How can computer modeling help growers decide when it’s best to start thinning? Research from the Northern New York Agricultural Development Program is trying to answer that question.
Three commercial apple orchards participated in an on-farm thinning trial last year that looked at pollen tube growth models.
"Thinning apples at bloom is an orchard practice with the greatest potential to increase apple size for the current year's harvest as well as to promote a return bloom the next year," says project leader Michael Basedow, a Cornell Extension tree fruit specialist.
Basedow's research is applying the use of computerized modeling to determine when growers should thin to help reduce the crop load to allow the trees to produce apples of optimal quality and size, and in numbers that also allow the trees to efficiently bloom again the next year.
The pollen tube growth model estimates the amount of time between pollination and fertilization of apple flowers to help growers plan for a first thinning application.
"Bloom thinning is a promising approach for managing crop load and is used extensively by apple growers in Washington state, but it is a difficult practice to perform as it requires precise timing of the thinning material applications," Basedow notes.
Three orchards participated in the trials: Everett Orchards, Forrence Orchards and Northern Orchard, all in Peru, N.Y.
The optimal number of fruits per tree — where yield, apple size and fruit quality are well-balanced to bring the greatest economic return to the grower — varies by apple variety. In last year’s trial, two blocks were Honeycrisp, and another block was Gala.
To gauge how well the trees respond to the thinning process, Basedow is evaluating the use of the Fruit Growth Rate model that estimates the amount of crop still on the trees after each thinning application. This helps determine if additional thinning is needed.
In the 2020 trials, the FGR modeling overpredicted the remaining crop load by 10% at the Gala site and by 160% at one of the Honeycrisp sites. The research team is evaluating factors, such as cold-temperature damage to buds in the spring and fruit drop during period of high heat stress and drought, for possible influence on the FGR model's accuracy.
This spring's bloom will let growers know how well the timing of their applications in 2020 aided this year’s return bloom.
Earlier precision apple management research results reports are posted on the Northern New York Agricultural Development Program website at nnyagdev.org.