Winter Sanitation:
The Foundation of
Navel Orangeworm
Control
Halloween isn’t the only time when
mummies are dangerous; that is,
mummy nuts in almond orchards.
In fact, now is the time to break the
link between mummy nuts – nuts
remaining on the tree after harvest –
and overwintering navel orangeworm
(NOW).
While winter sanitation is important
every year, it is increasingly critical
this year, with rejections from almonds
harvested in 2017 reported at higher
than two percent. These significant
rejection rates were due to an overly
wet winter that presented challenges
for mummy nut removal and follow
through of winter sanitation. Also,
the wet winter was followed by a
warmer-than-normal growing season
in 2017 that resulted in higher and
earlier NOW populations, with
an additional late-season NOW
generation that resulted in higher
insect pressure.
Keep Rejection Levels Below
Two Percent
According to the Almond Board of
California (ABC), the working goal
is to keep almond harvest rejection
levels below two percent and to
strive for one percent, or less. If a
grower’s average damage is over
two percent, it is critical they take a
closer look at overall practices and
specifically adopt stronger winter
sanitation measures, which are the
foundation for any NOW control
program.
•
Insight:
Reject numbers like
two percent on the grade sheet
translate to even higher losses
for growers. Estimates are that
actual losses are double what
the grade shows because a
good working assumption is
half of the damaged kernels
are blown out during harvest or
removed at shelling, and these
hidden losses are in addition
to handler reject quality
deductions shown on grade
sheets.
Concerns over rejection rates span
beyond direct crop damage and
quality because NOW damage is
also associated with aflatoxin. In
addition to the direct damage NOW
causes the kernel, the damage opens
the door to fungal infections and
contaminants, particularly to the fungi
Aspergillus spp. and the aflatoxin
contaminant it produces.
The stringent tolerances for aflatoxin
contamination in key export markets
like the EU and Japan raise the
importance of this yearly integrated
management practice.
Mummy Nut Removal Key
to Success
Winter sanitation, the cornerstone of
NOW pest management, involves the
removal and destruction of mummy
nuts to prevent overwintering NOW
and prevent two-year mummy kernels
being harvested the following year. It’s
also part of being a good neighbor,
as NOW can travel to other almond
orchards if many mummy nuts remain.
To reach the goal of two percent
damage or less, growers should
follow the guidelines below, which
vary by growing region.
1.
Before January 15, and
preferably earlier:
Count the
mummy nuts and examine 20 trees
per block. If an average of two or
more mummy nuts per tree (and even
lower in the southern San Joaquin
Valley) are found on or before
January 15, get out the shaker or
poling sticks and remove mummies
in the entire block.
• For the northern and central
growing areas, the guideline is
to remove mummies down to
an average of no more than
two mummies in the canopy per
tree. Cleaning both softshell and
hardshell varieties is important
as they are both overwintering
sites for NOW. For hardshells,
NOW readily overwinter in
the hulls instead of infesting the
kernels directly.
• For the southern growing
areas, the sanitation goal is
much lower and averages 0.2
mummies per tree in the canopy.
Furthermore, there should be no
more than eight mummies per
tree left on the ground that have
not been destroyed.
IN YOUR ORCHARD
4 4
A L M O N D F A C T S
