Crop Load Reduction and Fruit Size Following Multi-step Thinning of 'Empire' Apple

Abstract

<jats:p>Two years of field experiments were conducted in eastern New York to evaluate the efficacy of a multi-step thinning approach on reducing crop load (no. fruit per cm<jats:sup>2</jats:sup> trunk cross-sectional area) and increasing fruit size of 'Empire' apple (<jats:italic>Malus</jats:italic> ×<jats:italic>domestica</jats:italic> Borkh.). Applications of Endothall (ET) at 80% bloom, NAA + carbaryl (CB) at petal fall (PF), and Accel™ + CB at 10 mm king fruitlet diameter (KFD), alone and in all combinations, were compared to a nonthinned control and to the application of NAA + CB at 10 mm KFD (commercial standard). In both 1996 and 1997, orthogonal contrasts indicated the multi-step treatment significantly increased fruit size, reduced cropload, and reduced yield compared to single applications. Effects on cropload of consecutive treatments were largely predicted by multiplying effects of individual treatments. Although all thinning treatments except for NAA + CB at PF in 1997 significantly reduced cropload, no single treatment thinned sufficiently to ensure good return bloom. Compared to NAA + CB at 10 mm KFD, multi-step thinning with NAA + CB at PF followed by Accel™ + CB at 10 mm KFD produced bigger fruits in both years, and resulted in a higher percentage of spurs carrying a single fruit in 1996. When fruit size was evaluated after removing the effect of cropload (cropload adjusted fruit weight), NAA + CB at PF, Accel™ + CB at 10 mm, and the two applied sequentially, resulted in greater cropload adjusted fruit weight than the nonthinned control in both years, whereas NAA + CB at 10 mm did not. Contrast analysis of treatments with and without ET showed no significant effect of including ET on fruit size, though total cropload was reduced at <jats:italic>P</jats:italic> = 0.10 and total yield was reduced (<jats:italic>P</jats:italic> = 0.03 in 1996 and <jats:italic>P</jats:italic> = 0.12 in 1997). No deleterious effects from multi-step treatments have been observed. All thinning treatments significantly increased return bloom in 1996 and 1997 compared to the control with little difference observed between treatments. Chemical names used: naphthalene acetic acid (NAA); 1-naphthyl-<jats:italic>N</jats:italic>-methylcarbamate [carbaryl (CB)]; 6-benzyladenine [BA (Accel™)]; 7-oxabicyclo (2,2,1) heptane-2,3 dicarboxylic acid [ET (Endothall™)]</jats:p>

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

“…THINNING TREATMENTS. In 2002 and2003, water (C), 2% ammonium thiosulphate (ATS), a tank-mix of 2% fi sh oil + 2.5% lime sulphur (FOLS), and 3% vegetable oil emulsion (VOE) were each applied by air-blast sprayer at 200 gal/acre to heavily cropped 8and 9-year-old 'Bing'/'Gisela 5' sweet cherry canopies. Test trees were isolated by at least one untreated guard tree to the north and south.…”

“…fruit number per tree (i.e., cluster) is monitored often and modifi ed several times throughout a growing season and crop load management strategies are usually several-tiered. These may include a multiplicity of chemical blossom and postbloom thinners (Byers and Carbaugh, 1991;Dennis, 2000;Westwood, 1993), and hand thinning in the current season, as well as gibberellic acid to reduce (Bradley and Crane, 1959;Tromp, 1982), or ethephon or naphthaleneacetic acid (NAA) to increase, bloom density in the subsequent season (Byers, 1993;Stover et al, 2002). In contrast, crop load of many stone fruit species (Prunus L.) is reduced primarily by hand thinning, although research has shown potential for chemical thinning, especially for peach [P. persica (L.) Batsch.]…”

Comparison of Chemical Blossom Thinners Using ‘Golden Delicious’ and ‘Gala’ Pollen Tube Growth Models as Timing Aids

“…Research was conducted on interactions between ET and postbloom compounds in multistep thinning programs (Bound and Wilson, 2007;Stover et al, 2002). While assessing a multistep thinning program, Stover et al (2002) observed that the addition of a petal fall thinning application was beneficial in a 2-year trial, but the addition of a blossom-thinning spray with ET was not. Despite a significant reduction in crop load, ET reduced fruit weight when compared with the control.…”

Bloom and Postbloom Thinner Effects and Interactions on ‘Gala’ Fruit Growth Rate, Return Bloom, and Yield Responses at Three Locations

“…Additionally, abiotic factors such as solar radiation and temperature correlate to abscission rates (Lordan et al 2019). This variability necessitates a multistep thinning approach requiring multiple chemical thinner applications during the bloom and postbloom period (Stover et al 2002).…”