Background and Aims: This study was initiated to investigate local problems in obtaining consistentfruit-setting responses to a recommended treatment combination of gibberellic acid (GA3) and(2-chloroethyl)-trimethyl ammonium chloride (CCC), with vineyard managers returning to more traditionalmethods of either cincturing or applying 4-chlorophenoxy acetic acid (4-CPA).Methods and Results: Five vineyard study sites located in the Chittering–Bindoon region of WesternAustralia were characterised by multivariate analysis using measures of vegetative and reproductivebiomass. Two experiments were carried out in the vineyard to compare responses to combinations of GA3and CCC. 4-CPA was used as an industry control. Bunch number was used as a novel covariate to adjustresponses to individual vine and site factors. Berry volume increased in all vines and sites treated withGA3, irrespective of timing, but dry matter yield increased only in the youngest vineyards. The only siteto show a significant response to CCC application was that with the highest vegetative biomass.Conclusions: We conclude that site and management factors rather than growth regulator type, concentrationor timing determined yield responsiveness (sugar production).Significance of the Study: This study demonstrates a strong physiological and environmental effect onresponse to growth regulator application, reinforcing the importance of developing site-specific managementpractices. It shows how multivariate techniques may be used to characterise and compare vineyards,and also, how analysis of covariance using a new parameter, bunch number, may be used toenhance statistical of analysis of field experiments.