Fruit Thinning and Return Bloom

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Fruit Thinning and Return Bloom

• Rongcai Yuan
• AHS Agricultural Research and Extension Center,
  Virginia Tech

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Why Should We Thin Fruit?

• Increase fruit size / quality/fruit price
• Increase return bloom
• Maintain tree health, hardiness, and structure
• Chemical thinning is superior to hand thinning
• Earlier thinning gives best responses
• Less expensive

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Why can chemical thinners increase fruit size?
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Relation between fruit size and leaf number in
Delicious
Magness and Overley, 1931
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Fruit Size and leaf number in Stayman apples
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How Do Chemical Thinners Thin Apples ?
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What causes young fruit to set or abscise?

• Competition among young fruit for carbohydrates
  and hormones
• Competition between fruit and shoots

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Chemical thinners promote fruit abscission by
causing stresses

• NAA and BA reduce leaf Pn and reduce carbohydrate
  supply.
• NAA and BA also enhance ethylene production.
• Ethephon releases ethylene and promotes fruit
  abscission.

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6-BA on nonstructural carbohydrates levels of
McIntosh apple leaves
Yuan and Greene, 2000
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ReTain inhibited NAA-induced young fruit
abscission in Delicious apples-2007
Hong Zhu, 2007
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ReTain reduced NAA-induced expression of MdPG2
gene in Delicious
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Factors Affecting Chemical Thinning
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Chemical Thinners

• 6-BA, carbaryl, NAA, and ethephon
• Ethephon is temperature dependant.
• The combination of carbaryl and 6-BA or NAA is
  much stronger than either alone.
• NAA will cause pigmy fruit at low temperature (lt
  70 oF).
• NAA may cause pygmy fruit in Delicious if NAA
  is applied at concentrations greater than 5 ppm
  or applied when fruit size is larger than 10 mm.
• NAA BA will cause pigmy fruit.

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Chemical thinner NAA may cause small and pygmy
fruit in Delicious
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Fruit Size
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Effect of fruit size on fruit thinning of Golden
Delicious (2006)
a
NAA 4 oz Ethephon 1.5 pint Sevin XLR 1
pint Maxcel 2 pints Oil 4
pints Water 100 gal.
b
b
bc
c
c
Fruit size at application (mm)
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Effect of application date on fruit thinning of
Delicious/M26 in New York - 2007
NAA 3 oz Sevin XLR 1 pint Maxcel 3
pints Water 100 gal.
Courtesy of Dr. Robinson
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Effect of fruit size on fruit thinning of
Gala-2007
a
Ethephon 1.5 pint Sevin XLR 1 pint Maxcel 2
or 4 pints Oil 4 pints Water
100 gal.
b
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Fruit thinning on Gala fruit size
Sevin 6-BA
Control
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Summary

• Petal fall-7 mm Carbaryl
• 8-17 mm Carbaryl and NAA alone may effectively
  thin apples, but the combination of carbaryl and
  NAA or 6-BA is more aggressive than carbaryl,
  6-BA, or NAA alone.
• 18-28 mm Ethephon (1 to 1.5 pt/100 gal.) is
  effective.
• Carbaryl, 6-BA and NAA alone or in combination
  have a slight or no effect.
• 30 mm or bigger Ethephon has a slight or no
  effect.

Special case Fuji gt18 mm, ethephon has no
thinning effect Gala gt18 mm, ethephon can
remove some fruit
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Temperature

• Effects of day and night temperature on the
  efficacy of NAA in thinning apples when applied
  at 10 mm stage of fruit development

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NAA on Golden Delicious apple fruit thinning at
60/40 oF
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NAA on Golden Delicious apple fruit thinning at
70/50 oF
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NAA on Golden Delicious apple fruit thinning at
80/60 oF
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Summary

• 70 oF or higher is good for fruit thinning.
• 65 oF marginal for chemical thinners.
• lt60 oF too low for chemical thinners.
• NAA causes pigmy fruit at low temperature.
• Based on our field trials, the maximum air
  temperature in the first 2 and 3 days after spray
  is very important. More fruit thinning or
  overthinning will be expected when maximum
  temperature is gt85 oF in first 3 days after
  spray.
• 
  
  

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Varieties
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Recommended fruit thinning programs

• Easy or moderate to thin varieties
• 1). Carbaryl (1 to 2 pt) oil (4 pt)/100
  gal.
• 2). NAA (2.1 to 4 oz)/100 gal.
• Hard to thin varieties such as Golden Delicious
• 1). 4-6 oz NAA/100 gal water
• 2). Carbaryl (1-2 pt) NAA (2.1 oz)
  oil (4 pt)/100 gal
• 3). Carbaryl (1 to 2 pt) 6-BA (2 pt)
  oil (4 pt)/100 gal
  
• followed by ethephon (1.5 to 2 pt/100 gal.) when
  fruit size is 18 to 28 mm.

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• For Fuji 1-2 pt Carbaryl 3-4 pt 6-BA 4 pt
  oil/100 gal water. NAA will cause pygmy fruit.
• For Gala 1).1-2 pt Carbaryl 2-3 pt 6-BA 4 pt
  oil/100 gal water 2). 1-2 pt Carbaryl 2.1 3
  oz. NAA 4 pt oil/100 gal water.
• You need to increase the rate of 6-BA or NAA if
  you do not add oil to the solution.
• These rates are for dilute sprays. You need to
  increase the rates accordingly if you do
  concentrate sprays.

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Golden Supreme 6.4 mm
Average daytime high temperatures for the first
2 and 3 days after application were 63.2 and 65.8
oF.
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Effects of Sevin XLR and 6-BA on fruit thinning
of Red Delicious in 2007w
wFull bloom occurred on April 24, 2007. TRV was
200 gal./acre. xTreatments were applies with an
airblast sprayer. y Fruit/cm2 limb cross
sectional area was determined on June 14,
2007. zMean separation within column by Duncans
new Multiple Range Test.
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Delicious-2007
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Red Delicious-2008
Sevin 6-BA
Control
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Tree age and vigor

• Young trees are easier to thin than mature trees
  because the competition between young fruit and
  vegetative growth is more intense in young trees
  than mature trees.

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Return Bloom
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Effect of ethephon at 200 ppm applied in on
years on flowering of Delicious
xEthephon was applied in 1998, 2000, and
2002 zBloom density ranging from 1 to 10
(highest).
Bukovac et al., 2006
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Effect of NAA and ethephon on flowering of York
apples-2007x
xTreatments were applied on 5/22, 6/5, 6/19, and
7/5/ 2006. zBloom density ranging from 1 to 10
(highest).
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Effect of NAA and ethephon on flowering of York
apples-2008
XTrees were treated with Sevin XLR 6-BA for
thinning.
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NAA ethephon on return bloom in York apples
Unthinned control
Thinned control
Chemical Thinning NAA ethephon
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Summary

• Ethephon and NAA alone can increase return bloom
  in Red Delicious and Golden Delicious.
• The combination of NAA and ethephon had better
  effects than either alone in enhancing return
  bloom in York apples.

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Acknowledgement

• David H. Carbaugh
• Amelia G. Engelman

• Virginia Apple Research program
• Virginia Agricultural Council

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THANK YOU !HAVE A GOOD YEAR!