Chemical Suppression of Tall Fescue Seedhead Development and Growth

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Abstract
Maintenance procedures for cool‐season turfgrasses on nonagricultural areas often involve frequent mowings throughout the growing season to remove vegetative growth and two or more mowings in the spring to remove unsightly seedheads. Seedhead development suppression alone could reduce mowing requirements with realization of a possible savings in maintenance costs. The information reported herein may be useful to grounds maintenance personnel in assessing possible advantages of chemical growth retardants in turfgrass maintenance procedures.Field experiments were conducted in 1972 and 1973 at the Southern Illinois University‐University of Illinois Cooperative Research Center to evaluate the effectiveness of five chemical growth retardants applied at two dates in suppressing seedhead development and growth of clipped and unclipped tall fescue (Festuca arundinacea Schreb.). Chemicals applied at rates of 2.24 and 4.5 kg/ha were N‐phosphono methylimino diacetic acid (MON‐820); N,N‐Bis (phosphonomethyl) glycine (MON‐845); methyl‐2‐chloro‐9‐hydroxyfluorene‐9‐carboxylate, methyl‐9‐hydroxyfluorene‐9‐carboxylate, methyl 2,7‐dichloro‐9‐hydroxyfluorene‐9‐carboxylate (Maintain CF‐125); diethanolamine salt of 6‐hydroxy‐3‐(2H)‐pyridazinone (Slo‐Gro); and 3‐trifluoromethyl‐sulfonamido‐p‐acetotoluidide (MBR‐6033). MON‐820 was applied at 1.12 kg/ha also. All chemicals significantly reduced seedhead development both years. In addition, all early‐applied chemical treatments retarded vegetative growth throughout most of the experimental period. In 1972 Maintain CF‐125, Slo‐Gro, and MBR‐6033 effectively suppressed early seedhead development at the early application date and were at least as effective as other chemicals in reducing the final number of seedheads. Lower rates of MON‐820 and MON‐845 did not suppress early seedhead development when applied early but the 4.5 kg/ha rate resulted in both early and late suppression. MON‐820 and MON‐845 were more effective when applied on April 25 than April 1, whereas Maintain CF‐125 was less effective with late application. Color losses resulting from MON‐820, MON‐845, Slo‐Gro, and MBR‐6033 treatments were more severe with an April 25 applications. Mowing grass prior to spraying stimulated seedhead formation in 1972 but not in 1973. Most chemical treatments were less effective when applied to mowed grass as compared to unmowed grass. This can be attributed to removal of absorption capacity and activation of fertile tillers by mowing.MBR‐6033, Slo‐Gro, Maintain CF‐125, and MON‐845 were generally more effective in suppressing seedhead development than MON‐820 in 1973 studies. Early season color losses were serious in both unmowed and mowed grass experiments with Maintain CF‐125 and Slo‐Gro treatments, but this color deterioration was not evident later. Late chemical applications on May 4, 1973 were not effective in suppressing seedhead development or retarding grass growth. Maintain CF‐125, Slo‐Gro, and MBR‐6033 were the most effective chemicals both years in suppressing seedhead development of grass mowed prior to spraying.Results of these experiments indicate that seedhead development of unmowed tall fescue is suppressed effectively by early spring treatment with selected chemical growth retardants. Seedhead development suppression as well as grass growth retardation could reduce greatly the mowing maintenance requirements for tall fescue on highway roadbanks and several other kinds of turfgrass areas.

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