Strategies for Preventing and Managing Alternate Bearing in Trees

Alternate bearing in trees is one of the significant challenges in horticulture and agriculture, with notable impacts on production and the quality of crops. This phenomenon causes trees to produce a higher yield of fruit in certain years, while in other years, fruit production drastically decreases or even stops altogether. In this article, we will explore the causes of alternate bearing in trees and provide effective methods for preventing and controlling this phenomenon. By better understanding these factors and implementing appropriate strategies, it is possible to maintain and even increase crop production.

What is Alternate Bearing in Trees?

One of the biggest challenges faced by orchard growers is alternate bearing in trees. Alternate bearing, or biennial bearing, refers to a phenomenon where trees produce a large amount of fruit in some years and significantly less or no fruit in other years. Naturally, this phenomenon greatly affects the income of farmers. In addition to its impact on income, alternate bearing also poses problems for the health of the trees. Overproduction of fruit can cause damage to the tree due to the excessive burden. The tree’s resources are depleted, and the heavy strain placed on it leads to reduced fruit production in subsequent years.

Alternate bearing occurs in all fruit trees but is particularly common in trees such as pistachios, apples, and pears.

Causes of Alternate Bearing in Trees

Trees generally have two types of buds:

1. Vegetative buds
2. Reproductive buds

Reproductive buds, after going through their growth stages, develop into flowers and fruit. On the other hand, vegetative buds are responsible for the longitudinal growth of branches. For optimal fruit production, the growth of these two types of buds must be balanced and proportional. If the number of vegetative buds exceeds the number of reproductive buds, the tree’s fruit yield decreases, and the quality of the fruit declines. Conversely, if reproductive buds outnumber vegetative buds, the tree’s fruit production increases in the first year but significantly drops in subsequent years. Ultimately, we can conclude that to prevent alternate bearing, the growth of reproductive buds should not be halted.

But why does alternate bearing or the decline in reproductive buds occur? There are several important reasons for this:

1. Poor Nutrition: In high-yield years, trees often lack the ability to provide sufficient nutrients for fruit growth. As a result, the fruits compete for resources. If the tree does not receive adequate nutrients through fertilization, it depletes the stored nutrients in its tissues (including those in the leaves), consuming the tree’s energy. Therefore, the absence of a proper fertilization program leads to alternate bearing in trees. Using the best fertilizers is essential for tree productivity.
2. Environmental Stress: Climate changes, severe frost during flowering, heavy storms, or similar conditions can negatively impact fruit production.
3. Poor Orchard Management: Incorrect pruning, improper fertilization, inadequate irrigation, and overall mismanagement of the orchard can contribute to alternate bearing in trees.
4. Natural Mechanisms: Some trees naturally regulate their production cycles to maintain sustainability and improve fruit quality. However, this should not occur continuously.
5. Pests and Diseases: The presence of pests or diseases can lead to reduced fruit production in certain years.

Effective Methods for Preventing and Controlling Alternate Bearing in Trees

Preventing alternate bearing in trees requires proper management and attention to various details in the growth and production process. Below, we explain effective methods for preventing alternate bearing in trees.

Proper Fertilization

A well-planned fertilization program is the most important method for controlling alternate bearing in trees. By providing the necessary nutrients, you support the growth of reproductive buds. Based on the type of tree, its age, nutritional needs, and climatic conditions, a fertilization plan is developed to gradually supply nutrients throughout the growing season. Soil testing is essential to determine the tree’s specific needs.

Fertilization is particularly crucial during high-yield years. Instead of depleting its reserves to grow larger fruits, the tree utilizes the nutrients from the fertilizers. This ensures that bud formation for the following year is not disrupted. By adjusting fertilization, you can partially control the growth of vegetative and reproductive buds. For example, in a high-yield year, using nitrogen-based fertilizers can shift the tree’s growth focus toward branches and leaves (vegetative growth). This helps the tree bear the heavy fruit load while reducing its focus on fruit production. Conversely, in low-yield years, reducing nitrogen-based fertilizers shifts the tree’s focus away from vegetative growth.

To maximize the effectiveness of fertilizers, consider the rules of fertilizer mixing. Some fertilizers should not be used simultaneously, as they can neutralize each other’s effects. For selecting the right fertilizer, it is best to consult an agricultural expert or an experienced farmer.

Fruit Thinning

During high-yield years, removing some of the fruits can reduce the tree’s burden. This prevents the tree from expending excessive energy on forming and filling extra fruits, allowing it to store some energy for the reproductive buds of the following year. To do this, keep the largest fruits and remove the rest. It is best to ensure that the remaining fruits are spaced appropriately from one another.

Preferably, perform fruit thinning manually. However, some orchard owners with large-scale farms use chemical agents for thinning. Thinning fruits with chemicals requires expertise and, if not done carefully, can cause issues for the tree.

Proper and Timely Pruning of Branches

Proper and systematic pruning of trees is essential for controlling bud growth. Correct pruning helps balance vegetative and reproductive buds, preventing excessive growth of vegetative buds. By controlling the growth of vegetative buds, the tree’s focus shifts to reproductive buds and fruit production. Pruning offers many benefits for trees and should be done correctly every year. It ensures that sufficient light and oxygen reach the lower branches, increasing fruit yield. Additionally, pruning removes excess branches, allowing more energy to be directed to the main branches.

Irrigation Management

Timely and adequate irrigation supports the balanced growth of vegetative and reproductive buds. A well-planned irrigation schedule is determined based on soil type, geographical conditions, tree type, and tree age. If irrigation is not done on time during the growing season, reproductive buds and fruits may wither or fail to grow properly. Moreover, post-harvest irrigation is also crucial. Insufficient irrigation during this period can hinder flowering in the following season. Using a drip irrigation system can help maintain soil moisture and prevent water stress.

Other Methods for Controlling Alternate Bearing in Trees Include:

1. Ensure Proper Pollination Conditions: Create favorable conditions for tree pollination. The presence of insects, such as honeybees, plays a significant role in the pollination process.
2. Choose Suitable Tree Varieties: When purchasing and planting saplings, select species that are highly compatible with the local climate and environmental conditions.
3. Conduct Annual Soil Testing: Perform soil tests at the start of each growing season to identify the soil’s needs and deficiencies. This ensures that all necessary nutrients are provided to the soil and trees while preventing excessive or unnecessary fertilization.
4. Eliminate Weeds: Weeds absorb water and nutrients, depriving trees of these essential resources. This can lead to nutrient deficiencies and stunted growth in trees.
5. Prevent and Control Pests and Diseases: Managing pests and diseases helps maintain tree health and prevents reduced fruit production. Using biological methods and appropriate pesticides is effective in this regard. Regularly inspect trees to monitor their health and address issues promptly.
6. Mitigate Climate-Related Stress: Climate changes can impact the productivity of fruit trees. Protecting trees from frost damage, heat stress, water stress, and other environmental factors is crucial for maintaining productivity and preventing alternate bearing.

By implementing these methods, you can effectively manage and reduce the occurrence of alternate bearing in trees, ensuring consistent and healthy fruit production.