Effects Of Dormancy Breaking Chemicals On Advancing Wine-grape Maturity To Avoid The Monsoon In Jinshajiang Valley

Jinshajiang valley, where Sichuan and Yunnan provinces meet, is an important viticulture area in subtropical monsoon South China. The rainy season is from May to October. If the grape harvest occurs during the wet season, the grapes do not ripen fully and it is difficult to control diseases. In this experiment, 4 dormancy-breaking agents were used, at 3 timings on 4 wine-grape cultivars. The goal was to harvest fully mature grapes in the dry season. The following treatments were applied: 1) Calcium cyanamide (16.7%); 2) Cyanamide (0.5%, 1.0%, 1.5%, 2.0%); 3) Cyanamide (0.5%, 1.0%, 1.5%, 2.0%) + Tween80(1.0%); 4) Treatment (3) + Potassium nitrate (6%). Treatments (1), (2) and (3) were applied to different plots on Dec.25, Jan. 10 and Jan.25. Treatment (3) was subdivided and for Treatment (4) Potassium Nitrate was applied twice to one part only on Oct. 30 and Nov. 15. Cultivars were Chardonnay (early), Gamay (second-early), Merlot (mid-late), and Fox (late). The first three belong to V. vinifera, and the last one is Franco-American hybrid.Results showed that 1) The best time for dormancy-breaking treatment with minimum phytotoxicity was Jan. 10, except in treatment (4). 2) Treatment (3), Cyanamide + TweenSO, had the best dormancy-breaking effect, advancing harvest of Chardonnay, Gamay and Merlot by about 15 days. 3) In treatment (3), concentrations of 1.0% Cyanamide + 1.0% TweenSO were most effective.Although the chemical treatments had a significant effect on advancing grape maturity, it was limited. The goal to get fully mature grapes in the dry season was not reached. On the basis of this study, the following three methods combined are suggested: early-ripening cultivars with good resistance to diseases, chemical treatments as above, together with physical techniques such as defoliation or water-stress.