Under pot culture and field conditions, ethephon at rates up to 8 kg ha-t was more injurious to annual bluegrass than to Penncross creeping bentgrass. Ethephon significantly decreased the quality, spreading ability and shoot weight of annual bluegrass, whereas sward quality of the creeping bentgrass grown in pot culture was increased, spreading ability was unaffected and shoot dry weight decreased. Increasing the number of applications at all concentrations increased injury to annual bluegrass and a single application at I kg ha ' reduced annual bluegrass seedhead production. Mots cl6s: Poa annua, Agrostis palustris,6th6phon, qualit6 du gazon

No abstract

The effect of mefluidide, a growth regulator, on the growth of annual blue-grass (Poa annua L.) was evaluated under pot culture and field conditions. In pot culture, mefluidide caused a significant reduction in shoot and root dry weight and tiller number of single annual bluegrass plants, and of annual bluegrass planted at high densities. In the latter case, mefluidide also increased the success of ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.) overseeded into the annual bluegrass. Overseeding success of ‘Fiesta’ perennial ryegrass (Lolium perenne L.) in field trials increased significantly with increasing rates of mefluidide. No increase in success was noted in overseeding with creeping bentgrass in the field. There was a minimum detrimental effect of mefluidide to turf quality of the established turf species in the golf course fairway. Chemical names used: N-[2,4-dimethyl-5[[[trifluoromethyl] sulfonyl]amino]phenyl]acetamide (mefluidide).

Annual bluegrass (Poa annua L.) and ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.) were grown in monostand and polystand in silica sand and supplied with solutions in which 0%, 25%, 50%, 75% or 100% of the N was NH4+ and the remainder was NO3.– In polystand, annual bluegrass was more competitive than ‘Penncross’, producing more shoot and root dry weight and more tillers. Competitive ability of annual bluegrass was decreased as the percentage of NH4+ increased in nutrient solution. The decrease in competitive ability was reflected by a decline in tiller number and root and shoot dry weight. ‘Penncross’ was less affected by N form than was annual bluegrass.

The effectiveness of ethephon for reducing the growth of annual bluegrass (Poa annua L.), when grown as single plants in pot culture in the greenhouse or outdoors, and within a Kentucky bluegrass (Poa pratensis L.) sod, was evaluated. Ethephon reduced the growth of annual bluegrass more than that of Kentucky bluegrass. Concentration was more important in reducing plant spread than the number of applications. Ethephon applied to field grown turf reduced the leaf area per tiller of annual bluegrass but not Kentucky bluegrass. Leaves per tiller and the shoot dry weight of field grown Kentucky bluegrass increased with increasing ethephon rates compared to nontreated plots. Although significant growth retardation occurred for both species in pot culture, only Kentucky bluegrass canopy height decreased in the field with increasing ethephon rates. Decreased Kentucky bluegrass canopy height resulted from reduced sheath length. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon).