Sensitivity of Triploid Hybrid Bermudagrass Cultivars and Common Bermudagrass to Postemergence Herbicides

The potential weediness of hybrid bermudagrass cultivars in nontarget areas is an important factor when considering the development of herbicide-resistant cultivars. Field studies evaluated the response of common bermudagrass, hexaploid hybrid ‘Tifton-10’, and two triploid hybrid bermudagrass cultivars (‘TifEagle’ and ‘TifSport’) to clethodim, fluazifop-p, glufosinate, glyphosate, and quizalofop-p. Glyphosate was more consistent than clethodim and clethodim plus glyphosate in controlling common bermudagrass. The triploid cultivars were equally sensitive to each of these treatments, whereas Tifton-10 control was highest with treatments that included glyphosate. Variability between years in control of common bermudagrass was attributed to differences in plant size at application, with greater control of smaller plants. All herbicides reduced common bermudagrass plant diameters $ 93% in 1999 when grown without a crop. However, in 2001, only herbicide treatments that included two applications of 1.1 kg ai/ha glyphosate reduced plant diameters 6 to 59%. None of the other treatments reduced common bermudagrass plant diameters compared with pretreatment values. When grown with cotton, fluazifop-p and 4.5 kg/ha glyphosate were the only treatments consistent across cultivars and years. All herbicide treatments reduced triploid hybrid bermudagrass plant diameters $ 90%, whereas Tifton-10 plant diameters were reduced . 86% by all treatments, with the exception of clethodim. As in the non-cropland study, common bermudagrass plant diameters were reduced $ 97% by herbicides in 1999, whereas in 2001, only fluazifop-p and glyphosate treatments reduced plant diameters compared with the nontreated control. Both the lack of aggressiveness and susceptibility to common herbicides of the triploid hybrid cultivars relative to common bermudagrass indicates that these non–pollen-producing or -receiving cultivars are reasonable candidates for the introduction of herbicide resistance. Nomenclature: Clethodim; fluazifop-p; glufosinate; glyphosate; quizalofop-p; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA ‘Tifton-10’; hybrid bermudagrass, Cynodon dactylon (L.) Pers. 3 Cynodon transvaalensis Burtt-Davy ‘TifEagle’, ‘TifSport’; cotton, Gossypium hirsutum L. Additional index words: Transgenic turfgrass, turfgrass weed management. Abbreviations: fb, followed by; triploid hybrid cultivars, grouping of TifEagle and TifSport bermudagrass cultivars; WAP, weeks after transplanting.