Key Technical Points for Maintaining High and Stable Yields in Mature Longan Trees

Environmental factors such as warm winters have seriously affected the fruit set of longan, so much so that the yield of Putian longan in recent years has consistently been unsatisfactory. To ensure high yields in mature longan trees, the “four gates” must be strictly controlled.

The first is the variety gate. Years of practice by agricultural technology departments have shown that the “Songfengben” longan variety is the top choice for a good year, stable yield, and large fruit. It is recommended that growers boldly graft this superior variety.

The second is the pruning gate. Pruning focuses on the “four cuts”: First, frequently cut off weak twigs, densely growing branches, messy branches, shade branches, and diseased or pest-infested branches, to develop an umbrella-shaped canopy and thick, strong branches. Second, cut off excess flower spikes. When thinning flower spikes around Qingming, cut 1-2 nodes below the “gourd node”; when thinning around Guyu, cut at the “gourd node”; when thinning at Lixia, cut 1-2 nodes above the “gourd node.” Third, boldly cut off spring shoots, using a method similar to cutting flower spikes, which better promotes the sprouting of summer and autumn shoots. Fourth, cut off excess young branches. The two “bud thinning” rounds for summer shoots and autumn shoots are very important, leaving only 1-2 young branches per branch. The purpose of these “four cuts” is to organize the tree shape well, cultivate strong fruiting mother branches, and also prevent the occurrence of pests and diseases.

The third is the fertilization gate. To prevent winter shoots, effort must be put into fertilization. Mature trees are fertilized only 3 times per year, using the “one heavy, two balanced, three quick” method. “One heavy” means fertilization in early spring is especially important, and the amount of fertilizer must be sufficient and heavy. Not only nitrogen fertilizer but also phosphorus, potassium, and a small amount of boron fertilizer should be applied, along with large amounts of farmyard manure, straw, and cake fertilizer. This fertilization accounts for 60% of the total annual fertilizer application. “Two balanced” refers to the shoot-promoting and fruit-strengthening fertilizer in May, mainly applying human excrement and urine or urea, plus a small amount of imported compound fertilizer and potassium chloride, so that it is balanced and uniform. This fertilization accounts for 30% of the total annual fertilizer application. “Three quick” refers to pre-harvest fertilizer, applying quick-acting fertilizer about 15 days before harvest, accounting for 10% of the total annual fertilizer application. In addition, do not fertilize in winter, and also dig large holes at an appropriate time (when experience and observation indicate winter shoots are about to sprout). This not only prepares conditions for heavy fertilization the following spring but can also damage the root system, indirectly achieving the goal of preventing and controlling winter shoots.

The fourth is the pest and disease gate. For pest and disease control, one can “treat indirectly,” and cultivating a robust tree body is of utmost importance. Once pests or diseases are found, first immediately manually remove or destroy the affected branches and leaves to isolate the source of infection; second, use chemical control, and be sure to eliminate pests and diseases in the bud. In recent years, what deserves special attention from growers are the three major moth species that harm new shoots: the litchi fruit borer, the litchi twig borer, and the litchi leaf roller. The focus of prevention is in August-September (among them, control of the litchi fruit borer should also be carried out about 12 days after longan flowers fade), spraying once during the period when summer-extended autumn shoots and autumn shoots sprout, and spraying a second time after 7-10 days.