Thinning of Peach Trees Using High-Pressure Water

Abstract

Peach trees ( Prunus persica[L.] Batsch) annually produce an over-abundance of flowers that often set to produce an excessive number of unmarketable, small fruit. Hand-thinning fruits following natural fruit abscission in June is a costly but essential management practice growers undertake to ensure remaining fruits are marketable at harvest. Past thinning methods have focused on chemical and mechanical approaches to removing flowers or fruitlets. The focus of this two-year study was to outline a method using high-pressure water and demonstrate its proof of concept to thin peach trees non-chemically at bloom. 'Harrow Beauty' and 'Harrow Diamond' peach trees trained using a central leader spindle system were subjected to one of three high-pressure water spray treatments at full bloom based on amount of time spraying each tree: 1) 'LOW'- 45 s tree ^-1(5.7 L water tree ^-1); 2) "MED" - 60 s tree ^-1(7.6 L water tree ^-1), and; 3) "HIGH" -75 s tree ^-1(9.5 L watertree ^-1). An unsprayed hand-thinned ("HAND") treatment served as a control. All treatments, including HAND, were hand-thinned after 'June' drop. In year one, high-pressure water treatments reduced fruit set, the requirement for hand-thinning, crop load, total fruit per tree and yield at harvest and increased fruit weight of 'Harrow Beauty' by 27%. In year two, treatments reduced fruit set, the total number of fruit per tree and increased the fruit weight of 'Harrow Beauty' at harvest. Effects on the early ripening cultivar 'Harrow Diamond' were less pronounced; although, there was an increase in fruit weight at harvest in response to high-pressure sprays. Overall, increasing the duration of spraying resulted in greater treatment effects compared with the HAND treatment. High-pressure water treatments increased the percentage of fruit in the 2.25" (57 mm) and larger fruit diameter categories. In comparison with HAND and based on final crop load, the ideal rate of thinning using high-pressure water was in the range of 60-70s per tree requiring 7.6 – 9.5 L water per tree. The merits of this novel thinning approach and design factors for commercialization are discussed.