March/April 2024 - 18

Water stress
ne big challenge for nut
growers is identifying water
stress and timing irrigation in
ways that make sense.
That's the opinion of Mallika Nocco,
assistant adjunct professor in UC
Davis' Department of Land, Air and
Water Resources.
" What I think a lot of growers
struggle with is how to incorporate
estimates of stress into their irrigation
schedule, " she said. " From events
that I've done throughout the Central
Valley, it sounds like a lot of them put
together their irrigation schedules
for a season and stick to them, and
incorporating stress would take a
lot more thought and labor I know
some folks just don't have. But there
are times when it makes sense to
incorporate the measurements. "
With almonds, for example, Nocco
said during the hull-split period, where
growers want to intentionally stress
their trees, it would be a savvy time
to incorporate estimates of water
stress, either using pressure potential
measurements or sensors that can help
estimate water potential.
" More people today are accessing
remote sensing sources, " she said.
" There are companies who can provide
tools so growers can access stress
data around hull-splits that can be
informative to pull back irrigation. "
Another way useful for growers to
monitor water stress is knowing when
to activate irrigation in the spring.
" With a wet year, you're going to
have that full moisture profile all filled
up, so it would be wise to wait until
it's an appropriate time to turn on that
irrigation so that we can have root
development, take advantage of some
Tools to know
Gurreet Brar, a Fresno State
assistant professor of pomology who
specializes in pistachio physiology and
horticulture, noted that while recent
wet weather has helped build California
reservoir storage levels and get the
snow up in the Sierra, the water issues
are far from over.
" With SGMA regulations (California's
2014 Sustainable Groundwater
Management Act) imposing
groundwater pumping restrictions
in many areas of the Central Valley,
many orchards can still face water
stress during peak demand months this
summer, " he said.
Brar points to online decision
support tools like CropManage which
utilize evapotranspiration data and
crop-specific stress indices to help
growers make informed decisions for
precision irrigation.
" Tools and strategies like microirrigation
with precision, regulated
deficit irrigation, and plant-based
water stress monitoring have helped
the industry in not only saving water,
but also increasing crop water use
efficiency and mitigating disease
pressure, " Brar said. " Remote sensing
tools like satellite imagery are helping
growers and researchers in better
estimating crop water use or crop
water stress. Also, UAV imagery in
the NIR spectrum is being used for
precision irrigation. "
Ken Shackel, a UC Davis plant
scientist, agreed California's recent
record rains may not make water stress
oxygen, as well as water in those soils,
and not just over-water them right off
the bat, " Nocco said.
Tools and sensors can help with this pressing issue
as big an issue this year, but growers
are paying strict attention to their trees,
managing the water closely.
" There's a lot of buzz and companies
selling all kinds of different gadgets that
they say measure plant stress, " he said.
" Most of these gadgets will respond if
you take a tree and stop watering it;
the problem has been to develop a tool
that is consistently telling you when
it's responding and when it's not. The
consistency has been the hard thing,
especially for almonds and walnuts. "
The gold standard, Shackel said, is
the pressure bomb, which provides a
good number for whether the tree is
stressed or not and how much. Plus, it
doesn't change through the season.
The tried-and-true gold standard way
to measure water stress in nut trees is
to take estimates of water potential,
which Nocco admitted can be a hassle,
as they are time-consuming and require
someone trained to go out and commit
time to taking the measurements.
" Some other things to come out
recently are different tensiometer
sensors, which are providing
continuous estimates of stem water
potential based on a single tree, "
she said. " There are a few different
companies selling these now, and
there are slight differences to how
they are working. "
Over the last 10 years, Shackel
noted that the FloraPulse sensor, a
tensiometer, has been the best tool
he's found to mimic the measurement
that the pressure chamber takes on a
different scale and is becoming much
more popular among tree nut growers.
Nocco and her colleague, Isaya
Kisekka, have been comparison testing
sensors for stem water potential, and

March/April 2024

Table of Contents for the Digital Edition of March/April 2024

Editor's Letter
The blight phase of Botryosphaeria diseases in nut crops of California
Tree nut outlook for 2024
From the top
Water stress
Buzz pollination
Hazelnut crop concerns
Almond Board of California
Ad Index
March/April 2024 - 1
March/April 2024 - 2
March/April 2024 - 3
March/April 2024 - Editor's Letter
March/April 2024 - 5
March/April 2024 - The blight phase of Botryosphaeria diseases in nut crops of California
March/April 2024 - 7
March/April 2024 - 8
March/April 2024 - 9
March/April 2024 - Tree nut outlook for 2024
March/April 2024 - 11
March/April 2024 - 12
March/April 2024 - 13
March/April 2024 - From the top
March/April 2024 - 15
March/April 2024 - 16
March/April 2024 - 17
March/April 2024 - Water stress
March/April 2024 - 19
March/April 2024 - Buzz pollination
March/April 2024 - 21
March/April 2024 - Hazelnut crop concerns
March/April 2024 - 23
March/April 2024 - Business
March/April 2024 - 25
March/April 2024 - Almond Board of California
March/April 2024 - Events
March/April 2024 - 28