Red sunburn in Red Globe grapes is a non-invasive physiological disorder, primarily caused by intense sunlight and fluctuating temperatures during the fruit's early growth phase. When young fruits lack protective structures, they become vulnerable to high-temperature radiation, air dryness, and direct sunlight. This leads to moisture imbalance in the outer skin, causing damage. Additionally, water can be drawn from leaves with high osmotic pressure, further contributing to the burn. The ideal conditions for sunburn development include temperatures above 30°C, relative humidity below 30%, and soil moisture levels less than 40% of field capacity. Factors such as climate, trellis system, vine vigor, fruit position, crop load, timing and quality of bagging, and orchard management significantly influence the occurrence of this issue. After sudden rain, exposed fruits are more likely to suffer sunburn. Overly vigorous plants, weak vine health, and poor leaf canopy development also increase the risk. Fruits located on the outer parts of the vine are more susceptible to sun exposure. Delayed or improperly timed bagging, especially during hot weather, can worsen the condition. Early summer pruning, improper tip pinching, and excessive branch cutting may leave fruit without adequate shade, increasing the likelihood of sunburn.
To prevent and manage sunburn, several effective strategies can be implemented. First, choose an appropriate trellis system—such as a cross-shaped trellis—which helps provide better shading and reduces sun exposure. Second, apply balanced fertilization, including organic matter and essential nutrients like nitrogen, phosphorus, potassium, and micronutrients. During the growing season, foliar sprays of potassium and calcium can improve fruit resilience. In periods of high heat and dry weather, timely irrigation helps lower temperatures and reduce sunburn risk. After rainfall or irrigation, loosen the soil to maintain good aeration and support healthy root development.
Proper vine management is also crucial. Thin flower clusters appropriately and maintain a reasonable fruit load. During summer pruning, retain some leaves around the fruit clusters to provide natural shade and turn the clusters when necessary. If there are no fruit clusters, remove some leaves to avoid competition for water between leaves and fruit. Regularly prune excess foliage to ensure even distribution of resources.
Bagging is one of the most effective preventive measures. Bag the fruit as soon as the fruit set stabilizes. Use high-quality, waterproof, white paper bags with ventilation holes at the bottom. Before bagging, spray the entire vine with a protective bactericide. Wait until the spray dries before starting the bagging process. Avoid bagging during hot weather or after rain when dew is present. Ensure the bags are tightly sealed. Remove the bags about 10 days before harvest, not all at once. Start by opening the bottom of the bag, and choose to do so before 10 a.m. or after 4 p.m. On cloudy days, you can perform the task throughout the day. These practices help protect the fruit from sun damage while maintaining its quality and appearance.
Single Greenhouse
The bearing structure, fixed film systems and installation of this greenhouse is relatively simple. And due to it, raw material and manufacturing costs are affordable. Except the high strength woven film is higher, other kinds of antidrop film are economical. In general, the comprehensive cost of film greenhouse is lower 30% ~ 50% than the same size and specifications of the other types of greenhouse.
Single Span Greenhouse,Greenhouse Film,Tunnel Greenhouse,Plastic Film Greenhouse
JIANGSU SKYPLAN GREENHOUSE TECHNOLOGY CO.,LTD , https://www.spgreenhouse.com