By Kimberly Warren
Associate Editor
Research
being conducted in Washington and Oregon could help growers produce
better, bigger sweet cherries.
Researchers from a variety of horticultural research institutions
are using their knowledge of bloom thinning in apples to bring the
process to sweet cherry growers. This research has been going on for
around five years.
“In Washington, the emphasis for apples is on the fresh market;
the emphasis for (sweet) cherries is on the fresh market,” said
Jim McFerson, manager of the Washington Tree Fruit Research Commission.
“Increasingly, the demand for larger fruit sizes is dictating
to the producers that we have to produce larger fruit. There’s
been a gradual, incremental ratcheting up market demands for larger
fruit. Period. One way to achieve that larger fruit is thinning.”
With the introduction of dwarfing rootstock, McFerson said, the trees
come into production earlier with the potential to set a large crop
of fruit – small fruit.
“The tree is unable to produce enough carbohydrate to produce
the size of fruit necessary,” McFerson said. “We’re
kind of caught.”
Current hand thinning practices can be expensive – up to $1,500
per acre each season. But, McFerson said, that is money that needs
to be spent.
So, one way to get away from spending the money on hand thinning but
achieving the desired result it chemical thinning – a new idea
for sweet cherries and one still in the experimental stages.
“Our hope is to emulate that of apples with the right rates,
timing, coverage to reduce the fruit set and at the same time not
eliminate too many fruit,” McFerson said. “It’s
a tenuous balance between removing enough fruit for the remaining
to size up. We can produce few large size cherries.”
“In the past, there was no need for this (thinning) because
growers manipulated the tree architecture for the light distribution,”
said Matt Whiting, an assistant horticulturist and Extension specialist
at Washington State University.
These researchers are using three different chemicals in their thinning
trials: ammonium thiosulfate (ATS), vegetable oil emulsion and Crocker’s
Fish oil plus lime sulfur.
“One of the interesting conclusions and interesting results
is that every year is different,” Whiting said.
Whiting said that before the application of the chemicals, the researchers
take a sample branch and count the number of blossoms. And, at harvest,
they count the number of fruit. These show the results of the chemical
process.
Chemicals are applied with either a conventional orchard sprayer or
a hand sprayer.
“Our controls might set 30 percent of the flowers on untreated
branch,” Whiting said. “With the thinners, they typically
reduced that by 50 percent, or down to 15 percent (fruit set).”
The goal, Whiting said, is to balance the thinning and the yield and
quality of the fruit.
“If we reduce too much, we’re losing money. But if we
don’t thin enough, we’re losing money with small fruit,”
he said.
These chemicals actually burn off the blossoms, which do fall off.
The chemicals also reduce the amount of photosynthesis.
“It’s a transient effect,” McFerson said. “We’ve
measured photosynthesis, and the tree recovers within three to five
days (after application) to total capacity. It’s a temporary
shock – the tree recovers completely.”
When the chemical thinner touches the blossom, it causes parts of
the flower to dry up so they cannot be pollinated and fertilized –
therefore reducing the amount of fruit that will be set.
The thinning chemicals are applied twice during the blossom season
– once at about 25 percent bloom and again at about 80 percent
bloom, McFerson said.
Compared with the $1,500 for hand thinning used on apples, these chemical
thinning programs would cost a growers about $100 to $200 per season.
And, even though McFerson and Whiting both said that results were
not uniform, they are promising.
“It’s more profitable for the grower to involve him or
herself in crop load management even if the results are inconsistent,”
McFerson said. “We have not seen negative consequences of good,
aggressive thinning.”
The next step is to continue finding a way to get the largest sized
fruit possible. Enter Roberto Nuñez-Elisea.
Nuñez-Elisea has been researching chemical bloom thinners at
the Mid-Columbia Agricultural Research and Extension Center of Oregon
State University and will soon be adding an additional product to
his tool kit for larger cherries: plant growth regulators.
“The logic is to try to achieve two effects with one single
spray,” Nuñez-Elisea said. “When you mix ATS and
a plant growth regulator, what ATS will do is destroy a percentage
of the flowers. The purpose of the plant growth regulator, when applied
at the same time, is for those fruit that remain attached, the growth
regulator will stimulate growth of these fruitlets that are left.”
Nuñez-Elisea has only conducted one preliminary study on the
plant growth regulator research. He is set to begin the project in
the coming year.
The research being conducted by these researchers on chemical thinning
is still in its early phases, and growers can look for something coming
down the pipelines to them in the next three years.
“We work on programs that are reliable,” McFerson said.
“The next step is to get labels…I’m gonna say that
we’re working very hard as a group to provide materials for
growers that are more effective. I’d like to see within three
years a label that can be used with confidence and predictability.”
