Mar 17, 2020
Crop load management: thinning it out

Precision fruit growth and crop load management was emphasized during the International Fruit Tree Association’s “Precision Vision 2020” conference and tours held in Grand Rapids, Michigan, in February.

Terence Robinson, a tree fruit physiologist with Cornell University, discussed findings from an 18-year thinning study at Cornell’s Geneva, New York, campus.

“From 2000-17 we studied fruit thinning by applying the same thinning treatments every year to Gala/M.9, McIntosh/M.9 and Delicious/M.26 at Geneva, New York,” he said.

One important conclusion: “The final number of fruits per tree over 18 years was positively related to initial flower clusters per tree. This means that with more flower clusters on the tree the final number of fruits is greater. With fewer flower clusters per tree the final number of fruits is less.

Related: Precision key to ideal crop load management

To achieve a target number of final fruits requires not starting with too many flower clusters. Thus, precision pruning is essential.

Robinson said precision crop load management seeks to manage the number of apples on each tree in a precise manner to obtain the best possible economic outcome in an orchard with a $10,000 per acre value.

At its core, precision crop load management seeks to influence the process at three specific timings: Pruning, chemical thinning and hand thinning,” he said.

The first step is to establish a target number for final fruit per tree. Identify a goal based on the potential of the orchard and the climate. The final number of apples you end up with is positively related to the number of flower clusters per tree.

He advocated the use of precision pruning to pre-thin the trees, so chemical thinning will be more successful; eliminate one to three branches larger than threequarters of an inch in diameter; and columnarize (simplify) the rest of the branches.

“Calculate your target spur number and then count representative trees after pruning to ensure you’ve met that target,” he said.

Computer visioning is a technology that would revolutionize the process of counting buds. He said humans get bored and become ineffective counting buds. He believes a computer system could simplify the process and make it more precise.

Robinson anticipates that blossom thinning, used extensively in the Pacific Northwest, will take hold in Eastern growing regions. Honeycrisp, which requires considerable and precise bloom thinning, will lead the way in order to maintain profitability.

“To control biennial bearing in New York state, we need to learn to do blossom thinning,” he said.

Robinson warned against spraying caustic thinners under slow-drying and wet conditions or if there is frost; frost damages fruit skin, and caustic thinners can then cause russetting (which is more common in the East).

Photos: International Tree Fruit Association Precision Vision 2020 63rd Annual Post Conference and Tours 

An app version is available for users of the Lakso carbohydrate model (MaluSim). It can be downloaded to a phone, from the Google or Android store. Growers can determine the predicted carbohydrate balance of the trees, which can guide their daily thinning decisions.

Robinson said the improved model uses relative bloom density to adjust predicted thinning efficacy for any given spray; it also uses bloom date to calculate degree days.

He recommends growers precision prune Gala for fruit size. Honeycrisp should be pruned for return bloom at chemical thinning time.

— Gary Pullano, managing editor

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