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Effect of Environmental Conditions
[!] In two years of trials there has been no
significant difference in thinning or fruit size from
NAA/Sevin or Accel/Sevin when applied in days
with high temperature of 58-60 degrees F vs. 70-
75 degrees F.
[!]In one year there was significantly more
thinning when Accel was combined with oil,
Silwet, or Sevin as opposed to Regulaid or no
adjuvant when rain followed within two hours of
application.
[!]It appears that prolonged uptake under cool
conditions that provide long drying may be as
effective as more rapid but shorter uptake under
warm "ideal" conditions.
[!]There is considerable evidence that warm
weather in the few days after application is the
most important weather consideration for good
thinning.
Economics of Apple Thinning
[!]For most 'Empire' blocks, greatest
profitability (considering only the current season)
is at croploads too high to ensure good return
bloom -- thus greatest long term profitability
result from pushing cropping near but not up to
the point of compromising return bloom.
[!]To achieve croploads near the point of
maximum economic return it will be necessary
to:keep records on cropload and returns within
each block; and thin some blocks in stages,
evaluating cropload before each subsequent
treatment.
[!]Depending upon the block and the growing
season, 40-75% 100 count fruit may yield the
highest returns in "Empire" - thinning to higher
percent 100s, reduces number of 120's without
increasing 100s.
[!]For "Empire" in most blocks, use of Accel
or Accel/Sevin will likely enhance profits .
[!]In may "McIntosh"blocks, significant
thinning reduces profit -- in such blocks it is
probably best to use either Sevin only, 3 ppm
NAA only to break up clusters, or 35-50 ppm
Accel only to enhance fruit size.
General Recommendations
[!]Prepare to apply your primary thinner
(NAA/Sevin, NAA alone, or Sevin alone) as
early as conditions permit following petal fall.
Make this application when conditions are good
and warm weather is expected within 1-3 days.
[!]When poor weather conditions prevent
thinner application to all blocks under ideal
conditions -- if warm conditions are expected in
the next 2-3 days, rather than delay application
to large fruitlet size, it is probably better to make
some applications when conditions are cool but
provide good spray coverage.
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[!]
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For "Empire", Accel/Sevin appears to be the
best choice when a single thinning treatment will
be used.
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Suggested Beginners Chemical Thinning
Program From Win Cowgill
For growers who have never chemically thinned before or
are nervous about chemical thinning (if all the above is
confusing to you, try the following program developed by
Mike Thomas, retired fruit agent, MSU). I have used this
program with numerous growers in northern New Jersey
with good success. The idea is to get some NAA on all
apples. NAA will give some thinning response and will
assist with return bloom. The number of applications
you make will depend on your comfort level and the
weather.
NAA is one of our oldest most reliable thinners. It is
effective from bloom until 20mm fruit size, some times
are more optimal than others. NAA does not have a
'memory' and multiple applications after 24 hours are not
cumulative.
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[!]
[!]
[!]
[!]
[!]
[!]
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Spray #1- at petal fall of your latest blooming variety,
apply 3-5ppm NAA/100 gallons on all apples
(whether you think they need thinning or not). Do
not use this method on varieties ripening earlier than
Paulared.
Wait 5-7 days. Evaluate thinning results.
Note: no additional applications should be made to
spur Red Delicious.
Spray #2-Apply 7-15ppm of NAA/100 on those
varieties that still need thinning.
Wait 5-7 days and evaluate thinning.
Spray #3- Apply 10-20ppm of NAA/100 on varieties
that still need additional thinning.
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NAAis excellent for all varieties. It becomes active
within a few days of application and may be used at 10 or
20 ppm. At 10 ppm, drop is controlled for about 1 week;
and at 20 ppm, drop is controlled for about 10 to 14 days.
Ethephonis a growth regulator and it has been used
to a limited extent on McIntosh and most summer red
apples. Not all results have been satisfactory, but, in
most instances, ethephon has hastened maturity, increased
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