TIME TO CONSIDER
38
Almond Facts
NOVEMBER | DECEMBER 2016
Time To Consider
DAVID DOLL, UCCE Nut Crop Pomology Farm Advisor, Merced County
Although having the appearance of a quieter time, the dormant period is a time of preparation for
the coming cropping year. Activities include orchard and equipment maintenance, pruning, and
developing management practices for identified issues.
Pest Management
Considerations
Spur sampling for San Jose and Walnut Scale and mites
should be performed during the dormant period. I have
observed numerous orchards experiencing “lower limb
dieback” in the middle of the summer only to identify
high scale populations. This pest is the easiest to control
in the dormant period. Mite eggs often concentrate
around spurs and also can be identified at this time.
If populations are beyond thresholds, dormant sprays
should be considered. More information can be found
at the “Spur Sampling” link on the UC IPM Website:
/.
Winter Sanitation for Navel
Orangeworm (NOW) Control
The most effective way to reduce over-wintering NOW
populations is sanitation. By removing the ‘mummy’ nuts
from the tree and destroying them before mid-March
(when moths begin to emerge), NOW damage at harvest
can be reduced. These nuts serve as the overwintering
point for the pupae and developing larvae, and are the in-
season food source for adults and second flight larvae.
The recommended industry practice is to reduce the
average mummy nut count to less than two per tree. This
recommendation was developed by performing research
and reviewing the data collected from plots throughout the
San Joaquin and Sacramento Valley. The research showed
that for every mummy nut left in the tree, 1 percent
damage from NOW should be expected. In other words,
five mummies per tree equals 5 percent NOW damage.
Therefore, in order to meet the industry standard of 2
percent NOW damage levels, there should be two or fewer
mummies per tree.
Recent research, however, conducted by Brad Higbee
(Paramount Farms) and Joel Siegel (USDA-ARS) has
shown that a greater reduction of mummy nuts is needed
in areas with higher NOW pressure. In Kern County,
they have found that the standard for sanitation has to
be less than 0.7 mummy nuts per tree in order to keep
NOW damage below the industry standard of 2 percent.
They also found that the quantity of mummies on the
ground influences NOW damage – having more than
8.9 ground mummies per tree increased NOW damage
above the 2 percent industry standard. These results were
drawn from research conducted over a 5-year period
reviewing data from plots established on 50 orchards.
By reviewing this data, does that mean everyone across
the state needs to sanitize to less than 0.7 mummy
nuts per tree? The short answer is “it depends.” Insect
pressure will vary by location due to more degree days
and lower rainfall that is generally characteristic of the
southern San Joaquin Valley and some micro-climates
in the Sacramento Valley. Regardless of location, all of
the research indicates that the fewer mummies within the
orchard (both tree and ground), the less NOW damage
to expect at harvest. Therefore, higher standards of tree
and ground sanitation are recommended for orchards in
high pressure, higher heat unit/degree day areas. Growers
in cooler, low pressure areas should still reduce average
mummy nut counts to two or fewer per tree and destroy
any mummies that are on the ground.
Mummy nuts serve as the overwintering location of Navel Orangeworm.
These nuts should be removed from the tree and destroyed to reduce pest
pressure. Hard-shells, as pictures, also can harbor NOW and should be
managed similarly to soft-shell varieties.
Gurreet Brar, CSU Fresno.
