When is the best time to bag and unbag grapes

Abstract Grape bagging time: For open-field cultivated grapes in southern regions, bagging can be done promptly after fruit set following cluster trimming and berry thinning; while for greenhouse and rain-shelter cultivated grapes, bagging can be done 15-20 days after fruit set. Grape unbagging time: With traditional bagging, bags can be removed 10-15 days before harvest, while with smart sunlight bags, grapes can be sold directly with bags on.

I. Grape Bagging Time

1. The appropriate bagging time should be chosen according to different cultivation methods. Generally, for open-field cultivated grapes in southern regions, the principle of earlier rather than later should be followed for bagging. Bagging can be done promptly after fruit set following cluster trimming and berry thinning. Late bagging makes grapes susceptible to infection by anthracnose and other pathogens.

2. For greenhouse and rain-shelter cultivated grapes, bagging time can generally be appropriately delayed. During the physiological fruit drop period, that is, 15-20 days after fruit set, bagging can be done, which is when the berries have grown to the size of beans. After berry thinning and cluster trimming, bag immediately. If there is not enough time to bag at this point, then bagging can be done before the second berry enlargement stage. Bagging time can be chosen between 9-11 AM and 2-6 PM on sunny days.

II. Grape Bagging Methods

1. First, dip the opening end of the paper bag into water 5-6 cm deep to moisten and soften it, which makes it easier to tie the bag opening tightly. When bagging, open the bag mouth, then place the entire cluster into the bag from bottom to top, then gather the bag opening from both sides together onto the fruit stem, keeping it close to the new shoot and exposing as little of the fruit stem as possible. During this process, use the thin wire attached to the bag to tie the opening tightly.

2. Leave 1-1.5 cm of paper bag above the wire tie. Generally, bagging should be done immediately after spraying and the water has dried. It should be completed within 2 days. If not finished, spray once more, but the interval should not be too long, as a long interval makes clusters susceptible to disease and causes rotten berries in the bag. When bagging, try to avoid touching and rubbing the clusters with hands.

III. Grape Unbagging Time

1. Generally, when using traditional bags, grape varieties should have bags removed 10-15 days before harvest, which helps improve light and air permeability conditions to promote fruit coloring. With smart sunlight grape bags, there is no need for such complicated steps; grapes can color directly with bags on, and the ripening speed is relatively fast, allowing earlier market launch, which helps improve economic returns.

2. During this period, grapes can be sold with bags on, achieving truly green, healthy, and pollution-free produce. To avoid bird and insect damage and air pollution, with traditional bagging, the bags do not need to be removed all at once. First, open the bottom and prop it up in an umbrella shape, then remove all bags at harvest time.

IV. Management Techniques After Grape Unbagging

1. From after unbagging to before harvest, the main purpose is to let the berries color. After unbagging, remove old leaves, diseased leaves, and residual leaves around the clusters, prune excess branches and secondary shoots, and remove leaves within 20 cm around the clusters.

2. Generally, the standard is when there are sieve-like light shadows on the lower part of the trellis surface. Retain a portion of leaves to help shade the clusters, prevent berry sunburn, and at the same time allow timely cluster turning to ensure light exposure and promote rapid coloring of the clusters.