WCN December 2019

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more vigorous growth and not slowing
down as easily as their counterparts.
This is a bigger problem in growing
regions that are in low-lying areas, such
as old lake beds, where the cold air likes
to pond.
These complications target juvenile
trees, or those that are just coming into
bearing. For mature trees, there doesn’t
seem to be much of a problem, as they
appear to be far better equipped to
handle the abrupt changes in temperature.
Why that is, no one is quite sure
just yet, but speculation leans towards
the ideas of thicker bark, the bearing of
the tree, or maybe just a cyclical slowdown
after harvest.
As part of the slowdown,nitrogen
applications may be reduced during the
summer months, and drought conditions
encouraged.
“It also has to do with how much salt
is in the soil,” adds Kallsen.
Salt Leaching
Researchers are just starting to get a
handle on the rather complex phenomenon
that is a soil’s salt content.
Leaching salt from a pistachio
orchard’s soil is a very important
wintertime activity, and while experts
might disagree about the utilization of
fertilizers after harvest, it’s generally
not a good idea to add it if you’re going
to leach.
If fertilizers are added before salt
leaching, “[Grower’s] are just going
to wash a lot of these nutrients right
through the profile, and they won’t
be available for the tree’s roots,” says
Kallsen. “I tend to be more of a fan of
adding nutrients at the end of March,
beginning of April.”
For nutrient applications, like
nitrogen, there aren’t necessarily best
practices rather than suggestions from
advisors out in the field. The same
holds true for other customs that seem
to work well for pistachio trees, even if
there isn’t hard data for them. “We just
don’t have the database like they have
for almonds,” says Kallsen.
Along with irrigation shutoff and salt
leaching, another fall and winter activity
is tree training and pruning. Based on
observations in the field, trees seemed
to perform better. For those pruned
in-season, and especially for those
around three years old, they just stop
growing.
In-season training of trees in their
first full season of growth encourages
faster production of secondary scaffold
branches. After those first two years,
however, in-season training can causes
shoot growth to come to a standstill.
Not only that, but with bearing trees,
in-season pruning may remove a lot
of the bearing nut surface and can
decrease yield.
Preventing Pests
Another thing that can decrease
pistachio crop yield are pests, such as
navel orangeworm and Gill’s mealybug.
Gill’s mealybug likes to feed within
the pistachio cluster, and hinders nut
development by taking for itself the
carbohydrates and other nutrients that
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West Coast Nut December 2019