Blossom Thinning in Pome and Stone Fruit

Early thinning of apples is important because of its impact on fruit size and next season's flower bud initiation. In the past, apple cultivars were often sprayed with the blossom thinner sodium dinitro-ortho-cresol(Elgetol) during full bloom, followed by a post-bloom application of a fruit thinner such as carbaryl with or without naphthalene acetic acid (NAA). Elgetol was removed from the market in 1989 because of the high cost of re-registration. Full-bloom sprays of sulfcarbamide (Wilthin), pelargonic acid (Thinex), and endothalic acid (Endothal), ammonium thiosulfate (ATS) or petal fall spray of carbaryl (Sevin XLR Plus) were developed as replacements for Elgetol. Hydrogen cyanamide (HC) and other chemicals have been used to eliminate or to reduce chilling requirements of peaches grown under the warm desert conditions. HC applied at “pink bloom” stage was observed to reduce the number of open blooms in `Florda Prince' peach; therefore, it was first used for blossom thinning in this cultivar in Arizona. Later, HC was also found to be an effective blossom thinner for plums in Idaho. HC has recently been found to effectively thin apple and peach blossoms. Armothin has also been an effective blossom thinner for peach in California.

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Further studies on the use of 2-chloroethyl-phosphonic acid (ethephon) as a thinning agent for apples

Australian Journal of Experimental Agriculture ◽

10.1071/ea9790611 ◽

1979 ◽

Vol 19 (100) ◽

pp. 611 ◽

Cited By ~ 2

Author(s):

N Veinbrants

Keyword(s):

Acetic Acid ◽

Phosphonic Acid ◽

Growth Regulator ◽

Fruit Size ◽

Naphthalene Acetic Acid ◽

Full Bloom ◽

Golden Delicious ◽

Apple Cultivars ◽

Series Of Experiments

In a series of experiments the growth regulator 2-chloroethylphosphonic acid (ethephon) at concentrations from 50 ppm to 400 ppm was applied at various stages during and after flowering to apple cultivars Golden Delicious, Gravenstein, Jonathan, Richared and Starkrimson. On the heavy setting Golden Delicious, Gravenstein and Jonathan cultivars, adequate thinning and satisfactory fruit size was obtained when ethephon at 100 ppm was applied at or shortly after full bloom, followed by naphthalene acetic acid. On the lighter setting Richared and Starkrimson cultivars, one ethephon spray at 100 ppm applied at or shortly after full bloom resulted in adequate thinning. All fruit were eliminated on Jonathan, Richared and Gravenstein cultivars when ethephon was applied at 400 ppm, 300 ppm and 200 ppm, 36, 35 and 42 days after full bloom, respectively.

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Commercial-scale Use of Hydrogen Cyanamide for Apple and Peach Blossom Thinning

HortTechnology ◽

10.21273/horttech.8.4.556 ◽

1998 ◽

Vol 8 (4) ◽

pp. 556-560 ◽

Cited By ~ 8

Author(s):

Esmaeil Fallahi ◽

Randy R. Lee ◽

Gary A. Lee

Keyword(s):

Acetic Acid ◽

Prunus Persica ◽

Fruit Set ◽

Fruit Size ◽

Naphthalene Acetic Acid ◽

Full Bloom ◽

Hydrogen Cyanamide ◽

Air Blast ◽

Fruit Thinning ◽

Commercial Scale

Hydrogen cyanamide (Dormex, 50% a.i.) for blossom thinning `Early Spur Rome' and `Law Rome' apple (Malus×domestica Borkh.) and `Flavorcrest' peach (Prunus persica L.) was applied with air-blast sprayers on a commercial scale. Full-bloom applications of hydrogen cyanamide at 4 pts formulation per 200 gal/acre (1288 mg·L−1) and 5 pts formulation per 200 gal/acre (1610 mg·L−1) significantly reduced fruit set in apple and peach. In `Early Spur Rome', a postbloom application of carbaryl [Sevin XLR Plus, 4 lb a.i./gal (0.48 kg·L−1)] following a full-bloom spray of hydrogen cyanamide increased fruit thinning with a significant increase in fruit size compared to an application of hydrogen cyanamide alone. In `Law Rome', trees receiving a full-bloom application of hydrogen cyanamide followed by a postbloom application of 1-naphthyl-N-methylcarbamate (carbaryl) + naphthalene acetic acid (NAA) had significantly lower fruit set and larger fruit than those in the carbaryl + NAA treatment. Apples or peaches were not marked by hydrogen cyanamide.

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Thinning Golden Delicious apples with pre-bloom naphthalene acetic acid and later carbaryl sprays

Australian Journal of Experimental Agriculture ◽

10.1071/ea9840453 ◽

1984 ◽

Vol 24 (126) ◽

pp. 453 ◽

Cited By ~ 2

Author(s):

KM Jones ◽

TB Koen ◽

RJ Meredith

Keyword(s):

Acetic Acid ◽

Fruit Size ◽

Fruit Weight ◽

Naphthalene Acetic Acid ◽

Full Bloom ◽

Golden Delicious

A trial in southern Tasmania examined the thinning effects of naphthalene acetic acid (NAA) on Golden Delicious apples. The NAA was applied at pink bud or balloon blossom at 12, 18 and 24 ppm, with or without carbaryl at 1800 ppm applied 10 d after full bloom. Carbaryl was also applied alone 10 and 20 d after full bloom, and a hand thinned treatment was included. The higher concentrations of NAA did the most thinning but only the hand-thinned and 24 ppm NAA at balloon blossom with carbaryl treatment thinned enough to produce the required fruit size. The NAA sprays at balloon blossom thinned considerably more than those at pink bud. Neither NAA nor carbaryl alone was as effective as the combination. Reduction of fruit numbers increased mean fruit weight from 101 g in the control to 149 g in the 24 ppm NAA at balloon blossom with carbaryl. There was no evidence that increasing the concentration of NAA reduced mean fruit weight. This trial demonstrates that the effect of balloon stage sprays of NAA combined with later carbaryl sprays on Golden Delicious is similar to that achieved by the normal practice of spraying with NAA 7-14 d after full blossom, followed by carbaryl at 20 d. Reduction from 128 fruit/ 100 blossom clusters in the control to 76 after spraying at balloon blossom is still outside present aims of 30-50 fruit and is not considered to be severe enough thinning to assure adequate fruit size.

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Control of pudding spot in Crofton apple

Australian Journal of Experimental Agriculture ◽

10.1071/ea9920503 ◽

1992 ◽

Vol 32 (4) ◽

pp. 503

Author(s):

KM Jones ◽

SA Bound ◽

MJ Oakford ◽

TB Koen

Keyword(s):

Acetic Acid ◽

Fruit Size ◽

Fruit Weight ◽

The Other ◽

Naphthalene Acetic Acid ◽

Full Bloom ◽

Apple Trees ◽

Low Incidence ◽

Thinning Effect

Regularly cropped Crofton apple trees in southern Tasmania were thinned using sprays of naphthalene acetic acid (NAA) at 10 mg/L or ethephon at 200 mg/L at balloon blossom (BB), full bloom (FB), 10 days after full bloom (DAFB) or 20 DAFB. These treatments were compared with hand thinning and an unthinned control. Ethephon had a uniformly mild thinning effect (about 30% compared to control), except at 10 DAFB, where no thinning occurred. NAA was inconsistent, thinning well at BB (50%), overthinning at both FB (85%) and 10 DAFB (88%), and underthinning at 20 DAFB (similar to the control). Ethephon applied at BB and FB increased both mean fruit weight (12 and 22%) and fruit size (28 and 79%), but later applications did not. NAA applications generally resulted in increased mean fruit weight and size, except for the 20 DAFB treatment, which was similar to the control. All ethephon treatments had a low incidence (43%) of pudding spot similar to the controls and hand-thinned treatments. Most NAA treatments showed significantly higher levels of pudding spot than the other treatments. It is concluded that ethephon is a more predictable thinner for Crofton than NAA, and its use to control pudding spot is recommended.

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EFFECTS OF HYDROGEN CYANAMIDE ON APPLE AND PLUM FRUIT THINNING

HortScience ◽

10.21273/hortsci.27.6.690a ◽

1992 ◽

Vol 27 (6) ◽

pp. 690a-690

Author(s):

Esmaeil Fallahi ◽

Brenda R. Simons ◽

John K. Fellman ◽

W. Michael Colt

Keyword(s):

Malus Domestica ◽

Fruit Set ◽

Fruit Size ◽

Apple Fruit ◽

Fruit Weight ◽

Full Bloom ◽

Hydrogen Cyanamide ◽

Fruit Thinning ◽

Prunus Salicina

Influence of various concentrations of hydrogen cyanamide (HC) on fruit thinning of `Rome Beauty' apple (Malus domestica Borkh.), `Friar,' and `Simka' plums (Prunus salicina Lindley) were studied. A full bloom application of HC at all tested concentrations decreased `Rome Beauty' apple fruit set and yield, and increased fruit weight. Hydrogen cyanamide at 0.25% (V/V) resulted in adequate apple thinning, indicated by the production of an ideal fruit weight. Prebloom and full bloom applications of HC at greater than 0.75% reduced plum fruit set and yield in `Friar.' Full bloom application of HC at 0.25% to 0.50% showed a satisfactory fruit set, yield, and fruit size in `Friar' plum. Full bloom application decreased fruit set and yield in `Simka' plum. Hand thinning, as well as chemical thinning, is recommended for plums.

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EFFECTS OF HYDROGEN CYANAMIDE ON STONE FRUIT THINNING

HortScience ◽

10.21273/hortsci.25.9.1122a ◽

1990 ◽

Vol 25 (9) ◽

pp. 1122a-1122

Author(s):

Esmaeil Fallahi ◽

Michael Colt ◽

S. Krishna Mohan ◽

John Fellman

Keyword(s):

Fruit Set ◽

Fruit Size ◽

Stone Fruit ◽

Severe Toxicity ◽

Full Bloom ◽

Hydrogen Cyanamide ◽

Fruit Number ◽

Fruit Thinning

Influence of prebloom and full bloom applications of hydrogen cyanamide on `Simka' and `Friar' plums in Southwest Idaho and `Florda Prince' peach in Southwest Arizona was studied. Prebloom application of 0.5% hydrogen cyanamide caused severe toxicity to the fruit buds in `Friar' lure, while 2% hydrogen cyanamide did not cause toxicity in `Simka' plum. `Simka' fruit was effectively thinned with 1-2% prebloom application. At full bloom, 1.5% hydrogen cyanamide caused severe flower and leaf burning in both `Friar' and `Simka' plums, while concentrations between 0.1% and 1% thinned flowers (fruits) in both of the plum cultivars. Influence of hydrogen cyanamide on final fruit set, fruit size and maturity are also studied. Prebloom or full bloom applications of 2% or 3% hydrogen cyanamide eliminated 95 to 100% of the blooms, while application of this chemical at 1% sufficiently thinned the fruit. Number of commercially packed large peaches in trees receiving 1% hydrogen cyanamide was the same as that in trees thinned by hand, suggesting hydrogen cyanamide as a potential chemical for stone fruit thinning.

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295 The Effect of Cultivar, GA4+7, and Number of Fruit per Spur on Flower Initiation in Apple

HortScience ◽

10.21273/hortsci.34.3.493c ◽

1999 ◽

Vol 34 (3) ◽

pp. 493C-493

Author(s):

Emily Hoover ◽

S. McArtney ◽

S. Tustin ◽

M. White ◽

P. Hirst

Keyword(s):

Flower Initiation ◽

Leaf Fall ◽

Full Bloom ◽

Flower Bud ◽

Biennial Bearing ◽

Appendage Formation ◽

Commercial Crop ◽

Bud Initiation ◽

Number Of Seeds

Experiments were initiated to document the effect of cultivar, GA4+7, and number of fruit/spur on appendage number and flower bud initiation in apple. `Pacific Rose' is strongly biennial, `Braeburn' and `Fuji' are moderately biennial, and `Royal Gala' is not biennial. In the cultivar study, buds were sampled every 18 days starting at 50 days after full bloom and continuing through until leaf fall to determine the rate of appendage formation and appendage number in relation to doming. Because of the tendency for `Pacific Rose' to exhibit biennial bearing, the rate of appendage formation and the timing of doming were compared on nonfruiting trees, trees carrying a commercial crop, and trees sprayed with 300 PPM GA4+7 applied 14 days after full bloom. Number of appendages for the treatments were similar up to 100 days after full bloom. Presence of fruit on a spur has been demonstrated to inhibit flowering of apple. Spurs of `Pacific Rose', `Splendor', and `Royal Gala' were labeled with zero, one, two, and three fruit per spur and sampled three times during the season. As buds were harvested to count appendage number, the number of fruit per spur and the number of total seeds per spur were recorded. Correlation between number of seeds per spur and rate of appendage formation were done.

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Hydrogen Cyanamide Stimulates Early Foliation of `Misty' Southern Highbush Blueberry

HortScience ◽

10.21273/hortsci.32.3.537c ◽

1997 ◽

Vol 32 (3) ◽

pp. 537C-537

Author(s):

J.G. Williamson ◽

R.L. Darnell

Keyword(s):

Vegetative Growth ◽

Fruit Set ◽

Small Diameter ◽

Highbush Blueberry ◽

Full Bloom ◽

Flower Buds ◽

Flower Bud ◽

Hydrogen Cyanamide ◽

Southern Highbush ◽

Chilling Treatment

Two-year-old, container-grown `Misty' southern highbush blueberry plants were sprayed to drip with two concentrations of hydrogen cyanamide (HCN) (20.4 g·L–1 and 10.2 g·L–1) after exposure to 0, 150, or 300 hr of continuous chilling at 5.6°C. All plants were sprayed immediately after chilling and placed in a greenhouse for several weeks. The plants were moved outdoors during flowering to increase cross-pollination from nearby `Sharpblue' blueberry plants. HCN sprays killed some of the more advanced flower buds on shoot terminals and on small-diameter wood from the previous spring growth flush. Significantly greater flower bud mortality occurred for the 20.4 g·L–1 HCN sprays than for the 10.2 g·L–1 sprays. Flower buds subjected to 0 hr of chilling were more susceptible to spray burn than flower buds receiving 150 or 300 hr of chilling. Very little flower bud death occurred with the 10.2 g·L–1 HCN rate on plants receiving 300 hr of chilling. Vegetative budbreak was advanced for both HCN treatments compared to controls, regardless of chilling treatment. HCN-treated plants were heavily foliated at full bloom, while non-treated plants had very few to no leaves during bloom. HCN may be useful for stimulating vegetative growth in some southern highbush blueberry cultivars that suffer from poor foliation during flowering and fruit set.

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The Effects of Exogenous Bioregulators and Environment on Regular Cropping of Apple

HortScience ◽

10.21273/hortsci.33.3.554e ◽

1998 ◽

Vol 33 (3) ◽

pp. 554e-555

Author(s):

Kathleen M. Williams

Keyword(s):

Pacific Northwest ◽

Cultural Practices ◽

Negative Impact ◽

Fruit Size ◽

Physiological Status ◽

Naphthalene Acetic Acid ◽

Crop Load ◽

The Past ◽

The Pacific ◽

Return Bloom

Use of exogenous bioregulators (“hormones”) to adjust crop load in apple remains challenging to both researchers and producers. These hormones are sensitive to the rate and timing of application, to the physiological status of the tree, the choice of orchard system, variety and rootstock, and a myriad of cultural practices and environmental factors. All classes of plant bioregulators have been used over the past 30 to 40 years as chemical thinning materials. Most of the standard postbloom thinning programs involve application of a synthetic auxin, such as naphthalene acetic acid (NAA) in combination with carbaryl, a commonly used insecticide. The mode of action of these two compounds is not clearly understood. Gibberellins generally have not been effective thinning materials because of the negative impact on return bloom. Ethylene-releasing compounds have been used successfully as postbloom thinning materials. And cytokinins, particularly synthetic sources such as 6-BA, have been shown to effectively thin fruit and to enhance fruit size on many commercial varieties. The rate and timing of 6-BA applications are particularly critical to obtain the desirable thinning and size responses. Overall, these bioregulators are sensitive to temperature. The use of bloom thinning compounds and their efficacy in the Pacific Northwest will be discussed in the context of return bloom.

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186 INFLUENCE OF HYDROGEN CYANAMIDE AND WILTH IN ON BLOSSOM THINNING OF APPLE AND PLUM

HortScience ◽

10.21273/hortsci.29.5.455f ◽

1994 ◽

Vol 29 (5) ◽

pp. 455f-455

Author(s):

Esmaeil Fallahi ◽

Brenda R. Simons ◽

Max W. Williams

Keyword(s):

Fruit Quality ◽

Fruit Set ◽

Fruit Size ◽

Soluble Solids ◽

Full Bloom ◽

Mature Trees ◽

Hydrogen Cyanamide ◽

Fruit Thinning ◽

Yield And Quality

Effects of hydrogen cyanamide and Wilthin on blossom thinning and the consequences of thinning on fruit set, yield and fruit quality of `Rome Beauty' was studied. A full bloom application of hydrogen cyanamide at the rate of 0.25% (Dormex formulation) or 0.25% of Wilthin both followed by a fruit thinning by Sevin + NAA effectively thinned mature trees of `Rome Beauty' and had a similar effect on fruit set, yield and fruit quality. The effects of these two chemicals at these rates on several aspects of fruit set, yield and quality were similar to the effects of Elgetol. Hydrogen cyanamide, Elgetol and 0.25% Wilthin at full bloom resulted in a higher percentage of single fruit set, thus, less labor for hand thinning. Application of 0.37% Wilthin at 20% bloom or at full bloom resulted in larger fruit size, but induced fruit russetting. Soluble solids of fruit from trees with Elgetol, 0.37% Wilthin at 20% bloom or at full bloom were higher than fruit from other treatments. Hydrogen cyanamide at 0.50% resulted in a satisfactory level of blossom thinning in `Friar' plums.

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