Growth control of grass and other vegetation has been achieved on a limited scale by the use of chemical retardants on highway roadbanks and similar rough turfgrass areas. A few chemical growth retardants are available commercially and a number of experimental chemicals have been developed recently. Five greenhouse experiments and four field studies were conducted from 1970 to 1972 at Southern Illinois University to evaluate commercial and experimental chemical retardants on ‘Kentucky 31’ tall rescue (Festuca arundinacea Schreb.), one of the leading grasses used in Illinois for roadbank stabilization. Nineteen chemicals or formulations were tested with potted tall rescue in the greenhouse and several rates of eight different chemicals were evaluated under field conditions. On selected dates after treatment, grass plots were evaluated as to height, color maintenance, stand losses, and weed infestations.
In greenhouse trials the most promising results were obtained with Slo-Gro, a maleic hydrazide (MH) formulation [diethanolamine salt of 6-hydroxy-3-(2H)-pyridazinone]; MON-820 (N-phosphonomethylimino-diacetic acid); MON-845 [N,N-Bis(phosphonomethyl)glycine]; MBR-6033 (3-trifluoromethyl- sulfonamido-p-acetotoluidide); and Maintain CF-125 (methyl-2-chloro-9-hydroxyfluorene-9-carboxylate, methyl-9-hydroxyfluorene-9-carboxylate, methyl-2, 7 dichloro-9-hydroxyfiuorene-9-carboxylate). MBR-6033 showed considerable potential in providing balanced control of growth while enhancing or maintaining a desirable green color. Sustaining color was difficult with other chemicals evaluated when used at rates sufficient to reduce growth over a long time interval.
MON-820, MON-845, Slo-Gro (MH), and Maintain CF-125 reduced grass growth and dry matter yield markedly at selected rates in field studies. However, color deterioration, stand reduction, and weed infestation were serious at higher chemical rates. MON-814 (ethanolamine-p-nitrobenzene-sulfonylurea), MON-139 (phosphonomethylglycine, isopropyl-ammonium salt), and MON.464 (phosphonomethylglycine, calcium salt) were less consistent in reducing growth while sustaining color. Slo-Gro, MBR-6033, and Maintain CF-125 effectively suppressed tall rescue seedhead development.
Information gained from these studies indicates that treatment with selected commercial and experimental growth retardant chemicals can result in effective tall rescue growth control and seedhead suppression. In some instances, chemical treatment of grass resulted in some degree of phytotoxicity and grass color losses. A notable exception was treatment with MBR-6033 (Sustar), which gave good growth control while maintaining or enhancing grass color.