Be careful not to over-stress the trees. Cutting the water
to “force” hull-split is not advised as significant stress
at this period will decrease kernel weights and cause
“textured” kernels. If trees have been deficit irrigated
through the season due to drought conditions, RDI is not
advised. More information can be found in Publication
#8515 “Drought Management for California Almonds”
available for free at
.
Hull Rot Management
Hull rot is a fungal infection of the splitting hull by
either Rhizopus stolonifera, Monilinia spp. A new hull
rot pathogen, Aspergillus niger has been identified in
the south San Joaquin Valley. Toxins produced by these
fungi move into the tree, killing spurs and wood within
the canopy, impacting future production. Trees that are
over-fertilized and over-irrigated tend to have increased
hull rot. Nitrogen applications should be minimized
after kernel fill and, if possible, RDI should be applied.
Practices that reduce dust should also be reduced
around the timing of hull-split (late June to late July).
Fungicides have been shown to be effective in reducing
strikes by Rhizopus, but must be timed to the initial
splitting of the almond hull. This usually coincides with
NOW sprays. Hull-split fungicide sprays, however, do
not reduce hull rot by Monilinia spp. Data indicates that
fungicides for Monilinia need to be applied in early to
mid-June to reduce latent infections of the hull. Fungicides
when used without RDI and nitrogen management practices
have generally shown a reduction of only 10 to 25 percent
of hull rot infections, and highlights the value of an
integrated program.
Recent research has found that alkalizing treatments
applied at hull-split are able to reduce the severity of
hull rot to the level similar to many fungicides. The most
recent, promising work has shown that applications of
di-potassium phosphate at 48 ounces per acre applied
twice at early suture opening and mid-hull-split were as
effective as fungicide applications. This spray solution
is thought to either boost the health of the tree which
reduces infection or neutralize the acid compounds that
are produced by the hull rot pathogens and responsible
for twig dieback. If using this product with navel orangeworm
sprays, make sure to do a compatibility test.
Managing Navel Orangeworm
To protect the crop from navel orangeworm (NOW),
hull-split sprays should be made to protect the crop from
infestation. Sprays should be made at the onset of hull-
split (e.g. one to five percent). Often at this time, blanks
begin to split in the interior of the orchard. Most reduced-
risk pesticides need to be applied prior to egg laying or
hatching, supporting this earlier timing. Pyrethroids (e.g.
Brigade, Warrior), organophosphates (e.g. Lorsban), and
chlorantraniliprole (e.g. Altacor) as well as a few other
combination products have shown adult activity and may
be suitable for later timed hull-split sprays. Although lower
in cost, pyrethroids have been shown to impact spider
mite predators for at least six months after the application,
increasing the risk of spider-mite flare-ups into the following
year. Second sprays for 'Nonpareils' and coverage for
later splitting pollinators may be needed, especially in
areas with higher temperatures and NOW populations.
Work with your pest control advisor to determine the best
strategy for timings and pesticide selection.
Rust is a common foliar disease that can show symptoms
by mid-June. High rates of infection can lead to leaf drop,
successive re-foliation and next year’s crop loss. Most
fungicides are effective against rust, but treatments must occur
prior to infections are visible for maximum effectiveness. Rust
symptoms that show up after the end of June rarely lead to
defoliation. Photo courtesy of David Doll.
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