The effects of various chemicals and their concentrations on budbreak of ‘Pione’ grapevine (Vitis labrusca L. x V. vinifera L.) were studied by using single-bud cuttings obtained in endodormancy. When seven chemicals were applied to the upper half of cuttings, including bud, 2% hydrogen cyanamide (H2CN2) was most effective in budbreak, judging from acceleration and uniformity of budbreak. However, neither 10 % suspension of calcium cyanamide (CaCN2) nor 5% diallyl disulfide (C6H10S2) had any effect in breaking bud dormancy of ‘Pione’ cuttings. Budbreak in cuttings treated with 10 % hydrogen peroxide (H2O2) was inhibited slightly compared to the control cuttings. No effect of 2% potassium chlorate (KClO3), 2% sodium chlorate (NaClO3) or 2% paclobutrazol (PBZ) on breaking bud dormancy in ‘Pione’ cuttings was observed. The effects of CaCN2, H2CN2 and C6H10S2 on breaking bud dormancy in ‘Pione’ cuttings were compared at three to four concentrations. With CaCN2, a 20 % suspension significantly promoted budbreak, but a 5% suspension resulted in no effect. Both 5% and 2% of H2CN2
accelerated budbreak significantly and resulted in uniform budbreak, especially at 5 %, whereas at 0.5% H2CN2 no effect was observed. Of three concentration of C6H10S2, only a 10 % solution showed any effectiveness in budbreak. The results indicated that H2CN2 is most effective in breaking bud dormancy of ‘Pione’ grapevine cuttings, followed by CaCN2 and C6H10S2 in that order, although their effectiveness varied largely according to the concentrations for all chemicals.