Effect of Defoliation and Fertilizing Time on the Growth and Flowering of Kyoho Grapes after Summer Pruning

In tropical countries, grapevines grow as evergreen and they are pruned in the time of active growing. In such summer pruning, defoliation of mature leaves and application of fertilizers are recommended for promoting bud bursting. Using the cultivar Kyoho, we conducted summer pruning and tested the effect of defoliation and fertilizing time on the growth of new shoots and flowering. On the basis of the results, we discussed the nutritional condition of the vine. 1. When all leaves were defoliated from the primary shoot at summer pruning, bud bursting was delayed and the growth of new shoots was much reduced. The development of flower clusters was restricted severely, and the berries set were only few. 2. Chemical analysis of the leaves developed on new shoots showed that defoliated vines contained less starch than un-defoliated vines. Nitrogen content was also lower in defoliated vines at the early stage of shoot growth. The nitrogen content decreased rapidly as the shoot grew in un-defoliated vines, while it increased until blooming in defoliated vines. Sugar content was also higher in defoliated vines than in those of un-defoliated. These results may be an indication that the nutrient movement to growing shoot tip or flower cluster was inactive in defoliated vines. 3. Application of fertilizers in two weeks before pruning to the un-defoliated vines resulted the longest shoot growth, though the flower development was best in the vines applicated on the same day with pruning. The highest berry setting percentage was obtained by application in two weeks after pruning.