Pruning Timing According to Lunar Phases: Impact on Yield, Grape Quality, and Biochemical Properties of Xylem Sap in 'Black Magic' Grapevines

Abstract

This study explored the effects of pruning the 'Black Magic' grape variety during the dormancy period, guided by lunar phases as prescribed in biodynamic viticulture, on ripening, grape yield, and quality. Furthermore, it examined xylem sap flow under late pruning conditions, along with its phytochemical composition and potential associated losses. Pruning was conducted on experimental vines in December, January, February, and March, aligned with 16 different timings corresponding to the four lunar phases. Pruning during the New Moon phase in March, following the Full Moon and Last Quarter phases, resulted in a slight delay in bud break, though this delay did not influence the timing of ripening. However, pruning during the New Moon in March slightly reduced yield, cluster weight, and berry weight. Xylem sap bleeding was highest during the Full Moon (March 9, 683 mL) and Last Quarter (March 16, 622 mL) phases, with significantly reduced sap flow recorded during the New Moon (March 24, 67 mL). Phytochemical analysis of sap collected on March 9 and 16 revealed substantial levels of macronutrients (6.35%), micronutrients (189.84 ppm), amino acids (57,843 mu g L(-)1), sugars (115.01 mg L(-)1), organic acids (211.15 mg L(-)1), hormones (39.95 mu g mL(-)1), and antioxidative enzyme activities (55.33 eU mL(-)1). Notably, higher phytochemical values were observed in samples collected during the Last Quarter (March 16). These findings suggest that pruning should be completed by early March in lowland Mediterranean regions to minimize sap loss, preserve nutrients, support early shoot development, and enhance vine health and productivity.