Strawberries: Organic Production

1. Strawberries: Organic
ATTRA Production
A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.org
By Martin Guerena This publication provides an overview of organic strawberry production methods. It also covers inte-
and Holly Born grated pest management and weed control techniques that can reduce pesticide use in strawberry pro-
NCAT Agriculture duction. Included are discussions of weeds, pests, diseases, greenhouse production, plasticulture, fertil-
Specialists ity, economics, and marketing. Lists are provided of further resources, both electronic and in print.
©2007 NCAT
Contents
Introduction ..................... 1
Planting Systems ............ 2
Varieties ............................. 4
Fertility ............................... 4
Weed Control .................. 6
Insect and Mite
Control ............................... 9 Strawberries in hoophouse. Photos by Martin Plasticulture strawberries.
Disease Control ............. 13 Guerena
Greenhouse
Production ...................... 16
Introduction Excel lent cu ltura l i nformat ion for
S
Harvest and conventional strawberry production—
Postharvest ..................... 16 trawberries are a viable crop in most planting systems, pest control, cultivar
Economics ...................... 17 areas of the United States. Cultivars recommendations, etc.—can be obtained
Marketing ........................ 19 have been developed to suit most from the Cooperative Extension Service in
References ...................... 19 agro-climatic conditions. In many loca- most states (also see Further Resources
Further Resources ........ 22 tions, demand for locally produced berries below). ATTRA’s Overview of Organic Fruit
Appendix A: Sources of far exceeds available supplies; small-scale Production provides general information on
Thermal Weeders ......... 25 organic weed control, organic fertilization,
producers can thus get higher returns from
Appendix B: Recom- and some basic considerations for organic
mended Strawberry strawberries than from most other crops.
Varieties ........................... 26 disease and pest control. This publication
Organically grown berries may command will cover problems specific to strawber-
a price premium. Organic production ries and will offer organically acceptable
excludes the use of synthetic fertilizers and solutions. We have not attempted to
pesticides, and requires soil building and develop a one-size-fits-all prescription for
organic (or other ecologically based) straw-
biological pest control. Federal organic
berry production. Rather we have intro-
ATTRA—National Sustainable standards restrict claims of “organically duced the most common challenges and
Agriculture Information Service
is managed by the National Cen- grown” to those farms that are certified to offered some possible solutions and factors
ter for Appropriate Technology
(NCAT) and is funded under a be organic by a USDA-accredited certifica- for consideration.
grant from the United States tion agency. For more information, request
Department of Agriculture’s For many years, conventional strawberry
Rural Business-Cooperative Ser- the ATTRA publications Organic Farm Cer- growers have routinely used the soil fumi-
vice. Visit the NCAT Web site
(www.ncat.org/agri. tification and the National Organic Program gant methyl bromide to control weeds, soil-
html) for more informa-
tion on our sustainable
and Organic Orchard, Vineyard, and Berry borne diseases, nematodes, and soil-dwell-
agriculture projects. ���� Crop Documentation Forms. ing insects. In October, 1998, the Congress

2. attached an amendment to the Clean Air
Act which required EPA to make regulatory
changes to the US phase-out of methyl bro-
mide, resulting in a 100 percent reduction
by 2005. (Anon., 2002) Currently, a criti-
cal-use exception has been issued extending
the phase out to 2007 for those who believe
there are no technically and economically
feasible alternatives to methyl bromide.
There are feasible alternatives in straw-
berry production, as many organic growers Strawberries in a basket.
can attest. Photo courtesy of USDA/ARS
rows of plants with one drip line running
Planting Systems between them. The distance between beds
Planting systems for strawberries vary, averages 40 inches. Drip tape is buried at
a depth of about 2.5 inches. Wide beds
depending on the environment and
usually have four rows of plants and two
production goals. The grower must decide
Related ATTRA drip lines, with 64 inches between beds.
the relative priorities of yield, size, flavor, or
Publications Spacing between plants in both types of
other qualities of the fruit, and seek a sys-
bed averages 12 to 14 inches.
Organic Farm Cer- tem that balances these goals. Systems that
tification and the focus primarily on yield are the least sus- Plastic mulch is used in both narrow and
National Organic Pro- tainable because of the enormous amount wide beds and can vary from a single strip
gram of plastic laid between the plants to full bed
of energy used for maintenance, plastic,
Organic Orchard, Vine- and transportation. In many of these sys- coverage, where holes must be punched for
yard, and Berry Crop tems, the plants are grown on raised beds the plant to develop. Some conventional
Documentation Forms as annuals. This results in removal of the growers in California use clear plastic which
Overview of Organic plants, plastic mulch, and irrigation sys- warms the bed faster, stimulating early-
Fruit Production tem at the end of every season. Regard- season growth; these growers use fumiga-
less of the system used, conventional yields tion to control most weeds. Black plastic
Season Extension
Techniques for Market are usually higher than organic yields. is used in organic production, primarily for
Gardeners However, studies have shown that organic weed control. Since the black plastic pre-
producers can earn more profit per acre vents the sun’s rays from penetrating, the
Sources of Organic beds remain cool, resulting in slower initial
Fertilizers and Amend- than conventional producers. (Gliessman
ments et al., 1996) growth of the plants and reduced irrigation
frequency compared to clear plastic mulch.
Alternative Soil Raised Bed Plasticulture. Organic and There is a plastic mulch on the market that
Amendments conventional growers in California and Flor- selectively permits soil-warming radiation
Worms for Compost- ida, where most of the nation’s strawberries to penetrate while eliminating the light that
ing (Vermicompost- are produced, tend to favor this system. promotes weed growth. This type of plastic
ing) They grow plants as annuals, transplanting is preferred by growers in the southeast.
Overview of Cover
strawberry crowns in the late summer or
early fall. Production starts in the late win- Raised beds provide good drainage. Since
Crops and Green
ter and continues through the summer and they make the flowers and fruit easier to see
Manures
into late fall, depending on the area and and reach, raised beds also help growers
Biointensive Inte-
the varieties grown. Since methyl bromide to forecast yields, while making harvesting
grated Pest Manage- easier and faster. Some growers dig deep
ment is not allowed in organic production, crop
rotation, green manure crops and compost furrows between the beds so that harvest-
Farmscaping to ers do not have to stoop so low to search
are critical to control soil-borne diseases
Enhance Biological for fruit. In cold climates, plants in raised
Control and pests.
beds may be prone to freeze damage. Still,
Two types of raised beds are used in these raised beds usually out-produce flat beds.
intensive systems. Narrow beds have two Due to of increased aeration and protection
Page 2 ATTRA Strawberries: Organic Production

3. Plasticulture, Sustainability, and Organic Farming
Plasticulture is not without its serious critics. The plastic has to come from somewhere, and it has to be discarded at the end
of the one- to three-year production cycle. Clearly, critics say, this is not an environmentally sustainable system. And, says
Cornell University fruit researcher Marvin Pritts, PhD, if you consider all the environmental costs to society, plasticulture is also
not economically sustainable in the long run. Pritts also points out that even more plastic—in the form of row covers, tunnels,
hoop houses, etc.—is needed to make the system work in cold climates.
USDA researchers have shown that fields mulched with plastic cause four times more water runoff than fields mulched with
organic materials. Due to this high rate of runoff, fields mulched with plastic suffer up to fifteen times more soil erosion than
fields mulched with organic matter. (Anon., 1999c) Planting grasses or other types of vegetation alongside drainage ditches
can reduce the rate of erosion and provide habitat for beneficial insects.
Yet, even organic growers—especially those in California, where plasticulture has reigned the longest—are buying into the
plasticulture production model. Why? The answer is weeds. Strawberries are notoriously prone to weed encroachment
with resultant loss of productivity. Plasticulture provides good to excellent weed control without herbicides. The National
Organic Program (NOP) states that plastic or other synthetic mulches are allowed in organic production, provided that they
are removed from the field at the end of the growing or harvest season.
Pritts admits that implementing some of these ideas requires well-informed and committed management. Moreover, produc-
tion in each locale may require fine-tuning to get the right mix of groundcovers and timing for planting, mowing, and other
manipulations. This is probably not going to be as easy as rolling out the plastic sheeting. Nevertheless, using small amounts
of post-emergent herbicide, though not allowed in organic production, may be more sustainable than the continued use of
tons upon tons of non-renewable, non-recyclable plastic mulch. Corn- and soybean-based biodegradable plastics are being
developed, but it will be a while before a sturdy and durable biodegradable plastic capable of withstanding solar radiation,
moisture, and equipment is available for strawberry production. Synthetic biodegradable polymers are being developed,
but since they are synthetic, it seems unlikely they will be allowed in organic production any time soon.
from splashing soil particles, plants in plas- for their area. Otherwise, a complimentary
tic-mulched raised beds have less disease. copy of Nourse Farms Success with Plasti-
Machinery is available to shape the bed, culture can be obtained by calling Nourse
lay out the irrigation line, and cover the Farms at 413-665-2658.
bed with plastic mulch all in a single pass. Matted Row System. In this system the
Sources of bed-shapers and transplanters crowns are planted in early spring. As the
are listed in the ATTRA publication Sea-
plants produce flowers, the blossoms are
son Extension Techniques for Market Gar-
deners. Or check the following web pages: removed to encourage runner (or daughter
www.mechanicaltransplanter.com/layer.html plant) production. The daughters root on
www.marketfarm.com/cfms/mulch_layers.cfm the bed and produce a crop the following
spring. Weeds can be a problem in this
Recent research indicates that any variety system, and dead leaves and other debris
that normally does well in a specific region
must be removed to reduce disease and pest
will do well when grown using plasticul-
ture in that region. (Nourse, 1999) How- problems. However, once established, this
ever, some of the cultivars that come from system can produce for three to four years,
the California and Florida systems perform depending on pest pressure. The distance
best at a 12- to 14-inch spacing, while many between plants is 18 to 24 inches, and the
northern cultivars do best at an 8- to 10- distance between the rows varies from 36
inch spacing. to 50 inches, depending on the cultiva-
By now, growers and researchers in many tion equipment used. According to Marvin
states have adapted and validated at least Pritts of Cornell University, the matted row
parts of the production model described system offers northern strawberry growers
above. Growers should check with their a low-risk system that requires less focus
state Extension Fruit Specialist to see if spe- and time than annual plasticulture systems
cific plasticulture guidelines are available (Pritts, 2002).
www.attra.ncat.org ATTRA Page 3

4. Researchers at the USDA Agricultural stimulate flower formation and to increase
Research Service (ARS) in Maryland fruit size. At the end of the second sea-
have developed a “modified or advanced” son the planting can be changed to the mat-
matted row system to address weed and ted row system by letting the runners fill in
pathogenic pests. This system uses matted empty spaces on the beds.
row-type culture established on raised beds
with subsurface drip irrigation and organic Varieties
mulch. The mulch consists of a mixture of
hairy vetch (45 kg/hectare [40.1 lb/acre]), Selection of appropriate varieties is impor-
rye (78 kg/hectare [69.6 lb/a]), and crim- tant. Besides determining yields and qual-
son clover (34 kg/hectare [30.3 lb/acre]) ity, the variety also determines production
that fixes some nitrogen and provides an seasons and pest-control practices. Your
economical, biodegradable mulch for sup- county extension agent can usually rec-
Strawberry seeds. Photo
courtesy of USDA/ARS pressing weeds and diseases, and reducing ommend varieties that have been shown to
erosion. The organic mulch is cut or rolled respond well to the area’s climatic condi-
down in April and two weeks later the bare tions. However, variety trials are usually
root strawberry plants are planted through conducted utilizing conventional production
the layer. systems. The variety’s performance may be
different in an organic system. Therefore,
Since 1996, the small-fruit breeding pro- organic growers are advised to plant more
gram has conducted replicated performance than one of the recommended varieties and
trials on both the advanced matted row sys- conduct their own variety trials. Other
tem and a regional adaptation of annual hill organic growers in your area may also be
plasticulture. Both of these systems were able to advise you.
managed without methyl bromide fumiga-
tion or fungicide application. Data from Strawberry varieties are classified as
these trials were used to compare advanced either “June-bearing” or “Everbear-
matted row and plasticulture for yield, fruit ing.” June-bearing or short-day variet-
quality, and length of harvest season. Yield ies start forming flower buds as the day-
for the two systems was variety-dependent, length gets shorter and temperatures get
and the advanced matted row system had cooler. Everbearing or day-neutral variet-
later production and slightly ies are insensitive to day length and pro-
lower fruit quality. (Black duce fruit throughout the season as long as
et al., 2002) night-time temperatures drop below 60° F.
(Strand, 1993)
Ribbon Row System. This
system can employ high-den- Trials conducted in the northeast comparing
sity or low-density planting on strawberry varieties under conventional and
a single row. With low-density organic management systems demonstrated
planting, the spacing is 12 to that the “Honeoye” variety was the most
36 inches between rows and 14 productive in terms of numbers and weight
to 18 inches between plants. of harvested fruit and most profitable for
With high-density planting, organic producers. (Rhainds et al., 2002)
the distance between the rows
is the same but the distance See Appendix B for a list of recommended
between plants varies between strawberry varieties.
4 and 12 inches. The crowns
are planted in the fall. Once Fertility
they start blooming, the flow- ATTRA’s Overview of Organic Fruit Produc-
ers are not removed, and fruit tion covers organic fertility management in
Strawberries. Photo courtesy of USDA/ is produced in the first sea- a general way. However, there are at least
ARS
son. Runners are removed to two aspects of strawberry production that
Page 4 ATTRA Strawberries: Organic Production

5. are unique and distinct from other peren- weeds and will provide important long-
nial fruits with respect to fertility. term improvements in soil fertility and soil
organic matter. In areas such as coastal
June-bearing strawberries set buds for
California, long growing seasons and high
the following year’s fruit in the fall. (Most
land rents may make the extended use of
perennial fruit crops set their fruit buds in
cover crops uneconomical. However, many
the spring or early summer.) To get a good
bud set, the plants must have adequate growers believe that the long-term benefits
chilling and not be nutritionally stressed. of cover crops and rotations to soil fertility
Therefore, fertilizer applications are usu- and pest and disease suppression are worth
ally warranted in the late summer, giving the cost.
the organic fertilizer material enough time Compost can be used as a supplement or
to break down and provide nutrients for the alternative. Spreading and incorporat-
plants during the crucial fall bud-set. ing the compost on the beds only, avoiding
Timing is critical in supplying nitrogen to the furrows, will help concentrate fertility
berry crops and the nitrogen release rates and microorganisms where they are most
for organic fertilizers may not match the needed. Compost application rates vary
nitrogen needs of the crop. A study on from 10 tons/acre to 3 tons/acre. Sup-
plemental fertigation is necessary to carry Related ATTRA
organic fertilizers in California found great Publications
variability in the nitrogen availability of dif- the plants through the production season:
Research from Ohio has shown that vermi- Bug Vacuums for
ferent sources of fertilizers. (Gaskell, 2004) Organic Crop Protec-
These included guano, feather meal, liquid compost (compost made from earthworm tion
fish emulsion, fish meal, pelleted chicken waste) applications increased strawberry
growth and yields significantly. (Arancon et Sustainable Manage-
manure, compost, and a green manure ment of Soil-Borne
crop. Initially, the soil nitrate nitrogen from al., 2004) These responses seemed not to
Plant Diseases
the green manure crop and compost kept be dose-dependent. Strawberries at one site
the level of nitrogen at adequate amounts grew fastest and yielded most in response Notes on Compost
to the 10 ton/hectare (4.05 ton/acre) ver- Teas
(50 to 75 ppm) for three to four weeks and
then declined to background soil levels micompost application rate, whereas straw- Use of Baking Soda as
below 10 ppm. berries responded positively and similarly a Fungicide
to both the 5 ton/hectare (2.02 ton/acre) Direct Marketing
Supplemental fertilizing is therefore neces- and 10 ton/hectare rates of application at
sary to carry the crop through the season. another site. These responses could not Farmers’ Markets
Strawberry producers using the annual have been mediated by the availability of Community
plasticulture system must rely on soluble macronutrients, since all plots were supple- Supported
organic fertilizers applied through drip mented with inorganic fertilizers to equal- Agriculture
irrigation lines. Farmers using these sys- ize macronutrient inputs for all treatments. Selling to Restaurants
tems must face solubility and the capac- Based on other research in the laboratory,
ity of these products to be filtered through however, the responses could have been due Entertainment Farm-
fine mesh without plugging drip emitters. ing and Agri-Tourism
to production of plant growth regulators by
Products injected into the system may not microorganisms during vermicomposting. Organic Marketing
emerge at the same concentration. In other Resources
systems, foliar or side-dress applications The foliar application of aerobically-pre-
will be warranted. pared compost tea increased yields in a
British Columbia study. (Welke, 2004)
While all perennial fruit crops will bene-
Besides reducing incidences of Botrytis, the
fit from the fertility provided by pre-plant
compost tea treatment increased yields in
cover-cropping and green-manuring, straw-
strawberries by 20 percent compared to the
berries are so prone to weed problems that
control and water sprays.
pre-plant preparations to reduce weed pres-
sure are practically mandatory in organic For more information on organic fertilizers,
production. A thick cover crop of a grass/ vermicomposting, compost and cover crops,
legume mix will help to smother out many request these ATTRA publications: Sources
www.attra.ncat.org ATTRA Page 5

6. of Organic Fertilizers and Amendments, rotations. That is, a bed may be allowed
Alternative Soil Amendments, Worms for to fruit for two seasons before it is turned
Composting (Vermicomposting), and Overview under and replanted to a cover crop.
of Cover Crops and Green Manures.
A weed competition study in a mature
matted row planting was conducted over
Weed Control a three-year period by Marvin Pritts and
Weeds are one of the biggest problems Mary Jo Kelly of Cornell University (2004).
that organic strawberry growers face. Pre- The impact of weeds on subsequent produc-
plant site preparation is critical. Refer to tivity was determined. Plants in the weed-
ATTRA’s Overview of Organic Fruit Produc- free plots had the highest yield, while sea-
tion for site preparation strategies as well as son-long uncontrolled weed growth reduced
for basic weed-control ideas. productivity by 51 percent. However,
plants in several plots with a limited amount
Cultural Methods of weed competition had higher yields than
Organic growers will find that some hand those in the continuously weeded controls.
weeding is necessary. Weeds in organic This indicates that plants from a well-estab-
E
uropean plasticulture systems can become trouble- lished matted row planting may be tolerant
strawberry some even where black plastic mulch is to a limited amount of weed competition for
used. In such situations, the weeds emerge at least two years. Growers should direct
growers and
from the planting holes made for the straw- a majority of their efforts and resources
researchers have led towards controlling weeds in the planting
berry plants. The rows must be straight and
the way in innova- the plastic laid precisely to allow mechani- year. Once the planting is well established,
tions and research cal cultivation of the furrows without dam- growers may limit the number of times they
involving mechani- aging the beds and plastic. hand weed to two or three per season.
cal weed control in A variety of colored mulches have been Planters’ paper, a black paper mulch, was
strawberries. studied in California to determine their con- used in matted rows for a biodegradable
tribution to weed control and crop response. mulch study. (Weber, 2003) It reduced
Black mulch provides the best weed con- weeds but degraded quickly along the edges
trol but does not warm the soil as well as where it was covered by soil, allowing the
clear plastic. Soil warming with clear plas- wind to tear and blow large pieces off the
tic results in plants that grow and produce plots. The rate of degradation the first year
earlier in the season, but weeds are not con- was quick but the paper still reduced weed
trolled. Research determined that the effect population compared to clear mulch and
of mulch color on transmittance of photo- the control.
synthetically-active light (400 to 700 mm)
through mulches was the key weed-con- Mechanical Methods
trol factor. (Johnson and Fenimore, 2005) European strawberry growers and research-
Green and brown plastic mulches provided ers have led the way in innovations and
the best combination of soil warming and research involving mechanical weed con-
weed control benefits at all trial locations. trol in strawberries. Recent research in the
The matted row system (where plants from U.S. has confirmed the usefulness of the
runners form a 6- to 30-inch-wide solid bed) flex-tine harrow, the brush hoe, and the fin-
is commonly used by strawberry growers ger weeder for weeding strawberry plant-
in many regions of the U.S. This method ings. (Pritts and Kelly, 1999) For instance,
precludes mechanical cultivation for weed the brush hoe required only three passes
control within the bed, though cultivation per season plus two hand weedings for com-
is commonly used to renovate or narrow a plete weed control, compared to standard
bed. Weed problems tend to increase with cultivation with a rototiller, which required
the age of the planting. Many organic grow- three passes and four hand weedings. Visit
ers have therefore chosen shorter fruiting the European Weed Research Society’s
Page 6 ATTRA Strawberries: Organic Production

7. Physical Weed Control Web page www. habitat for spiders and has been known to
ewrs.org/pwc/glossary.htm for more informa- reduce diseases. A study in Ohio showed
tion on these and other mechanical cultiva- that straw mulch between strawberry rows
tion tools. In plasticulture systems, harvest was equally or more effective than fungi-
crews are sometimes used to weed when the cides for controlling leather rot (Phytoph-
weed pressure is high or when the harvest thora cactorum). (Ellis et al., 1998)
day is short. Research in West Virginia indicates that
shredded or chopped newsprint makes an
Biological Methods excellent and safe mulch. (Baniecki et al.,
Before the widespread adoption of herbi- 1995) It can be applied over the top of
cides, geese were commonly used for weed the plants at the onset of winter, just like
control in commercial-scale strawberry pro- straw. It should be applied in a layer 4 to
duction. In areas of concentrated crop pro- 5 inches thick (this will require about 500
duction, farmers often had the benefit of to 600 pounds of chopped paper per 1,000
weeder-geese services for hire. Weeder square feet), and will be subject to being
geese can still be used to control grasses windblown until it is stabilized by rain or
S
and a few broadleaf weeds, but close man- overhead irrigation. Only newspaper or trawberry
agement of the geese is essential. Not every other recycled paper, without glossy or col-
ored inks, may be used as mulch under the plants, espe-
farmer will find the extra requirements
National Organic Program standards. cially in the
suitable to his or her management regi-
men. The extra work may be offset to some North, are com-
Woolen landscaping fabric was the best
degree by on-farm consumption of the geese alternative treatment in a study conducted monly mulched with
or by sales of geese and their products. In in Minnesota. (Forcella et al., 2003) A straw over the win-
any case, the geese must be removed before one-ply woolen fabric centered over the crop ter to minimize cold
fruiting season, because they will eat straw- nearly eliminated weeds from rows, pro- damage.
berries before going after grass. moted daughter plant rooting, and allowed
Under the National Organic Program (NOP), maximum fruit yield equivalent to that
raw animal manure must be composted obtained in plots that were hand weeded.
unless it is incorporated into the soil not Cornell small-fruit researchers Marvin Pritts
less than 120 days prior to harvest of a crop and Mary Jo Kelly have worked extensively
whose edible portion has direct contact with with cover crops for weed suppression in
the soil surface or soil particles. Therefore, strawberries. They have tried several spe-
geese would need to be removed from the cies—including tall fescue, marigold, buck-
field and their manure incorporated at least wheat, and ryegrass—but sudangrass has
four months prior to the beginning of straw- the most desirable characteristics: rapid
berry harvest. ATTRA has more informa- establishment, low water use, low nutri-
tion on the proper management of weeder ent use, and competitive displacement of
geese available on request. weeds. Their research suggests that inter-
seeding sudangrass between beds and mow-
Organic Mulches ing it twice a year provides acceptable weed
Strawberry plants, especially in the North, control without herbicides, especially when
are commonly mulched with straw over the used in conjunction with a winter straw
winter to minimize cold damage. In the mulch. However, a later study found that a
spring, the straw is raked into the aisles sorghum-Sudan grass hybrid “killed” cover
crop suppressed pathogens and weeds but
where it provides some control of weeds and
adversely affected strawberry growth and
helps to keep the berries clean. Caution
yields. (LaMondia et al., 2002)
must be taken with some organic mulches
in that they may harbor pests like snails, See the Matted Row System section above
slugs, cutworms, earwigs, and sow bugs. for information on a USDA study using a
On the other hand, straw provides excellent killed cover crop mulch (hairy vetch, rye,
www.attra.ncat.org ATTRA Page 7

8. crimson clover) to suppress weeds and of the acidic solution degrading the leaf’s
reduce erosion. waxy cuticle layer, causing desiccation.
The thicker the cuticle layer on the weeds,
In USDA zones 6 and colder, another option
the more frequent the applications or the
is to plant spring oats in the fall. Freez-
more concentrated the solution should be.
ing weather will kill the oats, leaving a nice
If preparing a homemade solution of vin-
mulch. Yet another option is to plant sor-
egar herbicide, include citrus oil or lemon
ghum-Sudan grass in the late summer; it is
juice along with a small amount of liquid
not at all cold tolerant, and will be killed
soap as a surfactant. Some commercial for-
by the first frost. For information on the
mulations are Alldown™ (SommerSet Prod-
USDA’s hardiness zones, check the Web
ucts, www.sumrset.com) and Ground Force™
site www.usna.usda.gov/Hardzone/ushzmap.
html. (Abby Laboratories, www.abbylabs.com).
The Organic Materials Review Institute
Thermal Controls (OMRI) lists vinegar and clove oil herbicides
Thermal technology, from flamers to infra- as restricted, meaning the need for and
red burners, keeps evolving with new prod- use of these herbicides must be explained
T
iming is ucts emerging onto the market. At present, in the Organic System Plan. Essential oil
thermal control methods include handheld herbicides (clove, thyme, and mint oils)
critical for contain phytotoxic compounds that have
successful flamers, mounted row crop flamers, infrared
weeders, steamers, hot water, and hot foam. been reported to kill grasses and broad-
thermal control of
Timing is critical for successful thermal leaf weeds. Commercial products include
weeds. The younger control of weeds. The younger the weed, Xpress™ (Bio HumaNetics, www.biohuma-
the weed, the easier the easier it is to desiccate. Grasses can netics.com) which is a formulation of thyme
be burned back but the growing point usu- (10.4 percent) and clove (10.1 percent) oils
it is to desiccate.
ally sends out new growth. Some of these and Matran 2™ which is 45.6 percent clove
devices may not fit in a particular system oil. According to the manufacturer, the
but others may be successful components of addition of the yucca extract ThermX 70
a weed control program. (0.3 fl. oz. /gallon) with fulvic acid (6 fl. oz./
gallon) to Matran 2™ significantly enhances
For a list of thermal devices for weed con- its coverage and performance. Matran 2™
trol, see Appendix A. is also used in combination with vinegar.
Be careful when spraying weeds and keep
Vinegar and Essential the sprays off strawberry plants. Also care
Oil Herbicides needs to be taken to avoid contact or inhala-
tion, as the high acid content will burn skin
The use of vinegar for weed control has and lung tissue. For more information on
been the least-toxic choice of many home vinegar as an herbicide, check the USDA
gardeners. Its effectiveness varies, depend- Web site www.ars.usda.gov/Services/docs.
ing on the type of weeds sprayed and the
htm?docid=9666.
concentration of acetic acid. Most vinegar
available commercially is 5 percent acetic
acid. Through distillation, the concentra- Woven Synthetic Fabric Mulches
tion can increase to 15 percent and by other Synthetic fabric mulches (trade names:
non-synthetic processes to 30 percent acetic Weed Lock, Weed Barrier, Weed Stopper,
acid. Caution must be taken with formula- etc.) offer some of the same weed suppres-
tions greater than 5 percent. Though there sion as regular plastic mulches, but have
are more concentrated solutions of acetic the advantage of being water- and air-per-
acid that are derived synthetically, these meable. Though initially more expensive
types are not allowed in organic production than regular plastic, the higher-quality
systems. Some commercial formulations grades of fabric mulch can be used year
of vinegar herbicide include lemon juice after year. These woven mulches are used
or citrus oil. The mode of action consists in essentially the same way as plastics in the
Page 8 ATTRA Strawberries: Organic Production

9. systems described above. However, because White Grubs
they are water-permeable, it should not be
Primarily a problem in the eastern U.S.,
necessary to add irrigation lines under the white grubs can cause serious damage if
mulches in areas with adequate rainfall. strawberries are planted immediately after
a sod crop. White grubs are the larvae of
Insect and Mite Control May and June beetles and other beetles in
Numerous insects feed on strawberry plants Scarabaeidae. Late-summer or early-fall
and threaten yields. Extension Service spe- plowing destroys many larvae, pupae, and
cialists are familiar with pests common to adults in the soil and also exposes these
specific areas and can help with proper stages to predators. The milky-spore-dis-
identification, which is the first step in pest ease bacteria, Bacillus popillae and Bacillus
management. A scouting program with reg- lentimorbus, are important natural enemies
ular monitoring can help growers determine of Scarab beetles. Grubs ingest spores of
both the pest pressure and presence of ben- these bacteria on the thatch or roots of the
eficial insects. Once pest pressure reaches grasses they eat. The spores then germinate
the economic threshold, control actions and the bacteria multiply inside the grubs,
C
are necessary. If biological controls are which die and disintegrate, leaving many
ommon
to be used, they must be deployed before new, viable spores to spread the disease to
succeeding generations. (Daar, 1988) strawberry
the pests reach critical levels. That is why
monitoring is so important. In large opera- pests include
Beneficial nematodes are also effective
tions, where harvest crews are used regu- white grubs, straw-
against soil-dwelling grubs. Steinernema
larly, training the crew foreman to identify carpocapsae will infect its host near the soil berry weevils, straw-
insect pests and diseases can help in the surface while Heterorhabditus bacteriophora berry rootworms,
monitoring process. actively searches for its host below the soil caterpillar worms,
Beneficial-insect habitats planted along- surface. (Flint and Dreistadt, 1998) These lygus bugs, and spi-
side strawberry fields provide shelter, pol- nematodes and milky-spore bacteria are
der mites.
len, and nectar sources to predators and widely available through mail-order garden
parasites of insect pests. Beneficial insects supply companies.
are able to take refuge in the habitat when
fields are treated with a pesticide. When Strawberry Clipper (Strawberry
purchased beneficial insects are released, Bud Weevil)
these habitats encourage the beneficials to The strawberry clipper or bud weevil,
remain and continue their lifecycles, help- Anthonomus signatus, occurs only east of the
ing reduce pest populations. Some pests Rockies. Adult beetles emerge in the early
may also inhabit the refuge along with spring, lay eggs in the buds, and then cut
beneficials, so it is important to monitor partly through the stem, causing strawberry
these habitats: For additional informa- buds to fall over or fall to the ground.
tion, request ATTRA’s Biointensive Inte-
grated Pest Management and Farmscaping Contrasting studies on strawberry clip-
to Enhance Biological Control. per or bud weevil have been conducted.
One study found that most of the 12 vari-
Although pest problems vary with location, eties studied compensated for a significant
common strawberry pests include white amount of flower bud loss, provided that
grubs, strawberry weevils, strawberry root- the loss occurs early in the development of
worms, caterpillar worms, lygus bugs, and the inflorescence. (Pritts et al., 1999) A
spider mites. For more detailed information later study showed that liberal thresholds
on the pests themselves, refer to the publi- developed from the previous studies were
cations listed in the Further Resources exceeded in two of the three research sites
section below (see especially the publica- and damage levels were severe enough to
tions by Funt et al., 1997, Kovach et al., reduce yields significantly. (Handley et al.,
1990, Maas, 1987, and Strand, 1993). 2002) The clipper moves at the very slow
www.attra.ncat.org ATTRA Page 9

10. rate of 30 feet per season. In a new plant- attack from ground beetles and from par-
ing, it is unlikely that the damage would asitic nematodes such as Steinernema or
extend more than 30 feet from the perime- Heterorhabditus species. The root weevils
ter into the plot. Damage may be somewhat are crawling insects that also have been
more extensive in older plantings, but still excluded from fields by fences, trenches
limited by the rate of movement of the clip- and barriers like sticky tape. (Bomford and
pers (they will have moved approximately Vernon, 2005; Strand, 1993)
60 feet into a two-year planting and 90 feet
into a three-year planting). Organic growers Lygus Bugs
should destroy damaged buds, which con-
tain eggs, eliminate trash and nearby foli- The tarnished plant bug or lygus bug (pri-
age that provide hibernation sites for adult marily Lygus lineolaris in the East and L.
weevils, and apply an organically approved hesperus in the West) can be troublesome,
insecticide as a last resort. especially in plantings of day-neutral vari-
eties which fruit throughout the growing
season. Adults and nymphs (the nymphs
Strawberry Rootworm cause the most damage) suck sap from the
Strawberry rootworm (Paria fragariae) plant and inject a toxic saliva. This feed-
adults feed mainly at night, making holes ing results in a characteristic deformation of
in the leaves. The larvae feed on fine the fruits called cat-facing, which makes the
roots and eat the crowns close to the berries unusable and unmarketable.
ground. Cultural control consists of
plowing infested fields after harvest and
setting new plantings away from woods
(favorable hibernation sites) and from older
strawberry plantings.
Apparently, IPM damage thresholds have
not been established for the rootworm. If
the grower feels that pesticide treatment
is necessary based on scouting, nocturnal
treatment should be aimed at the foliar-
feeding adults, since there are no effective
or registered insecticides available for con-
trol of the larvae. Soil-dwelling predators
such as ground beetles or insect-attacking
nematodes like Steinernema species may Lygus bug. Photo courtesy of USDA/ARS
provide some control. Keeping any groundcover well clipped for a
distance of five to ten yards around a straw-
Strawberry Root Weevil berry field, and otherwise destroying places
The adults of these species feed mostly on favorable for hibernation, may help reduce
leaves, causing minor damage. The larval lygus-bug populations. Adult lygus bugs
stage is the problem, as the larvae feed on hibernate under leaves, stones, and bark.
roots and crowns of the strawberry plants. They usually lay eggs in the stems of her-
Root weevils have many alternate hosts baceous cultivated plants and broadleaf
including other small fruits, cranberries, weeds. Legumes (vetches, clovers, alfalfa,
grapes, mint, hops and many ornamental etc.) can harbor large populations of these
plants. Rotation with nonhost crops like pests. This must be considered if beneficial
corn, wheat, clover, and alfalfa can reduce habitats using these plants are established
populations. (Berry, 1998) near strawberry plantings.
Like other ground-dwelling pests, Straw- Trap crops are also useful in lygus bug
berry Root Weevils are susceptible to management. In California, an annual trap
Page 10 ATTRA Strawberries: Organic Production

11. crop mix of one dormant and one semi-dor- A fungus, Beauveria bassiana, has some
mant alfalfa variety, two radish varieties efficacy against lygus bugs. In New York,
(Daikon and Cherry Belle) and sweet alys- three years of tests concluded that the com-
sum has been used with success. Lygus mercial formulation of B. bassiana, Myco-
bugs move in from surrounding fields and trol™, reduced lygus damage about 50 per-
settle on the trap crops, which can then cent compared to untreated controls, but
be treated with insecticides or vacuumed. was still considerably less effective than
(Dufour, 2000) Bug vacs range from trac- synthetic insecticides such as malathion.
tor-mounted machines to small hand-held (Kovach and English-Loeb, 1997) Myco-
devices and are actually vacuum cleaners trol™ worked best when targeted at younger
for pests. A trial by University of Califor- nymphs and when humidity levels were
nia researchers concluded that three similar adequate. In combination with other cul-
grower-designed vacuum machines reduced tural controls (choosing the right cultivar
lygus bug damage compared to untreated and close mowing near the planting), use of
controls, but were not equal to chemical Mycotrol O™ (Laverlam Intl.), Botanagard
control with a pyrethroid insecticide. The (Laverlam Intl.) or Naturalis (Troy Biosci-
damage, though reduced, was still consid- ences) could be of help to organic growers
S
ered economically unacceptable. (Pickel et in controlling lygus. ince lygus
al., 1995) Research done in Watsonville, nymphs are
While the lygus bug has several natural
California, demonstrated that lygus bugs most trouble-
insect enemies, none of the native ones has
were more attracted to a field-edge alfalfa
proved consistently effective in providing some, aim scouting
trap crop than to a radish/mustard or straw-
a commercial level of control in strawber- efforts at this life
berry row. (Swezey, 2004a) Vacuuming
ries. A small (1/8th-inch) wasp, Peristenus stage. Start check-
the alfalfa trap crop with a tractor-mounted
digoneutis, was introduced from Europe in
bug vac reduced damage due to lygus bug ing for nymphs as
1984 and has exhibited excellent control
feeding in associated strawberry rows when soon as flowers
potential. However, this nymphal parasitoid
compared to vacuuming the whole field. appear.
is difficult to rear, and is not commercially
available. While it is spreading naturally
in the northeastern U.S., it has not moved
south of latitude 41°N (New York City).
(Day et al., 1990) In California, Periste-
nus digoneutis and P. stygicus were released
in 1998. They have become established
and annual increases in parasitism were
noted in 2000-2002. (Fuester et al., 2004)
Higher rates of parasitism by P. digoneutis
were observed in New York on organic or
casually sprayed farms than on intensively
Bug vacuum. Photo courtesy of USDA/ARS treated farms. (Tilmon and Hoffmann,
This saved operating costs of the bug 2003) Anaphes ioles is a lygus egg parasit-
vac and increased marketable fruit. For oid that has been used in California and in
more information on Bug Vacs, see the other states with some success. Research-
ATTRA publication Bug Vacuums for ers who released 15,000 A. iole weekly on
Organic Crop Protection. one-acre strawberry plots observed a 64
percent suppression of Lygus hesperus com-
Research conducted in New England found
pared to a 44.7 percent reduction achieved
variation in susceptibility to the lygus bug
with a pesticide application. (Udayagiri
among 20 strawberry cultivars. (Handley
et al., 2000)
et al., 1991) Honeoye, Sparkle, Veestar,
and Canoga suffered the least from feeding, Since lygus nymphs are most troublesome,
while Kent, MicMac, Scott, Blomidon, and aim scouting efforts at this life stage. Start
Redchief suffered most. checking for nymphs as soon as flowers
www.attra.ncat.org ATTRA Page 11

12. appear. Tap 10 to 15 flower clusters over a two-spotted spider mite, Pacific spider mite,
white plastic saucer so that the bright green and strawberry spider mite, among others.
nymphs can be seen and counted. Deter- These plant-feeding mites consume juices
mine the average number of nymphs per from strawberry leaves. Large populations
cluster (total number of nymphs divided can reduce photosynthetic capacity, result-
by total number of clusters). If sampling ing in weakened plants and reduced fruit
is concentrated near weedy borders, the yields. Some growers who do not often
action threshold is 1 nymph per cluster, but use botanical pesticides may see very few
if done randomly throughout the planting, mites—if not reduced by pesticides, the nat-
0.5 nymphs per cluster should be consid- ural enemies of the mites will usually keep
ered adequate to prompt a pesticide treat- them in check. These natural enemies
ment. (Kovach et al., 1993) However, Cor- include other mites such as Phytoseiulus per-
nell researchers caution that growers who similis, Metaseiulus occidentalis, and Neosei-
intend to use the slow-acting biological ulus californicus, and insects like bigeyed
insecticide B. bassiana may need to use a bugs, damsel bugs, minute pirate bugs,
lower threshold. (Kovach and English-Loeb, lacewings, spider mite destroyers, and six-
spotted thrips. Growers can buy some of
A
1997) If other natural enemies of lygus
scouting are present—such as spiders, bigeyed bugs these predators from commercial insecta-
method for (Geocoris species), assassin bugs (Zelus and ries to release on the farm. The predators
two-spot- Sinea species), damsel bugs (Nabis species), can also be attracted and conserved natu-
and lacewing larvae (Chrysoperla species)— rally through the use of insect habitats.
ted spider mites has
been developed in you might want to consider adjusting the Insecticidal soaps, “narrow range” oils,
threshold numbers accordingly. vegetable oils, neem-based products such
British Columbia
as Trilogy®, and sulfur are acceptable miti-
and successfully
cides in organic production (check with
implemented both your certifier regarding specific products).
there and in New Application instruments must thoroughly
York. cover the leaves’ undersides, and products
that are diluted must be applied in high
volumes (more than 100 gallons of water
per acre) to achieve complete coverage.
Both oils and soaps can burn plants if
over-applied or if high temperatures
(greater than 80° F) occur during and
after treatments.
A scouting method for two-spotted spi-
der mites has been developed in British
Columbia and successfully implemented
both there and in New York. (Kovach et al.,
1993) To sample for these mites, walk diag-
onally across the planting while randomly
picking one mature, fully expanded leaflet
from every other row, until 60 leaves are
collected. If 25 percent are infested with
mites (about 5 mites per leaflet), treatment
Parasitic wasp Peristenus digoneutis. Photo courtesy of
may be in order. Again, the number of
USDA/ARS natural enemies should also be considered
when determining a threshold for chemical
Mites treatment. While this scouting method is
The web-spinning spider mites are in the probably applicable to most areas, growers
genus Tetranychus, which includes the outside the New York region should check
Page 12 ATTRA Strawberries: Organic Production

13. with their local Cooperative Extension Ser- If they become a problem, consult your
vice for scouting guidelines. local farm advisor, visit the numerous
websites listed below under Further
Contact Information for Beneficial Resources, or call ATTRA’s toll-free num-
Organisms ber for information.
Companies that sell mites and other beneficial
organisms are listed in the California Environ-
mental Protection Agency’s Department of Pes-
Disease Control
ticide Regulation booklet, Suppliers of Beneficial Diseases in plants occur when a pathogen
Organisms in North America. (Hunter, 1997) An is present, the host is susceptible, and the
online PDF booklet is free online and contains environment is favorable for the disease to
contact information for 142 commercial suppli- develop. Altering any one of these three
ers of the more than 130 beneficial organisms factors may prevent the disease from occur-
that are currently used in biological pest control.
ring. Organisms responsible for plant
It not only indexes the suppliers by the natural
enemies they sell, it also matches the beneficial
diseases include fungi, bacteria, nematodes,
organisms with their target pests. and viruses. If these organisms are pres-
ent, then manipulation of the environment
S
and the host, to make it less susceptible, oil health and
Some of the mites you see when scouting helps manage diseases on strawberries.
management
may be predator mites. You may need a
Soil health and management are the keys are the keys
magnifying glass to distinguish between
for successful control of plant disease. A for successful con-
these beneficial mites and the pest mites.
soil with adequate organic matter can
One key to telling them apart is that the trol of plant disease.
house numerous organisms such as bac-
beneficial predator mites are generally more
teria, fungi, nematodes, protozoa, arthro-
active than the two-spotted mites—they
pods, and earthworms that may suppress
typically move quickly about the leaf sur-
soil-borne pathogens. This disease sup-
face looking for prey. Depending on your
pression is caused by either antagonism,
geographical area and the species involved,
competition for nutrients, or competition for
the recommended ratio of beneficial mites
space around the root (the rhizosphere) and
to pest mites varies, but seems to aver-
induced systemic resistance (ISR) or sys-
age approximately 1:10. That is, if there
temic acquired resistance (SAR) triggered
appears to be at least one beneficial mite
in the plant. Increasing soil organic mat-
for every 10 pest mites, control of the pest
ter by incorporating cover crops or add-
mites will probably be achieved naturally
ing compost and organic fertilizers will
without the intervention of miticidal sprays.
help maintain these beneficial organisms.
Dust that accumulates on the spider mite’s For more information, see the ATTRA
webbing creates an ideal shelter for the publication Sustainable Management of Soil-
mites and their eggs. These little dust Borne Plant Diseases.
“tents” discourage predators and pre-
Rotating strawberries with other crops is
vent the miticide from reaching the mites
a critical factor in organic production and
and their offspring. California growers
many certifying agencies require it as a
commonly water roads, post “slow” signs,
component of the organic system plan.
plant windbreaks and beneficial insect
Crop rotation reduces insect, disease and
habitats, and use fencing to decrease dust in
weed pests, improves soil fertility, improves
strawberry fields.
soil tilth and structure, reduces soil erosion
and improves water management. Cover
Other Pests crops, vegetable crops, legumes, and cereals
Other arthropods that will occasionally are recommended rotation choices. Avoid
reach pest status include aphids, spittle- Solanaceous crops like tomatoes, potatoes,
bugs, whiteflies, Cyclamen mite, various peppers, and eggplant that may harbor dis-
caterpillars, earwigs, and leafhoppers. eases such as Verticillium. Research in
www.attra.ncat.org ATTRA Page 13

14. the Salinas Valley of California found that Elemental copper and sulfur have long been
incorporating broccoli residues reduced Ver- used by conventional and organic growers
ticillium dahliae in the soil and that rotation as pesticides for foliar bacterial diseases
with broccoli may be a feasible approach to and powdery mildew, respectively.
manage Verticillium diseases in susceptible
crops. (Subbarao et al., 1999) Root Rot Complex
Compost teas or extracts and other innova- Soil borne fungi such as Phytophthora,
tive concoctions such as yeast-sugar solu- Pythium, Rhizoctonia species, and Verticil-
tions, sodium bicarbonate (baking soda), lium dahliae are major pathogens that affect
and milk have become popular as foliar strawberries worldwide. In organic produc-
disease preventatives among many organic tion, the cultural methods described above
growers. Compost teas and yeasts intro- —crop rotation, compost application, and
duce non-plant-pathogenic microorganisms solarization—aid in the control of these dis-
and biocontrol agents that compete with eases. Other cultural controls include using
and antagonize disease spores as they try resistant varieties, planting strawberries in
to establish themselves on the host. Baking a pathogen-free, well-drained soil, avoiding
soda works at the chemical level, interfering over-watering, and planting only certified
in spore germination. For more informa- disease-free plants. Some growers inocu-
tion, request ATTRA’s publications Notes late the soil or the plants with a variety of
on Compost Teas and Use of Baking Soda as commercially available biological products
a Fungicide. such as Vesicular Arbuscular Mycorrhizae
Soil Solarization
Imagine harnessing the sun’s energy to destroy your enemies. Like Archimedes—the ancient Greek who used mirrors to con-
centrate sunlight to burn the Roman fleet—farmers can destroy or disable insects, diseases, nematodes, and weeds in the field.
The technique known as solarization consists of laying clear plastic mulch on moist soil. Heat is trapped under the plastic,
raising the soil’s temperature, killing or debilitating pests. Most of the research worldwide has concentrated on hot and arid
areas, but any place with hot summers is a potential site for this system. Usually this soil pasteurization process takes four to
six weeks, but the amount of time depends on many factors such as rain, wind, day length, soil texture, and the quality of the
polyethylene mulch. Ultraviolet-protected plastic is recommended so the mulch can be removed and re-used.
Before solarization, certain types of organic matter, such as compost and residues from Brassica crops such as broccoli and
the mustards, can be added to the soil for “bio-fumigation.” When heated in the solarization process, this organic matter
releases volatile compounds that are toxic to many pests. Before solarization takes place, the land where the crop is to be
seeded or transplanted must be prepared for planting. Beds must be shaped, drip tape installed, and fields leveled. This is
to avoid stirring up the soil after solarization, which would bring fresh pest organisms to the soil surface. Depending on out-
side temperature, intensity of sunlight, and types of pests, soil solarization can provide good pest control 8 to 10 inches deep,
although the best control is generally obtained down to 6 inches.
Special caution: During solarization, drip tape must be buried at least one inch deep to avoid damage from the sun’s rays. In
experiments where the tape was placed on the surface of the bed and then covered with clear plastic, the drip tape was dam-
aged by sunlight that was magnified by water droplets condensing on the underside of the plastic.
Research conducted in southern California and Oregon has demonstrated that solarization has potential as a component in an
integrated pest management program for root diseases in strawberry production. (Hartz et al., 1993; Pinkerton et al., 2002)
Soil Solarization websites
Soil Solarization Home: http://agri3.huji.ac.il/~katan
International Workgroup on Soil Solarization and Integrated Management of Soil-borne Pests: www.uckac.edu/iwgss
Soil Solarization: A Nonchemical Method for Controlling Diseases and Pests:
http://ucce.ucdavis.edu/fi les/filelibrary/40/942.pdf
Page 14 ATTRA Strawberries: Organic Production

15. (VAM) or Arbuscular Mycorrhizae (AM), agents (a yeast and bacterium) resulted in
Trichoderma species (Promot, SoilGard), better suppression of Botrytis and reduced
Streptomyces griseovirdis (Mycostop), and the variability of disease control. (Guetsky
Streptomyces lydicus (Actinovate). et al., 2001)
Although there is not a high level of gray-
Anthracnose mold resistance in any one strawberry cul-
Anthracnose can be very serious, causing tivar, Earliglow is relatively resistant com-
strawberry plants to die out in midsummer. pared to most cultivars. (Turns, 1990)
The disease produces a rust color through-
out the crown and eventually stops the
plants from growing. Symptoms are most
Leaf Spot
noticeable during summer dry spells. Leaf spot diseases—identified by the pres-
ence of spots on strawberry leaves and
Since high soil fertility favors anthracnose, stems—can be caused by the fungi Myco-
little or no fertilizer should be applied sphaerella fragariae, Ramularia tulasnei,
when disease pressure is strong. However,
or Phomopis obscurans, or by the bacte-
resistant cultivars can be grown success-
S
rium Xanthomomas fragaiae. These patho-
fully at much higher fertility levels. (Maas, ome diseases
gens are spread by splashing water and are
1987) Anthracnose is more prevalent in of straw-
the Southeast than elsewhere. Commer- harbored by dead leaves and other plant
debris. Sanitation, as well as the recom- berries are
cial growers in the Southeast should avoid
mendations mentioned above on foliar dis- anthracnose, gray
planting on former strawberry sites and use
locally adapted resistant cultivars. ease preventatives, apply to leaf spot. mold, leaf spot, and
powdery mildew.
Botrytis (gray mold) Please Note
Gray mold, caused by the fungus Botrytis Preventive treatments such as sulfur, copper, or
cinerea, is one of the most common and compost teas applied prior to wet weather are
serious fruit rot diseases. The fungus grows advisable for many diseases like leaf spot, gray
best in cool damp weather, and gray mold mold, and powdery mildew. Also, studies have
can be devastating if rainy weather coin- shown that systems using organic mulches have
cides with harvest, when strawberry fruit is a reduced incidence of soil-borne pathogens.
at its ripest and most susceptible. Pickers
handling infected berries can spread the
infection to healthy berries. Control of gray Powdery Mildew
mold is aided by removing infected debris Powdery mildew is a fungal disease that
from the field and by providing good drain- affects strawberry foliage, flowers, and
age. Infected fruit can be picked off the fruit. Caused by Sphaerotheca macularis,
plants and placed in the furrow as long as its spores prefer intermittently moist condi-
a cultivator can go through the field and tions and will not germinate in free-stand-
bury this fruit. Clean mulch, which keeps ing water. In coastal California strawberry
fruit off the ground, is also highly recom- fields, the practically year-round production
mended. Removing leaves from the field as season, foggy cool nights, and warm days
soon as the harvest season ends can signifi- make the disease a major and very per-
cantly reduce the incidence of gray mold on sistent problem. Sulfur is the most com-
fruit in June of the following year. (Sutton mon control agent on both conventional and
et al., 1988) organic farms. Milk has been used success-
The following biorational products are fully against powdery mildew on cucurbit
available commercially for Botrytis control: crops. (Bettiol, 1999) Sonata™ is an OMRI-
Serenade (Agraquest), Mycostop (Verdera approved commercial formulation of Bacil-
Oy), and Promot (JH Biotech). Research in lus pumilis that is used on strawberries for
Israel found that combining two biocontrol powdery mildew control. Seven-to fourteen
www.attra.ncat.org ATTRA Page 15

16. day application intervals are recommended, Finally, prospective greenhouse growers
depending on disease pressure. should spend some time exploring local
markets (restaurants, groceries, etc.) Off-
Greenhouse Production season greenhouse growers will be compet-
ing with strawberries from California, Mex-
Five factors—light, heat, pollination, pest
ico, Chile, and Florida. Prices will have
control, and economics—make winter straw-
to offset the costs of production, so grow-
berry production in a greenhouse very dif-
ers will have to produce an outstanding
ferent from field production.
product. Cornell researcher Marvin Pritts
Lighting is critical for winter production. found that the break-even price for green-
The day-neutral cultivars (e.g., Tribute and house-grown strawberries was $3/pint.
Tristar) or the short-day types (e.g., Jewel) He reports, however, that a small but sig-
are much easier to grow during the short nificant number of consumers are willing
days of winter than most of the traditional to pay that price for high-quality berries.
June-bearing types. It is difficult and For more detailed information on green-
expensive to get the June-bearing types to house strawberry production, go to www.
fruit out of season. Even with the day-neu-
S
trawber-
hort.cornell.edu/department/faculty/pritts/
tral types, some supplementary lighting will BerryDoc/Berrydoc.htm.
ries must be be necessary to get high-quality fruit.
picked and Supplementary heat will have to be avail- Harvest and Postharvest
handled very care- able (in some cases the lighting will provide Strawberries must be picked and handled
fully. enough heat). While some non-fruiting veg- very carefully. The fruit must be firm, well-
etables (e.g., leafy greens, such as spinach) colored, and free from rot. When harvested
can produce well in unheated greenhouses, at the right time and handled properly,
strawberry plants need about a 68º F day strawberries will remain in good condition
and 54º F night to produce good yields of for many days. Most California- or Florida-
high-quality berries. grown strawberries found in supermarkets
The grower will have to provide pollination. are picked three-quarters ripe to withstand
Bumblebees are probably the best polli- shipping. The color of these strawberries
nators in a greenhouse environment. Two is a full red but the taste is disappointing.
commercial sources, GB Systems (P.O. Box Small-scale growers who pick ripe fruit
300, Locke, NY 13092; 315-497-3129) can easily compete with supermarket
and The Green Spot (93 Priest Rd., Not- berries by offering a tastier, fresher berry
tingham, NH 03290; 603-942-8925) sell to local consumers.
bumblebees and bumblebee nesting boxes. Proper postharvest handling of strawberries
Certain pests (usually the larger ones, is essential. Cooling the berries will remove
e.g., tarnished plant bugs) can be effec- field heat and increase shelf life. Harvest-
tively excluded from greenhouses, but oth- ing early in the day while temperatures
ers, such as mites, aphids, whitefly, thrips, are cool and then pre-cooling the fruit
and fungus gnats are likely to thrive and before shipping will extend the shelf
proliferate. Due to the need for bumble- life significantly.
bees for pollination, controlling these pests Forced-air cooling is the most common
with conventional pesticides is not a good method used on strawberries. The flats
idea. Fortunately, they can be effectively are stacked parallel to each other in a
managed with biological controls, such as cold room with an open space between the
beneficial mites and lacewing larvae. For flats. A tarp is then placed over the top
the details of greenhouse pest management, and ends of the stacked cartons, with a fan
contact ATTRA for our series of publica- located between stacks. The fan pulls cold
tions on greenhouse IPM (or go directly to air between the gaps of the stacked flats,
www.attra.org/attra-pub/gh-ipm.html). removing the field heat from the berries. It
Page 16 ATTRA Strawberries: Organic Production

17. is vital that the fruit be cooled as soon as the Tectrol® system go to the Transfresh
possible. The more the delay between har- web site at www.transfresh.com/index.asp.
vesting and cooling exceeds one hour, the
greater the losses to deterioration. (Kader, Economics
1992) Water loss from strawberries can Strawberries are one of the most popular
be a problem, so it is critical to main- fruits in the U.S. The majority of commer-
tain high humidity in the cooling facility. cial production is in California, Florida,
Avoid wetting the fruit, which can cause Oregon, and Washington. Growers in these
decay problems. states produce 95 percent of reported U.S.
Fresh-market strawberries are usually sold output. Growers in the South, East, and
in pint or quart baskets covered with plas- Midwest generally have small strawberry
tic wrap. However, one-piece molded-plas- acreages located near population centers,
tic containers called “clamshells” are rap- and rely on direct-market sales.
idly replacing this packaging. The time Strawberries are a high-value crop, but they
and labor involved in packing the fruit in also have special production requirements,
the traditional pint-size plastic baskets is a short shelf life, and a brief marketing sea-
S
considerable, because shippers and buyers son. Initial investment in land preparation, trawberries
grade fruit packed in this manner by the irrigation and other equipment can cost are one of the
arrangement of the fruit in the flat. This about $2,000 per acre for a matted row most popular
puts additional burden on the farm worker system (Ernst, 2003) to $10,000 per acre fruits in the U.S.
to pack the fruit correctly. The use of clam- for a plasticulture system. (Karcher, 2002).
shells makes the strawberry pickers’ job a However, plasticulture systems produce ear-
little easier; the wholesalers are not as con- lier and have higher yields—up to double
cerned with the appearance of the fruit the yield of matted row systems. Earlier
pack since it looks uniform with the clear harvest may allow producers to receive the
lid. Many of these clamshells are recycla- higher prices available at the beginning of
ble. A drawback to the clamshells is the the season.
greater difficulty of cooling the fruit. The
holes in the containers are not big enough to Organic strawberries are in high demand
allow for rapid cooling, so extra time in the and this segment of the organic industry
forced-air cooler is necessary. The clam- continues to grow at a rapid pace. Organic
shell containers also hold less fruit than the strawberries now rank sixth among all
pint baskets and are sometimes sold at a California organic fresh commodities,
lower price. If you sell wholesale or directly with over 160 organic strawberry growers
to stores, the buyers may require this type registered with the California Organic Pro-
gram. (Swezey, 2004b).
of packaging.
Continuous cropping of strawberries is not
Wholesale strawberries that are shipped
possible in an organic system that relies
long distances are placed on pallets and
on crop rotations. The production cycle is
are covered by bags that are injected with
shorter (one to two fruiting years) and yields
carbon dioxide after the fruit is thoroughly
are both lower and more variable than in
cooled. This modified-atmosphere process
conventional systems. Labor requirements
is patented by the Transfresh Corporation
may be as much as twice those of a conven-
of Salinas, California and is known as the
tional system. (Pritts and Handley, 1999)
Tectrol® Atmosphere Pallet System. The
Since they face higher costs of production
process extends the shelf life of the fruit,
(Table 1), organic growers must secure a
allowing for transport and marketing. It
premium price in order to make a profit.
is also accepted in organic production. It
should be noted that large volumes need to California research shows that at median
be shipped to make this process economi- organic production levels, profitable organic
cally feasible. For more information on production can begin at an average price of
www.attra.ncat.org ATTRA Page 17