What are the key management techniques during the grape berry development period?

How should grapes be managed during the berry development period?

Shoot pinching and foliar fertilizer application for the canes and vines, to maintain a good tree appearance.One month after flowering, the new shoots basically stop growing; those that have not stopped are pinched to control them, so as to concentrate nutrients for berry development. The fully expanded functional leaves near the trunk and canes should remain dark green. When nitrogen fertilizer is insufficient, leaf color turns pale; when nitrogen fertilizer is excessive, the new shoots grow too vigorously and leaf color also turns pale; when gibberellin is applied (for seedlessness), the rapid enlargement of berries sharply increases the demand for nitrogen, which can also cause the leaves near the cluster to turn pale, lose green, or become chlorotic, so urea can be applied to the leaves to supplement nitrogen; the berry coloring stage requires more nitrogen, and the intense competition with the leaves for nitrogen will cause leaf yellowing. To avoid foliar fertilizer application during the berry coloring stage contaminating the berry surface (except for bagged fruit), nitrogen fertilizer can be applied in advance during the berry softening stage (before the berries color). A good tree appearance is shown by most new shoots stopping growth one month after flowering, with the leaves divided into upper, middle and lower parts: the upper leaves are smaller, upright, and cupped upward like a hand holding water; the middle leaves are larger and droop under strong light; the lower leaves are horizontal to capture light to the maximum extent.

Soil topdressing and watering.In vineyards with good fertility and a relatively high level of management, apply nitrogen fertilizer as topdressing, mixed with fertilizers of other elements. Leaf color turning pale or about to turn pale is the suitable time for nitrogen topdressing. Quick-acting nitrogen fertilizers such as urea, ammonium sulfate and ammonium nitrate are best, and the application rate is determined according to the fruit load, new shoot vigor and leaf color. If the target yield for 666.7 sq m is 1500 kg, apply 25 kg of urea when the new shoots are weak and the leaf color is pale; when the new shoots are growing well and the leaf color is normal, apply half the rate; when the new shoots are vigorous and the leaf color is dark, do not apply. Apply as appropriate according to the growth of the new shoots and changes in leaf color. Promote water-saving irrigation and maintain a balanced water supply. In sunny weather, irrigate once a week, with an irrigation amount of 10-15 mm for drip irrigation, 15-20 mm for micro-sprinkler irrigation, and 20-30 mm for furrow irrigation. When it rains, no standing water should remain in the orchard. In the early stage of berry development, supply sufficient water so that the berries enlarge normally and the skin develops well, enhancing resistance to fruit cracking. Before ripening, the sugar content of the berries increases rapidly and the water demand is high, so the water supply must be ensured even more [Jishan Huayao].

Reasonable fruit retention to improve fruit quality.Determine the number of clusters and the number of berries per cluster according to the yield. Thinning clusters and berries early, and finishing at the latest before the berries soften, is beneficial for berry enlargement, skin coloring and sugar accumulation. For a vineyard with a berry sugar content set above 15% and a leaf area index of 3, each 666.7 sq m can synthesize about 6-7 kg of dry matter on sunny days, of which about 4-4.5 kg of dry matter is transferred to the berries; based on a berry development period of 100 days, the theoretical yield does not exceed 2500 kg. After deducting for rainy days, reduced light utilization caused by uneven leaf distribution, nutrient waste caused by poor control of new shoot growth and too-late cluster and berry thinning, and the influence of pests and diseases and other factors, the yield of a high-quality vineyard per 666.7 sq m should be controlled below 1500 kg, and that of a premium vineyard at around 1000 kg. For young trees, the fruit load is estimated according to the total length of new shoots one month after flowering; taking Kyoho as an example, 1 cluster is suitable for every 2 m of new shoot length. The fruit load is related to the total number of shoots (effective photosynthetic leaf area), and is not related to the length of the new shoots, the clusters retained, or the size of the berries, because weaker new shoots can also transport nutrients from other new shoots for berry enlargement and sugar accumulation.

Girdling of vigorous canes and trunks.If the canes and vines grow too vigorously, berry enlargement and coloring become difficult, affecting fruit quality. For young vigorous trees and water sprouts, girdling can be carried out one month after flowering: on the base of the cane or on the trunk or main branch, use a sharp blade to remove a ring of outer bark 1-1.5 cm wide without injuring the cambium, and wrap the cut tightly with plastic film. Because girdling weakens tree vigor, the trunk is generally not girdled, and after girdling the yield increase should not exceed 20%.

Cane and vine regulation.During the berry development period, if the new shoots are too dense, thin the shoots; if the canes and vines are too vigorous, pinch the tips to control growth. For varieties of the Kyoho group, for example, when the new shoots stop growing one month after flowering, the total length of new shoots per 666.7 sq m should be controlled at 8000-10000 m, that is, retain 8000-10000 new shoots with an average length of 1 m.