Timing and Specific Methods for Bud Thinning and Shoot Thinning in Grapes

When planting grapes, to achieve high yields, in addition to basic management work, you also need to carry out bud thinning and shoot thinning, because there are many grape varieties, and after bud break, bud thinning reduces nutrient consumption and promotes flower cluster development. So when should grapes be bud thinned and shoot thinned? How exactly should it be done?

When the buds of grapes have swollen but not yet unfolded, selecting which sprouted buds to keep and which to remove is called bud thinning. When new shoots have grown to 15-20 cm and it can already be distinguished whether they have flower clusters, selecting which new shoots to keep and which to remove is called shoot thinning.

Bud thinning and shoot thinning further adjust the winter pruning amount to a reasonable level, and are also an important operation that determines fruit quality and yield. This is because the winter pruning amount for grapes is usually very large, which easily stimulates the buds on the canes to sprout, thereby producing more new shoots. If new shoots are too dense, the tree body's ventilation and light penetration become poor. At the same time, it disperses the tree's nutrients, affects new shoot growth, and thus causes a low fruit-setting rate and reduced fruit quality. Through bud thinning and shoot thinning, the nutritional status within the tree body and the growth direction of new shoots can be regulated, making nutrients more concentrated, in order to promote new shoot growth and flower cluster development. Experiments on bud thinning of Kyoho grapes show that when the bud thinning degree in April was 50%, the new shoot growth length in June was more than 80 cm, while in the treatment without bud thinning, the new shoot growth length was about 50 cm, indicating that bud thinning during the bud break stage can significantly promote new shoot growth. In addition, by reducing unnecessary branches and shoots through bud thinning and shoot thinning, the distribution of new shoots on the trellis surface becomes reasonable, improving the tree body's ventilation and light penetration conditions. This thereby increases the fruit-setting rate and fruit quality.

1. Bud thinning

Generally carried out in two rounds. The first bud thinning is carried out in the early stage of bud break. This bud thinning mainly removes the buds at the base of the trunk and main canes, buds on parts already decided not to keep shoots, and secondary buds among triple buds and twin buds. Note that strong and large buds should be kept, and the principle of keeping more where sparse, keeping fewer where dense, and not keeping weak buds should be followed. The second bud thinning is carried out about 10 days after the first bud thinning. At this time, the uniformity of bud break can basically be clearly seen. Weak buds that sprout later, jammed branch buds with no growth space, thin and weak buds near the base of the mother cane, and adventitious buds in improper positions are removed according to the size of the space and the need for shoots. After bud thinning, the tree body's ventilation and light penetration must be ensured.

2. Shoot thinning

This can determine the plant's branch and shoot layout, the ratio of fruiting shoots, and yield, so that a reasonable shoot density is achieved on the trellis surface. Shoot thinning generally begins about 20 days after leaf unfolding. At this time, new shoots have grown to 10-20 cm. Thick and strong new shoots with flower clusters can be selected to keep, dense branches and weak branches are removed, and at the same time note that the retained new shoots should grow basically uniformly and consistently.

In addition to considering pruning factors, the number of shoots to keep should generally be determined according to the density of new shoots on the trellis surface. The shoot thinning amount is generally one new shoot kept every 10-15 cm on the mother cane. For a trellis, keep 10-15 new shoots per sq m of trellis surface. For a hedge trellis surface (V-shaped, Y-shaped), keep 10-12 new shoots per sq m. The overall ratio of fruiting shoots to vegetative shoots is 1:2. For varieties with a high fruit-setting rate and large clusters, generally keep 4,000-5,000 new shoots per 667 sq m. For the Kyoho variety, because flower drop and fruit drop are serious, stabilizing tree vigor is especially important. Generally, about 8,000 new shoots are retained per 667 sq m before flowering, and after fruit set is stable, combined with fruit thinning, about 6,000 new shoots are kept per 667 sq m. For a hedge trellis, when branches are tied horizontally, the branch spacing on a single hedge trellis is 6-10 cm, and the branch spacing on a double hedge trellis is 10-15 cm. With the management method of drooping new shoots, the shoot retention density can still be appropriately increased.

Under the premise of the specified shoot retention amount, carry out the selection of keeping and discarding according to the “five keep” and “five do not keep” principles, namely keep early and not late (meaning keep strong buds that sprout early), keep fat and not thin (meaning keep plump buds and thick strong new shoots), keep flower and not empty (meaning keep new shoots with flower clusters), keep lower and not upper (meaning keep new shoots near the base of the mother cane), keep along and not jammed (meaning keep new shoots that have growth space).