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Abstract

Two field experiments were initiated to determine the effects of herbicides on turfgrass quality and spring to summer transition from overseeded perennial ryegrass (Lolium perenne L.) back to ‘Tifway’ bermudagrass [Cynodon transvaalensis Burtt-Davy × Cynodon dactylon (L.) Pers.]. Pendimethalin applied at 3.3 kg·ha⁻¹ in early March hastened the transition from ryegrass to bermudagrass in one of two years, but 1.7 kg·ha⁻¹ applied in each of two applications did not. A single application of pronamide at 0.28 kg·ha⁻¹ hastened the transition of overseeded ryegrass to bermudagrass without severely injuring either turfgrass. Oryzalin, oryzalin + benefin, or paraquat severely reduced the quality of ryegrass, while oxadiazon at 3.3 kg·ha⁻¹, oxadiazon + benefin, glyphosate, metribuzin, or MSMA did not affect transition from overseeded ryegrass to bermudagrass when compared with nontreated turfgrass. This study illustrates the potential for some herbicides to enhance the transition from perennial ryegrass to bermudagrass. Chemical names used: N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine (benefin); dimethyl 2,3,5,6-tetrachloro-1,4-benzenedicarboxylate (DCPA); (±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate (ethofumesate); N-(phosphonomethyl)glycine (glyphosate); N-[2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl]amino]phenyI]acetamide (mefluidide); 4-amino-6-(1,1-dimethylethyl)-3-(methylthiol)-1,2,4-triazin-5(4H)-one (metribuzin); monosodium salt of MAA (MSMA); 4-(dipropylamino)-3,5-dinitrobenzene-sulfonamide (oryzalin); 3-[2,4-dichloro-5-(1-methylethoxy)-phenyl)-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one-(oxadiazon); 1,1'-dimethyl-4,4'-bipyridinium salts (paraquat); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzamine (pendimethalin); and 3,5-dichloro(N-1,1-dimethyl-2-propynyl)benamide (pronamide).

Two separate experiments (one and two applications and dates of treatment) were conducted on plant growth regulator (PGR) injury and seedhead suppression of centipedegrass [Eremochloa ophiuroides (Munro) Hack.]. Mefluidide caused less injury to centipedegrass than either imazethapyr or flurprimidol + mefluidide. Mefluidide applied at 0.56 kg·ha^-1 in each of two applications at 2-week intervals suppressed seedheads of centipedegrass for 10 weeks. A single 0.56-kg·ha^-1 application of the mefluidide failed to suppress seedheads when applied any time from mid-June until late July. A single treatment with flurprimidol + mefluidide severely injured centipedegrass, and seedhead suppression was poor regardless of date of treatment. Centipedegrass was severely injured when flurprimidol + mefluidide was applied at 1.68 + 0.28 kg·ha^-1 in each of two applications, but seedheads were suppressed for 10 weeks. Imazethapyr applied at 0.30 and followed by 0.15 kg·ha^-1 suppressed seedheads 10 weeks after treatment in 1987 and 6 weeks after treatment in 1988 without reducing turf density. When this PGR was applied as a single treatment at 0.30 kg·ha^-1, seedhead suppression was generally greater for 8 weeks when applied mid- to late July than mid- to late June. Chemical names used: N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide (mefluidide); α -(1-methylethyl)- α -[4-(trifluoromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol); and (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxlic acid (imazethapyr).

Field experiments were conducted to determine the effects of foliar iron (Fe) applied with postemergence herbicides on injury, color, and quality of `Tifway' bermudagrass [Cynodon transvaalensis Burtt-Davy × Cynodon dactylon (L.) Pers.]. Iron significantly decreased injury and improved quality and color of `Tifway' bermudagrass in conjunction with herbicide treatment. Turf injury was less for 4 to 18 days after the initial MSMA application when Fe was added. Injury was also less from sequential Fe treatment with MSMA + metribuzin (up to 4 days) and MSMA + imazaquin (from 4 to 10 days) compared to the respective herbicides applied alone. There was no difference in turf injury from Fe when imazaquin at 1.3 kg·ha^-1 was applied as a single treatment. However, turf treated with Fe and two applications of imazaquin (9- to 10-day interval) recovered from herbicide injury faster than when treated only with the herbicide. Iron did not prevent immediate 2,4-D + mecoprop + dicamba injury to the bermudagrass, but did hasten turf recovery from injury at 26 days after treatment. With a few exceptions, `Tifway' bermudagrass quality was higher and color improved when Fe was added. However, injury expressed as loss of shoot density was not affected by Fe and only injury expressed as color loss was improved by Fe. Chemical names used: 3,6-dichloro-2-methoxybenzoic acid (dicamba), 2-[4,5-dihydro-4-methyl)-4-(1-methylethyl)-5-oxo-1H-imidazol-2yl]-3-quinolinecarboxylic acid (imazaquin), (±)-2-(4-chloro-2-methylphenoxy)propanoic acid (mecoprop), 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin), monosodium salt of MAA (MSMA), and (2,4-dichlorophenoxy)acetic acid (2,4-D).