Grape bagging is a crucial practice during the cultivation process, aimed at enhancing fruit quality and protecting the crop from pests and diseases. It is essential to use high-quality, grape-specific paper bags and avoid counterfeit or low-quality alternatives. Reused paper bags are generally ineffective and should not be used again. The choice of bag type should be based on the grape variety and local climate conditions. For example, Kyoho grapes typically require white, amniotic-treated paper bags that are suitable for red varieties. Perforated cellophane or plastic film bags can also be used to help increase internal temperature.
In regions where large-ear grape varieties such as European-American hybrids are grown, 30 cm and 20 cm bags are commonly used. Larger-ear Eurasian varieties like Red Earth may benefit from 40 cm or 30 cm bags, while smaller-ear varieties may require 25 cm or 20 cm sizes. For very small-ear varieties, even smaller bags are recommended.
Timing is critical when it comes to bagging. It's best to start early, ideally after fruit set and when the young fruit is about the size of a soybean. Delaying bagging can lead to increased susceptibility to pests, sunburn, and disease. If rain occurs followed by sudden sunlight, it's advisable to wait 2–3 days before bagging, allowing the fruit to acclimate to higher temperatures first.
Before bagging, the clusters should be sprayed with insecticides and fungicides to prevent infestation. Once the spray has dried, the bag mouth should be moistened by dipping it in water to make it easier to seal tightly. This helps prevent pests and rain from entering the bag. When placing the cluster inside, ensure the bag is fully expanded and then carefully inserted from bottom to top. The opening should be securely tied to a new shoot to prevent wind damage. A small gap of 1–1.5 cm above the wire should be maintained, and the fruit should not be touched during this process.
Thinning the fruit is another important step. Proper thinning helps control yield, improves fruit quality, and prevents issues like uneven size and poor coloration. One week before flowering, flower spikes should be pruned, removing excess buds and ensuring proper spacing. After two weeks of fruit set, thinning should begin, focusing on removing damaged, deformed, or underdeveloped fruits. A 20–30% buffer should be reserved to account for possible losses due to pests or environmental factors.
Bagging offers several advantages, including protection against diseases like black rot, anthracnose, and sunburn, as well as reducing pesticide use. However, it also has some drawbacks, such as slower coloring and a delayed harvest by 5–7 days. Additionally, the process requires more labor and increases production costs.
After bagging, ongoing management is necessary. Soil and fertilizer practices should be optimized, and pruning should be done to improve fruit quality. Regular monitoring for pests and diseases, especially leafhoppers, mealybugs, and thrips, is essential. In severe cases, targeted sprays can be applied through the bags.
When harvesting, the timing depends on the variety and the color development inside the bag. For red varieties, the fruit may need to be left in the bag for about 10 days before harvest to enhance color. However, excessive bagging time can lead to over-coloring. Some varieties, like Kyoho, may not require bag removal if the paper allows sufficient light transmission.
Harvesting should be done gradually, not all at once. The bottom of the bag should be opened first to allow the fruit to be collected without damaging the ear. Best times for picking are early morning or late afternoon, avoiding direct sunlight. On cloudy days, harvesting can be done throughout the day.
After removing the bags, no additional spraying is needed, but pest activity must still be monitored. Leaves near the fruit should be pruned carefully to improve air circulation and light exposure. Avoid over-pruning, as it can stress the plant and affect future growth. Leaf removal should be done in stages to prevent sunburn and maintain the vine’s health.
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