[PDF]Organic Blueberry Production

800-346-9140




Organic Blueberry
Production



Horticulture Production Guide



www.attra. nca t org



ATTRA is the national sustainable agriculture information center funded by the USDA's Rural Business — Cooperative Service.



Abstract: This publication focuses on organic production practices for blueberry culture, with some
information on marketing outlook. A list of resources includes websites.



By George L. Kuepper & Steve Diver
NCAT Agriculture Specialists
Updated by K. Adam, February 2000



organic certification agency or organic growers
organization should be contacted to determine
exact requirements and a list of prohibited
practices and substances.



Introduction

The following is an
introduction to organic
blueberry production,
designed to
supplement
information from
conventional sources
on basic cultivation
practices. Matters such
as pruning, training,
variety choice, sources
of propagation
material, and planting
are essentially the same
in both organic and
conventional culture.
Generic blueberry
information can be
obtained from the
Cooperative Extension Service and common
horticultural texts and periodicals.

The word organic has precise legal definitions in
most states, and there are certification groups that
maintain standards for what can be certified and
marketed as organically grown, as well as
prescribed record-keeping procedures. An




However, some smaller
producers may wish to
follow organic
practices without
becoming formally
certified. The
information provided
here should be useful
to them, as well.

This publication is
generally applicable to
organic culture of all
three cultivated
blueberry species.
Information on
improved blueberry
cultivars is continually
being released by
research and extension
agencies.



Additional ATTRA publications on
organic certification include:

Organic Certifiers Resource List
Resources for Organic Marketing



Contents

Introduction 1

Soils and Fertility 2

Cultural Considerations 6

Pests 8

(chart) 10

Diseases 9

(chart) 11

Bird and Rodent Control 9

Marketing 9

Summary 9

References 12

Additional Resources 13



^sH^ Al 1 KA. IS A PROJECT OF THE NATIONAL CENTER FOR APPROPRIATE TECHNOLOGY



Rabbiteye (Vaccinium ashei)— adapted type in
the South (roughly south of Interstate 40).

Highbush {V. carymbosum)— adapted to
intermediate climates.

Southern highbush (V. ashei x carymbosum)



In the Far North, low-bush and dwarf highbush
blueberry cultivars are more climatically
adapted than are highbush types. The lowbush
wild blueberry (V. angustifolium) is
commercially important in Maine. The Wild
Blueberry Association of North America
(WBANA) website

(http: / / www.wildblueberries.com) promotes
marketing and is an excellent source of
information on production practices.

Blueberries have fewer pest problems than most
other fruits, offering an advantage for organic
production. Most insect and disease problems
can be controlled through cultural manipulation.
Blueberries have a relatively low nitrogen
requirement and thrive on organic sources.
Adjusting soil pH low enough and protecting
from predatory birds and mammals are the major
production constraints. Weather fluctuations and
geographic seasonal advantage are the major
economic considerations.

Generally, non-organic transplants can be used
for establishing perennial crops. However, most
certifiers require the plants to be grown at least 12
months under organic conditions after trans-
planting before any harvested product can be
marketed as organic.



Soils and Fertility

The Importance of Soil pH

Blueberries are distinct among fruit crops in their
soil and fertility requirements. As members of
the Rhododendron family, blueberries require an
acid soil, preferably in the 4.8-5.5 pH range. The
reasons for this are several. First of all, when soil
pH is appreciably higher than 5.5, iron chlorosis
often results; when soil pH drops below 4.8, the
possibility of manganese toxicity arises. In either
case, plants do not perform well.

Soils with a native pH above 5.5 pose special
problems for organic producers. Recurrent
applications of acidifying agents are necessary in
order to keep pH from drifting back to its natural
level. Non-organic methods may depend on
acidifying agents such as ammonium sulfate or
di-ammonium phosphate which are not allowed
under organic certification criteria. Not all
certifiers allow the usual flowers of sulfur and
ferrous sulfate for pH correction in organic
culture. Acceptable substitutes are cottonseed
meal (from organic cotton) and, if pH is not too
high, sawdust or pine needle mulches, which can
assist in lowering pH a few tenths of a unit.

Soil pH also plays a significant role in crop
nitrogen management. Research has shown that
blueberries are preferential to soil and fertilizer
nitrogen in the ammonium form, absorbing and
utilizing it much more efficiently than nitrate
nitrogen — the form preferred by most other
commercial crop plants. Neutral and basic soils
favor nitrification — the rapid conversion of
ammonium nitrogen to nitrate through the
activity of nitrifying microorganisms. When an
acidic soil environment is maintained, the
ammonium form of nitrogen predominates and is
readily available to blueberries.

This principle also applies to the addition of
supplemental nitrogen fertilizers. Conventional
recommendations routinely emphasize the use of
ammonium fertilizers, particularly ammonium
sulfate, which also acts as a soil acidifier. When a
slow-release organic fertilizer like fish meal is
applied, the nitrogen in the proteins is converted



For more information about marketing
options, see the ATTRA publications Direct
Marketing and Farmers' Markets. On-farm
value-added blueberry products usually
require setting up a second rural enterprise
besides farming, and may entail considerable
additional planning, management, and start-
up expense.



wiLr ATTRA. // Organic Blueberry Production



Page 2



first into ammonium. The ammonium— which
would rapidly convert to nitrate under neutral
soil conditions— tends to remain in the desired,
ammoniated form.

One preferred method of lowering soil pH in
organic culture is application of sulfur. Pre-plant
incorporation of sulfur to lower the pH to an
optimal blueberry range of 4.8-5.5 should be
based on a soil pH test. Because soil pH is subject
to considerable seasonal fluctuation— especially
on cropped soils— it is advisable to do soil
sampling and testing in winter or very early
spring, when biological activity is at a low level.

The table below provides guidelines for sulfur
application on different soil types.



detrimentally affect soil biology if overused.
Organic growers sometimes increase their
applications of peat moss at planting time as it,
too, is a soil acidifier (pH 4.8), reducing the need
for sulfur. The Ozark Organic Growers
Association suggests as much as 5-10 gallons of
peat moss per blueberry plant. While costly, peat
is resistant to decomposition and provides the
benefit of soil humus.

Those seeking alternatives to spaghnum peat
moss might consider the use of pine bark or
similar amendments incorporated in the planting
rows or holes. While viewed as less desirable
than spaghnum peat moss, pine bark can often be
obtained locally at a much lower cost. A new



Approximate pounds per acre of sulfur or ground limestone to change soil pH one unit (1).


Soil Texture


Pounds per acre of sulfur to
lower soil pH one unit (e.g. 6.0 to 5.0)


Pounds per acre of lime to raise
soil pH one unit (e.g. 4.0 to 5.0)


Sand (CEC=5)


435 to 650


1000


Loam (CEC=15)


870 to 1300


2800


Clay (CEC=25)


1300 to 1750


4400



Powdered sulfur takes about one year to oxidize
and reduce soil pH. Prilled sulfur takes
somewhat longer. Limestone, too, requires time
to effect changes in pH and reactive time is
highly dependent on the fineness of grind.

Single applications of sulfur should not exceed
400 pounds. Best results are obtained by
applying 200 pounds in spring, followed by 200
later in the fall for as many intervals as is
required to deliver the total amount. It is
advisable to re-test the soil one year after each
application to determine if additional
acidification is truly necessary (2).

Organic growers are advised to be conservative
in the application of soil sulfur. Sulfur has both
fungicidal and insecticidal action and can



commercial substitute for peat called coir, made
from coconut fiber pith, appears promising, but
only if it becomes available at a reasonable price.

It is advisable to monitor soil pH over time as
production practices can cause gradual changes
to occur. Irrigation water often contains calcium
and magnesium, which may cause soil pH to
creep upwards, while repeated use of acidifying
fertilizers, such as ammonium sulfate or
cottonseed meal, may lower pH. Fortunately, the
presence of abundant organic materials such as
peat and the breakdown products of sawdust and
woodchip mulches tend to buffer soil pH.
(Several organic growers have even observed that
blueberries grown in high organic matter soils
will perform well at a pH as high as 6.0 with few
apparent problems.) As a result, additional



wiLr ATTRA. // Organic Blueberry Production



Page 3



NATURAL MATERIALS FOR SUPPLEMENTARY FERTILIZATION


Material


Estimated N-P-K


Characteristics


Alfalfa meal


3-1-2


Good trace mineral source.


Blood meal


12-1.3-0.7


Medium N release rate of 6-8 weeks.


Cottonseed meal


7-2-2


Slow to medium N release of 4-6 months. Soil
acidifier


Feather meal


13-0-0


Slow N release of 4-6 months


Fish meal


10-2-2


Slow to medium N release of 4-6 months.


Leather meal


10-0-0


Slow N release. Restricted use in organics due to
heavy metal contamination.


Compost and compost-
blended fertilizers


Analysis is highly variable depending on raw materials in compost and materials
added to fortify the blend. Analyses commonly range from less than 1% to
about 8% N. Considered a slow-release source of N, but preferred overall as a
fertilizer.



sulfur (or lime for that matter) is seldom needed.
When it is needed, top dressing is usually done,
but delivery of soluble sulfur through drip
irrigation lines is also an option.

Blueberry Fertilization Practices

Soil building practices prior to establishment can
go a long way towards providing the fertility
necessary to a healthy blueberry planting. High
levels of soil organic matter are especially
important in blueberry culture, contributing to
the soil's ability to retain and supply moisture to
the crop, buffering pH and releasing nutrients
through the decay process. Organic-rich soils are
also a desirable environment for symbiotic
mycorrhizal fungi that assist blueberry roots in
absorbing water, nitrogen, phosphate and other
minerals. Cover crop and green manures can
play an important part in cycling organic matter
into the soil system, as can applications of
composts and livestock manures. ATTRA has
several publications which can be useful in these



areas including Overview of Cover Crops and Green
Manures and Farm-Scale Composting Resource List.

Once a blueberry planting is established,
supplemental fertilization can be applied in a
number of forms and by several means.
Generally, supplemental nitrogen is the greatest
concern, followed by potassium. Blueberries have
a low phosphorus requirement and typically
require little, if any, phosphorus fertilization. In
fact, excessive phosphate has been one of the
factors linked to iron chlorosis in blueberries.
High calcium levels are also considered
problematic.

Nitrogen fertilizer recommendations vary
somewhat from region to region. As a general
guideline, 100-120 lbs. of nitrogen per acre are
commonly recommended on mulched berries; a
reduced rate of 50-60 lbs. per acre is advised
where little or no mulch is used (3). Nitrogen is
often applied in three split applications — one at
bud break, followed by two more at six week



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Page 4



intervals. These recommendations apply to
conventional soluble fertilizers, and adjustments
may be appropriate for less-soluble organic
fertilizers. One rule of thumb suggests that
organics be applied from 1-4 weeks ahead of the
schedule recommended for soluble fertilizers.
This allows additional time for decomposition
processes to make nutrients available.
Applications after mid-July are discouraged, as
plants tend to develop late growth that is
particularly sensitive to freeze damage. A table
of natural materials used by organic growers for
supplementary fertilization is provided on
p. 10 (4).

Current fertilization practices among organic
growers vary considerably. In one example (5),
an organic blueberry grower in the Missouri
Ozarks applies 1/2 pound of f eathermeal per
mulched plant in late May of the establishment
year followed by a similar application 4-6 weeks
later. In subsequent years, an additional (third)
application of 1/2 pound feather meal is made
earlier in mid to late March. As the feather meal
products available in this region contain roughly
13% nitrogen, this grower is applying approxi-
mately 141 pounds of actual N per acre in the
establishment year, and an annual total of 212
pounds per acre thereafter .

Using the same schedule of split applications,
another organic grower in the Arkansas Ozarks,
also growing mulched berries, applies cottonseed
meal (estimated at 7% N) at 1 lb. per plant each
time. At these rates this grower is applying
roughly 152 lbs. per acre N in the establishment
year and about 229 lbs. per acre in subsequent
years (6). (It should be noted that the use of
cottonseed meal in certified organic production is
controversial because cotton is one of the most
heavily sprayed agronomic crops and the
presence of residues is a concern. In addition,
certified organic growers should specify
"mechanically extracted" cottonseed meal and not
"chemically extracted" or "solvent extracted"
cottonseed meal.)

Associate professor John Clark (3) at the
University of Arkansas believes the fertilization
rates used by these organic growers are probably
excessive. Despite the slower availability of



organic-based nitrogen, the carry-over from
previous seasons should result in roughly the
same amount of nitrogen released each season as
is being applied. But since detailed research is
lacking, no one can be certain of the best rates to
use.

Clark suggests that the best way to determine
whether fertilization rates are "on target" is to
annually test foliar nitrogen levels. This is
accomplished in late July or early August (in
Arkansas) by sampling leaves from the mid-
shoot area on fruiting canes and sending them to
an appropriate laboratory. Lab results showing
nitrogen levels below 1.6% indicate a nitrogen
deficiency; a level in excess of 2.2% indicates
nitrogen excess. This service is available through
Cooperative Extension in Arkansas and several
other states. Several commercial laboratories also
provide foliar analysis. ATTRA can provide a
short list of laboratories that offer various soil
and plant tissue testing services.

Potassium needs in blueberries are often
provided through decaying mulches. The need
for further supplementation should be
determined by soil and/ or tissue testing. Where
additional potassium is needed, it may be applied
in a number of forms — including sul-po-mag,
epsom salts, granite meal, and greensand. The
latter two sources are relatively low in available
potash and are not usually advisable from an
economic standpoint if potash supplementation
is the sole objective. Since chloride-based
fertilizers have proven detrimental to blueberries,
natural sources of potassium chloride (though
acceptable to some certifying agencies) should
not be applied in significant amounts.

An all-around good blueberry fertilizer is high
quality compost. Depending on the humus
condition and biological activity in the soil,
compost may be able to provide all the fertility
needs of the crop. Where compost is of average
quality, it may still function as a good soil
conditioner. The use of aged animal manures in
blueberry production is also possible, but is less
common.

Fertigation of blueberries — the practice of
injecting soluble fertilizers through drip irrigation



wiLr ATTRA. // Organic Blueberry Production



Page 5



lines — is a common practice in conventional
production. Since fertigation is based on the
complete solubility of fertilizers in water, there
are limited options among organic fertilizers.
Attempts at fertigation with blood meal by
Arkansas blueberry growers have resulted in
clogged emitters and algae growth. More
recently, however, researchers in California
demonstrated the use of spray-dried fish protein
and poultry protein in drip systems (7). In
addition, several liquid fertilizers used by organic
greenhouse growers (Green Juice™, Simeon's
Super Tea™) look promising.

As previously mentioned, the root systems of
blueberry plants are also limited with regard
to where they grow within the soil
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