Sensitivity of Triploid Hybrid Bermudagrass Cultivars and Common Bermudagrass to Postemergence Herbicides¹

Abstract

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.

Bermudagrass (Cynodon spp) dose–response relationships with clethodim, glufosinate and glyphosate

“…One potential alternative to methyl bromide in turfgrass renovation systems involves the development of non‐pollen‐ and non‐seed‐forming herbicide‐resistant turfgrasses,7, 8 such as hybrid bermudagrass cultivars 9, 10. New herbicide‐resistant cultivars can be developed by traditional breeding or utilizing transgenic technology (ie genetically modified organisms).…”

“…When grown from similar initial plant diameters in the absence of plant competition, common bermudagrass plants increased in size >3.8 times and >1.5 times relative to plants of TifEagle and TifSport , respectively 8. Triploid hybrid bermudagrass cultivars were more sensitive than tetraploid bermudagrasses (ie common bermudagrass) to clethodim, clethodim plus glyphosate, dalapon, glyphosate, quizalofop and trichloroacetic acid 8, 16. As a result, common bermudagrass and triploid hybrid bermudagrass cultivars should be considered distinctly different.…”

“…Previous research evaluated the sensitivities of various bermudagrass populations to glyphosate,8, 17–22 clethodim8, 23–27 and glufosinate 28. However, these studies did not evaluate the relationship between herbicide dose (all studies tested up to three herbicide rates) and bermudagrass growth over a broad range of herbicide rates.…”

An update on genetically modified crops

“…There are several approaches for mitigation or elimination of introgression of transgenes: (A) Use sterile varieties. For example, Webster et al (2003) recommended triploid, nonpollen producing or -receiving cultivars of bermudagrass for introduction of herbicidetolerant turf. (B) Utilize isolation requirements for achieving transgene confinement depending on the type and the pollinator activity.…”

Acetyl‐CoA Carboxylase Herbicide Tolerance in Bermudagrass

“…In most intensely managed turf areas, improved varieties of bermudagrass such as the sterile hybrids made from crosses between C. dactylon and C. transvaalensis are preferred because of their superior aesthetics and performance throughout many years and in different situations (Bunnell et al, 2005; Webster et al, 2003). These sterile hybrids are clonally propagated and are transplanted as sod or sprigs when established in new turf areas.…”