3. Manage Hull Rot from Day One
Almond hulls are susceptible to hull rot fungi from the
beginning of hull-split until the hulls dry, typically a
month long. This period may vary, however, depending
on fertilization and irrigation. Successful hull rot control
is based upon effective strategic deficit irrigation and
nitrogen management.
Strategic Deficit Irrigation (SDI)
SDI, also known as regulated deficit irrigation, or RDI,
is the practice of stressing almond trees at specific
crop stages to reduce water use without impacting crop
productivity. By managing SDI, growers can reduce
hull rot by 60 to 90 percent and experience a more
uniform hull-split and earlier harvest. These factors may
contribute to less crop damage from weather, late-
season NOW flights and aflatoxin contamination.
The target period of stressing trees is from the start of hull-
split through 90 percent hull-split, a period of about two
weeks. The most accurate way to practice SDI is to use a
pressure chamber to track and maintain slight tree water
stress levels, between -14 bars and -18 bars, depending
on the weather. Information about the pressure chamber
is available on the UC Davis Fruit and Nut Research and
Information webpage (fruitsandnuts.ucdavis.edu).
Growers who do not rely on pressure chambers,
particularly those with a history of hull rot and a visual
baseline from which plant stress can be observed, may
achieve similar results by irrigating at 50 percent of
normal tree demand, using crop evapotranspiration (ETc)
calculations during hull-split.
The onset of hull-split will vary according to orchard
conditions; stress levels vary with soil type and other
factors. In shallow soils where trees may dry quickly,
initiate stress when blanks start to split, usually about
a week before the onset of hull-split. On deeper, well-
drained soils, it can take up to 20 to 30 days to reach
mild-to-moderate stress levels. In this case, growers may
want to use the UC Almond Hull-Split Prediction Model
to determine when to initiate water stress.
Nitrogen Management
Almond Board-funded research has found that excessive
nitrogen increases incidences of hull rot. It is critical
that a proper nitrogen budgeting plan is in place for
the growing season to ensure that only the necessary
amount of nitrogen is applied. It is important to follow
the nitrogen budgeting plan during the whole season,
which is a function of crop load. For instance, the
application during kernel fill typically occurs the during
the end of May through early June.
Find additional information on nitrogen budgeting and
management at almonds.com/nutrients.
4. If Applying AF36 Prevail, Aim for One-to-Two
Weeks Before Hull-Split
Recently approved for use in almond orchards, the
Aspergillus flavus biocontrol agent AF36 Prevail offers
a supplementary approach to reducing aflatoxin
contamination in the orchard. If you plan to apply AF36
Prevail this season, look to make your application one-
to-two weeks in advance of hull-split.
Strategic Deficit Irrigation is recommended from the start of
hull-split through 90 percent hull-split, about two weeks long.
Utilize a pressure chamber to track and maintain tree water
stress levels between -14 and -18 bars.
IN YOUR ORCHARD
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A L M O N D F A C T S
