In 2020, a greenhouse experiment was conducted to investigate the suppression of annual bluegrass (Poa annua), which is a difficult weed to manage in cool-season in turfgrass mixtures on football pitches. The efficacy of prohexadione calcium (Pc), ethephon (Eth) and Pseudomonas fluorescens against P. annua, Lolium perenne and Poa pratensis was tested, as the latter two most commonly occur in turfgrass mixtures on football pitches. Mesotrione (Mes) was used as a positive control, and nontreated grass was used as a negative control. Only a single grass species was sown in each pot. Treatments were randomly distributed for two experiments conducted separately: first – unmown grass before the beginning of spraying and second – grass mowed before the beginning of spraying. In both experiments, plant height and the number of tillers were measured/counted several times during the growing season. In both experiments, grasses were sprayed six times with Pc, Eth and P. fluorescens, while Mes was applied twice. Based on the performed study, the efficacy of the tested products is connected to grass species and whether the grass was mowed/cut before spraying. It has been detected in the present study that spraying with Pc could reduce the height of annual bluegrass, while spraying with P. fluorescens has reduced the number of tillers. Spraying was more effective on grasses that were mowed/cut before the beginning of spraying. Mes should cause severe damage to annual bluegrass but without confirmation in this study. Results of this study have indicated that the application of Pc and P. fluorescens can inhibit the spread of annual bluegrass in football pitches; however, testing their effectiveness against P. annua under field conditions should be performed as well.
