What is the main reason for the physiological fruit drop in the second stage of longan?

Longkuang is a cyme with male and female flowers, a few bisexual flowers and denatured flowers. The quantity and quality of female flowers are the basis of fruit. Longan is a fruit tree with flower bud differentiation, flowering and fruiting. Physiological differentiation and heading of flower buds need relative drought and suitable low temperature. Flower bud differentiation usually occurs from June 65438+February to June 65438+1October of the following year. At this time, it is necessary to stop the growth of vegetative organs such as branches and leaves to promote the accumulation of nutrients. Ears usually germinate from early February to late March, and then morphological development begins to gradually form a complete ear. During this period, the daily average temperature is 18~20℃, and there is more rain, so it is easy to "grab bamboo shoots" in the ear, which leads to longan bearing fruit every other year.

The flowering period of longan is generally from early April to late May, which varies with different regions, climate, varieties, tree potential and shoot-out period. Longan consumes a lot of nutrients during flowering. Female flower of the same mother tree in the same orchard. Male flowers often coexist alternately, with more pollination opportunities and high fruit setting rate, but the physiological fruit drop rate is also high. The physiological fruit drop of longan is the most in 3~20 days after flowering and pollination (from mid-May to early June), accounting for 40%~70% of the total fruit drop, mainly due to poor flower development, pollination and fertilization, and the direct inducement is related to climate factors. From mid-June to mid-July, the second stage of physiological fruit drop will occur, mainly due to insufficient fertilizer and water and malnutrition, which will seriously affect the yield. Pests and disastrous climate (rainstorm, continuous rain, drought, strong wind, etc.). ) will also aggravate the fruit drop. Therefore, longan must ensure sufficient fertilizer and water supply during the fruit expansion period, which is the key period of fertilization and yield increase.