The Crush - October 2021 - 2

FEATURE STORY
It may be best applied prior to rain or mixed with standard
irrigation water to dilute excess concentrations.
FERTILIZATION AND MINERAL NUTRITION
Recent and historical data for the vineyard site can be used to
make fertilizer and nutrient decisions based on soil analysis,
tissue/petiole analysis, visual assessment, crop yields and
seasonal vine stress factors. The presence of nutrients in
irrigation water and soil, based on analysis, should be factored
into nutrient replacement amounts. Applications by fertigation
through the drip system are recommended this year given the
uncertainty of rain amounts and timing.
The most important macronutrients required by grapevines
are: nitrogen (N), phosphorous (P), potassium (K), magnesium
(Mg), sulfur (S) and calcium (Ca). The period after harvest and
before leaf drop is one of the best times for vines to uptake N
and K. UCCE viticulture research provides the following general
guidelines for post-harvest nutrient replacements for each ton of
fruit removed:
N: 3 pounds P: 0.5 pound
Ca: 1 pound Mg: 0.2 pound
K: 5 pounds
In a recent presentation to Lodi growers, viticulture consultant
Stan Grant, with Progressive Viticulture based in Turlock,
discussed macronutrient allocations during the four main
grapevine development stages. For post-harvest, he suggested
the following percentages of total annual additions:
N: 15%-25% P: 15%-35%
K: 25%-35%
Ca: 0-10%
Mg: 0-10%
Compost can be a good way to add nutrients while also acting to
maintain soil moisture content. This year, Kurtural recommends
banded compost applications rather than broadcasting
throughout the vineyard. Post-harvest can also be a good time to
apply soil amendments such as sulfur and gypsum to adjust soil
pH and improve water infiltration.
VINEYARD FLOOR MANAGEMENT
Reducing tillage can help with soil moisture retention, but
under-vine weed control is still advised. An alternative floor
management option to tillage and herbicide use is grazing
animals for post-harvest weed and vine cleanup. No-till
alternatives also help maintain healthy soil microbiota and
improve carbon sequestration. Some winegrape growers own
sheep for grazing. Grazing service providers operate in many
grape growing regions that will transport sheep to vineyards and
manage their grazing activity on an as needed basis. In hillside
vineyards, sheep grazing may be more practical than mechanized
mowing and tilling and to prevent erosion.
Post-harvest fall is a good time to plant, or reseed, cover crops
between vine rows that grow during winter, and go dormant in
spring when the vines begin their growth cycle.
2 OCTOBER 2021
Compost pile ready for post-harvest vineyard application. Photo: Ted Rieger
WEATHER MONITORING
Monitor weather forecasts for rain to effectively time fertilizer
and nutrient applications (for non-fertigation applications), for
seeding cover crops, and for soil applications of herbicides.
Growers are advised to monitor fall forecasts for low
temperatures for potential cold damage to vines prior to
dormancy. Many California growing areas suffered cold injury
vine damage resulting from an early November 2020 freeze. In
the Lodi AVA, overnight temperatures dipped below 30 F for
five consecutive days from Nov. 8-12, resulting in vine tissue
damage and restricted or delayed spring vine growth in 2021.
Cold damage is more likely to occur in younger vines (3 years
old and younger) as they tend to stay active later in the growing
season, and in cane pruned vines, when freezing temperatures
follow a period of warmer than normal temperatures. UCCE
viticulture specialist Matthew Fidelibus says rootstocks such as
Freedom and Harmony, and varieties such as chardonnay and
cabernet sauvignon, can be more susceptible to cold damage.
Cold damage was also reported in sauvignon blanc, pinot noir,
pinot gris and zinfandel.
Moderate fall weather with extended warm temperatures allow
vines to grow later and growers sometimes take advantage
of this to build vine reserves with extended irrigation and
nutrient additions. However, this may increase cold injury risk if
temperatures drop suddenly, before vines properly acclimate to
cold weather or before dormancy.
Maintaining soil moisture through winter is desired, but excess
water in vine tissue may contribute to cold injury. Lodi growers
sought advice from Cornell University research and extension
viticulturist Terry Bates, who more commonly sees cold damage
in New York vineyards. When considering later fall irrigations,
Bates advises looking at the 7- to 10-day weather forecast, and
not irrigating if temperatures are expected to drop into the 20s.
Vines damaged by cold injury resulted in a 2021 season of lost
crop production in many cases. Young vines damaged in new
vineyards had to be cut back and retrained resulting in a lost
season of growth.
The Crush - October 2021

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