(1) spring pruning refers to the pruning of walnut trees from germination to leaf development. As the temperature rises, after the trees germinate, the nutrients stored in the roots are continuously transported upwards, and the nutrients begin to transform. At this time, the tree needs more nutrients, so pruning will cause bleeding, a large part of nutrients will be lost, which will weaken the tree vigor, reduce the fruit setting rate, affect the yield, reduce the quality and reduce the income. If it is a barren tree or a overgrown tree, pruning at this time can control the growth well, weaken the tree potential and bear fruit early. Therefore, it is not suitable to prune the early-fruiting walnut trees that enter the initial fruit stage in spring, but should prune the trees that are too prosperous and fruitless; Pruning late-maturing varieties in spring before the first fruiting period can promote their early fruiting.
(2) Summer pruning Summer pruning must master the pruning period. If the temperature reaches 30℃ after pruning, the walnut fruit will be exposed, which is easy to cause burns and reduce the nutritional quality, thus reducing the benefits. It is observed that the pruning effect is the best from the end of May to the end of June. At this time, pruning is combined with cutting, mainly short cuttings, with branches up to 3 cm in length, external buds or lateral buds and spacing between layers; Loosen the branches that are too dense and recover the drooping branches. Management of fertilizer and water must be strengthened after cutting. Specific practice: from the end of June to the defoliation stage, spray 300 times of potassium dihydrogen phosphate every 10 day. Stop applying nitrogen fertilizer after July and increase the application of phosphorus and potassium fertilizer; Don't water the leaves before August; Spraying paclobutrazol in mid-September to control growth and enhance pruning effect.
(3) Pruning in autumn should be carried out after harvesting and before leaves turn yellow (from mid-September to165438+1early October). At this time, the leaves have not fallen and there is no bleeding. Too dense branches and shaded branches are easy to see, so they should be thinned out to facilitate ventilation and light transmission. But at this time, the nutrients did not completely flow back, and the cut leaves and branches contained a lot of nutrients that did not flow back. Moreover, if the temperature is unstable in autumn and winter, there will still be bleeding, and the branches with a diameter less than 1.5 cm are slightly heavier (about 2 cm). Therefore, autumn pruning is suitable for pruning weak trees, old trees and walnut trees on the hillside. At this time, it can move the big branches smoothly without injury, and promote the tree force.
(4) Theoretically, the best time for pruning in winter is from the great cold to the Spring Festival. The bleeding of walnut trees generally begins after defoliation and stops after germination in the following spring. However, not all dormancy periods have bleeding. When the temperature fluctuates around 0℃, sometimes bleeding does not occur, and when the temperature is stable above or below 0℃ for a long time, bleeding appears slight or does not occur. In addition, the size of bleeding has a great relationship with tree potential, environment and soil moisture, and the bleeding of trees decreases with the increase of branch order. It can be seen that it is feasible to take advantage of the favorable opportunity to prune in winter every year according to the actual situation of temperature and climate, but the middle branches should be pruned at a critical period. Pruning at this time can alleviate the time conflict between spring and autumn and busy farming.
In short, the pruning of walnut trees should follow the following points: strengthen pruning in summer and do a good job in post-pruning management. Pruning in autumn and winter, big branches in autumn and small branches in winter. Growers can choose the suitable pruning period according to their actual situation.