Key Technical Points for Flower and Fruit Retention in Citrus Cultivation
The 2-3 months from bud emergence to fruit set stabilization is the most important period of the year for citrus trees. For a good harvest, comprehensive flower and fruit retention measures must be taken according to the growth conditions of the citrus trees and changes in weather.
1. Reasonable fertilization: For citrus orchards that were not fertilized last winter, organic fertilizer should be supplemented as soon as possible. For adult trees, apply 5-10 kg of chicken manure or 1-2 loads of farmyard manure per tree, plus an appropriate amount of urea, and bury it around the root zone. The fertilization principle during the flower and fruit retention period is: nitrogen-based in the early stage, emphasis on potassium with phosphorus supplementation in the later stage; combining soil fertilization with foliar feeding. For the post-bloom fertilizer, apply compound fertilizer plus an appropriate amount of urea during the flower-falling period to promptly replenish nutrients consumed during flowering; for the fruit-setting fertilizer, apply potassium fertilizer plus an appropriate amount of phosphorus fertilizer; for the fruit-swelling fertilizer, apply compound fertilizer plus potassium fertilizer. For foliar feeding, spray 0.2% monopotassium phosphate twice from spring bud break to before flowering, spray nucleotides during rainy days, and add 0.1% borax to one of the applications; during the young fruit stage, spray foliar fertilizer 2-3 times in combination with pest and disease control or fruit retention, with the first foliar spray including 0.1% magnesium sulfate and 0.1% zinc sulfate.
2. Soil management: Repair drainage ditches inside and outside the orchard to remove standing water, so that waterlogging on rainy days does not affect root growth or even cause root rot leading to flower and fruit drop. During continuous dry and hot weather lasting more than 10 days, irrigate promptly to keep the soil moist and loose, which helps the root system absorb water and nutrients.
3. Scientific use of growth regulators: Plant growth regulators commonly used for citrus fruit retention include 2,4-D, fruit-retention hormone, triacontanol, 920, and fruit-retention agents. Use them 2-3 times after flower drop, spraying once every about 15 days. Alternating different growth regulators gives better results. For seedless and few-seeded citrus varieties, using 920 or triacontanol for fruit retention gives better results.
4. Pest and disease control: During the flowering and fruiting period, the main pests and diseases include red spider mites, rust mites, aphids, citrus blossom midges, tortrix moths, anthracnose, and scab. For aphid control during the spring shoot stage, use omethoate or monocrotophos; in early to mid-April (or early March if drought occurs), control red spider mites, and in mid-to-late April control rust mites, using acaricides or biological pesticides for spraying; spray organophosphorus pesticides at the early bud stage to kill citrus blossom midges and tortrix moths; for diseases, focus on prevention, using fungicides such as copper oxychloride or thiophanate-methyl.
5. Control early summer shoots: From May to mid-June, promptly remove early summer shoots to avoid competition between shoots and fruit for nutrients, which benefits young fruit development and reduces fruit drop. For vigorous trees with few flowers and few fruits, girdle the trunk 25 days after flower drop to retain fruit, which can also control summer shoots.