What is the reason for grape drop

Grape shedding may be caused by physiological shedding, water imbalance, nutrient deficiency, disease infection, or mechanical damage. Grape shedding is a common phenomenon during fruit development, which requires comprehensive analysis based on specific growth stages and environmental factors.

1. Physiological abscission

Grapes naturally eliminate underdeveloped young fruits during the fruiting period, which belongs to the plant's self-regulation mechanism. At this stage, the shedding of seeds usually occurs within two weeks after flowering, and the fallen fruits often appear withered or deformed. Reasonable fruit thinning can help preserve high-quality fruits and reduce nutrient waste.

2. Water imbalance

Sudden dryness and wetness of soil can lead to abnormal cell division in the abscission layer of fruit stalks. During the swelling period, sudden watering after encountering drought, or continuous rainy weather causing root hypoxia, may lead to a large amount of fruit drop. Maintaining soil moisture at around 60% and using drip irrigation can effectively prevent it.

III. Nutrient Deficiency

Calcium deficiency can make the cell wall structure of fruit stalks fragile, and boron deficiency affects the formation of nutrient transport channels. When there is a lack of trace elements from the flowering period to the young fruit stage, the fruit stem is prone to delamination. Foliar supplementation of sugar alcohol calcium and sodium octaborate tetrahydrate can enhance fruit adhesion, and preventive spraying should be started before flowering.

Fourth, Disease Infection

Gray mold and powdery mildew can directly damage the fruit stem tissue, leading to the rupture of the disease spot. After infection by Alternaria, it produces abscisic substances that induce healthy fruit abscission. In the early stages of the disease, azoxystrobin or pyraclostrobin can be used for prevention and treatment. In severe cases, the diseased fruits should be removed and destroyed in a centralized manner.

5. Mechanical damage

Physical particle shedding can occur due to strong winds, collisions during agricultural operations, or bird pecking. The degree of lignification of the fruit stem decreases during the color changing period, making it more susceptible to external forces. Strengthening the windproof net on the frame and avoiding frequent contact with the fruit clusters during the color changing period can reduce the probability of mechanical damage. Preventing grape drop requires comprehensive management, maintaining a balanced supply of water and fertilizer during the growth period, increasing the application of phosphorus and potassium fertilizers before flowering to improve fruit setting rate, and controlling nitrogen fertilizer during the color changing period to avoid excessive growth. Regularly inspect orchards to promptly detect pests and diseases, and clear drainage ditches before the rainy season to prevent waterlogging. Stopping irrigation two weeks before harvesting can enhance the resilience of fruit stalks, and combined with plant growth regulators such as gibberellin treatment can further reduce pre harvest fruit drop. It is recommended to develop targeted management plans based on climate conditions and variety characteristics, and consult agricultural technicians for on-site diagnosis if necessary.