5
shows that proper sprayer speed and
spray volume are often overlooked
during hullsplit even though the
research repeatedly shows that
slowing down improves spray
coverage. This research should not
be overlooked, especially since the
focus for hullsplit NOW sprays
is to reach the trees' hard-to-reach
nut sutures.
Don't forget disease: hull rot at
hullsplit
On the disease front, almond hulls
are susceptible to hull rot from the
beginning of hullsplit until the hulls
dry.
3
Hull rot may be caused by one
of three different fungal pathogens,
which may affect a grower's choice
of which fungicide to use.
Dr. Brent Holtz, a UCCE farm
advisor in San Joaquin County,
states that successful management
of hull rot relies on both cultural
and chemical controls that take
localized growing conditions into
consideration.
"The problem with hull rot is that if
the hull gets infected then the fungus
releases the toxin fumaric acid,
which can run through the wood and
kill the fruit wood and buds during the
next season," Holtz said. To succeed
in hull rot control, growers should
reduce the level of irrigation for
a two-to-four-week window at the
onset of hullsplit. This practice
involves a 10–20% reduction in
applied water, which is best
monitored by measuring midday leaf
water potential to ensure the trees
are moderately (-15-18 bars), but not
excessively, water stressed.
ABC-funded research also finds that
excessive nitrogen levels increase
the frequency of hull rot, so it is
imperative that a proper nitrogen
budgeting plan is in place for the
growing season to ensure that only
the necessary amount of nitrogen
is applied. Holtz noted that when
proper leaf sampling takes place,
the critical value for midsummer
leaf nitrogen percentage should be
between 2.2–2.5%. Growers should
use the Almond Board's Almond
Nitrogen Budgeting tool to determine
appropriate nitrogen applications
and visit Almonds.com/Nutrients/
Budgeting for more.
Applying strategic deficit irrigation
at hullsplit and avoiding excess
nitrogen also improves growers'
ability to control NOW because it
improves the evenness of ripening
and the rate of hullsplit. These
factors, in turn, improve the efficacy
of NOW sprays and reduce the
chance of a second spray being
necessary. Furthermore, a tree that
experiences even more ripening will
be easier to shake at harvest, thus
reducing the number of leftover
nuts in the tree that may become
overwintering sites for NOW as
mummy nuts. This, therefore, is
a demonstration of what optimal
integrated pest management looks
like in the orchard: using a variety of
controls that do not out-compete or
contradict each other to manage not
only the pests at hand but to prevent
further damage down the road.
Gabriele Ludwig, Ph.D., the director
of Sustainability and Environmental
Affairs at the Almond Board of
California, notes, "Understanding
the interactions between different
growing practices on key almond
pests is key to maintaining an
integrated pest management
program. The year-round use of
integrated pest management is
critical to minimizing pest issues
at hullsplit, thus ensuring all the
resources growers invest in
growing their crop are realized
in marketable yields."
Ultimately, strategic IPM during
hullsplit is essential in the almond
industry's effort to achieve the
Almond Orchard 2025 Goal
of increasing the adoption of
environmentally friendly pest
management tools by 25% by 2025.
To learn more about how to
effectively manage orchard pests
throughout the growing season,
growers should visit IPM.UCANR.edu,
as well as Almonds.com/Pests.
Growers should time their NOW sprays — if sprays are needed — to the beginning of hullsplit
and NOW's second flight. (Photo credit: David Haviland/UCCE)
1
https://www2.ipm.ucanr.edu/agriculture/
almond/Webspinning-Spider-Mites/
2
https://www2.ipm.ucanr.edu/agriculture/
almond/navel-orangeworm/
3
https://www2.ipm.ucanr.edu/agriculture/
almond/hull-rot/
