This article is part 1 in a 4 part series exploring apple thinning techniques and tools. This first part will cover the benefits of thinning as well as the main methods for setting targets to achieve when thinning. The following articles will get into the specifics of mechanical thinning, manual thinning and chemical thinning practices.

Thinning is a crucial practice in apple orchards that positively influences fruit quality, tree health, and overall orchard sustainability and profitability. It is a proactive approach to managing the fruit load (the number of fruit per tree) and ensuring that the orchard consistently produces high-quality apples. While thinning involves labor costs, the improved quality and marketability of the harvested fruit results in higher returns for growers.

Effective thinning has many benefits. Here are some key advantages of thinning apple trees:

Fruit Size and Quality:

Tree Health and Sustainability:

Shows a person measuring a trunk

One of the first steps in effective thinning practices, no matter the method, is setting target fruit counts/distribution. Maintaining a consistent target fruit count contributes to a more even yield from year to year, reducing the risk of biennial bearing. Trees with an optimal fruit load can allocate resources such as nutrients and energy more efficiently, promoting better overall fruit quality, tree health and growth. By regularly assessing and adjusting the target fruit count as the trees grow, orchard managers can fine-tune their orchard management practices for optimal results in terms of fruit quality, tree health, and overall orchard sustainability.

Setting targets involves many factors about the tree’s themselves. Overall health and vigor of the apple tree, tree size, growing style, age, variety and historical yield all affect target setting. Often historical data from the orchard is relied upon in conjunction with calculations using either the Trunk Diameter Method or the Desired Yield Method.

The Trunk Diameter Method method involves measuring the diameter of the tree trunk as an indicator of the tree's ability to support and sustain a certain number of fruits. The idea is that the trunk diameter correlates with the overall vigor and size of the tree, influencing its capacity to produce and support a specific fruit load.

Shows a person measuring a trunk

Here's how the Trunk Diameter Method is typically applied:

  • Measure the diameter of the tree trunk of several representative trees in the area, roughly ~4-5ft from the ground / or ~3ft above the graft line.
  • Refer to a predetermined reference chart or formula that correlates trunk diameter with the recommended target fruit count. This chart or formula is based on research, experience, growing region and the specific characteristics of the apple variety being grown. The recommended target fruit count may be expressed as a range or specific number of fruits.
  • Throughout the growing season, monitor the development of the fruit on the tree. If necessary, adjustments to the fruit load can be made based on visual assessments, historical data and taking into account factors such as fruitlet drop rates, weather events and overall tree health.

The Trunk Diameter Method is relatively simple and quick to apply, making it accessible to orchard managers with varying levels of expertise. By using a reference chart or formula, orchard managers can apply a consistent approach to determining target fruit counts across the orchard. While the Trunk Diameter Method provides a helpful guideline, it's important to note that other factors, such as weather conditions and orchard health, should be considered in the overall management strategy. Orchards may use a combination of methods to refine their approach to fruit thinning and achieve optimal fruit quality and yield.

The Desired Yield Method involves considering the desired yield for the entire orchard and then allocating a portion of that yield to each individual tree based on factors such as tree size, variety, and overall orchard management goals.

Shows apples stacked together in cartons

Here's how the Desired Yield Method is generally applied:

  • Establish a target yield for the entire orchard, usually measured in terms of bushels and target carton size.
  • Allocate a portion of the overall orchard yield goal to each tree based on its individual factors like age, size, growing style, variety and overall tree vigor. This could be a percentage or a specific number of fruits assigned to each tree.

Let's say you have an apple orchard with 5000 trees in a specific area, and you want to achieve a total yield of 10,000 bushels of size 88 apples for the entire orchard. Keep in mind that the following is a simplified illustration, and actual calculations would depend on specific orchard conditions, apple varieties, and market considerations.

Total Orchard Yield Goal = 10,000 bushels
Average Yield per Tree = Total Orchard Yield Goal x desired Carton Size / Number of Trees
Average Yield per Tree = 10,000 bushels x 88 / 500 trees = 176 apples per tree

It's important to note that the Desired Yield Method requires a good understanding of the orchard's capacity, the characteristics of individual trees, and the market dynamics. Orchards may use a combination of methods, including the Desired Yield Method, to optimize fruit thinning and achieve their goals for fruit quality and yield.

Thinning is pivotal for orchard sustainability, positively impacting fruit quality, tree health, and overall profitability. Despite associated labor costs, the improved marketability of the harvest results in higher returns for growers. Effective thinning ensures optimal fruit size, quality, and even ripening while preventing issues like biennial bearing and branch breakage. Setting target fruit counts, whether using the Trunk Diameter Method or the Desired Yield Method, serves as a crucial initial step, allowing orchards to fine-tune management practices for consistent yield and sustainability. As we progress in the series, we will delve further into thinning techniques and tools, and methodologies.

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