Causes of Apple Biennial Bearing and Control Measures

In apple production, biennial bearing is a fairly common phenomenon. It seriously affects apple yields and growers' income, and is a headache for many fruit growers. So how should biennial bearing in apples be controlled? Follow along with the editor to take a detailed look below.

I. Causes of Biennial Bearing

1. Nutrient competition

Nutrient competition is the root cause of biennial bearing. In an "on" year, the apple tree produces many flowers and fruits, so it naturally consumes more nutrients, while other organs, especially the terminal buds, receive greatly reduced nutrients, making it impossible to form flower buds that year. Therefore, an "on" year is followed by an "off" year. In an "off" year, because there are fewer flowers and fruits, the tree accumulates more nutrients and flower bud differentiation is good, so the following year is an "on" year, and the cycle repeats.

2. Influence of plant endogenous hormones

Fewer flower buds form in an "on" year not only because of insufficient nutrients, but also because gibberellins produced in the fruit seeds inhibit flower bud differentiation. Since the fruit load is large, the number of seeds is also relatively high, so more gibberellins are produced, which promotes new shoot growth but inhibits flower bud formation. Therefore, an "on" year is followed by an "off" year.

3. Other causes

Besides the two causes above, harsh natural conditions and unreasonable cultivation management can also lead to biennial bearing. For example, too much rainy weather during the flowering period or flower bud differentiation period, or drought during fruit set, or late frost causing a large amount of flower and fruit drop, can all produce biennial bearing.

II. Control Methods

1. Planned and orderly water and fertilizer management

Apple trees in an "on" year consume relatively more nutrients, so tree nutrients need to be supplemented in time to meet the needs of plant growth, flowering and fruiting each year. Before flowering and during the fruit expansion period, more quick-acting nitrogen fertilizers such as urea can be applied to promote the growth of branches and leaves, so as to achieve better photosynthesis and ensure the needs of tree growth. After fruit harvest, apply base fertilizer early to promote flower bud differentiation and improve flowering quality and fruit set rate the following year. For trees in an "off" year, focus on fertilizer and water management to avoid flower and fruit drop caused by insufficient fertility. Apply nitrogen fertilizer once before bud break and one week before and after flowering, and spray an appropriate amount of 1%-3% superphosphate solution after flowering to promote fruit growth.

2. Reasonable pruning

Many fruit growers, because they have not received professional training, always follow the principle of "prune less, keep more, get more fruit" when pruning. Year after year they use light pruning and delayed pruning methods, do not pay attention to cultivating reserve branches, and keep developing fruiting branches without restraint. This leads to the formation of a large number of flower buds, many fruits, fruit that is too small, and poor quality, while the number of flower buds formed the following year is small, resulting in an "off" year. In this situation, besides strengthening one's own professional knowledge, it is also necessary to prune biennial-bearing fruit trees with an appropriate balance of heavy and light pruning, so as to achieve the goal of "not too heavy in an on year, not too light in an off year."

3. Flower and fruit thinning

When the tree load is too heavy and nutrient consumption is excessive, making it impossible to meet the nutritional needs of flower bud differentiation, reasonable flower and fruit thinning can not only balance the relationship between vegetative growth and reproductive growth of the tree, but also improve fruit quality and increase per-mu returns.

The above is an introduction to the causes of apple biennial bearing and control measures. I hope it can help you. To learn more related knowledge, please stay tuned to us.