Causes of Biennial Bearing in Apples and the Latest Control Measures

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

I. Causes of Biennial Bearing

1. Nutrient competition

Nutrient competition is the root cause of biennial bearing. In an "on" year, the apple tree flowers and fruits heavily, 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; thus an "on" year is followed by an "off" year. In an "off" year, because there are few flowers and fruits, the tree accumulates more nutrients and flower bud differentiation is good, so the following year is an "on" year, and this cycle repeats.

2. Influence of plant endogenous hormones

The small number of flower buds formed in an "on" year is related not only to insufficient nutrients but also to gibberellins produced in the fruit seeds, which inhibit flower bud differentiation. Because the fruit load is heavy, the number of seeds is also relatively large, so more gibberellins are produced, which promotes new shoot growth but inhibits flower bud formation; thus an "on" year is followed by an "off" year.

3. Other causes

In addition to the two causes above, harsh natural environments and unreasonable cultivation and management can also cause biennial bearing. For example, too much rainy weather during the flowering period or flower bud differentiation period, or drought during the fruit-setting period, or late frost causing a large amount of flower and fruit drop, can also lead to 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 replenished in time to meet the needs of plant growth, flowering and fruiting each year. Before flowering and during the fruit enlargement stage, more quick-acting nitrogen fertilizers such as urea can be applied to promote branch and leaf growth, 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 the flowering quality and fruit-setting rate of the year. For trees in an "off" year, focus on fertilizer and water management to avoid insufficient fertility causing flower and fruit drop. A nitrogen fertilizer can be applied once before sprouting and one week before and after flowering, and after flowering, an appropriate amount of 1%-3% superphosphate solution can be sprayed to promote fruit growth.

2. Reasonable pruning

Because many growers have not received professional training, they always follow the principle of "prune less, leave more, and get more fruit" when pruning, using light pruning and delayed release year after year, not paying attention to cultivating reserve branches, and developing fruiting branches without restraint. This leads to the formation of a large number of flower buds, many fruits, small fruits, and poor quality, and the number of flower buds formed the following year is small, resulting in an "off" year. For this situation, in addition to strengthening one's own professional knowledge, biennial-bearing fruit trees also need to be pruned with an appropriate balance of heavy and light pruning, so as to achieve the goal of not having too heavy an "on" year and not too light an "off" year.

3. Flower and fruit thinning

When the tree load is too heavy and nutrient consumption is too great to meet the nutritional needs of flower bud differentiation, reasonable flower and fruit thinning at this time can not only balance the relationship between vegetative growth and reproductive growth of the tree, but also improve fruit quality and increase the benefit per mu.

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