Watermelon fruit drop, also known as "frozen prickly heat," is a common issue in watermelon cultivation. The symptoms typically appear around the seeds, where water-soaked spots develop, turning purple or dark brown. In severe cases, the seeds become rotten, making the fruit inedible and reducing its market value. According to field surveys, several factors contribute to this problem.
First, the choice of rootstock plays a significant role. Comparisons between different plots show that rootstocks with white pumpkin seeds have a lower incidence of the disease (around 5%), while those with loquat seeds are more susceptible, with an incidence rate as high as 90%. Areas like Sunrise Office and Boluopu Town, which have large areas of gourd rootstocks, suffer from serious fruit drop, whereas towns like Tangchi and Shagangzi, with more white pumpkin rootstocks, experience fewer issues.
Second, inadequate nutrition during seedling development can lead to weak plants. When both rootstocks and scions are sown in the same small nutrient container (10 cm x 10 cm), overcrowding and high night temperatures can cause elongated, weak seedlings with reduced resistance.
Third, overuse of certain fertilizers, particularly chicken manure, can raise soil alkalinity and reduce soil permeability, creating unfavorable growing conditions.
Fourth, early planting followed by cold spring weather can be disastrous. For example, in 2006, a farmer in Huchanglai, Xihu Village, planted 5 acres of greenhouse watermelons on April 8th. Just six days later, a cold snap dropped the temperature to 2.5°C, causing the seedlings to yellow and grow slowly. This delay in growth led to a high percentage of fruit drop—85% of all fruits were affected. Despite investing 90,000 yuan in a greenhouse, the farmer only recovered 20,000 yuan, suffering heavy losses.
Fifth, insufficient temperature differences and excessive humidity inside greenhouses can promote diseases such as anthracnose and other fungal infections. High nighttime temperatures hinder plant assimilation, weakening both seedlings and fruits.
Sixth, delayed harvesting can result in sunburn damage. When watermelons mature, organic matter should be transformed and accumulated. However, if the fruit is exposed to intense sunlight in the late stages, it can lead to sunburn and prickly fruit symptoms.
Seventh, viral infections during the seedling or early fruiting stage can also cause fruit drop. All affected fruits in these cases showed signs of virus infection.
To prevent and control watermelon fruit drop, several measures can be taken:
1. Use disease-free seeds for both rootstocks and scions. Avoid introducing seeds from infected areas, and treat them with dry heat or chemical methods before planting.
2. Grow healthy seedlings using disease-free soil. Choose fertile soil far from previous melon fields and mix it with a "vegetable nursery agent" to improve sterilization and strengthen the seedlings. Prepare about 500 seedling bags, each mixed with one bag of the agent, to cover up to 1,500 pots.
3. Practice crop rotation. Rotating with non-cucurbit crops like eggplants, legumes, or onions every 2–3 years can significantly reduce disease risk.
4. Use white pumpkin seeds as rootstocks, as they are less prone to fruit drop.
5. Disinfect tools regularly. Grafting knives should be disinfected with 75% alcohol after each use. Avoid damaging plants during agricultural operations to prevent virus transmission.
6. Apply fertilizers scientifically. Use bio-organic compound fertilizer as a base, at 100 kg per mu, and fully decompose chicken manure. Add two loads of compost per shed, along with 15 kg of compound fertilizer and essential micronutrients like boron, calcium, and magnesium.
7. Protect against cold snaps. Planting usually occurs in early April, a time when cold weather is still possible. Prepare cold protection materials in advance, and use fumigation agents to control both cold and disease risks, ensuring greenhouse temperatures stay above 15°C.
8. Manage humidity effectively. Watermelon plants are not tolerant of wet soil, and high humidity increases the risk of disease. Use drip irrigation under the mulch to keep the air dry and reduce disease spread.
9. Control temperature carefully. Maintain a temperature range of 24–30°C, with a minimum of 15°C. Watermelons thrive in warm, well-drained soils with good aeration, a pH of 5–7, and sufficient light.
10. Shade ripening fruits. As the fruits mature, protect them from strong sunlight by covering them with leaves to prevent sunburn and maintain quality.
11. Prevent viral diseases. Viral infections are a major cause of fruit drop. Symptoms include stunted, yellow-green, and uneven leaves. Alongside using disease-free seeds and crop rotation, apply "Green" pesticides that destroy virus structures and restore plant health. Field trials over two years have shown this to be an effective solution for viral outbreaks.
Aluminium Parts
Changzhou Ziying Metal Products Co., Ltd , https://www.ziyingmetal.com