Summer pruning is performed during the active growing season of fruit trees, which is also referred to as growth-stage pruning. This technique involves cutting branches and leaves, which can significantly impact tree growth. Therefore, it should be done carefully to avoid excessive vegetative growth. Summer pruning serves as a supplementary practice to winter pruning, helping to manage new shoots by retaining the best ones and removing the weaker ones. It helps regulate their growth direction and posture, making future winter pruning more efficient and less damaging to the tree.
1. **Bud Girdling**: Also known as "eye injury," this technique involves making a crescent-shaped cut with a knife or scissors just above or below a bud or shoot before spring budding. The cut reaches the xylem, approximately 0.2 to 0.3 cm deep. When applied above a bud, it restricts nutrient flow, encouraging stronger growth. Conversely, when made below, it weakens the bud’s growth. Bud girdling is particularly effective for young trees. Key considerations include: not cutting the first four buds on main branches, injuring 10-15 cm on either side of the remaining buds, avoiding back buds, and not girdling branches that are too thin or thick.
2. **Shoot Thinning**: From spring to early summer, unnecessary or harmful branches are removed, a process known as de-emergence. This helps control growth, promote better development of main branches, and prevent overcrowding. Removing excess shoots ensures better light penetration and reduces nutrient competition. For example, in fruit trees with short fruiting branches, dense buds may hinder flower bud formation, so weak buds should be removed to allow stronger ones to develop into productive branches.
3. **Multi-loop Girdling**: To prevent branch baldness, strong-growing branches are treated before budding. A ring cutter or shears are used to make multiple rings around the branch, reaching the xylem every 15-20 cm. This promotes the growth of medium and long branches while preventing weak, bare shoots from forming.
4. **Ring Barking**: Also called ring peeling, this technique involves stripping a 3-5 cm section of bark from the base of a branch, typically about 1/8-1/10 of the branch's diameter. It disrupts nutrient flow to the roots, reducing tree vigor and promoting fruiting. However, improper application can harm the tree. Modern techniques often combine ring barking with Kao Hua Wang No. 2, which helps accumulate nutrients without severe damage. Proper water and fertilizer management is essential after this procedure.
5. **Topping**: This involves removing the tip of a young shoot during the growing season. Topping helps control growth, encourages nutrient accumulation, and promotes flower bud formation. It also stimulates the growth of secondary branches and improves fruit setting rates. In May-June, topping can be done 2-3 times to encourage flowering and improve fruit quality. In early August, it helps form apical buds, and when branches reach 60 cm, it aids in canopy expansion and earlier fruit production.
6. **Twisting Shoot Tips**: From late May to mid-June, upright or competitive shoots are twisted at their base, about 5-6 cm from the tip. By twisting them 180 degrees and bending them downward, vegetative growth is reduced, and nutrients are concentrated in the lower part. This promotes shorter shoots and enhances flower bud formation. Care must be taken to avoid breaking the twigs or damaging the leaves.
7. **Branch Pulling**: This technique involves manually pulling branches to adjust their angle and direction. In spring, it helps open up the tree structure, promote budding, and prevent barren spots. The ideal angles are 45-50 degrees at the base, 60-70 degrees in the middle, and horizontal for lateral branches. In late June to July, branch pulling improves air circulation, light penetration, and fruit quality.
8. **Litchi Technique (Branch Dropping)**: This method is used from July to August. Branches are bent at their base, about 10 cm from the tip, and repeatedly pressed to slightly damage the xylem, causing them to droop horizontally or at an angle. This controls vigorous growth and promotes flower bud development, especially for upright branches.
9. **Summer Pruning (Xia Shu)**: In mid to late August, excessive branches on secondary branches are removed to improve light exposure and enhance flower bud quality. Young shoots can be shortened using a "cap shear" to encourage secondary branching and flower bud formation.
It's important to note that while summer pruning plays a vital role in maintaining consistent fruit production and yield stability, it should be combined with winter pruning, proper orchard management, and adequate soil and water care. These practices together ensure long-term tree health and productivity. (China Plant Protection Network: Wei Linfei)
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