String Blossom Thinner Designed for Variable Tree Forms Increases Crop Load Management Efficiency in Trials in Four Peach Growing Regions

Hand thinning is a necessary but costly management practice in peach (Prunus persica) production.  Stone fruit producers are finding it increasingly difficult to find a workforce to manually thin fruit crops, and the cost of farm labor is increasing.  Research conducted in 2008 and 2009 on string blossom thinner prototypes for vertical and open-center tree canopies, respectively, demonstrated that this new mechanical flower removal mechanism has potential to reduce labor requirement and improve fruit size and quality.  A new “hybrid” string thinner prototype designed to adjust crop load in either vase or angled tree canopies was evaluated in processing and fresh fruit plantings in varying production systems in four growing regions in 2009.  Data were uniformly collected across regions to determine blossom removal rate, fruit set, labor required for follow-up hand thinning, fruit size distribution at harvest, yield, and socio-economic impact.  String thinner trials with the variable tree forms demonstrated reduced labor costs compared to hand thinned controls and increased crop value due to a larger distribution of fruit in higher market value sizes.  Blossom removal ranged from 17 to 56%, hand thinning requirement was reduced by 19 to 100%, and fruit yield and size distribution improved in at least one string thinning treatment per experiment.  Net economic impact at optimum tractor and spindle speeds was $462 to $1490 and $230 to $934 per acre for processing and fresh market peaches, respectively.  Case study interviews of growers who thinned a total of 154 acres indicated that commercial adoption of string thinning technology would likely have positive socio-economic impacts.