September 2022 - 10

Ridgefest examines replant disorder in
apple trees, cherry research, cider expansion
By Gary Pullano
FGN Senior Correspondent
As old apple orchards are removed to
make way for more valuable cultivars,
apple replant disease can be an issue
causing early decline of trees planted into
old orchard ground.
Replant disorder occurs when new
trees are planted where old trees once
grew. The big root systems left behind
in the soil can support huge amounts of
fungi and pests, including nematodes and
pathogens - all of which might suppress
the growth of the new trees.
Replant disorder has yet to have
a widespread impact in Michigan,
and researchers from Michigan State
University (MSU) are working to keep it
that way. Their project is evaluating seven
varying pre-plant treatments and two
different apple rootstocks to determine
which combinations result in better
soil and tree health and productivity in
Honeycrisp apples.
Preliminary findings of the work
were presented July 28 as Michigan
Pomesters had its 11th annual Ridgefest
field day, touring research trials at
MSU's Clarksville Research Center. The
presentation was one of several reviews
of emerging best practices for tree fruit
producers.
MSU tree fruit specialist Julianna
Wilson indicated replant disorder stems
from particular soil and environmental
conditions. The project at Clarksville
began in 2017 with pre-plant treatments
applied in 2018, and the new orchard
planted in the spring of 2019.
Soil testing was done to characterize
the microbial community and measure
soil health. Measurements of tree
vigor and productivity were collected,
Ridgefest field tour participants travel the expansive grounds at the Clarksville Research
Center in Clarksville, Michigan. Photos: Gary Pullano
including the first harvest in 2021 and an
assessment of bitter pit.
Highlights of results
According to research on rootstock
and treatment effects:
* Trees on G.214 surpassed the top
wire in the third leaf; trees on B.9
are noticeably shorter than the
G.214 across all plots; however,
both rootstocks produced slightly
taller trees in the rows that overlap
the old drive row than those that
overlapped the tree row.
* Cover crops planted in the interval
year provided a slight boost in B.9
tree height.
* More fruit were produced on trees
on B.9 by the third leaf than on
trees on G.214; however, average
fruit weight did not differ between
the rootstocks, and there was no
difference in fruit color at harvest.
* Frequency of bitter bit was highest in
" immediate replant " plots and lower
when cover crops had been used in
the interval between orchards.
Researchers reported that belowground
effects include:
* It appears the greatest difference
across treatments for nematodes
were in the year in which the
pre-plant treatments were
implemented; also, in that
year, Wilson said they saw
some differences between old
drive lanes and old tree rows.
Researchers are still working on
summarizing the results of the
soil microbial community.
* Cover crops planted in the
interval year showed the greatest
positive impacts on most
measures of soil health.
The rapid transition from older, lowdensity
orchards to newer, high-density
orchards in Michigan offers the potential
for apple replant disease to proliferate,
Wilson said. Small, modern trees on
vigor-suppressing rootstocks are more
Michigan State University tree fruit specialist
Julianna Wilson reports on apple replant
disorder research.
likely to be sensitive to replant disorder.
A full summary of the apple replant
research findings will be presented at
the Great Lakes Fruit, Vegetable & Farm
Market EXPO in December.
Other presentations
Several updates of ongoing research
projects were presented to Ridgefest
tour visitors.
Horticulture professor and cherry
specialist Greg Lang outlined his findings
regarding planar sweet cherries, a training
system architectural approach that Lang
anticipates will achieve widespread
grower adaptation in years to come.
" This is kind of the culmination of 20
years of various kinds of trials. Every
new trial, we try to make incremental
progress, " said Lang, who was presented a
plaque for being the Michigan Pomesters'
2022 Fruit Person of the Year for
dedicating much of his tenure at MSU to
the tree fruit industry.
Lang emphasized that he has found
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September 2022

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