What are the technical measures for flower and fruit retention in lychee?
1. Strengthening flowers and retaining flowers. (1) Apply flower-strengthening fertilizer in time. Flower-strengthening fertilizer is generally applied when the flower panicle emerges and flower buds are visible (also called fertilizing at flowering). The amount applied depends on the number of flowers formed and tree vigor; generally, for every 50 kg of fruit produced by the tree, apply 1 kg of compound fertilizer plus 0.2-0.5 kg of urea, or apply 0.5 kg each of urea, superphosphate, and potassium chloride....
1. Strengthening flowers and retaining flowers. (1) Apply flower-strengthening fertilizer in time. Flower-strengthening fertilizer is generally applied when the flower panicle emerges and flower buds are visible (also called fertilizing at flowering). The amount applied depends on the number of flowers formed and tree vigor; generally, for every 50 kg of fruit produced by the tree, apply 1 kg of compound fertilizer plus 0.2-0.5 kg of urea, or apply 0.5 kg each of urea, superphosphate, and potassium chloride. In addition, about 20 days before flowering, spray the leaves with 0.3% monopotassium phosphate, or 1000 times Lvwang No. 1 (high potassium) plus 0.05% borax, which can promote flower panicle development. (2) Reasonably control the panicle. Production practice shows that early-emerging flower panicles and excessively long flower panicles generally have poor flower quality, a lower proportion of female flowers, and a low fruit-setting rate. Especially for varieties with large flower panicles (such as Feizixiao), flower quantity and flower quantity should be reasonably regulated and controlled to increase the fruit-setting rate. ① Artificial short pruning of flower panicles. Short pruning of flower panicles can reduce flower quantity and improve flower quality. The severity of flower panicle short pruning should depend on the variety; for varieties with strong panicle regeneration ability and easy emergence of secondary flower panicles, such as Feizixiao and Sanyuehong, it can be heavier. ② Drugs used to control panicles include lychee high-yield hormone, ethephon, etc. to control flower panicles. (4) Prevent and control pests and diseases. The main pests and diseases harming lychee flower panicles include lychee stink bug, lychee erinose mite, looper, aphid, and lychee downy blight. Control can be carried out with drugs such as Lorsban, Comite, imidacloprid, Methomyl, trichlorfon, Yalike, and Ridomil MZ, Sandofan, Daconil M-45, metalaxyl, etc.
2. Strengthen management during the flowering period to increase the fruit-setting rate. Main points to focus on: (1) Release bees for pollination. Generally, one box of bees is required for every 3-5 mu. (2) Artificial supplementary pollination. A commonly used method of artificial supplementary pollination is: use a wet towel to gently shake back and forth on the just-opened male flower panicles to collect pollen, then place the towel in clean water, repeating many times, so that the pollen suspension becomes a pale yellow turbid liquid, then spray it onto female flowers. Notes for artificial pollination: First, it should be done on sunny days with a temperature above 16°C; second, the prepared pollen liquid should not be left for more than 20 minutes, otherwise the pollen loses viability and pollination effectiveness is affected. (3) Spray water in dry weather to prevent flower drying. (4) Shake trees in rainy weather to prevent flower rot.
3. Retain fruit and strengthen fruit. (1) Fertilize to strengthen fruit and retain fruit. Lychee flowering consumes a large amount of nutrients from the tree. To ensure the nutrients needed for fruit growth and development, apply fruit-strengthening fertilizer in time after flower drop and when young fruit are the size of mung beans. The amount applied should depend on tree vigor and fruit load, and at the same time, attention should be paid to foliar topdressing. (2) Girdling to retain fruit. For vigorously growing trees, begin girdling 10-15 days after female flowers drop, on large branches 4-6 cm thick, cut one ring deep to the xylem. Do not girdle weak trees. (3) Apply plant growth regulators to retain fruit. When fruit are the size of mung beans, use 20 mg/L gibberellin to retain fruit. (4) Strengthen water management to retain fruit. Irrigate during drought; during high temperature and strong sunlight, spray water on the canopy; when there is excessive rain and water accumulation, drain promptly. (5) Prevent and control pests and diseases in time to retain fruit. The main diseases during the lychee fruit development period include lychee downy blight, lychee sooty mold, and lychee anthracnose; the main pests include lychee fruit borer, lychee stink bug, and lychee small gray butterfly, etc. Pest and disease control should focus on the young fruit stage of lychee.