May 2019 - 12

Root pruning during bloom can increase pear yields
By David Jones
Michigan State University
Michigan's pear industry primarily
produces Bartlett pears, used for
processed product by Gerber/Nestle
Company. Most pear orchards in
Michigan are 40 or more years old, and
poor flower efficiency is a perennial
frustration for growers who manage
these trees.
Growers are actively looking for
Research funds from Gerber/Nestle provide new information on management practices for
growers with established Bartlett pear acreage. Graphic: Mark Longstroth
strategies to increase the productivity
of their existing acreage to help make
future pear ventures more profitable.
Root pruning during bloom is a strategy
that has been successfully deployed on
the west coast to increase fruit set of
established D'Anjou pear. This same
strategy had not been applied to Bartlett
pear in Michigan, so trials to evaluate
this practice were set out by Gerber/
Nestle and Michigan State University
Extension in 2017 and 2018.
Methods
In 2017, two blocks of at least 50 trees
were root pruned approximately 3 feet
deep at 4 feet from the trunk. In 2018,
another two blocks of at least 50 trees
were root pruned in the same way. Two
control blocks of at least 50 trees were not
root pruned in either 2017 or 2018.
In the spring of 2018, a single limb
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of 30 trees in each of the six treatment
blocks was randomly selected prior to
bloom. At bloom, all flowers on each
limb were counted. In late August, the
number of fruits on each of these same
limbs was counted. The number of fruit
recorded immediately prior to harvest
was divided by the total number of
flowers counted during bloom for each
tree to determine flower efficiency. This
data collection will be repeated in these
treatments in 2019 and 2020 to examine
the long-term impacts of the practice. A
one-way analysis of variance (ANOVA)
and pairwise tests were conducted
across the means of each treatment to
determine any significant differences
between treatments.
Results
The trees that were root pruned during
bloom in 2018 were more productive
at 5 percent fruit set than the 2017 root
prune treatment or the control (ANOVA,
p<0.05). The 2017 root prune treatment
was the second most productive treatment
at 4.37 percent fruit set, while the control
treatment was the least productive at 2.38
percent (p<0.05). All three treatments
were significantly different from one
another (Fig. 1).
Discussion
These results indicate that root pruning
at a 3-foot depth at a 4-foot spacing from
trunks is effective in increasing yields
in established Bartlett pear plantings in
Michigan. Both the 2017 and 2018 root
pruning treatments were 1.5-2 times
more productive than the unpruned
control treatment. Furthermore, the
heightened yield from the 2017 root
pruning treatment indicates that this
treatment has positive effects that carry in
to at least the following season in addition
increasing yield in the season in which it
is conducted.
The continuation of this project in 2019
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and 2020 will help to further this subject
and understand how many seasons postprune
an increase in yield could be seen.
This strategy could prove to be a costeffective
way for farmers with established
Bartlett pear acreage to reinvigorate yield
in shy-bearing trees.
Todd Einhorn, MSU Department of
Horticulture; and Drew Afton, Gerber/
Nestle Company contributed to this
report. FGN
12 | FruitGrowersNews.com

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May 2019

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