Detailed Explanation of Key Points of Plum Trellis Cultivation Technology
In recent years, the plum cultivation area in various regions has increased rapidly. Most tree shapes are natural open-center or sparse stratified forms, and pruning adopts the method of light pruning, long shoot laying, and retaining many branches. Although this has played a certain role in early fruiting, some new problems have also appeared, such as slow formation of young trees, low branch load capacity, alternate bearing, declining fruit quality, a small proportion of high-quality premium fruit, and poor economic returns. In the spring of 2005, the author carried out trellis conversion on 4-year-old open-center Hongbulin and Aoli 14 plum trees in Luoju Village, Zaolin Town, Qishan County, Baoji City, on 0.6 sq m, raising the orchard coverage rate from 42% before trellising to more than 70%. In 2005 and 2006, the yields per 666.7 sq m were 1232 and 2180 kg respectively, with premium fruit of 60 mm diameter or more accounting for more than 80%. The goal of high yield, high quality, and high efficiency was achieved. The technology is summarized as follows.
1 Trellis structure
Set up the trellis along the tree row direction. The trellis height is generally 180-200 cm. Two wires are stretched horizontally on the trellis. The first wire is 140 cm from the ground, and the second wire is 40-60 cm from the first. Alternatively, use a wide-top trellis with a crossbeam on the upright posts, forming a “T” shape, with the crossbeam 80-100 cm wide. Stretch one wire at each end of the crossbeam, and tie the 4-6 main branches of each tree respectively to both sides, with one on each upper wire and one or two on each lower side. The suitable density is 150-200 cm between plants and 400-600 cm between rows.
2 Tree structure
The trunk height is 80-100 cm, and the training zone is 50-70 cm long, bearing 4-6 main branches. The main branches are 150-200 cm long, with an angle of more than 70°, arranged in a spiral and staggered manner. Generally, no secondary branches are retained on the main branches; long, medium, short, and bouquet fruiting branches as well as small fruiting branch groups are directly borne on them, arranged in an orderly manner with high, medium, and low positions and reasonable combination. The canopy thickness is about 1.5 m.
3 Key points of training technology
3.1 Cultivation of main branches
Select and cultivate suitable branches within the training zone and remove excess branches. If there are not enough main branches, shorten or strongly bend the uppermost dominant branch on the central leader to promote branching and directionally cultivate 4-6 main branches. The spacing between main branches is 10-15 cm. When a 1-year-old branch is cultivated as a main branch, it should be shortened once at 100 cm or notched during the growing season to cultivate branches and increase load capacity. Combine winter pruning and pre-bloom supplementary pruning to adjust the ratio of flower buds to leaf buds to 1:4-5, and remove some flower buds.
3.2 Spring tying and fixing
Carry out branch tying and fixing when sap flows and branches become soft. Before opening the angle, first rub and smooth the base of the branch to be bent; after it softens, pull it open, and tie the main branches evenly and separately to the wires on both sides. When there are 4 main branches, place one on each side above and below; when there are 6, place one on each side above and two on each side below. Branches less than 120 cm long can be temporarily left unpruned.
3.3 Bud removal and sprout removal
When buds sprout, remove excess sprouts from the base. Mainly remove buds at pruning cuts, buds at saw cuts, and excessive sprouts on the back after branch bending. For buds on the back, retain one every 20-30 cm and remove the rest early. For main branches that are not long enough, retain one vigorous bud with a good orientation as the extension leader, and remove other competitive branches promptly, which can save nutrients and regulate growth vigor.
3.4 Notching and girdling
The main purpose is to promote flower bud differentiation so as to bear fruit earlier and achieve early high yield. In addition, it also has the effects of inhibiting growth, increasing fruit set rate, and cultivating renewal fruiting branches. Notching is carried out above the buds on both sides of the main branches that can produce dominant branches. For girdling, make the first girdle on the main branch 15 cm from the trunk, and make the second and third girdles every 10-15 d. Keep a distance of about 10 cm between adjacent girdles. The number of girdles should be determined according to the tree growth status.
3.5 Branch thinning and shoot twisting
A large number of new shoots are cultivated through measures such as branch bending, notching, and girdling, often causing excessive tree vigor and a closed canopy. Therefore, starting in mid-June, combine summer pruning to promptly thin out some dense branches, upright branches, overlapping branches, and crossing branches, and twist useful upright branches.
3.6 Autumn angle opening and branch tying
When the main branches grow to more than 120 cm, they can be tied to the trellis. Opening the angle at this time results in plump and full buds and no vigorous shoots on the back. In addition to opening the angle and tying the main branches, all kinds of large and medium fruiting branches and branch groups should also be opened by pulling, weighing down, or propping, and the angle should be greater than that of the main branches so that the tree is balanced from top to bottom and inside to outside.
To give full play to the effectiveness of the trellis form and make plums high-yielding, stable-yielding, and high-quality, it must also be combined with corresponding supporting technologies. Specific supporting measures include selecting improved varieties, reasonable density, increasing organic fertilizer application, flower and fruit thinning, scientific pest and disease prevention, fruit bagging, and timely harvest in batches.