Detailed Explanation of Key Points in Plum Cultivation and Management Techniques
????I. Cultivation Techniques
(1) Seedling Selection
Select plum seedlings with pure varietal characteristics, intact root systems, vigorous growth, plump buds, and free from quarantine pests and diseases.
(2) Planting
The general spacing between plants and rows is 2.5 m x 4 m, and planting should be done before buds sprout (preferably before April 20).
Plums exhibit self-incompatibility, so a single cultivar should not be planted alone. Different cultivars with the same flowering period should be planted at certain intervals as pollinizer trees, at a ratio of 4:1 or 8:1.
????II. Fertilizer and Water Management
(1) Fertilization
1. Base fertilizer
Base fertilizer is the basic fertilizer that can supply plum trees with multiple nutrients over a relatively long period. It generally consists mainly of slow-release farmyard manure, such as compost, stable manure, crop straw, green manure, fallen leaves, etc. Base fertilizer is best applied in autumn. For mature plum trees, apply 50-100 kg of farmyard manure per tree.
2. Topdressing
(1) Topdressing before flowering: About 10 days before plum trees sprout (early April), apply 0.5-1 kg of quick-acting nitrogen fertilizer or 25 kg of decomposed human manure per tree.
(2) Topdressing after flowering: Quick-acting nitrogen and potassium fertilizer should be applied in a timely manner to reduce physiological fruit drop. From late May to mid-June, apply 0.5 kg per tree.
(3) Topdressing during fruit enlargement and flower bud differentiation: After physiological fruit drop and before the fruit enters the rapid enlargement stage (late June to mid-August), apply a quick-acting nitrogen, phosphorus, and potassium compound fertilizer at 0.5-1 kg per tree.
(4) Topdressing during the late stage of fruit growth: Apply fertilizer from the beginning of fruit coloring to harvest. This application should focus on phosphorus and potassium fertilizers. Quick-acting nitrogen fertilizer is best applied as a foliar spray at a concentration of 0.2-0.3%, combined with pesticide spraying.
(2) Irrigation
Plum trees require a certain amount of water during each phenological period throughout the year. Irrigation should be carried out before bud break, during the young fruit enlargement stage, and during the new shoot growth stage. Before winter arrives, one irrigation of frozen soil water is needed. In addition, plum trees are susceptible to waterlogging, so drainage systems should be installed in plum orchards to avoid waterlogging damage.
III. Training and Pruning
(1) Tree Form
The tree forms commonly used for plum trees are the natural open-center form and the two-tier open-center form. The natural
open-center form is characterized by good ventilation and light penetration, a high fruiting rate and long lifespan of fruiting branches in the inner canopy and lower parts, and ease of management. The two-tier open-center form has a tree structure with 3 primary scaffold branches in the first tier, with an inter-tier spacing of about 80 cm, and 2 primary scaffold branches in the second tier, with the top cut back to open the center.
(2) Pruning
1. Young tree stage
① Natural open-center form: In the year of planting, cut back the trunk at 40-60 cm above ground to establish the main stem. The first bud below the cut should face the wind direction (southwest), and the cut should be slanted. The upper side of the slant should be slightly above the bud tip, and the lower side of the slant should be level with or slightly above the bud base. In the following spring, select 3-4 branches distributed in all directions from the new growth of the trunk-establishment year as primary scaffold branches (if insufficient, select them the next year). The angles and distances between primary scaffold branches are as shown in the diagram. If branch angles are unreasonable, methods such as bending or tying branches can be used to correct them. Remove overly dense branches; keep non-dense branches as auxiliary nurturing branches. Shorten appropriately according to the growth of each primary scaffold branch, cutting off 1/4-1/3 of the total length. In the spring of the third year, for each primary scaffold branch, select 1 well-angled, vigorous branch as the extension branch of the primary scaffold branch and shorten it, cutting off about 1/2 of the total branch length. Also select 1-2 outward-growing branches on the lower part of each primary scaffold branch as lateral branches and shorten them by about 1/3. Keep as many small branches under 5 cm on the primary scaffold branches as possible, training them into short fruit branches or bouquet fruit branches, and appropriately shorten medium and long fruit branches. In this way, after 3-4 years the tree form is basically established, and thereafter the pruning method for the extension branches of primary and lateral branches each year is the same as the previous year.
② Two-tier open-center form: This tree form is suitable for cultivars with strong growth vigor and relatively upright tree habit. In the year of planting, establish the trunk at a height of 40-60 cm. In the following spring, select the vigorous upright branch at the top as the central leader, then select 3-4 well-angled branches on the trunk as the first tier of primary scaffold branches and shorten them by about 1/3, with the angle between each primary scaffold branch and the trunk at 50-60°. Other relatively upright branches can be removed, while medium and short branches should be retained as fruiting branches. In the spring pruning of the third year, on the primary scaffold branches retained from the previous year, select 1-2 well-angled branches as lateral branches and extension branches, then select 2-3 primary scaffold branches on the central leader as the second tier, staggered from the first tier primary scaffold branches, with an inter-tier spacing of 50-60 cm, and at the same time cut back the central leader to open the center. The pruning methods for other branches are the same as for the natural open-center form. The form can be established after 3-4 years.
2. Full fruiting stage
Use the method of frequently renewing the leaders of scaffold branches to control tree size. Upper-tier branches and peripheral branches should be managed by combining thinning with renewal pruning, that is, thin out dense growth and retain sparse growth, remove vigorous growth and retain strong growth. Retained branches are left unpruned and renewed the following year at a suitable branching point, reducing peripheral branches and foliage, improving light conditions in the inner canopy and lower layers, and moderating the growth vigor of the upper and outer canopy. For fruiting branch groups, thin out weak ones and retain strong ones, remove old ones and retain new ones, and renew and rejuvenate them in a planned, staged, and batched manner, controlling their density and length. Remove overly dense branches, crossing branches, diseased and pest-infested branches, and thin weak branches to conserve nutrients and improve ventilation and light penetration.
3. Senescence stage
Timely renew and rejuvenate primary and lateral branches. Overly long and overly old branch groups should also be appropriately renewed. After renewal, generally more vigorous branches will sprout, and new scaffold branches and branch groups can be trained to form a new canopy.
(3) Summer pruning
Summer pruning refers to pruning carried out during the growing season, generally from mid-June to early July. The following methods can be used.
① Pinching: Remove the growing point of branches during the growth period. The specific timing should be determined according to cultivar, cultivation conditions, and purpose. ② Twisting: Twist and injure the tip of new shoots without breaking them. Generally, vigorous water sprouts with utilization value can be treated this way to inhibit growth. Twisting should be done when the new shoot has grown long enough, and the injured part should be at the semi-lignified position. ③ Girdling: Carry out when new shoots are close to stopping growth. Remove a ring of bark from the trunk or large branches of vigorous trees, with the girdling width about 1/10 of the diameter of the branch being girdled. The flower-promoting effect is obvious. ④ Branch bending: Hold the middle-lower part of the branch with the hand and repeatedly pinch and squeeze to damage the branch tissues, causing it to grow horizontally or obliquely. Each summer pruning measure must be applied at the correct time and to the correct target (young trees or non-fruiting vigorous trees). During summer pruning, remove water sprouts, adventitious shoots, and dead branches.
????IV. Pest and Disease Control
The main diseases damaging plum trees include plum red spot disease and plum gummosis; the main insect pests include the plum fruit moth, aphids, red spider mites, etc.