Cauliflower.
Photo courtesy of USDA. |
Abstract
Cole crops and other brassicas are grown throughout the U.S. These
crops are an excellent choice for many organic farmers because of
the variety of crops in this family, their nutritional qualities,
health benefits, compatibility in planting rotations, and pest-suppressive
qualities. This publication covers soils, fertility, planting, irrigation,
pest management, harvesting and marketing.
Table of Contents
Introduction
Brassicaceae (the mustard family, previously Cruciferae or the
crucifers) include many food, forage, ornamental, and weed plants.
The brassicas are classified as “cool season,” meaning
that they are relatively resistant to frost and light freezes. Throughout
the U.S. they are grown in the spring or fall, so that development
takes place when temperatures are cool. The northern Midwest, Pacific
Northwest, and New England produce brassicas in the summer, while
winter production takes place in the Southwest and other Sunbelt
states. California is able to produce brassicas year-round because
of the moderating effect of the cold Pacific current.
Cole crops are a group in Brassicaceae that includes varieties
of the species Brassica oleracea such as broccoli, cabbage, cauliflower,
and Brussels sprouts. Optimal growing temperatures for most cole
crops are 60 to 65°F. (Maynard and Hochmuth,
1997) An important fact to keep in mind is that these plants
are closely related and share similar climatic requirements as well
as pests and diseases. However, though similar, they are not identical.
There may be larger differences between varieties of broccoli than
between broccoli and cauliflower. Many varieties from each group
have been developed so that they vary in pest susceptibility, temperature
tolerances, shape, color, and length of growing season. Check with
other farmers in your area or your Extension agent to see which
varieties are adapted to your local conditions.
The genus and species Brassica oleracea was developed in western
and central Europe from wild species found in the Mediterranean
region. (Nieuwhof, 1969) Brassica rapa, a similar
species developed in Asia, consists of turnips, Chinese cabbage,
bok choi, rapini, canola, and the mustards. Other plants in Brassicaceae
from other genera are: radishes (Raphanus), watercress (Nasturtium),
and horseradish (Armoracia). Nutritionally, brassicas are high in
carotenoids, vitamins C and A, calcium, iron, magnesium, and dietary
fiber. Broccoli and broccoli-seed sprouts in particular contain
high levels of antioxidant sulphoraphanes, which are anticarcinogenic
compounds. The sulphoraphanes are also thought to protect eyes from
the damage caused by UV light that can lead to macular degeneration
(Xiangqun and Talalay, 2004) and to prevent
high blood pressure, heart disease, and stroke. (Lingyun
et al., 2004) Glucosinolates, chemical precursors to sulphoraphines,
form isothiocyanates in the soil. Isothiocyanates are biologically
active compounds that are of considerable interest to farmers because
of their ability to suppress some insects, diseases, nematodes,
and weeds in a process known as biofumigation.
Ornamental crops in the mustard family make up about 50 genera,
including Arabis, Erysimum (Cheiranthus), Hesperis,
Iberis, Lobularia, Lunaria, and Matthiola. (Watson
and Dallwitz, 1992) The number of crops in this family, their
nutritional qualities, health benefits, compatibility in planting
rotations, and pest suppressive qualities make these crops an excellent
choice for many organic farmers.
Table 1 includes the scientific and common
names of members of the mustard family and
lists the plant part eaten.
Table
1. Brassicaceae Food Crops |
Common Name |
Scientific Name |
Plant Part Eaten |
Horseradish |
Armoracia rustica |
Root, leaf, sprouted seed |
Upland cress |
Barbarea verna |
Leaf |
Mustards |
Brassica juncea |
Leaf, stems and seeds |
Rutabaga |
Brassica napus var. napobrassica |
Root, leaf |
Rape |
Brassica napus var. napus |
Leaf, flower stalk |
Kale and collards |
Brassica oleracea var. acephala |
Leaf |
Chinese kale or Chinese broccoli |
Brassica oleracea var. alboglabra |
Leaf, flower stalk |
Cauliflower |
Brassica oleracea var. botrytis |
Immature flower stalk |
Cabbage |
Brassica oleracea var. capitata |
Leaf |
Portuguese cabbage |
Brassica oleracea var. costata |
Leaf and inflorescence |
Brussels sprouts |
Brassica oleracea var. gemmifera |
Axillary bud |
Kohlrabi |
Brassica oleracea var. gongylodes |
Enlarged stem |
Broccoli |
Brassica oleracea var. italica |
Immature flower stalk |
Savoy cabbage |
Brassica oleracea var. sabauda |
Leaf |
Bok choi, Pak choi |
Brassica rapa var. chinensis |
Leaf |
Mizuma |
Brassica rapa var. japonica |
Leaf |
Kotasuma |
Brassica rapa var komatsuma |
Leaf |
Rosette pak choi |
Brassica rapa var. narinosa |
Leaf |
Choi sum, Mock pak choi |
Brassica rapa var. parachinensis |
Leaf |
Chinese cabbage, nappa |
Brassica rapa var. pekinensis |
Leaf |
Turnip |
Brassica rapa var. rapa |
Enlarged root, leaf |
Rapine, Broccoli-raap |
Brassica rapa var. ruvo |
Leaf and young flower stalk |
Arugula |
Eruca vesicaria |
Leaf |
Garden cress |
Lepidium sativum |
Leaf |
Watercress |
Nasturtium officinale |
Leaf |
Radish |
Raphanus sativus Radicula group |
Root |
Daikon |
Raphanus sativus Daikon group |
Root |
White mustard |
Sinapis alba |
Leaf and young flower stalk |
Wasabi |
Wasabia japonica |
Rhizome, shoots |
|
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Organic Production
Organic production of brassica crops, or any commodity, relies
on management techniques that replenish and maintain long-term soil
fertility by optimizing the soil's biological activity. This is
achieved through crop rotation, cover cropping, composting, and
by using organically accepted fertilizer products that feed the
soil while providing plants with nutrients. Besides producing high
quality crops, a healthy, well-balanced soil can help plants develop
natural resistance to insect pests and diseases. When pest controls
are needed, organic farmers manage insects, diseases, weeds, and
other pests with cultural, mechanical, biological, and—as
a last resort—organically accepted biorational and chemical
controls.
In 2002, the USDA implemented the National Organic Standards regulating
organic production nationwide. All farmers and ranchers wishing
to market their products as organic must be certified. An exception
to this requirement is made for farmers who sell less than $5,000
annually. For more information on organic crop production and organic
farm certification, see ATTRA's Organic
Crop Production Overview and Organic
Farm Certification and the National Organic Program.
Back to top
Soil and Fertility
The brassicas are heavy feeders that can grow on a variety of soils
as long as the soils provide adequate nutrients and moisture and
are well drained. The soil is where plant health begins and ends.
A healthy soil will have a greater capacity to moderate the uptake
of fertilizers and will allow a more balanced uptake of nutrients,
creating a healthy plant that is less attractive to pests and more
resistant to pest damage.
Soil components—minerals, air, water, and organic matter—vary
widely depending on geography and climate. The challenge on farmland
is to maintain healthy soils with adequate levels of organic matter.
Healthy soils will demonstrate the following characteristics: good
tilth, good habitat for numerous and diverse microorganisms, absorption
and retention of water, the ability to buffer salts and pH, an “earthy
smell,” resistance to erosion by either wind or water, and
production of healthy crops.
Organic matter is the soil component primarily responsible for
these traits. Organic matter is broken down by soil organisms, creating
humus. Humus in turn provides nutrients to crop plants. Sustainable
soil management maintains soil health and productivity by taking
care of and increasing the soil's organic matter. Cultural practices,
such as the application of manures and compost, using cover crops,
and rotating crops are methods to achieve this. Healthy soil can
be considered a living organism that must be nurtured in order to
sustain its life and productivity.
Throughout their life cycles, brassica crops require particular
nutrients in varying quantities to support optimal growth and reproduction.
Nitrogen is the nutritional element that most cultivated crops need
in the greatest amounts. Plants use it to form proteins, chlorophyll,
protoplasm, and enzymes. In cole crops, it's most important for
overall growth, and adequate amounts are necessary for best yields.
Usually the initial nitrogen available from green manure or compost
is enough, but as the plant develops it may need supplemental nitrogen,
and succeeding crops may also need a nitrogen boost. Organic sources
of supplemental nitrogen include guano, pelleted compost, fish emulsion,
blood meal, feather meal, cottonseed meal, alfalfa meal, and kelp,
and they should be applied as soon as the plants are strong enough
(usually about 6 inches tall) to withstand the side-dressing operation.
The mineralization of nitrogen and its availability to plants varies
greatly, depending on the nitrogen source, the temperature, humidity,
texture of the material, and microbial activity. In a transitional
or newly certified operation, growers should keep records of the
materials they used and how the crops responded to them. Once growers
learn how each material reacts to specific conditions, and as the
soil's organic matter builds, fertility management usually improves.
Composted manure and cover crop residues usually provide enough
phosphorus for brassicas. If additional phosphorus is needed, rock
phosphate may be an option.
Potassium (potash) requirements for cole crops are high. Composted
manures, composted straw and hay (especially animal bedding), granite
dust, material derived from langbeinite, kelp meal, and wood ash
(if not contaminated with colored paper, plastic, or other synthetic
substances) are acceptable sources of potash.
The macronutrients calcium and micronutrients boron, manganese,
molybdenum, and iron are important for cole crop development. Biologically
active soils with adequate organic matter usually supply enough
of these nutrients. Compost and seaweed products are sources of
supplemental micronutrients. For more information on soils and fertilizers
see the ATTRA publications Sustainable
Soil Management, Alternative
Soil Amendments, and Sources
of Organic Fertilizers and Amendments.
Back to top
Planting and Transplanting
Most brassicas are direct-seeded into prepared seedbeds. The optimal
time to plant is when soil temperatures are between 65 and 75°F,
though some varieties can germinate in soils with temperatures as
lowas 45°F and as high as 85°F. (Lorenz
and Maynard, 1980) The seedbed should be pre-irrigated or solarized
to reduce potential weed problems. Seeding machines such as the
ICS vegetable precision planter, Earthway planter, Planet Junior,
and Stanhay planters are suitable for both small and larger scale
operations and can place seed at any desired space. If the bed is
seeded too closely, thinning is necessary to achieve proper spacing.
Good quality seed with a high germination percentage is important
when establishing a direct-seeded stand.
Some crops that have high seed costs, long growing seasons, and
special growing requirements, such as cauliflower and Brussels sprouts,
are usually transplanted from greenhouses to the field. Crops like
cabbage and broccoli can either be direct-seeded or transplanted,
depending on conditions such as season and costs. Direct-seeding
broccoli during mid-summer for a fall crop is less expensive than
using transplants. During late winter, using transplanted broccoli
may open a marketing window for spring production that could be
economically advantageous. Transplanting can overcome some problems,
such as soil crusting and high or low soil temperatures, that can
cause uneven seedling emergence. Factors like these should be taken
into consideration when choosing the type of plant establishment.
Growing transplants requires great experience and skill. Transplants
can be purchased commercially and must be certified organic if they
are used in a certified organic operation. For more information
on transplant production, see the ATTRA publication Plug
and Transplant Production for Organic Systems.
Advantages in using transplants are uniform stand and quality,
efficient use of seed, season extension, reduced weeding costs,
reduced irrigation, shortened cropping period in the field, and
less exposure to pests. Transplants should be free of pests, weather
hardened, and not be long or leggy. Hardening is the process of
gradually acclimating young greenhouse plants to the outside environment.
Most transplants are hardened two weeks before planting in the field.
Transplants should also be well irrigated prior to planting, so
that the plants can survive until they are irrigated in the field.
Also, transplanting should be done during cool weather and with
minimal root disturbance to reduce transplant shock. Transplant
shock is the stress every transplant experiences while adjusting
to its new environment.
In California most cole crops are grown on raised beds, making
cultivation and irrigation easier. Broccoli and cabbage are planted
in 2 rows per 40-inch bed. Broccoli is spaced at 8 inches and cabbage
at 12 inches apart within the row. Cauliflower is usually grown
on a single, narrower row (36 to 38 inches), off center along one
side. As irrigation water evaporates, salts accumulate on the ridge
of the mounded row. The seedlings are planted below the ridge to
avoid salt accumulation in the root zone. Depending on the variety,
cauliflower can also be grown on 2 rows per 40-inch bed, 12 to 14
inches apart.
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Irrigation
Linear or lateral move irrigation system in broccoli.
NCAT photo by Martin Guerena. |
Soil texture, environmental conditions, and crop age are factors
to consider when irrigating any crop. Cole crops are generally shallow-rooted,
with roots ranging from 18 to 24 inches long. Some exceptions to
this are mustard, rutabaga, and turnips, whose roots range from
36 to 48 inches. (Doneen and MacGillivray, 1943)
Chinese cabbage and pak choi have shallow root systems that respond
well to light, frequent irrigations. (Larkcom, 1991)
Essentially, the art of irrigation is applying the right amount
of water to the plants so that they produce an economically viable
crop. Too much water is wasteful and can cause problems with diseases
and weeds. Too little water causes plants to slow their development,
eventually causing stress, pest susceptibility, and lower yields.
So, how much is enough?
A rule of thumb is that vegetables will need about 1 inch of water
per week from rain or supplemental irrigation in order to grow vigorously.
In arid regions about 2 inches are required. (Lorenz
and Maynard, 1980)
Sprinkler irrigation should be used for germinating seeds and establishing
transplants. Once the plants are established, furrow or drip irrigation
is recommended.
Back to top
Organic Integrated
Pest Management
Integrated Pest Management (IPM) is a broad ecological approach
to pest management using a variety of pest control techniques that
target the entire pest complex of a crop ecosystem. Integrated management
of pests ensures high-quality agricultural production in a sustainable,
environmentally safe, and economically sound manner. (Bajwa
and Kogan, 2002)
Soil health is based on soil biology, which is responsible for
the cycling of nutrients. The complex interactions of this biological
community are known as the soil food web. The soil ecosystem is
composed of bacteria, fungi, protozoa, nematodes, algae, arthropods
(insects and mites), and large soil-dwelling mammals like moles,
ground squirrels, and gophers. The photosynthesizers or primary
producers in this system use the sun's energy to convert atmospheric
carbon into sugars. Other organisms feed off these primary producers.
Dead organisms and their byproducts decompose, becoming the soil's
organic matter that stores nutrients and energy. Plants use these
nutrients, preventing them from accumulating in soil and water.
The life cycle of all these organisms improves the condition of
soils by enhancing structure, water-infiltration and water-holding
capacity, and aeration. This results in healthy plants that are
more productive and resistant to pests.
Larry Phelan and his colleagues from Ohio State University found
that fewer corn borer eggs were laid on corn grown in organic soil.
The researchers took soil from an organic farm and from a conventional
farm and repeated the experiment in a greenhouse. They treated each
soil with organic or chemical fertilizers to determine whether the
results were due to short-term nutrient uptake. Again, corn grown
in organic soil had fewer eggs on it, regardless of the fertilizer
that was applied. Modern agricultural methods are not conducive
to maintaining ecological equilibrium because of constant tilling
and synthetic inputs to the soil. During their evolution, plants
obtained nutrients solely from the soil food web. According to Phelan,
it is the slow release of nitrogen in this system that ultimately
causes the corn borer to lay fewer eggs. The plants in the conventional
system were nutritionally out-of-balance, receiving too much nitrogen.
The extra nitrogen formed free amino acids that were not tied up
in proteins, stimulating the insects to feed and deposit eggs.
Another plant protection phenomena attributed to soil microbial
activity is induced and acquired systemic resistance, in which the
plant's immune system is stimulated to resist pest attack. In one
study, the soil fungus Trichoderma hamatum induced systemic
resistance in cucumber against Phytophthora crown rot and
leaf blight. (Khan et al., 2004) The concept
of healthy soils being responsible for plant health has long been
known to organic farmers, and scientists are just starting to document
it.
IPM is based on the following components: pest identification,
monitoring, mechanical and physical controls, cultural controls,
biological controls, and chemical controls. For a detailed description
of integrated pest management concepts, see the ATTRA publication
Biointensive Integrated
Pest Management.
The biological and cultural insect controls for cole crops involve
understanding the ecology of agricultural systems. We invite pest
problems by planting large expanses of a single, susceptible crop.
When there is a diverse farmscape involving many types of plants
and animals, the likelihood of severe insect pest outbreaks diminishes
considerably. That is why farmers must create production methods
that complement natural systems. The use of beneficial insect habitats
along crop field borders increases the presence of beneficial insects.
(Grez and Prado, 2000; White
et al., 1995; Bugg, 1993) These habitats
provide shelter, food (pollen and nectar), and act as refuges that
attract pests' natural enemies to fields. When purchased beneficial
insects are released, these field-edge habitats will encourage the
beneficials to remain and continue their life cycle there, helping
to reduce pest populations. Some pests may also inhabit the field-edge
habitats; therefore, these habitats should be monitored along with
the crop. For additional information, see ATTRA's Farmscaping
to Enhance Biological Control.
Aphids
Cabbage aphid.
Photo by Jack Kelly Clark. Courtesy of UC Statewide IPM Program. |
The cabbage aphid, Brevicoryne brassicae, is a major pest
of cole crops worldwide. It is small (1/8 inch long), dark green,
and exudes a gray, waxy secretion. What it lacks in size it makes
up in numbers, reaching adulthood in 8 to 12 days and producing
5 to 6 nymphs asexually per day for 30 days. (Hines
and Hutchison, 2002) Aphids pierce plants and suck their juices,
distorting leaves and growing points. Large colonies infest leaves,
heads, and flower stalks, making products unmarketable. Other aphids
such as the green peach aphid and turnip aphid will feed on brassicas,
but they usually do not cause economic damage.
Cabbage aphids have many natural enemies that can be attracted
to fields with habitat plantings. These include aphid and syrphid
flies, lacewings, and the predaceous midge (all of which produce
larvae that consume aphids), minute pirate bugs, bigeyed bugs, lady
beetles (the adults and larvae of which both consume aphids), soldier
beetles, and parasitic wasps like Diaeretiella rapae. In
some humid areas there are outbreaks of naturally existing fungi
that cause epidemics among aphid colonies. The insect-consuming fungus
Beauveria bassiana, which is sold commercially as a bioinsecticide,
is not effective on cabbage aphid due to a fatty-acid secretion produced
by the aphid that is likely involved in resistance to the fungus.
(Szafranek et al., 2001)
Cultural controls that reduce aphid populations include the use
of sprinkler irrigation, where water at high pressure dislodges
the insects from plants. This practice may work when plants are
young and cupping or when inflorescence development has not yet
occurred. Broccoli and cabbage plants interplanted in clover used
as a living mulch showed a reduction in aphids, compared to plants
in clean cultivated fields. (Costello and Altieri,
1994; Theunissen et al., 1995) In the broccoli
trial, the clover mulches had to be mowed early in the cropping
cycle to give the broccoli plants a growth advantage. Mowing of
the cover crop may be limited by lack of labor and/or equipment.
The cabbage trial was not mowed and produced smaller but more marketable
heads than the clean monocrop. Other interplanting strategies to
combat cabbage aphid include the use of mustard or collards as trap
crops and the use of different varieties of the same crop in sequential
plantings. Cabbage aphids exhibit a preference for certain species
and will also discriminate among varieties and plants of varying
age. (Altieri and Schmidt, 1987; Kloen
and Altieri, 1990)
Nitrogen management can have an effect on aphid infestations.
Studies in Great Britain showed that Brussels sprouts treated with
high nitrogen (3.2 mg/g plant fresh wt.) grew more rapidly than
those with low nitrogen (0.64 mg/g plant fresh wt.), but the improved
growth with high nitrogen was offset by the increased population
of aphids. (Koritas and Garsed, 1984) However,
too little nitrogen can also cause stress in plants and make them
susceptible to insect attack.
Organically accepted insecticides include insecticidal soap, neem,
rotenone, and pyrethrum. The waxy leaf cuticle of brassicas and
the white, waxy secretions of the cabbage aphid tend to repel water-based
insecticides, so a spreader-sticker is recommended. Many growers
use soap to overcome this problem. Water hardness will reduce the
efficacy of insecticidal soap, because calcium, iron, and magnesium
will precipitate the fatty acids and make the soap much less effective
against the insects. The best way to determine how well your water
will work is to use the soap-jar test. Let a jar full of spray solution
sit for 20 minutes, then look for precipitates in the soap-water
solution.
Caterpillar pests
Cabbage looper.
Photo by W. L. Sterling. Department of Entomology, Texas A&M University. |
The cabbage looper (Trichoplusia ni), diamondback moth
(Plutella xylostella), and imported cabbage worm (Pieris
rapae) are the major caterpillar pests of cole crops. Other
caterpillar pests can be regional or seasonal problems, like armyworms,
cutworms, cabbage webworms, corn earworms, cross striped cabbageworms,
gulf white cabbageworms, and southern cabbageworms.
Caterpillars have many natural enemies that help keep their populations
down. Predators such as ground beetles, spiders, damsel bugs, minute
pirate bugs, assassin bugs, bigeyed bugs, and lacewing larvae attack
caterpillars. The parasitic wasps Trichogramma spp., Copidosoma
spp., Apanteles spp., Diadegma spp., and Hyposoter
spp. sting and parasitize eggs and larvae. Some of these organisms
are available commercially, or they may occur naturally in the environment.
For information on suppliers of beneficial insects, contact your
local Extension office or visit the Suppliers of Beneficial Organisms
in North America Web site: www.cdpr.ca.gov/docs/ipminov/ben_supp/ben_sup2.htm.
Cabbage
looper moth.
Photo by W.L. Sterling. Department of
Entomology, Texas A & M University. |
Biopesticides or microbial controls consist of Bacillus thuringiensis
(Bt), insect-consuming fungi, and viruses. Bt is a naturally occurring
bacterium that produces a toxin that causes paralysis of a caterpillar's
digestive tract. A caterpillar may continue to live for some hours
after ingestion, but will not continue to feed.
Bt strains are available in a number of commercial products, under
various trade names. The following products have been approved for
organic production by the Organic Materials Review Institute (OMRI):
Prolong, from Cillus Technology Inc.; Britz BT Dust, from Britz
Fertilizers Inc.; DiPel™ and Xantari™, from Valent Biosciences;
Agree™, Deliver™, and Javelin™, from Certis USA.
Diamondback
moth larva.
Department of Entomology, Texas A&M University. |
Bt degrades rapidly in sunlight and requires careful timing or
repeated applications. Bt must be ingested in sufficient amounts
by the caterpillar to be effective. Consequently, growers must understand
the feeding habits of the pests, so that proper formulations are
used and timing of applications is optimal. Caterpillars in their
early stages of development (first and second instars) are more
susceptible to this toxin. Older and bigger worms are harder to
kill.
Entrust™ from Dow Agrosciences is derived from the soil
organism, Saccharopolyspora spinosa. It is OMRI-approved
and registered for control of armyworm, corn earworm, diamondback
moth, imported cabbageworm, and loopers on cole crops.
Organically
Accepted Materials to Combat Caterpillars |
Commercial Products |
Biopesticides |
|
Bacillus thuringiensis |
Agree, Deliver, Javelin, Dipel, Xantari,
Prolong, Britz BT Dust |
Spinosad |
Entrust |
Viruses |
Spod-X, Gemstar |
Beauveria bassiana |
Mycotrol, Naturalis, Botanigard |
Botanical Insecticides |
|
Neem |
Neemix, Argoneem, Azadirect |
Pyrethrin |
Pyganic |
Pyrethrin + Diatomaceous Earth |
Diatect V |
Repellents |
|
Garlic |
Cropguard, Garlic Barrier |
Diamondback
pupae and adult.
Photo by Chris Campbell. Courtesy of
VegEdge, University of Minnesota. |
Spod-X LC™ and Gemstar LC™ from Certis USA are nuclear
polyhedrosis virus products available commercially and are OMRI-approved
for the control of armyworm and corn earworm, respectively, on cabbage,
cauliflower, and broccoli. Other naturally occurring granulosis
viruses and nuclear polyhedrosis viruses sometimes occur in high
density caterpillar populations.
Imported cabbageworm.
Photo by Jack Kelly Clark. Courtesy of UC Statewide IPM Program. |
Beauveria bassiana, the insect-eating fungus, will infect
caterpillars if humidity and temperature are adequate. Commercial
products include Naturalis L™, Mycotrol™, and Botanigard™.
Botanical insecticides include neem products (Agroneem™ and
Neemix™) that act as repellents, antifeedants, and insect
growth regulators. Pyrethrin and rotenone-based products are broad
spectrum and will kill beneficial insects as well as pests, so monitoring
is important. Beneficial insect populations must also be considered
when a pest population is present. Many times the beneficial population
may be keeping the pest under the economic threshold, which is the
level below economic injury to the crop. An application of a broad
spectrum insecticide may damage both the pest and beneficial insect
populations, and other minor pests may become a big problem. This
is known as a secondary pest outbreak.
Imported cabbageworm moths.
Courtesy of VegEdge, University of Minnesota. |
Other management practices to reduce caterpillar infestation include
using floating row overs over a young crop to exclude egg-laying
females, nocturnal overhead sprinkler irrigation, pheromone misters
or emitters to disrupt mating, and pepper, garlic, and herbal repellents.
Some of the control methods mentioned for cabbage looper, diamondback
moth, and imported cabbage worm may work on armyworms, cutworms,
cabbage webworm, corn earworm, cross striped cabbageworm, gulf white
cabbageworm, and southern cabbageworm. If the problem is severe,
contact your local farm advisor or the ATTRA project.
Cabbage maggot
The cabbage maggot or cabbage fly (Delia redicum) will
lay eggs in clusters near the stems of many cole crops or in the
debris of a previous cole crop. Once hatched, the larvae bury themselves
and start consuming feeder roots, eventually burrowing into the
tap root. This provides entry sites for pathogens like clubroot
(Plasmodiaphora brassicae). Maggots feed for three to five
weeks, then pupate in the roots or in the surrounding soil. (Anon.,
2003a) In Chinese cabbage, eggs laid on the surface of a maturing
head hatch maggots that burrow into the head, making it unmarketable.
Cabbage flies will have three to four generations per year starting
in the spring through the early autumn. (Anon.,
1998)
A study in Denmark demonstrated the susceptibility of cabbage maggot
and pupae to Sternernema nematodes. (Neilsen,
2003) These insect-eating nematodes are available
commercially through companies such as Biocontrol
network, Arbico,
and Growquest.
Cabbage
maggot.
Photo by Jack Kelly Clark. Courtesy
of UC Statewide IPM Program. |
Compost and straw mulches significantly reduce the population of
root maggots infesting broccoli. The mulch acts as a barrier, preventing
the flies from laying eggs directly in the soil. It also serves
as a habitat for ground beetle and rove beetle that parasitize and
prey on the cabbage maggot. (Prasad and Henderson,
2002) Other predators include spiders, harvestmen or daddy longlegs,
and ants.
Floating row covers will prevent cabbage flies from depositing
eggs during the critical period after plant emergence or transplanting
and will also reduce egg-laying on mature Chinese cabbage. Intercropping
clovers or other legumes or letting non-brassica weeds fill in the
spaces between crop rows, will keep root flies from finding open
ground near a brassica stem. An experiment in England demonstrated
that carboxylic acids (oxalic acid found in rhubarb, acetic acid,
or vinegar) are potent inhibitors of egg laying by the cabbage fly.
(Jones and Finch, 1989) Thus, a solution of
crushed rhubarb leaves or a vinegar solution sprayed periodically
around cole crop plants may deter the cabbage maggot. Symptoms of
flea-beetle feeding are small, rounded, irregular holes. Heavy feeding
makes leaves look as if they have been peppered with fine shot.
Further damage may be done by the larvae, which feed on plant roots.
Organic Control
Options for Flea Beetles
Cultural Controls
- Living mulches or polycultures
- Trap Crops
- Chinese Southern Giant Mustard (Brassica juncea var.
crispifolia) plant every 55 yards between rows
of broccoli, cabbage or cauliflower, or as a border
around a field. Chinese-type cabbages may be more attractive
to flea beetle than Giant Mustard.
- Radishes interplant Chinese Daikon and Snow
Belle at 6 to 12 inch intervals along cole crops.
- Rowcovers such as Reemay can be used to cover seedlings
and provide a barrier to adult beetles. It is advisable
to get the row cover in place at or before emergence for
maximum protection.
- White and yellow sticky traps placed every 15 to 30 feet
of row. Encircling the field with continuous sticky tape
is also a common method.
- Destroy overwintering adults in plant debris by destroying
refuge sites. Plowing or rototilling grassy and solanaceous
(Potato family) weeds adjacent to a field.
Biological Controls
- Microcotonus vittage Muesebeck, a native braconid wasp,
parasitizes and kills the adult flea beetle.
- Commercial formulations of insect-eating nematodes are
effective agents for controlling flea beetles. Applied to
the soil, the nematodes attack the beetle's larval
stage, reducing root feeding and helping to prevent emergence
of the next cycle of adults.
Chemical Controls
- Botanical insecticides such as neem, rotenone, pyrethrin,
sabadilla, and formulations of these in some combination.
- Combinations of rotenone and insecticidal soap are very
effective.
- Garlic, onion, and mint extracts have been used as flea
beetle repellants.
- Diatomaceous earth reduces flea-beetle populations and
is sometimes recommended.
- The kaolin-clay-based product Surround may provide
some protection against flea beetle.
(Kuepper, 2003) |
Back to top
Diseases
Diseases in plants occur when a pathogen is present, the host is
susceptible, and the environment is favorable for the disease to
develop. Altering any one of these three factors may prevent the
disease from occurring. Organisms responsible for plant diseases
include fungi, bacteria, nematodes, and viruses. If these organisms
are present, then manipulation of the environment and the host,
to make it less susceptible, helps to more sustainably manage diseases
on cole crops.
Once again, soil health and management are the key for successful
control of plant disease. A soil with adequate organic matter can
house uncountable numbers of organisms such as bacteria, fungi,
nematodes, protozoa, arthropods, and earthworms that deter harmful
fungi, bacteria, nematodes, and arthropods from attacking plants.
These beneficial organisms also help create a healthy plant that
is able to resist pest attack. For more information, see the ATTRA
publication Sustainable
Management of Soil-Borne Plant Diseases.
The leaf surface can also host beneficial organisms that compete
with pathogens for space. A disease spore landing on a leaf has
to find a suitable niche in order for it to germinate, penetrate,
and infect the plant. The more beneficial organisms there are on
the leaf, the harder it is for the disease spore to find its niche.
Applying compost teas adds beneficial microorganisms to the leaf,
making it more difficult for diseases to establish themselves. For
more information on foliar disease controls, see the ATTRA publications Notes
on Compost Teas, Use
of Baking Soda as a Fungicide, Organic
Alternatives for Late Blight Control on Potatoes, and Downy
Mildew Control on Cucurbits.
Clubroot
Clubroot.
Photo by Jack Kelly Clark. Courtesy of UC Statewide IPM Program. |
Clubroot is caused by the fungus Plasmodiophora brassicae.
It infects cole crops through the root hairs or through wounds on
larger roots. As the fungus spreads it distorts and disfigures the
roots, causing them to swell and crack, allowing secondary organisms
to invade and aid in decay. The disease is favored by acid soils;
therefore, liming is recommended if the soil pH is lower than 7.2.
(Anon., 2003b)
Other methods to control clubroot include rotating out of cole
crops for a couple of years, having good drainage, and controlling
brassica-type weeds. Cole crops vary in their susceptibility to clubroot,
with cabbage, Chinese cabbage, Brussels sprouts, and some turnips
being very susceptible. Broccoli, cauliflower, collards, kale, kohlrabi,
and some radishes have medium susceptibility. Garden cress, mustard,
and some turnips and radishes are resistant. (Averre,
2000)
Black leg
Black
leg.
Photo by Jack Kelly Clark. Courtesy
of UC Statewide IPM Program. |
The fungus Phoma lingam causes black leg of cole crops.
The fungus causes yellow to tan spots with black specks to form
on leaves, and stem cankers form usually below the soil line. The
fungus interferes with water conduction in tissues, wilting and
debilitating plants. Seedlings can be killed, and surviving plants
may be stunted. The disease can come in with the seed or be present
on cole crop debris or brassica-type weeds.
Controls include the use of clean, certified or hot-water treated
seed, good soil drainage, rotation with non-brassica type crops,
control of brassica-type weeds, deep incorporation of cole crop
residues, and planting resistant varieties. To avoid blackleg, it
is best to avoid planting near other cole crops or near fields that
harbored cole crops during the past season.
Fusarium yellows
Fusarium yellows are caused by the soilborne fungus Fusarium
oxysporum f. conglutinans. Symptoms are yellowing
leaves, usually more pronounced on one side of the plant, the loss
of lower leaves, curvature of petioles and midribs, and wilting.
The ideal temperature range for the development of this disease
is 75 to 85°F., with 60°F. being the lower limit (Anon.,
1987), so it is observed from mid-spring through summer and
is not a problem in early plantings. The fungus is persistent in
the soil and has many plant hosts, so resistant varieties, good
drainage, and soil-building practices such as cover crops and compost
are recommended.
Sclerotinia white rot
The fungi Sclerotinia sclerotiorum and Sclerotinia
minor both can cause this rot favored by cool, wet conditions.
The fungi have many hosts, including many commercial crops and cover
crops that fit in a rotation with cole crops, though grasses are
not affected. Good drainage and irrigation practices that reduce
humidity in fields can reduce the disease. Deep plowing is often recommended, but the results are temporary and very disruptive to soil microorganisms. Biological controls include the fungus Coniothyrium minitans, which attacks sclerotia. Coniothyrium is available commercially
in the product Contans™, from Sylvian Bioproducts, Inc.
Black rot
Black rot.
Courtesy of Meg McGrath, Cornell
University. |
Black rot is caused by the bacterium Xanthomonas campestris.
This bacterium favors humid, rainy conditions, and is dispersed
by the splashing of droplets of water. Xanthomonas enters
the plant at leaf margins or through wounds. Leaf margins develop
yellowish patches that turn brown with black veins. The infection
works its way down the leaves, leaving a “V” pattern
in its wake. The pathogen may eventually invade the vascular system,
spreading throughout the plant. Controls include rotation, weed
control, thorough debris incorporation, the use of clean seed, and
application of approved copper products. Compost tea was successfully
used in a study in the Willamette Valley of Oregon to suppress carrot
bacterial leaf blight, Xanthomonas campestris pv. carotae.
(Reinten and Salter, 2002)
Downy mildew
Downy mildew.
Courtesy of Wyatt Brown, PhD, Cal Poly St. Univ., SLO. |
Downy mildew is a disease caused by the fungus Peronospora
parasitica. Infection and development are favored by cool,
wet weather, and the fungus attacks cole crops at all stages of
growth. Once Peronospora invades a plant, it consumes the
contents of the plant's cells and then sporulates, sending
sporangia out to form cottony white masses, usually under leaves.
The tops of leaves develop purplish spots that later turn yellow
or brown. These spots correspond to the sporulating areas on the
undersurfaces of the leaves. Infected young seedlings may die, while
cauliflower curd, broccoli florets, radish roots, and cabbage heads
may all become unmarketable. Management includes promoting good
drainage, increasing spacing for better aeration, controlling brassica-type
weeds, using resistant varieties, rotating with non-cole crops,
incorporating plant debris, and avoiding the use of overhead irrigation.
Alternaria leaf spot
Alternaria leaf spot.
Photo by Jack Kelly Clark. Courtesy of UC Statewide IPM Program. |
This disease is caused by the fungi Alternaria brassicae
and/or A. brassicola. Small dark spots initially form on
leaves, but later develop into tan spots with target-like concentric
rings. When dried, these spots fall from the leaves, resulting in
a “shot-hole” effect. Prolonged periods of high humidity,
cool temperature, and rain favor its development. Infected cabbage
heads will have spots on several leaves, and Brussels sprout buds
will have several layers infected. It discolors broccoli and cauliflower
heads, and Chinese cabbages are more susceptible than other cole
crops.
Management practices include using clean, certified seed, rotating
with non-host crops, deeply incorporating plant debris, avoiding
overhead irrigation, and promoting air circulation in the canopy.
Back to top
Physiological Disorders
Tipburn is the browning of internal leaf edges or tips
within the heads of cabbage, Brussels sprouts, and cauliflower.
These brown spots tend to break down during storage or transport,
allowing secondary organisms to decay the product. The problem is
related to rapid growth caused by excessive nitrogen, high temperature,
water stress, and calcium deficiency. Calcium can be present in
the soil but its translocation to the plant is limited, and it may
not be available to accommodate rapid growth. Supplemental nitrogen
applications should be timed to avoid rapid growth in the later
stages of plant development.
Riceyness of cauliflower causes the curds to become uneven
and fuzzy, reducing marketability. Warm temperatures (> 68º
F) during curd development are the cause of this disorder. Some
newer hybrids can develop heads at 68 to 80ºF. (Dianello,
2003)
Hollow stem in broccoli and other cole crops is caused
by rapid growth, usually due to excessive nitrogen levels and high
temperatures. The plant stem experiences rapid growth, and the core
or pith cracks, leaving the stem hollow. Another factor that contributes
to this disorder is plant spacing. The closer the plant spacing,
the less likely this phenomenon will occur.
Buttoning of broccoli and cauliflower occurs when immature
plants are exposed to consistently
low temperatures for a prolonged period. This stimulates the young
plants to produce reproductive structures —the flower buds
and curd—and small, loose heads are formed.
Bolting is caused by many factors and depends on the crop
and the varieties grown. Stress caused by too much or too little
water, transplant shock, day lengths of more than 12 hours, and
low temperatures during the early stages of development are all
contributing factors.
Back to top
Weeds
There are many weeds in Brassicaceae that are troublesome in cole
crop plantings, because they compete for water, nutrients, and light,
and they harbor insect and diseases that can affect the crop. Table
2 lists many of these weeds and includes both their common and
scientific names.
Weed control in organic systems, especially in vegetable production,
relies heavily on crop rotations, cover crops, and cultivation.
Of these, cultivation is the most critical to reduce weeds in an
established cole crop stand. For cultivation to be successful, a
straight, well-made bed, as well as straight seeding or transplant
lines, is necessary in order for cultivating implements to remove most weeds while leaving the crop undisturbed. Cultivation implements will cut, bury, or turn over most young weeds, leaving
the crop undisturbed and with reduced competition. In California,
it usually takes two cultivations before a young cole crop starts
to out-compete weeds. Hand hoeing may be necessary after the first
cultivation to reduce weeds in the plant line. If the crop is direct-seeded,
weeding and thinning take place after the first cultivation. For
more information on weed control, check ATTRA's publications Principles
of Sustainable Weed Management for Croplands, Alternative
Control of Johnsongrass, Thistle
Control Alternatives, and Field
Bindweed Control Alternatives.
Table 2: Brassicaceae Weeds |
Common name |
Scientific name |
Common name |
Scientific name |
alpine pennycress |
Thlaspi montanum |
golden draba |
Draba aurea |
field pennycress |
Thlaspi arvense |
tansy mustard |
Descurainia pinata |
desert princesplume |
Stanleya pinnata |
flixweed |
Descurainia sophia |
London rocket |
Sisymbrium irio |
blue mustard |
Chorispora tenella |
tumble mustard |
Sisymbrium altissimum |
hoary cress |
Cardaria draba |
wild mustard |
Raphanus sativus |
heartleaf bittercress |
Cardamine cordifolia |
roundtip twinpod |
Physaria vitulifera |
shepherd's purse |
Capsella bursa-pastoris |
front range twinpod |
Physaria bellii |
smallseed falseflax |
Camellina microcarpa |
foothill bladderpod |
Lesquerella ludoviciana |
birdsrape mustard or wild turnip |
Brassica rapa |
clasping pepperweed |
Lepidium perfoliatum |
black mustard |
Brassica nigra |
perennial pepperweed |
Lepidium latifolium |
wild mustard |
Brassica kaber |
field pepperweed |
Lepidium campestre |
wintercress |
Barbarea orthoceras |
dyer's woad |
Isatis tinctoria |
yellow alyssum |
Alyssum alyssoides |
Pursh's wallflower |
Erysimum capitatum purshii |
garlic mustard |
Alliaria petiolata |
sanddune wallflower |
Erysimum capitatum capitatum |
|
|
|
Back to top
Harvesting
Cabbages are harvested when the heads are firm and solid.
Sizes may vary, but firmness is the determining factor. If solid
heads are left too long in the field to size up, they may crack
or split. Cabbages should be sorted, packed, and stored according
to size.
Cauliflower heads with white firm curds 6 to 8 inches
in diameter are what consumers prefer. Blanching or tying the outer
leaves is done with certain varieties when the heads are about 3
to 4 inches in diameter, to keep sunlight from yellowing the curds.
Curds should be handled carefully since they bruise easily and will
develop discolored patches on these bruises. The surrounding trimmed
leaves should be kept on the head for handling purposes to protect
the curd. Some operations field-wrap the trimmed curds in cellophane
or plastic bags before cooling and storing them in refrigeration.
Broccoli is harvested when most heads are tight, 5 to
7 inches in diameter, and of a blue-green color. They are cut with
a 6-inch stem. If left in the field, heads tend to loosen and expand,
reducing quality. Fields should be harvested every three days, due
to the rapid growth of this crop. Once the head is harvested, side
shoots may develop from lateral axils on the stem, producing smaller
inflorescences that may also be marketed.
Brussels sprouts produce many small buds in leaf axils
along the entire stem. The lowest sprouts on the stem are picked
first, along with the leaves, and harvest progresses upward as the
other sprouts mature. Sprouts may crack if left on the stem too
long.
Kale and collards are harvested leaves with petioles and
are usually bunched together with a wire tie. Bunches are typically
about 8 to 14 inches long.
Kohlrabi should be harvested when the swollen stem is
2 to 3 inches in diameter. There are green and purple varieties.
If left in the field for too long the swollen stem becomes woody.
Chinese cabbage heads should feel solid and not collapse
when pressed firmly with both hands. The wrapper leaves surrounding
the cabbage should be stripped to leave only a couple to cover the
firm head.
Pak choi can be harvested a few leaves at a time, cutting
the outer leaves when they reach a desired size, or by harvesting
the whole head. Some varieties are very brittle and should be left
to wilt slightly to avoid breaking before packing.
Back to top
Postharvest
Once a cole crop is harvested it continues its biological processes
until it deteriorates to an unsaleable product. The key to successful
postharvest handling is to delay these processes in order to get
the product to the consumer in the best condition possible. Temperature
is the most important factor affecting harvested produce. It directly
affects the rates of all vital processes: respiration, ripening,
moisture loss, and the development and spread of decaying organisms.
The higher the temperature, the faster these processes occur. Therefore,
proper temperature management is important throughout the supply
chain, from harvesting to consumption. The sooner the field heat
is removed from the product, the longer it will last, giving the
producer more time to sell the product.
Cooling methods vary according to the commodity; the most common
are cold rooms, forced air cooling, hydrocooling, and icing. Cold
rooms involve placing the product in containers in a cold room.
The less field heat accumulated in the product, the quicker this
system will cool the product. Forced air cooling is done in a cold
room and requires containers with vents so that the cold air can
flow through. The containers are stacked in rows placed on either
side of a fan, leaving an aisle between the rows. The aisle and
the open end are covered with a tarp to create a tunnel. The fan
draws air from outside the tunnel through the openings in the containers,
forcing cold air around the warm product.
Hydrocooling uses cold water to rapidly cool commodities. Containers
must be waterproof and allow water to enter to pass over product.
Cartons or lugs are either submerged in cold water or showered from
above with recirculated cold water.
Icing consists of placing ice on the product in the container.
This is usually done with broccoli, Brussels sprouts, and turnips.
All brassica crops last the longest when stored at 32ºF, just
above the freezing point. (Hardenburg et al., 1986)
See ATTRA's publication Postharvest
Handling of Fruits and Vegetables for more information.
Back to top
Economics and Marketing
The economics of growing cole crops vary enormously from crop to
crop and in different regions. The following budgets were developed
for growing organic cauliflower in the Northeast and organic broccoli
in California. The organic cauliflower budget was prepared by Rutgers
Cooperative Extension in cooperation with the Northeast Farm Management
Committee in 1996. The organic broccoli budget was developed by
the University of California Cooperative Extension in 2004.
These budgets are intended as references in order for farmers to
develop their own budgets based on local conditions. Large and some
medium producers market their products to wholesalers, brokers,
and terminal markets. These marketing options are not advantageous
for some medium and smaller growers, because of low returns, uncertainty
of prices, risk of rejection, and strict packing standards.
Costs of Production for Cauliflower, Per Acre Organic Production Practices Northeastern United States, 1996 |
ITEM |
UNIT |
PRICE |
QUANTITY |
TOTAL |
Variable Costs |
|
|
|
|
Soil Amendments |
|
|
|
|
Compost w/gypsum |
ton |
$34.40 |
6 |
$212.40 |
Pest Management |
|
|
|
|
Approved organic pesticides |
acre |
$150.00 |
1 |
$150.00 |
Transplants |
|
|
|
|
Cauliflower |
thousand |
$19.50 |
13 |
$250.90 |
Labor |
|
|
|
|
Operator |
hr |
$14.48 |
8.33 |
$120.62 |
Regular Hired |
hr |
$10.13 |
36.6 |
$370.76 |
Seasonal Hired |
hr |
$7.24 |
76 |
$550.24 |
Irrigation |
|
|
|
|
Overhead Irrigation |
acre |
$192.00 |
1 |
$192.00 |
Machinery Repair and Fuel |
|
|
|
|
Machinery Repair |
acre |
$38.28 |
1 |
$38.28 |
Marketing Costs |
|
|
|
|
Packing Crates |
crate |
$1.50 |
800 |
$1200.00 |
Sub-Total |
|
|
|
|
Interest on Operating Capital |
acre |
10% |
1 |
$56.84 |
Total Variable Costs |
acre |
|
1 |
$3142.04 |
Fixed Costs |
|
|
|
|
Machinery and equipment |
acre |
$212.59 |
1 |
$212.59 |
Land |
acre |
$100.00 |
1 |
$100.00 |
Total Fixed Costs |
acre |
|
1 |
$312.59 |
Total Fixed and Variable Costs |
acre |
|
1 |
$3454.63 |
Management Fees |
acre |
7% |
1 |
$150.82 |
Total Costs |
acre |
|
1 |
$3605.45 |
|
Cost of Production per acre for Organic Broccoli on the Central Coast of California, 2004 |
Operation |
Operation
Time Hr/Ac |
Labor Costs |
Fuel & Repairs |
Material Costs |
Custom Rent |
Total Costs/Ac |
Fertilizer |
|
|
|
119 |
|
199 |
Land prep: sub, disc, roll, chisel, landplane |
1.49 |
25 |
55 |
0 |
0 |
79 |
Cover Crop |
0.24 |
3 |
6 |
11 |
0 |
20 |
Land prep: roll, list, fert, and shape beds |
0.58 |
10 |
14 |
262 |
0 |
286 |
Plant |
0.28 |
7 |
6 |
442 |
0 |
445 |
Insectary plants |
0.07 |
1 |
1 |
1 |
0 |
3 |
Irrigate up to 3X |
0.75 |
9 |
0 |
40 |
0 |
49 |
Fertilize (bloodmeal) |
0.2 |
3 |
2 |
225 |
0 |
231 |
Weed: Cultivate/Furrow 3X |
0.44 |
7 |
8 |
0 |
0 |
16 |
Insect: Worm (Entrust) |
0 |
0 |
0 |
7 |
16 |
23 |
Weed: Hand Hoe |
21.5 |
254 |
0 |
0 |
0 |
254 |
Irrigate 8X |
6.5 |
77 |
0 |
360 |
0 |
436 |
Pest Management Consultant |
0 |
0 |
0 |
0 |
30 |
30 |
Pickup truck |
1.43 |
24 |
15 |
0 |
0 |
39 |
Total Cultural Cost |
33.48 |
420 |
107 |
1466 |
46 |
2039 |
Total Harvest Costs |
0 |
0 |
0 |
0 |
4290 |
4290 |
Total Operating Costs/Acre |
|
423 |
110 |
1491 |
4336 |
6438 |
Total Cash Overhead Costs |
|
|
|
|
|
1024 |
Total Cash Costs/Acre |
|
|
|
|
|
7462 |
|
Alternative markets exist for smaller producers, such as marketing
directly to consumers through farmers' markets, community supported
agriculture (CSA), and roadside stands. Direct sales to restaurants
and small, independent grocers are other choices. For more information
on alternative marketing, see the following ATTRA publications:
Selling
to Restaurants, Community Supported Agriculture, Direct
Marketing, Evaluating
a Rural Enterprise, Farmers'
Markets, Green
Markets for Farm Products, and Organic
Marketing Resources.
Back to top
Summary
The number of crops in the brassica family, their nutritional qualities,
health benefits, compatibility in planting rotations, and pest suppressive
qualities make these crops an excellent choice for any organic farmers.
They grow in all regions in different seasons and add diversity
to a farmer's income and products.
Acknowledgment
The author wishes to thank Wyatt Brown, PhD, of the Horticulture
and Crop Sciences Department at Cal Poly San Luis Obispo, for his
thoughtful and thorough review of this publication.
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Cole Crops and Other Brassicas: Organic Production
By Martin Guerena
NCAT Agriculture Specialist
Paul Driscoll, Editor
Cole Loeffler, HTML Production
IP 275
Slot 275
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