Darwin Mechanical Blossom Thinning
Update
Several peach orchards and one apple orchard in Ontario were blossom thinned
in the Spring of 2010. Data were collected with positive results: 32-76%
of the bloom was removed
The goals of the project were to repeat the trial that initiated in 2009
and to analyze and compare the effectiveness of the Darwin to remove peach
blossoms using different orchard training systems, tractor speeds, string
orientation, rotation speeds of the strings, etc. Approximately 50% of
the blossoms should be removed to attain positive benefits of improved
fruit size and reduced time compared to hand thinning. All trees were
pruned except part of a row of Harrow Diamond and the blossom thinning
was done once at full bloom between April 22 and 26 for the peaches and
April 28 for the apples. Based on the 2009 mechanical peach thinning trials
and the previous reports from the trials at Penn State in Biglerville,
Pennsylvania, 2.5 to 3 miles per hour tractor speed and 180 to 220 rpm
had the most desired affect for mechanically thinning peaches.
Highlights of the blossom thinning include:
- EP 51 nectarine (approximately 6th leaf) which has a very heavy bloom
was thinned at 3 mph and 200 rpm rotation speed of the strings. The
trees were pruned to central leader. 41% of the bloom was removed from
the top half of the tree and 47% was removed from the lower half.
- Allstar (4th leaf) was thinned at 2.5 mph and 185 rpm which resulted
in 36% blossom thinning on the east side and 47% on the west side.
- Harrow Beauty (6th leaf), was thinned at 2.5 mph and 200 rpm at the
same site which resulted in a higher thinning rate at 76% on the east
side and 66% on the west side.
- Harrow Diamond, (mature tree) was thinned at 3.5 mph and 190 rpm which
resulted in 37% thinning in the higher part of the tree and 33% thinning
in the lower part of the tree. The same row with the same treatment
for unpruned trees resulted in a slightly lower rate of thinning at
32%. In follow up counts prior to hand thinning, 66% of the unpruned
branches had been removed by pruning. Blossom thinning unpruned trees
does not have the desired effect. Many of the thinned blossoms on the
outer branches are pruned off and the remaining inner branches are usually
missed or partially thinned by the mechanical blossom thinner.
- Idared apples were also thinned at the "King" bloom stage
with 23% of the apple flower clusters removed and 39% of the blossoms
removed
Highlights of EP 51 nectarine after blossom thinning:
- Only 8-15% of peach blossoms are needed to set a commercial crop
- Prior to fruit thinning - average of 33% of the blossoms/fruit
remained (38% in the high part of the tree and 28% in the lower part)
after the mechanical thinning treatment and after the normal June drop.
- After fruit thinning - average of 11% of the fruit remained
(12% in the high part of the tree and 10% in the lower part)
Summary
Previous data from 2009 resulted in labour savings of 12 to 51% in thinning
costs. There was also an increase in fruit size of 5 to 18% using mechanical
blossom thinning versus no blossom thinning at all (after they were both
hand thinned).
Most of the results have been positive for growers using the Darwin in
commercial orchards. Future peach trials will continue as growers look
forward to new technology to reduce labour costs in the orchard and increase
profitability. To date, there is not a single solution for tractor speed
or string rotation speed for each site, cultivar, tree age and training
system. Trial and error needs to continue to see what fits best. Try different
travel and string speeds in your orchard to determine which gives the
best results.
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