Technique for Top-Grafting Mixed Pear Trees to Nanguo Pear in Western Liaoning

1. Re-grafting. Whether a mixed pear top-grafted to Nanguo pear has survived can be determined 20 to 25 days after grafting. On surviving Nanguo pear scions, the bark remains green, and the buds begin to sprout; those that have not survived show shrunken, dried bark. Re-graft those that failed as soon as possible: in spring, cut off the dead stub and then cleft-graft; in summer, after the bark slips, green-wood bark grafting can be used. After re-grafting, cover promptly with paper bags to aid survival. If plastic bags are used, the high outside temperature can easily cause the scions to lose water.

2. Unbinding. The new shoots of Nanguo pear from spring cleft grafting or side-veneer grafting enter a rapid growth period in June and July, and the plastic strips should be untied promptly. For spring top-grafting where plastic bags were used, when the new shoots have grown 2 to 3 leaves, first tear the plastic bags open gradually, and after the graft union has healed, loosen the plastic strips.

3. Removing sprouts. After top-grafting, because the nutrient supply between the above-ground and below-ground parts of the tree is unbalanced, buds below the graft union sprout very easily, which leaves the top-grafted parts with insufficient nutrient supply, causing slow early growth or even gradual death. Therefore, for successfully top-grafted Nanguo pear branches, promptly remove the sprouts of the original variety below the graft union; remove sprouts once a week, 5 to 7 times over the year.

4. Tying to supports. When the new Nanguo pear shoots produced after top-grafting reach 25 to 35 cm, promptly tie them to stakes at the graft union; after the new shoots have lignified and the graft union has healed firmly, remove the stakes.

5. Timely fertilisation. For pear trees intended for top-grafting, organic fertiliser should be applied in good time in the autumn of the previous year or the spring of the same year before top-grafting, to maintain the nutrient supply of the top-grafted trees. Top-dressing should be carried out after the top-grafting has survived; strip trenches, ring trenches and other methods are all suitable, with 1 to 1.5 kg of top-dressing per mature tree.

6. Foliar feeding. To promote the growth and maturation of the new shoots of top-grafted Nanguo pear, spray 0.3% to 0.5% urea solution 1 to 2 times in June and July, and spray 0.3% to 0.5% monopotassium phosphate solution 1 to 2 times in August and September. All the above foliar sprays can speed up the growth and maturation of top-grafted Nanguo pear branches.

7. Timely irrigation. Immediately after top-grafting, give the top-grafted trees one thorough watering to ensure sufficient humidity in the orchard and promote wound healing. In mid-to-late June, when the top-grafted new shoots are growing, give another thorough watering according to the water needs of the top-grafted orchard. Practice has shown that fertilising and irrigating top-grafted Nanguo pear trees in the same year, with strengthened management, allows a good number of flower buds to form that same year and a certain yield the following year.

8. Reasonable summer and winter pruning. To control excessive growth of the grafted branches and shoots, carry out summer pruning of the grafted branches; when the new shoots of the grafted branches reach 40 cm, pinch off the tips at 3 cm to promote branching, expand the canopy and encourage early fruiting. For grafted branch groups on the inner part of the canopy, pinch lightly in mid-to-late June to promote flower bud formation, and bend down branches whose growth angle is not ideal. For vigorous upright branches, ring-barking can be done, or notching can be done the following spring. Winter pruning should follow the principle of light pruning and few thinning cuts; for vigorous branches in good top-grafted positions, cut back at a plump bud. For top-grafted branches on the same branch head, to promote wound healing, the strong ones can be removed and the weak ones kept to control growth. By the second year after grafting the canopy has already expanded, and normal pruning can then be carried out.

9. Timely control of pests and diseases. Because the grafted buds after top-grafting sprout relatively late and the shoots are young and tender, they are most vulnerable to damage by pests such as red spider mites and pear stem sawflies, so control should be carried out promptly according to pest conditions. At the same time, before the rainy season arrives in mid-to-late June, spray a fungicide once to control pear scab and other diseases, ensuring normal growth of the new shoots so that they reach lignification.