 5.3 kg/ha in each of three applications for a cumulative total of 15.9 kg/ha suppressed K-3 from 37 to 66%, Sea Isle 2000 from 55 to 66%, and Sea Isle 1 from 59 to 65% for 13 wk. The suppression of three paspalum cultivars at 13 wk from tank mixes of MSMA plus 2,4-D plus dicamba applied at a total of 4.5 kg/ha in each of three applications for a total cumulative of 13.5 kg/ha was 7 to 12% lower using the four-way combination treatments. Injury to the bermudagrass cultivars from herbicide treatments was not a problem. In some instances, all herbicides caused some degree of bermudagrass injury on selected dates of treatment. Maximum injury from the herbicides ranged from 18 to 40% for 'common' bermudagrass, 18 to 39% for 'Tifway' and 30% for 'TifEagle' bermudagrass. When injury occurred, bermudagrass recovery was within 1- to 2-wk following treatments.