Key Points of Post-Grafting Management Techniques for Top-Grafting and Variety Conversion of Citrus
1. Do well in cutting the rootstock stubs. After using side grafting with exposed buds, the rootstock stubs should be cut or sawed off. This should be done in two steps. First, leave about 15cm of rootstock stub above the graft union. After the new shoots have become lignified, cut the stub flush with the graft union and smooth the cut surface with a knife.
2. Do well in removing sprouts. After top-grafting, because the apical dominance has been removed, the tree's nutrient supply becomes abundant, and a large number of sprouts often emerge. These should be removed early with a blade; otherwise they will affect the growth of the grafted buds. Generally, remove sprouts about once a week.
3. Expose buds at the right time. If buds are tied with exposure, the film should be removed after the first flush has become lignified. If buds are wrapped and sealed, the buds should be exposed promptly when they survive and begin to sprout. Buds grafted in autumn should be exposed when the spring buds begin to sprout the following year. Check for survival 1 month after spring grafting and half a month after summer grafting, and expose the buds promptly. Re-graft any that have not survived.
4. Do well in pinching. When new shoots grow to about 20cm, pinch off the growing tips to promote new shoots, expand the canopy, and encourage earlier fruiting.
5. Do well in fertilizer and water management. After top-grafting, in order to promote the growth of the three flushes in spring, summer, and autumn and accelerate canopy recovery, fertilizer and water supply should be fully guaranteed. In fertilization, increase the amount of nitrogen fertilizer and ensure one topdressing before each of the spring, summer, and autumn flushes. Summer and autumn in particular are peak periods for citrus fertilizer uptake, when demand for various nutrient elements is high. Compound fertilizer or urea plus decomposed human and livestock manure and urine should be used.
6. Do well in pest and disease control. After citrus top-grafting, the main problem is insect damage, mainly red spider mites, yellow spider mites, citrus aphids, and citrus leafminers. From March to May, observe the occurrence of red and yellow spider mites at any time. If, in a survey of 100 leaves, the average is more than two mites per leaf, spray for control. Pesticides such as isocarbophos, omethoate, and pyridaben can be used alternately. After aphids damage citrus, the leaves curl, greatly affecting the growth of branches and leaves. During the spring and summer flushes, often pay attention to the occurrence of aphids and control them promptly. A 1000-fold solution of omethoate or a 5000-fold solution of 20% fenvalerate can be used for control. When the autumn flush emerges, special attention should be paid to preventing citrus leafminer. Start spraying when tender buds have emerged 2-3mm and the emergence rate in the whole orchard is above 50%. A 1000-fold emulsion of 20% fenpropathrin can be used for control.