Persimmon trees often experience fruit drop, which can significantly impact yield and economic returns. There are two main causes: physiological fruit drop, due to internal imbalances in the tree, and fruit drop caused by pests or diseases. Both can lead to severe losses in certain years.
**Causes of Physiological Fruit Drop**
1. **Nutrient Imbalance**: When new shoots grow vigorously, they consume nutrients that would otherwise support fruit development, leading to premature fruit drop. Poor flower bud differentiation can also cause early fruit loss.
2. **Inadequate Pollination**: Some persimmon varieties, like the large grinding disc, don't require pollination, making them less prone to fruit drop. However, most sweet Japanese varieties need cross-pollination. If pollination is hindered by rain or poor weather, fruit drop becomes more common.
3. **Poor Tree Structure**: Trees with tall, dense branches and poor air circulation may struggle to accumulate enough nutrients in their shoots, weakening the tree and causing fruits to fall prematurely.
4. **Insufficient Water and Fertilizer**: Prolonged drought or poor soil quality reduces nutrient uptake, increasing fruit drop. Conversely, excessive moisture can also reduce root absorption, even with added fertilizers, leading to nutrient deficiency and fruit loss.
5. **Rainfall Impact**: Heavy rainfall during the fruiting period can reduce sunlight and weaken photosynthesis, leading to nutrient deficiencies and fruit drop.
**Pest and Disease-Related Fruit Drop**
1. **Persimmon Worms**: These pests damage fruit before and after harvest, causing soft, fallen fruit and reducing yield.
2. **Tree Shrews (Persimmon Tree Beetles)**: They feed on the tree and cause significant fruit drop.
3. **Anthracnose**: This fungal disease commonly appears in September, leading to widespread fruit drop.
**Prevention and Control Measures**
1. **Improve Fertilization and Irrigation**: Ensure the tree has sufficient nutrients and water to maintain strong growth and balanced nutrient distribution.
2. **Prune Effectively**: Especially during summer, remove unnecessary shoots to improve light and air circulation. Drain excess water in rainy seasons and irrigate during dry periods.
3. **Use Pollination Trees and Artificial Pollination**: For varieties requiring cross-pollination, plant male trees or use artificial pollination. Apply it in 3–4 stages after flowering for best results.
4. **Girdling**: Girdling the trunk or main branches of healthy trees can promote flower bud formation and reduce fruit drop. It should be done at half bloom, with a width of no more than 1.5 cm. Avoid annual girdling to prevent tree weakening.
5. **Pest and Disease Management**: Spray lime sulfur before bud break, and use Bordeaux mixture in mid-June and mid-August. Remove infected fruit, destroy larvae, and apply insecticides like Lethbone and Avermectin to control scale insects.
6. **Use Growth Regulators**: Spraying 500ppm gibberellin or adding 1% urea to young fruit can effectively prevent fruit drop and increase fruit set.
By implementing these strategies, growers can significantly reduce fruit drop and improve persimmon yields.
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