A Detailed Explanation of Common Grapevine Cane Renewal Methods and Management Techniques

Canes refer to the stems of the grapevine at various ages, and can be divided into the trunk, main canes, secondary canes, one-year-old canes (also called fruiting mother canes), new shoots and lateral shoots, etc. The stem emerging from the ground is called the trunk; the main canes grow on the trunk. In regions where vines are buried in soil to overwinter, no trunk is retained, and the main canes grow from near the ground surface. The perennial canes growing on the main canes are called secondary canes, and the one-year-old canes bearing mixed buds are called fruiting mother canes. What are the commonly used cane renewal methods and management techniques for grapes?

I. Grapevine Cane Renewal Methods

In order to prevent and correct the drawbacks of the fruiting zone shifting forward and the base becoming bare, cane renewal must be carried out continuously during training and pruning, so as to maintain the growth vigor and the inherent position of the canes in every part of the entire trellis surface. Several of the most commonly used cane renewal methods are introduced below:

1. Renewal of the fruiting unit

This renewal method is limited to the fruiting unit. Its purposes are: first, to keep the fruiting position stable; second, to maintain the growth advantage of the fruiting mother cane. The following two methods are generally used.

(1) Two-cane renewal

This method is mostly used in head-trained forms among fixed-cane training systems, in long-cane-pruned horizontal training, and in medium-cane pruning in the dragon-boat trellis training, etc. In order to keep the fruiting zone from moving outward, a short spur with two buds must be left below the long fruiting mother cane as a renewal spur. After the long fruiting mother cane has sent out shoots and borne fruit, this fruiting mother cane is cut back together with the one-year-old canes on it and a section of the three-year-old cane below it, while the two new shoots growing from the renewal spur are pruned long at the front and short at the rear. In this way, year after year, the fruiting zone can be kept from shifting outward.

(2) Single-cane renewal

This method is mostly used on trained plants whose fruiting mother canes are pruned short to 1-3 buds year after year. Because the fruiting mother cane itself is very short, no renewal spur needs to be left to keep the fruiting position from shifting outward. This method is generally suitable for the horizontal form on vertical trellises, the dragon-boat form on pergolas, and the two-arm form on high, wide, drooping trellises, etc. For two-shoot single-cane renewal, leave 2 viable buds and 2 new shoots; for single-shoot single-cane renewal, leave 1-2 viable buds and 1 new shoot.

2. Renewal of the framework canes

After various training methods have grown for a certain period, the framework canes easily become locally weakened and bare, so renewal of varying degrees must be carried out to fill in the bare parts and restore growth vigor. Because the renewal site and degree differ, it is further divided into three types: small renewal, medium renewal and large renewal. They are introduced separately below:

(1) Small renewal

Renewal carried out on the front section of the main canes and secondary canes is small renewal. This is the first-level renewal method most often used in training and pruning, especially for fan-shaped training in which the main and secondary canes are not fixed; the pruning method of cutting back the front and retaining the rear must frequently be used to keep the fruiting zone from shifting forward too quickly.

(2) Medium renewal

Renewal carried out on the middle section of the main canes and near the base of the large secondary canes is medium renewal. It is generally used in the following two situations. First, when the canes at the rear part of the main and secondary canes grow weakly, the front part is cut off to restore the growth vigor of the middle and rear canes; second, to prevent the base from becoming bare, the canes above the middle are cut back so that the apical dominance is transferred to the base, thereby restoring the shoots at the base.

(3) Large renewal

Cutting off most or all of the main cane is large renewal. It is generally done when the canes above the base of the main cane have been damaged by severe freezing injury or disease, or when the canes are old and weakened while new shoots and suckers at the base can take their place; the main cane can then be cut off and replaced by a new shoot. This renewal method must be carried out with caution; a new shoot can first be well developed before the old cane is removed. If the old cane has already died or has no productive value, the old cane can also be cut off first and the replacement awaited once suckers emerge.

II. Grapevine Cane Management Techniques

In early spring, once the fruit clusters are visible, shoot thinning can begin: leave 18-20 fruit-bearing buds per plant (to protect against wind damage and hail destroying the new shoots); before flowering, according to growth vigor, leave 12-15 new shoots with clusters (to prevent poor cluster shape or poor fruit set), and carry out fruit cluster management; after flowering, leave 10-12 new shoots bearing grapes.

When pinching the tips, observe the size of the topmost leaf. When the top leaf is smaller than 1/3 of a normal leaf (smaller than a goose egg), the lateral shoots at the tip develop very slowly, because the nutrients produced by the leaf through photosynthesis cannot be self-sufficient and need to compete with the lateral shoots for nutrients. At this time, generally the second lateral shoot from the top emerges first. Therefore, after pinching, when removing the side shoots, be sure to check the size of the top leaf. If it is larger than a goose egg, remove all the side shoots below and keep the topmost one; if it is smaller than a goose egg, remove the lower ones and keep the second lateral shoot from the top.

Many friends like to leave one leaf at the axil when removing side shoots; this can increase leaf area, also channel nutrients, and prevent the winter buds from bursting. When the leaf is the size of a chicken egg, it can already be self-sufficient through photosynthesis; at this point this side shoot will burst its bud again (summer bud) because of sufficient nutrients. The second sprouting of the summer bud will compete with the winter buds for nutrients, increase labor input, cause downy mildew infection, and also spread powdery mildew. When breaking off the side shoots, the size of the axillary leaf cannot be controlled, but we can use reasonable techniques to prevent the axillary summer bud from sprouting a second time. In this way, the axillary leaf only produces nutrients and does not consume them.

Grapevine cane management helps adjust the tree shape, balance growth, extend the fruiting years, and control the yield and quality of the grapes. It can also effectively prevent and control pests and diseases.