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Micronutrients
Boron
When it comes to micronutrients,
Doll said he thinks boron and zinc are
probably the more critical ones to apply.
Boron is a strong influencer on yield
so it’s important, even if trees are in sufficient
range, that a foliar application of
boron is made between postharvest and
pink bud, Doll said.
“This application is essentially going
to be about 0.2 to 0.4 pounds of actual
boron per acre,” Doll said, adding that’s
one to two pounds of solubor in a 100
gallons of water, which is what has been
traditionally applied.
Ground applications, made at higher
rates, should be applied in the postharvest
all the way up to the beginning of
the season, but again that should be soil
type dependent, Doll said. The amount
should be based on a hull analysis taken
during harvest.
Areas that are prone to a boron
deficiency are areas with very clean water—predominately
the east side of the
San Joaquin Valley as well as up in the
Sacramento Valley, Doll said.
Clay and loam soils can be made earlier
in the year, but with coarser, sandier
soils it should be applied later in the
year, Doll said.
“Often people make the soil application
of boron with an irrigation. They
just mix it in,” Doll said.
Applications of boron should be limited
if adequate values are found within
the hull. Hull boron greater than 100
ppm indicates the reduced need for soil
applications. “Unless there’s deficiencies,
there’s not much value in adding multiple
foliar applications,” Doll said, as the
data is less clear about the value of these
applications.
Zinc
per acre.
Applying high rates of zinc sulfate,
more than 15 pounds to the acre, will
prevent the tree from receiving other
tank mixed applied nutrients like nitrogen
and boron.
Young Trees
With young trees it’s important to
remember that they don’t require a lot of
nitrogen, Doll said.
Nitrogen requirements for young
orchards is density dependent, Doll said.
“Optimal nitrogen rates for first and
second leaf trees appear to be around
three to four ounces of actual nitrogen
per tree. This means that rates for developing
orchards are getting higher due to
tree count,” Doll said.
It’s also important to remember with
young trees that when nitrogen is being
applied, it is a relatively inefficient application,
Doll said.
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“That’s due to the root system essentially
being limited, and the irrigation
system not applying all the material to
the root zone of the tree,” Doll said.
“I wouldn’t want to see any fertilizer
applied to first leaf trees until they have
12 inches or more growth on them,
and even then, very small applications
are best—less than one ounce of actual
nitrogen per tree, per application,” Doll
said.
“Making nitrogen applications too
early can be damaging to the young
tree’s roots, and I’ve seen more harm that
good come with too early of nitrogen
applications on newly planted trees. It
actually can kill them,” Doll said, so it’s
better to wait until the trees have some
growth on them.
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f l. Performance
ul. Performance
ce.
Many orchards are deficient in zinc.
To increase zinc tissue content, low
applications of zinc sulfate, two to five
pounds to the acre, can be made in the
late fall without defoliating the tree. If
the goal is to defoliate, higher rates of
zinc sulfate are needed, 25-30 pounds
December 2017
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