High-Grafting Methods and Supporting Management Techniques for Nanguo Pear

In recent years, with the promotion of the Nanguo pear (Dananguo, Hongnanguo) series cultivars, in order to quickly adapt to changes in the pear cultivar market, we carried out high-grafting improvement on 3,500 mixed pear trees in 2002. Because post-grafting management techniques were in place, the survival rate of high grafting that year reached 95%, the tree vigor was restored the following year, and by the 3rd year the original pear orchard yield was basically restored, achieving good results. The high-grafting methods and supporting management techniques are described below.

1 High-grafting methods

1.1 High-grafting period

In the semi-arid region of northwestern Liaoning, spring is the most suitable time for high grafting mixed pear trees to Nanguo pear. The specific time should be controlled to begin after sap flow starts, that is, from late March until late May; however, late high grafting must have good scion storage conditions, and the scions must not sprout, otherwise the survival rate of high grafting will be reduced.

1.2 High-grafting technique

1.2.1 Treatment of high-grafting positions and their scaffold branches For perennial mixed pear trees high-grafted to Nanguo pear, the scaffold branches are usually selected and retained according to the tree structure of the open-center three-main-branch layered form. For irregular tree shapes, do not forcibly change the tree shape. Generally, the high-grafting positions should be controlled below 4- to 6-year-old branches, or branches with a diameter not exceeding 6 cm. Do not "cut and fell extensively", otherwise the wounds will be too large and difficult to heal.

1.2.2 High-grafting method Mixed pear trees high-grafted to Nanguo pear mostly use the cleft grafting method. The specific method is to saw off the branch at the position on the rootstock tree where cleft grafting is to be done, smooth the saw cut, and use a cleft grafting knife to split vertically downward at the center or near one side to make a cut 5-6 cm long. Then prepare the scion by making a wedge-shaped cut about 3-4 cm long on each of the two symmetrical sides at the base of the scion. The cut surfaces should be smooth, with one side slightly thicker. Keep 3-4 buds on the scion and then cut it off from the top, with the cut surface flat, to reduce water evaporation. Insert the prepared scion into the cleft of the rootstock branch, with the slightly thicker side facing outward, so that the cambium layers of the rootstock and scion align. Bind tightly with plastic strips, seal the upper cut of the scion with a protective agent, and then cover it with a plastic bag to maintain humidity. When the rootstock is relatively thick, one cleft can hold 2 scions.

2 Timely supplementary grafting and unbinding

2.1 Supplementary grafting

Whether mixed pear high-grafted to Nanguo pear has survived can be determined 20-25 days later. On surviving Nanguo pear scions, the bark remains green, and the buds begin to sprout; those that have not survived show shrunken and dried bark. Supplementary grafting should be done promptly for those that did not survive high grafting. The method is to cut off the dead stub in spring and then perform cleft grafting; in early summer, after the bark slips on fruit trees, the green-branch bark grafting method can be used. After supplementary grafting, paper bags should be put on promptly to favor survival. Use plastic bags. Plastic bags are used because the external temperature is too high at this time, and the scions easily lose water due to high temperature.

2.2 Unbinding

Nanguo pear grafted shoots from spring high grafting or supplementary grafting enter rapid growth from June to July, and the plastic strips should be untied promptly; for those that used plastic bagging in spring high grafting, when the grafted shoots have grown 2-3 leaves, the plastic bags should first be gradually torn open, and after the grafted site has healed, the plastic strips should then be loosened.

3 Shoot removal and tying

3.1 Shoot removal

For surviving Nanguo pear grafted shoots from high grafting, sprouts of the original cultivar growing below the graft union should be removed promptly. This should be done 5-7 times throughout the year, with timely shoot removal once a week.

3.2 Tying

For surviving new Nanguo pear shoots from high grafting, support stakes should be used promptly for tying. This is done when the new high-grafted shoots reach 25-35 cm in length. Tie a support stake at the grafted site, and remove it after the new shoot has lignified and the graft union has healed firmly.

4 Strengthening fertilizer and water management

4.1 Increasing organic fertilizer application and timely topdressing with chemical fertilizers

For pear trees intended for high grafting, organic fertilizer should be applied in a timely manner in the autumn of the previous year or the spring of the current year before high grafting, preferably 100-150 kg of high-quality farmyard manure per tree, to maintain nutrient supply for the high-grafted trees. At the same time, topdressing should be done promptly. Topdressing is carried out after the high grafting has survived, and methods such as strip ditches or ring ditches can all be used. Each mature tree should be given 1-1.5 kg of special fertilizer for pear trees (nitrogen:phosphorus:potassium = 2:1:1).

4.2 Foliar fertilizer spraying

In order to promote the growth and maturity of new shoots of high-grafted Nanguo pear, spray 0.3%-0.5% urea aqueous solution 1-2 times in June to July; spray 0.3%-0.5% monopotassium phosphate aqueous solution 1-2 times in August to September, to accelerate the growth and maturity of high-grafted Nanguo pear branches.

4.3 Timely irrigation

After high grafting, the high-grafted trees should immediately be given 1 thorough irrigation to ensure sufficient humidity in the orchard and promote wound healing. In mid-to-late June, when the new high-grafted shoots accelerate their growth, another thorough irrigation should be given according to the water requirements of the high-grafted orchard.

Practice has shown that by applying fertilizer and irrigating high-grafted Nanguo pear trees in the same year and strengthening management, more flower buds can be formed that year, and a certain yield can be obtained the 2nd year.

5 Attaching importance to summer pruning and carrying out reasonable winter pruning

In order to control excessive growth of grafted branches and shoots, summer pruning should be carried out on grafted branches in summer. The specific method is that when the new shoots of grafted branches grow to 40 cm, pinch the tips at 30 cm to promote branching, expand the canopy, and promote early fruiting. For branch groups grafted in the inner canopy, pinch the tips in mid-to-late June to promote flower bud formation. For those with undesirable growth angles, branch bending should also be carried out. For upright, strong, vigorous branches, ring cutting should also be carried out, or scoring should be done the following spring. Winter pruning should mainly be light. Based on the principles of light pruning and less thinning, short-cut strong vigorous branches at good high-grafting positions at plump buds; for high-grafted branches on the same branch head, in order to promote wound healing, the strong can be removed and the weak retained to control growth. In the 2nd year after grafting, the canopy has already expanded, and normal pruning can then be implemented.

6 Pest and disease control

After high grafting, the grafted buds sprout later than normal new shoots, and the new shoots are tender, making them most susceptible to damage by pests and diseases such as red spider mites and pear stem sawflies, so control should be carried out promptly according to pest conditions. For red spider mites, spray 0.3-0.5° Baumé lime sulfur mixture or 5% hexythiazox 2000-2500 times solution or 20% amitraz 1000 times solution during the peak emergence period after overwintering at the full bloom stage of pear (when the daily average temperature is 9°C). For pear stem sawfly, spray 50% parathion emulsifiable concentrate 1500-2000 times solution or 40% chlorpyrifos emulsifiable concentrate 2500-3000 times solution around mid-May during the peak occurrence period of adults. At the same time, before the rainy season arrives in mid-to-late June, spray 1 application of a fungicide such as 50% thiophanate-methyl wettable powder 500-800 times solution to control pear scab and other diseases, so that new shoots grow normally and reach lignification.