What are the key points of apple autumn pruning techniques?

I. Autumn physiological characteristics: 1. In the late stage of new shoot nutrition (August to November), leaf photosynthates are transported downward in large quantities into buds, fruits, branches and trunks, and roots. 2. In the fruit ripening stage, including early, mid and late maturing varieties. 3. In the late stage of flower bud differentiation, with continued physiological differentiation and morphological differentiation. 4. In the late stage of the root growth low period (the high-temperature low period in July to August), the autumn peak period in August to October, and the peak period after fruit harvest. 5. The whole tree is in a state of preparation for overwintering; before leaf fall, leaf photosynthates are transported into buds, branches, trunks and roots and stored there for winter and spring root growth, bud differentiation, and the following spring and summer's new shoot growth, flowering, fruit set and young fruit development.

II. Pruning principles: 1. Prune according to the standard of three sparse and three dense (that is, the distribution of branches and leaves in the canopy should be sparse at the top and dense at the bottom, sparse on the outside and dense on the inside, sparse on large branches and dense on small branches), improve ventilation and light conditions, and improve fruit and flower bud quality. 2. Cut back excessively vigorous young autumn shoots to reduce nutrient consumption, plump up buds, promote continued flower bud differentiation and improve fruit quality. 3. In September to November (or after fruit harvest and before leaf fall), in combination with the application of base fertilizer, trench and cut roots to promote deeper root development and increase the absorption area and the root system's supply capacity (such as cytokinins, etc.). 4. To further improve fruit quality, remove bags about 20 days before fruit harvest, remove shading leaves and turn the fruit. 5. During pruning, diseased and pest-infested branches, leaves and fruits must be cut off at any time to prevent the occurrence and spread of diseases and pests.