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- Author or Editor: Douglas Nichols x
- HortScience x
To determine the effect of blossom and fruitlet thinners on crop load, fruit weight, seed development during the year of treatment, and the subsequent year effect on return bloom, fruit weight and yield, a field trial using the biennial apple cultivar `Northern Spy' (Malus × domestica Borkh.) was established. Treatments applied at full bloom included ATS (ammonium thiosulphate) [12% (w/v) nitrogen, 26% (w/v) S]; TD [15.9% (w/v) diacarboxylic acid, 5.5% (w/v) dimethylalkylamine salt (Endothal)] and SCY [57% (w/v) pelargonic acid (Scythe)]. At 18 days after full bloom (DAFB), oil treatments [98% (w/v) mineral oil (Superior “70” oil)] were applied with S [480 g·L-1 a.i. carbaryl (Sevin XLR)] and without as a means of increasing the efficacy of S. BA [19 g·L-1 a.i. 6-benzyladenine/1.9 g·L-1 a.i. gibberellins 4+7 (Accel)]; S; and/or SA [100% (w/w) 2-hydroxybenzoic acid (salicylic acid)], were also applied in a factorial arrangement on the same day. Fruit abscission was significantly increased the year of treatment with BA, S, BA + S, BA + SA, S + SA, BA + S + SA, oil, and S + oil. Average fruit weight was enhanced by S, BA + S, BA + SA, S + SA, BA + S + SA, and S + oil although in the latter treatment the crop load was very low. Only treatments that included BA reduced the number of fully developed seeds per fruit and seed number per trunk cross-sectional area (TCA) and increased return bloom. Defining the number of fully developed seeds per tree coupled with crop load is proposed as a predictor of return bloom in `Northern Spy'.
From 2003 to 2006, the blossom level and crop load of ‘Honeycrisp’ apple (Malus × domestica Borkh.) trees on M.26 rootstocks were adjusted to improve fruit quality and return bloom. The treatments consisted of manually removing flower clusters to 50, 100, and 150 per tree, then at ≈50 d after full bloom, the crop load was adjusted to 3, 6, and 9 fruit/cm2 trunk cross-sectional area (TCSA), respectively. All flower and crop load adjustment significantly increased TCSA and canopy volume compared with the control. Classic biennial bearing was observed on the untreated control trees and those thinned to 150 blossom clusters per tree and 9 fruit/cm2 TCSA and was mitigated for trees with 50 and 100 blossom clusters followed by crop load adjustment to 3 and 6 fruit/cm2 TCSA, respectively. Fruit color the “on” year was always lower on the control trees; no difference was found in the “off” year. The treatments increased fruit weight proportional to crop load except for the 2004 “off” year. This study illustrates that for trees with ≈1 m3 canopy volume, the combined effects of blossom and crop load adjustment to 100 blossom clusters/tree followed by fruitlet adjustment to 6 fruit/cm2 TCSA and below will induce consistent annual production for ‘Honeycrisp’.
Tree fruit growers use chemical and mechanical thinning techniques in an attempt to maintain regular annual flower production and maximum repeatable yields of varieties susceptible to biennial bearing. If the percentage of floral buds an apple tree could produce without causing yield depression in subsequent years was known, it would be possible to better manage crop-thinning regimes. This study proposes that thinning is a partial transfer of potential flower buds from one year to the next year and estimates the maximum repeatable sequence of flower buds without biennial bearing. The conceptual framework is tested on a 50-year simulation with 0% to 100% transfer of thinned flower buds. Results indicate that the maximum repeatable sequence of flower buds rises sharply when the final years of the orchard approach and declines when the percent transfer of thinned buds is near 0%.