Grape bagging is a critical practice during the fruit development stage, and it's essential to use high-quality, species-specific fruit bags. Avoid using low-quality or recycled paper bags, as they may not provide the necessary protection. The choice of bag should be based on the grape variety and local climate conditions. For example, Kyoho grapes are typically wrapped in white paper treated with amniotic fluid, which is ideal for red varieties. In contrast, European-American hybrids with large clusters can use 30cm or 20cm bags, while smaller-ear varieties might benefit from 25cm or 20cm sizes. It's important to match the bag size to the ear size for optimal results.
Timing is crucial when it comes to bagging. It’s better to start earlier rather than later to prevent disease and pest infestation. Ideally, bagging should begin after fruit set, when the young fruit is about the size of soybeans. Delaying this process can lead to issues like sunburn, pests, and poor fruit quality. Also, avoid bagging immediately after rain if the weather turns sunny quickly, as this increases the risk of sunburn. Wait for 2–3 days to allow the fruit to adjust to higher temperatures before proceeding.
Before bagging, it's recommended to spray the clusters with insecticides and fungicides to protect against pests and diseases. Make sure the solution is fully dried before starting the bagging process. Soak the bag mouth in water for 6–7 cm to make it soft and easier to seal. When placing the bag over the cluster, ensure it is fully inflated and tightly sealed at the top. Secure the bag to a new shoot to prevent it from being blown away by the wind. Keep at least 1–1.5 cm of space between the bag and the wire to avoid any damage to the fruit.
Thinning is another key step in grape cultivation. Proper thinning helps regulate yield, improve fruit quality, and reduce the risk of uneven growth. This should be done one week before flowering, removing excess inflorescences and small, weak buds. After fruit set, further thinning is carried out when the fruit is about the size of soybeans. Focus on removing poorly developed, deformed, or damaged fruits. Always use scissors to avoid damaging the remaining fruit. It’s also wise to leave an extra 20–30% of fruit as a safety measure against pests and environmental risks.
Bagging offers several benefits, including protection from diseases like black rot, powdery mildew, and sunburn, as well as reducing pesticide use. However, there are some drawbacks, such as slower color development and increased labor costs. Additionally, the ripening period may be delayed by 5–7 days due to reduced light exposure inside the bag.
After bagging, continued monitoring is essential. Pay attention to leaf diseases and pests like aphids and thrips. If needed, you can apply pesticides through the bag. For red varieties, the color development may be slightly delayed, so it’s advisable to remove the bag about 10 days before harvest to enhance coloration. However, don’t remove the bag if the fruit inside is already well-colored. Some varieties, like Kyoho, don’t require bag removal if the paper allows sufficient light transmission.
When harvesting, avoid removing all the bags at once. Open the bottom first to protect the fruit from birds and sunburn. Harvesting should be done early in the morning or late in the afternoon to avoid heat stress. On cloudy days, you can work throughout the day.
After removing the bags, continue to monitor the fruit for pests and color development. Remove old or dense leaves near the clusters to improve air circulation and light exposure. Avoid removing too many leaves at once, as this can stress the plant and affect its future growth. Always harvest in stages to minimize sunburn and maintain fruit quality.
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