Mechanical String Thinner Reduces Crop Load at Variable Stages of Bloom Development of Peach and Nectarine Trees

Abstract

<jats:p>Thinning of blossoms or fruitlets is a labor-intensive requirement in the production of peach and nectarine (<jats:italic>Prunus persica</jats:italic>) fruit of optimum size and quality. Prior research conducted by the authors on string blossom thinners for managing peach tree crop load demonstrated that this new technology reduces labor requirement and improves fruit size. The research reported in the current article was conducted over 2 years on ‘Sugar Giant’ peach and ‘Arctic Sweet’ nectarine to evaluate string blossom thinner efficacy at variable stages of bloom development ranging from pink to petal fall. Blossom removal at the pink stage of bloom development was lower than at other stages in 2008; however, a 150-rpm versus 120-rpm spindle rotation speed resulted in blossom removal similar to the 80% full bloom (FB) treatment in 2009. Blossom removal at the petal fall stage was similar to the open bloom stage with the exception of the 2009 ‘Sugar Giant’ trial, in which blossom removal was higher at 80% FB. Flower density and fruit set of the bloom stage compared with hand-thinned control treatments followed a similar trend with the exception that there were fewer differences in 2009 and in lower canopy regions. Follow-up hand thinning time was reduced by all string thinning/year combinations except ‘Arctic Sweet’ at pink in 2008 and 2009 and at petal fall in 2009. The best treatments reduced follow-up hand thinning time compared with green fruit hand thinning alone by 51% and 41% for ‘Sugar Giant’ and by 42% and 22% for ‘Arctic Sweet’ in Years 1 and 2, respectively. In 2008, the percentage of fruit in the “7.0 cm or greater” size category was increased by all bloom stage treatments in both cultivars. The 2009 size distribution of ‘Arctic Sweet’ fruit was unaffected, but the percentage of ‘Sugar Giant’ fruit in higher market value size categories was increased by the 80% FB and higher rpm pink treatments. Savings in hand thinning time and/or increases in fruit size in both years associated with the bloom stage treatments resulted in a net positive impact of $123/ha to 1368/ha compared with hand thinning alone.</jats:p>

Efficacy of blossom thinning treatments to reduce fruit set and increase fruit size of Ambrosia and Aurora Golden Gala™ apples

“…The impracticality and cost of HBT and the inconsistent performance of chemical thinners has spurred interest in mechanical blossom thinning. Several machines based on rotating brushes, strings or ropes have decreased fruit set, reduced the time needed for hand thinning and increased the proportion of fruit in large size categories in tests on several tree fruit species (Schupp et al 2008;Weibel et al 2008;Damerow and Blanke 2009;Auxt Baugher et al 2010). Peach and nectarine seem especially amenable because they bear single flowers on 1-yr-old wood (Schupp et al 2008;Auxt Baugher et al 2010;Miller et al 2011).…”

“…Several machines based on rotating brushes, strings or ropes have decreased fruit set, reduced the time needed for hand thinning and increased the proportion of fruit in large size categories in tests on several tree fruit species (Schupp et al 2008;Weibel et al 2008;Damerow and Blanke 2009;Auxt Baugher et al 2010). Peach and nectarine seem especially amenable because they bear single flowers on 1-yr-old wood (Schupp et al 2008;Auxt Baugher et al 2010;Miller et al 2011). In apple and pear, which have more complex flowering, mechanical thinning can damage spurs and shoots (Weibel et al 2008), and it significantly raises the risk of spreading fire blight (Ngugi and Schupp 2009).…”

Peach Blossom String Thinner Performance Improved with Selective Pruning

“…Uniform numbers of fruiting shoots were left in each treatment within a training system-60 in perpendicular V-trained trees and 125 in open center-trained trees. Based on earlier studies that determined optimum bloom stage for thinning, trees were mechanically thinned when 20% to 80% of the blossoms were open (Baugher et al, 2010b). Mechanically thinned pruning treatments were compared with green fruit hand-thinned (35 DAFB) control treatments on trees with standard pruning.…”

“…The next year, a string thinner was manufactured that operated in either a vertical or horizontal position, and trials conducted in four peachproducing regions on both narrow vertical and open-center canopies demonstrated reductions in follow-up hand-thinning requirement and increases in yield and fruit size (Baugher et al, 2010a). Pennsylvania trials conducted with the hybrid thinner on both perpendicular V-and open center-trained trees at various bloom stages showed that the window for thinning peach and nectarine trees ranges from the pink to the petal fall stage of bloom development (Baugher et al, 2010b).…”

Efficacy of ACC (1-aminocyclopropane-1-carboxylic acid) as a Chemical Thinner Alone or Combined with Mechanical Thinning for Japanese Plums (Prunus salacina)

“…In addition, the effect of mechanical thinning is immediate and not influenced by climatic conditions (Martín et al, 2010). Inconsistent results, however, have hampered the successful implementation of mechanical thinning in stone fruit (Reighard and Byers, 2009 Schupp et al (2008) found added economic benefits in producing larger peach fruit while reducing follow-up hand thinning when they combined mechanical bloom thinning with green-fruit hand thinning (Miller et al, 2011;Baugher et al, 2009;Baugher et al, 2010;Schupp et al, 2008). The Darwinä does not thin selectively enough and will therefore not replace hand thinning completely (Miller et al, 2011).…”