Chemical Blossom Thinners Vary in Their Effect on Sweet Cherry Fruit Set, Yield, Fruit Quality, and Crop Value

Abstract

<jats:p>The commercial adoption of the relatively new rootstock `Gisela 5' (<jats:italic>Prunus cerasus</jats:italic> L. × <jats:italic>P. canescens</jats:italic> L.) has been limited in the United States sweet cherry (<jats:italic>P. avium</jats:italic> L.) industry despite its ability to induce precocity and productivity and reduce scion vigor compared to the standard Mazzard (<jats:italic>P. avium</jats:italic>). This is due in large part to inadequate crop load management that has led to high yields of small fruit. This paper reports on sweet cherry chemical blossom thinning trials conducted in 2002 and 2003. Two percent ammonium thiosulphate (ATS), 3% to 4% vegetable oil emulsion (VOE), and tank mixes of 2% fish oil + 2.5% lime sulphur (FOLS) were applied to entire 8- and 9-year-old `Bing'/`Gisela 5' sweet cherry canopies at about 10% full bloom (FB) and again at about 90% FB. In both years, ATS and FOLS reduced fruit set by 66% to 33% compared to the control (C). VOE reduced fruit set by 50% compared to C in 2002 but had no effect in 2003. In 2002, fruit yield was 30% to 60% lower from thinned trees. In 2003, fruit yield was unaffected by thinning treatment. In 2002, ATS and FOLS improved fruit soluble solids but had no effect in 2003. VOE did not affect fruit soluble solids in 2002 and reduced fruit soluble solids by 12%, compared to C, in 2003. In 2002, each thinning treatment nearly eliminated the yield of the small fruit (≤21.5-mm diameter) and increased yield of large fruit (≥26.5 mm) by more than 400%, compared to C. In 2003, ATS and FOLS did not affect yield of small fruit but increased the yield of large fruit by 60%. In 2003, VOE-treated trees yielded 4.3 kg of small fruit per tree compared to about 0.15 kg from C, suggesting a phytotoxic response to VOE beyond that which may effect thinning. Compared to C, ATS and FOLS consistently reduced fruit set and improved fruit quality. We conclude that commercially acceptable yields of excellent quality `Bing' sweet cherries can be grown on size-controlling and precocious rootstocks.</jats:p>

Cell number regulator genes in Prunus provide candidate genes for the control of fruit size in sweet and sour cherry

“…Cultivars that consistently produce large fruits are critical for grower profitability. For example, for the fresh-market sweet cherry, fruit size is the main criterion by which the fruit is graded for sale (Whiting et al 2006). Therefore, obtaining new large-fruited cultivars is a major breeding goal.…”

Crop Load Management Does Not Consistently Improve Crop Value of ‘Sweetheart’/‘Mazzard’ Sweet Cherry Trees

“…Crop load management strategies to maintain fruit size via some form of pre or postbloom flower/fruit thinning has been the subject of recent investigation (Schoedl et al, 2009;Whiting and Ophardt, 2005;Whiting et al, 2006). To date, inconsistent response of fruit to chemical thinning strategies has limited commercial adoption.…”

Fish Oil Plus Lime Sulfur Shows Potential as a Sweet Cherry Postbloom Thinning Agent

“…Application of fish oil + lime sulphur (FOLS) about 14 d after full bloom (DAFB) reduced sweet cherry fruit set by 29% compared to the control (Table 1). This reduction is about 15% to 20% less than that previously reported from two applications of the same concentration of FOLS during bloom (Lenahan, 2005;Whiting et al, 2006). This suggests that trees are less susceptible to thinning later in the growing season though it is also likely that FOLS applied during bloom reduces fruit set via interference with fertilization (i.e., a caustic effect directly on flowers), an effect it can not have 14 DAFB.…”

“…However, due to their effects on whole-tree source-sink relations, new crop load management strategies must be developed to yield commercially acceptable quantities of high quality (i.e., large diameter, firm) fruit on these rootstocks (Whiting and Lang, 2004). Though it is not currently a commercially used strategy, there is new evidence showing the potential for blossom thinning to reduce fruit set and improve sweet cherry fruit quality Whiting et al, 2006). Indeed, chemical blossom thinning is beneficial and employed regularly in other tree fruit species, apple (Malus ×domestica Borkh.)…”

“…Other research has shown potential for thinning blossoms of peach (P. persica) (Myers et al, 1993;Southwick et al, 1996) to reduce the need for costly hand thinning. Recent trials within high efficiency sweet cherry orchards have also shown potential to reduce fruit set and improve fruit quality and crop value with caustic bloom thinners (Whiting et al, 2006).…”