Litchi yield is often low, with few fruits collected or even no fruit at all. In many cases, the issue isn't a lack of flowers but rather an imbalance in internal and external conditions that are essential for flower bud differentiation, flowering, and fruit development. These imbalances can disrupt normal embryo and fruit development, leading to continuous fruit loss or even complete fruit drop. This phenomenon, known as "flowering without fruiting," is a critical challenge in litchi cultivation and plays a vital role in ensuring a good harvest.
To achieve successful fruit set, several key factors must be considered:
1. **Normal Pollination and Fertilization**
Litchi has large inflorescences with a high number of flowers, most of which are bisexual. For female ovaries to develop into marketable fruits, proper pollination and fertilization must occur. Ensuring favorable conditions for pollination is crucial, as it forms the foundation for fruit development. Without this, even a large number of flowers will not result in a good yield.
2. **Sufficient Nutrient Supply During Fruit Development**
Litchi requires a significant amount of nutrients during the flowering and fruiting stages. A steady supply of minerals, carbohydrates, and nitrogenous compounds is necessary throughout the growth cycle. If this supply is interrupted, fruit development may stop, leading to severe fruit drop. The nutrients come from two main sources: those stored in the tree before flowering and those produced through photosynthesis after flowering. The health of the parent branches and the metabolic conditions during flowering directly impact fruit development.
3. **Balanced Vegetative and Reproductive Growth**
Excessive vegetative growth during the flowering and fruiting period can consume valuable nutrients and disrupt hormonal balance, reducing the availability of resources for fruit development. Controlling the growth of new shoots and leaves is essential to ensure that nutrients are directed toward the developing fruits rather than being used for unnecessary growth.
4. **Optimal Environmental Conditions**
Appropriate temperature, humidity, and weather conditions are essential for successful pollination and fruit development. Extreme temperatures, heavy rain, drought, or waterlogging can interfere with these processes, leading to physiological disorders such as fruit cracking and premature fruit drop.
**Physiological Fruit Drop in Litchi**
During the fruit development stage, litchi may shed fruit at various times, with several peak periods of fruit drop. These include:
- **First Peak (7–12 days after flowering):** Caused by poor pollination and fertilization.
- **Second Peak (around 25 days after flowering):** Due to endosperm degeneration, affecting embryo development and hormone balance.
- **Third Peak (50–55 days after flowering):** Related to rapid fruit growth and competition with new shoot development.
- **Pre-harvest Drop:** Occurs just before harvest, often due to nutrient shortages or adverse weather conditions.
- **Disease and Pest Infestations:** Pests like Phytophthora capsici and anthracnose can also contribute to fruit drop and cracking.
**Key Techniques for Strong Flowering and Fruiting**
To improve fruit setting and increase yield, several techniques are recommended:
1. **Cultivate Robust Flower Buds**
Strengthen the management of litchi trees, focusing on producing strong, healthy parent shoots. Techniques such as using specialized flower promoters and controlling shoot growth help create ideal conditions for flowering and fruiting.
2. **Control Flowering and Flower Quantity**
Adjust the timing and volume of flowering through pruning, artificial shortening of spikes, and chemical treatments. This helps increase the proportion of female flowers and reduce competition for nutrients.
3. **Enhance Pollination and Fertilization**
Ensure optimal environmental conditions for pollination, including suitable temperature and humidity. Bee pollination is effective, but artificial methods like pollen collection and spraying can also be used when natural pollinators are limited.
4. **Regulate Tree Growth**
Control excessive vegetative growth by pruning and applying balanced fertilizers. Avoid overuse of nitrogen, which can promote leafy growth instead of fruit development.
5. **Ring Girdling**
A technique used to restrict nutrient flow to the roots, directing more energy to the fruit. It is most effective on vigorous trees but should be avoided on weak or old trees.
6. **Use of Growth Regulators**
Apply plant growth regulators at key stages to reduce fruit drop. Spraying them about 15 days after flowering and again a few weeks later can significantly improve fruit retention.
By implementing these strategies, litchi growers can overcome the challenges of low yield and fruit drop, ultimately achieving better harvests and higher productivity.
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