Search Results

The effect of ethephon on flowering and cropping of strongly alternate bearing spur-type `Delicious' apple (Malus domestica Borkh.) was evaluated in a 6-year study. Ethephon (200 mg·L^–1), applied at 3, 3 + 6, and 3 + 6 + 9 weeks after full bloom in “on years,” increased flowering in “off years” by 33% and reduced flowering in “on years” by 17% compared with the control. The mean yield per tree for ethephon-treated trees over three “on years” and three “off years” was almost identical to that of the controls (82 vs. 80 kg/tree). However, the distribution of yield between “on” and “off” years was changed, 24% greater in “off years” and 10% less in “on years.” Ethephon reduced both the variation in yield, particularly in “off years,” and the magnitude of alternation. Ethephon had a direct effect on flower initiation because 1) it did not reduce shoot growth or yield in the “on years” (years of ethephon application) and 2) ethephon-treated trees initiated more flowers per kilogram of fruit produced than did the controls. The additional flowers initiated were functional because the amount of fruit produced per unit bloom density did not differ between control and ethephon-treated trees. Harvest maturity indices, namely internal ethylene concentration, firmness, starch index, soluble solids, and color, were not significantly affected, although internal ethylene concentration and starch index tended to be higher in fruit from treated trees.

NAA and BA are important compounds for regulating crop load in apples (Malus domestica Borkh.). When used for fruit thinning, both induce abscission, but at an equivalent crop load NAA tends to reduce and BA to increase fruit size. There is a strong interaction between NAA and BA when used together on ‘Delicious’ and ‘Fuji’, leading to excessive development of pygmy and small fruit (<65 mm diameter). The combination of BA (as Promalin, 1:1 BA + GA₄₊₇) applied at king bloom (KB) and NAAm (amide) at petal fall increased the percentage of small fruit by 3.3- or 5.1-fold compared with BA or NAAm alone. Similar results were obtained with BA (Promalin) at KB oversprayed with NAA at 10 to 12 mm king fruit diameter (KFD). When NAA was oversprayed with BA during fruitlet development, i.e., 5 to 6 mm, 10 to 12 mm, and ≈18 mm KFD, the greatest inhibition of fruit growth occurred at the 10- to 12-mm KFD stage, and there was no significant effect at 18 mm KFD. Inhibition by treatment at the 5- to 6-mm stage was intermediate and trees were overthinned. NAA + BA inhibition of fruit growth in ‘Delicious’ and ‘Fuji’ was not crop load-dependent. In all experiments, crop load (wt basis) of trees treated with NAA + BA was similar or less than of those treated with NAA or BA alone, but they produced 2.5- to 5-fold more small fruit. NAA + BA increased the number of fruit per cluster, many of which failed to fully develop. Increasing the ratio of BA to NAA from 25:15 to 125:15 mg·L⁻¹ increased small fruit formation. The presence of GA₄₊₇ in commercial formulations of BA (0:100, Maxcel; 10:100, Accel; 50:50, Promalin) did not significantly affect the NAA + BA response. Fruit growth was not inhibited by the NAA + BA combination in large-fruited ‘Golden Delicious’ and ‘Jonagold’ and was increased in small-fruited ‘Elstar’ and ‘Gala’ compared with the nontreated control.

The `Honeycrisp' apple has unique characteristics favored by consumers that has provided exceptional return to growers. This cultivar also has some traits that challenge plant management. There appears to be a strong inhibitory effect of crop load on flower initiation and thus annual cropping. We studied the relationship between fruit load, established by post-bloom hand and chemical thinning, and effect of ethephon and gibberellin (GA<sub>4+7</sub>) on flower initiation and thereby annual cropping. Initially, return bloom (RB) was related to previous season's crop load in three thinning studies on 3- and 9-year-old `Honeycrisp'/M 9, Pajam 1 trees. The RB density was rated 1–10 on trees (n=172), which produced 0-60 kg of fruit/tree. Return bloom ratings (RBR) on the 3-year-old trees ranged from 0–9. Percentage of trees with RBR >5 for previous season's yield of <5 kg, 5–10, 10–15, and 15–20 was 70, 9, 2.5, and 0, respectively. There was dramatic inhibition of flowering at a crop load of >5 kg/tree. In the second study (9-year-old trees), crop load ranged from 15–60 kg/tree (n=24). RBR for trees in the 30–40 kg/tree class ranged from 0–8 with high variability. Thirty-one percent of trees with crop load between 20–30 kg had RBR of 5–8, and 26% between 0–5. Twenty-one percent of trees in the 30–40 kg/tree class flowered and all but one had a RBR of 5 or less. Yields ranged from 22–81 kg/tree in the third study (n=60); crop load was normally distributed among trees. Flower initiation was almost completely inhibited. Fifty percent of the trees did not flower; the remainder had a RBR of <1, i.e. <10%. In the ethephon/GA study, RBR ranged 8–10 on trees producing <12 kg/tree, then decreased rapidly to <2 for yields of 25–50; greatest variation at 20–40 kg.