| Abstract/Contents: | Suppression of top growth and seedheads of close-cut lawn grasses can be obtained by the use of chemical regulators. However, most treatments have resulted in some grass discoloration or injury. To evaluate newer chemicals, alone and in various combinations, tests were initiated on three separate lawn grasses in each of three years. Chemicals were applied as sprays to replicated plots in early or mid-May. Growth response was determined by grass height measurements, estimates of seedhead number and visual estimates of grass injury on a scale of 0 to 10 where 10 equals brown and a reading of 2 could be considered objectionable. Good top growth suppression of Kentucky bluegrass, red fescue and perennial ryegrass was obtained with certain rates of MH, MH + CF, mefluidide, MBR-18337, EL500, PP333 and combinations of mefluidide with either EL500 or PP333. Grasses treated with EL500 or PP333, alone or in combinations, were held at the lowest heights for the longest time. Most mefluidide, MBR-18337, EL500, PP333 or mefluidide combination treatments suppressed kentucky bluegrass growth more than red fescue or perennial ryegrass growth. Seedhead suppression was good with MH, MH + CF, mefluidide, MBR-18337 and combinations of mefluidide with EL500 or PP333. Applications of EL500 or PP333 alone were ineffective for seedhead suppression. In the 1980 Kentucky bluegrass trial, seedheads were not suppressed and this has been observed in other research where treatments were made less than a week or so before seedheads start to appear. Perennial ryegrass seedheads seemed to be more difficult to suppress than kentucky bluegrass or red fescue seedheads when using mefluidide or MBR-18337. Although there is variability in the data, it is evident that all chemicals have the potential of causing some grass discoloration or injury. Some of the treatments did cause objectionable grass injury (a reading of 2 or more on the 0 to 10 scale). Ryegrass appeared to be more tolerant than bluegrass or fescue to mefluidide, MBR-18337 and combinations of mefluidide with EL500 or PP333. The tolerance of the three grass species to MH, MH + CF, EL500, and PP333 appeared to be about equal. Many of the chemical treatments in these trials could be used successfully for grass growth suppression in turf areas where some discoloration or injury can be tolerated. The mefluidide combination treatments with EL500 or PP333 provided greater top growth grass suppression than that obtained with either material applied alone at equivalent rates. These combination treatments offer considerable promise and should be investigated further, especially at lower rates, in the hopes of reducing the potential for grass discoloration or injury. |
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