Apple growers can more effectively optimize crop loads — critical to profitability, yet easy to get wrong without proper attention — by taking advantage of recent advancements, according to Michigan State University pomologist Todd Einhorn.

Einhorn, who spoke at the Idaho State Horticultural Society annual convention Nov. 16-17 in Nampa, said controlling crop load is the most critical management practice in apple production, and profit can be reduced when the load is too high or too low.

New prediction models, technologies and thinning chemistries can help apple growers as they work to best manage crop loads, he said.

“Capturing the most light that you can” is a longtime principle that still holds, Einhorn said in an interview.

“What has changed is that the grower needs to return the investment rapidly” given high labor and land costs that drive increased orchard density, he said, adding that management is more intensive and has less margin for error.

Managing an apple orchard is also made more complex by new cultivars and a changing market, Einhorn said.

“Some cultivars that produce very well have fallen out of favor,” he said.

Fruit weights also decrease as loads increase, Einhorn said.

Fundamentals of precision crop load management include growing trees that fill the orchard space with high-quality wood as early as possible, creating balanced leaf-to-fruit ratios, establishing high interception and distribution of light and emphasizing cell formation.

Apple size at harvest depends on the number of cells formed, a process completed a month or so following bloom.

If a tree is stressed and leaves and other parts of it compete too briskly for resources during the critical period of cell formation and division, “cell numbers will be reduced, and essentially it doesn’t matter how good your management practices are in the next three months. You can’t make up the lost growth,” Einhorn said.

Managing apple crop loads requires much less guesswork thanks to new technical information that drives predictive models, and updated protocols for applying interventions and management strategies, he said. The strategies include pruning specifically for bud load and chemical thinning.

Using updated models and real-time weather data can help the orchardist avoid “thinning as we always used to,” Einhorn said.

New models integrate temperature and sunlight over time to help project carbohydrate-fueled growth. Lower carbohydrate production could signal that over-thinning would result from applying a chemical at a standard rate.

Apple growers have more time periods available for thinning thanks to new chemical formulations, Einhorn said.

“Because new chemistries are coming, there is a need to evaluate their efficacy in different regions,” he said.

Einhorn previously worked at Oregon State and Fresno State universities.