Organic Gardening Kentucky Master Gardener Manual
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COOPERATIVE EXTENSION SERVICE • UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546
HO-100
Organic Gardening
Kentucky Master Gardener Manual Chapter 18
By Krista Jacobsen, assistant professor, Department of Horticulture, University of Kentucky
O
rganic farming and gardening have grown in popularity
In this chapter: in recent years as consumers and producers have sought
alternatives to synthetic fertilizers and pesticides in favor
Planning Your Organic Garden......................278 of biologically-based management. A 2008 survey by the National
Organic Transplants and Seed Sources......281
Gardening Association found that 12% of American household
gardens (12 million households) use all-natural management tech-
Pest Management: Weeds, Insects, niques, an increase of 7% from 2004. This number is anticipated to
Diseases.................................................................281 grow by as much as 42%, to 17 million, if other households follow
Additional Resources........................................287 through on their plans to switch to all-natural methods.
The U.S. Department of Agriculture (USDA) National Organic
Program (NOP) defines the rules for USDA Certified Organic
production practices. (The label used to designate certified organic
products is shown in Figure 1. See the USDA-NOP website at
http://www.ams.usda.gov/AMSv1.0/nop for additional details).
This publication provides an overview of the principles and prac-
tices of organic agriculture for the home gardener, whether he or
she wants to grow a completely organic garden or adopt select
practices to lower input costs and build soil fertility. The fertilizer
and pest control strategies in this publication are consistent with
spirit of the USDA-NOP guidelines. However, gardeners who want
to meet the “letter” of those guidelines should explore the Organic
Materials Review Institute (OMRI) list of NOP-approved materi-
als at www.omri.org. or look for the OMRI label when purchasing
garden supplies (Figure 2).
Organic gardening offers the gardener many benefits—a safe,
Figure 1. USDA Certified low-chemical gardening environment, produce free from synthetic
Organic label.
pesticide residues, and gardens that can increase in fertility and
natural pest control over time. However, reaping the benefits of
organic management requires planning, observation, and thinking
about the garden as an interconnected system of soils, plants, pests,
and beneficial organisms. Principles and practices include:
• Building long-term soil fertility with composts, manures, and
Figure 2.
OMRI label.
mulches
• Rotating crops
• Using good planning practices to avoid insect, disease, and
weed pests and using biological or mechanical controls when
necessary
Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Economic Development
EXTENSION278 • Organic Gardening Chapter 18
Planning Your Organic Garden (primarily nitrogen) requirements have
been described as heavy feeders, those with
Crop Rotation moderate fertility requirements as medium
or light feeders, and crops that contribute
Crop rotation is alternating crops grown
nutrients are “givers.” (See Jeavons’ book in
in a particular bed or field between grow-
Additional Resources.) Crops are rotated
ing seasons. By rotating crops, you can
in a cycle from heavy givers to light feeders
avoid buildup of certain pests and also
to heavy feeders and back to heavy givers.
enable nutrients in the soil to be used more
Examples of crops in these categories are:
efficiently.
• Heavy givers: Beans (snap, pole, bush),
The most popular type of rotation is
peas, green manure crops such as clo-
alternating crops by botanical family. For
vers, and field peas
example, diseases that affect tomatoes can
• Light feeders: Beets, carrots, garlic, onions,
also affect other members of the Solanaceae
sweet potatoes, turnips
family, including peppers, potatoes, and
• Heavy feeders: Broccoli, cabbage, corn,
eggplants.
cucumbers, squash, tomatoes
Rotating crops in the Solanaceae family
with crops in other families can minimize
If you plan to practice rotation, it’s
losses from these diseases. Similarly, rotat-
important to keep records and a year-
ing among crops that have different growth
by-year map of your garden. Flashcards
habits can help deter pests. For example, if
also can be useful in the garden planning
root crops such as sweet potatoes or car-
process. Using this technique, flashcards
rots are planted in the same location year
are made for each crop, with a copy of the
after year, soil-dwelling insect pests, such as
flashcard for that crop for every year in
white grubs, wireworms, and some nema-
the rotation (e.g., three potato flashcards
todes, may proliferate. Rotating among
for three years of potatoes). You can then
plants with different root architecture may
manipulate the cards for a three-to-five-year
prevent proliferation or help break these
timeline for the entire garden. This exercise,
pest cycles.
using the botanical family as the guide to
One common rotation method is based
the rotation. is outlined in The New Organic
on the fertility requirements for each
Grower by Eliot Coleman (see Additional
crop. With this method, you categorize
Resources).
crops by whether they “feed” or “give”
Common vegetables and their botanical
nutrients to the soil over the course of the
families are listed in Table 1.
growing season. Crops with high fertility
Table 1. Common garden vegetables and their botanical families.
Botanical Common
Family Family Name Crop
Solanaceae Nightshade Tomato, pepper, potato, eggplant, tomatillo
Brassicaceae Cole crop Broccoli, cauliflower, cabbage, kale, Brussels sprouts, radish,
rutabaga, turnip
Cucurbitaceae Gourd Winter squash, summer squash, melons, cucumber, pumpkin
Apiaceae Carrot Carrot, parsley, celery, parsnip
Chenopodiaceae Goosefoot Beet, chard, spinach
Fabaceae Legume Pea, bean
Asteraceae Sunflower Lettuce
Liliaceae Lily Onion, garlic, shallot, leek
Poaceae Grass CornChapter 18 Organic Gardening • 279
Soil Fertility and Table 2 shows the nutrient contents
(N-P-K) of several common sources of
Organic Fertilizers fertility in organic gardens.
A central tenet in sustainable and Organic fertilizers rarely contain the
organic agriculture is to “feed the soil to N-P-K ratios to match recommendation
feed the crop”—restoring and maintaining from a soil test report. However, you can
the soil organic matter that ultimately feeds use the steps below to figure out how much
crop plants. Soil organic matter accumu- fertilizer you need, whether you use the val-
lates through use of organic amendments ues in Table 2 or those listed in the nutrient
such as composts, manures, cover crops, analysis of a purchased amendment.
and mulches. Over time, these amend- A soil test report recommends 2-3 lb
ments sustain fertility, relieve compaction, of N, 1-2 lb of P2O5, and 3-5 lb of K2O per
improve both drainage and water holding 1,000 square feet of garden. To calculate
capacity, and improve nutrient retention. the organic fertilizer required from several
However, organic amendments are deliv- sources, complete the following steps:
ered more slowly and less consistently than 1. Calculate the nitrogen (N) recommenda-
standard synthetic fertilizers because they tion first.
become available as microbes and other soil 2. Calculate the phosphorus (P205) recom-
organisms decompose. mendation next.
3. Calculate the potassium (K2O) recom-
mendation next.
Table 2. Nutrient content and release rates of organic fertilizers.
An example of these calculations is pro-
Relative vided in Figure 3.
Materials N (%) P2O5 (%) K2O (%) Availability
Alfalfa meal 3.0 1.0 2.0 Medium-Slow
It’s fairly easy to use organic sources to
Blood meal 12.0 1.5 0.6 Medium-Rapid
Bone meal 0.7-4.0 11.0-34.0 0.0 Slow-Medium
meet your garden’s fertility requirements,
Feather meal 11.0-15.0 0.0 0.0 Slow and organic fertilizers are increasingly
Fertrell “Super N” 4.0 2.0 4.0 Slow accessible. However, it is important to
Fish meal 10.0 4.0 0.0 Slow understand that for nutrients to become
Fish emulsion 5.0 1.0 2.0 Medium-Rapid available from most organic sources (other
Greensand 0.0 1.0-2.0 5.0 Slow than minerals and rock powders), they must
Kelp1 0.9 0.5 1.0-4.0 Slow be decomposed by soil organisms. Thus, it is
Manure2 (fresh) important to understand how temperature,
Cattle 0.25 0.15 0.25 Medium moisture, and other environmental factors
Horse 0.3 0.15 0.5 Medium affect soil organisms and the decomposition
Poultry (50% water) 2.0 2.0 1.0 Medium-Rapid process. The effects of pH and temperature
Poultry (15% water) 6.0 4.0 3.0 Medium-Rapid are described briefly below. For addi-
Manure2 (dry) tional information, Jeff Lowenfel’s book,
Dairy 0.7 0.3 0.6 Medium
Teaming with Microbes, is an excellent
Steer 2.0 0.5 1.9 Medium
gardener-friendly primer on soil ecology
Horse 0.7 0.3 0.5 Medium
Marl 0.0 2.0 4.5 Very Slow
and the activity of soil microorganisms (see
Mushroom compost 0.7 0.9 0.6 Medium
Additional Resources).
Sulfate of potash 0.0 0.0 22.0 Rapid-Medium
magnesia (K-Mag)
Soybean meal 6.7 1.6 2.3 Slow
Wood ashes3 0.0 1.0-2.0 3.0-7.0 Rapid
Source: Adapted from How to Convert an Inorganic Fertilizer Recommendation to
an Organic One, University of Georgia Cooperative Extension. Adapted from Boyhan,
2009. See Additional Resources.
1 Kelp also contains common salt, sodium carbonates, and sodium and potassium
sulfates.
2 Manure contents may vary with amount of straw/bedding included, feed quality, and
method of storage. (See the health and safety questions in the Cooperative Extension
Publication Composting (ID-192).
3 Potash content depends on the tree species burned. Wood ashes are alkaline and
contain approximately 32% CaO.280 • Organic Gardening Chapter 18
Figure 3. Example calculation to determine organic fertilizer required to meet soil test report recom-
mendations for 1,000 square feet of garden space.
1. Calculate the nitrogen (N) recommendation first. In this example, we will use blood meal for
the nitrogen source (12-1.5-0.6, see Table 2). For the 3 lb of N recommended, the quantity of blood
meal required to meet the nitrogen recommendation can be calculated as:
(3 lb N ÷ 1000 ft2) x (1 lb blood meal ÷ 0.12 lb N) = (25 lb blood meal ÷ 1000 ft2)
2. Calculate the phosphorus (P205) recommendation next. Subtract the amount of P supplied by
the N source (blood meal):
25 lb blood meal x (0.015 lb P2O5 ÷ 1 lb blood meal) = 0.375 lb P2O5
Use bone meal (approx. 1-11-0) for the phosphorus source to fulfill the remaining P requirement.
1.5 lb P2O5 – 0.375 lb P2O5 from blood meal = 1.125 lb P2O5
(1.125 lb P2O5 ÷ 1000 ft2) x (1 lb bone meal ÷ 0.11 lb P2O5) = (10 lb bone meal ÷ 1000 ft2)
3. Calculate the potassium (K20) recommendation next. The quantity of K supplied in the bone
and blood meal is negligible, so the K recommendation can be calculated without subtracting the
K present in the N and P sources. Using K-mag (sulfate of potash magnesia) to complete the fertility
plan:
(4 lb K2O ÷ 1000 ft2) x (1 lb K-Mag ÷ 0.22 lb K2O) = (18 lb K-Mag ÷ 1000ft2)
Based on these calculations, meeting the soil test report fertilizer recommendations will
require 25 lb blood meal, 10 lb bone meal, and 18 lb K-Mag for 1000 square feet of garden
space.
pH and liming Temperature
Garden plants typically grow best in a Cool temperatures in early spring also
pH from 6.0 to 6.5, and microbial activity limit microbial activity. Soils must be warm
is restricted when pH is less than 5.5. Soil enough to stimulate microbial activity in
testing and adjusting pH according to lime order to decompose organic fertilizers and
recommendations helps ensure that soil make nutrients available to crop plants.
organisms are operating under optimal Growth may be stunted early in the season
conditions. Calcium, the neutralizing agent if plants don’t get enough nutrients or those
in agricultural lime, will not spread quickly nutrients are immobilized by decomposing
throughout the soil profile. For that reason, microbes (also known as “N rob”).
it must be thoroughly incorporated before To avoid stunted growth, use a readily-
planting—ideally two to three months available organic fertilizer such as fish
before planting—throughout the root- emulsion or other liquid organic fertilizer
ing zone, at a depth of 6 to 8 inches. If you when you transplant, and use it weekly for
can’t apply lime this early, it will still help if one to two weeks after transplant. Using
you can apply and incorporate it at least a healthy transplants with enough fertility in
month before seeding or transplanting. the transplant mix to carry some nutrient
forward into the garden bed will also help
make up for insufficient soil nutrients early
in the season.Chapter 18 Organic Gardening • 281
Organic Transplants Pest Management: Weeds,
and Seed Sources Insects, Diseases
Organic seedling mix can be expen- One of the main differences between
sive, and nutrient delivery tends to be organic gardening and conventional
less consistent than with conventional gardening is the use of pesticides. Organic
seedling mixes (though there are notable gardeners choose not to use any synthetic
exceptions). Add fertilizer once the first chemicals to control weeds, insects, or
set of true leaves appear. Typically, organic diseases. Instead, they use a combination of
gardeners use a liquid, fish emulsion-based cultural, physical, and biological controls.
organic fertilizer. To avoid burning plants, The philosophy behind organic pest control
follow dilution directions on the packaging. is that using “many little hammers” allow
The cost of organic seedling mixes the organic gardener to beat back pests to
increases rapidly with soil or compost- a manageable threshold even though these
based mixes, so many organic gardeners techniques lack the chemical strength of
and farmers make their seedling mix. many conventional garden inputs.
Several common recipes used in organic Cultural controls, used to prevent pests
seedling production are listed in Table from ever becoming a threat, are the first
3. For additional information on organic line of defense in the garden. They include
seedling mix ingredients, nutrient release proper plant selection, fertility manage-
rates, and additional recipes, see the ment, crop rotation, and physical exclusion.
publication Potting Mixes for Certified Physical or mechanical controls manually
Organic Production at http://attra.ncat. remove pests from the garden. Biological
org/attra-pub/potmix.html. Note that one controls, which can be organic pesticides
recipe is intended for use with “soil block- or beneficial organisms, are used to man-
ers,” which are hand tools designed to form age an existing insect or disease problem.
free-standing blocks of potting soil that It is a common misconception that organic
substitute for peat pots, seedling flats, etc. gardening prohibits the use of pesticides
Soil blockers have been popular among in any form. A number of pesticides that
small-scale producers, and are readily avail- are derived directly from biological or
able through some garden suppliers special- mineral sources are organically approved.
izing in organic production (see Additional They may be highly toxic, but they typi-
Resources). cally break down much more quickly in the
Table 3. Common recipes for organic potting and germination mixes.
Organic substitute Classic soil-based Vegetable
for Cornell Mix mix1 Soil blocking mix Organic potting mix transplant recipe
• ½ cu. yd sphagnum • 1⁄3 mature com- • 3 buckets2 • 1 part sphagnum peat Equal parts by
peat post or leaf mold, • brown peat • 1 part peat humus (short volume of: compost,
• ½ cu. yd screened • ½ cup lime (mix well) fiber) peat moss, and per-
vermiculite • 1⁄3 garden topsoil • 2 buckets coarse sand or • 1 part compost lite or vermiculite
• 10 lb bone meal • 1⁄3 sharp sand perlite • 1 part sharp sand (builder’s)
• 5 lb ground • 3 cups base fertilizer (blood To every 80 qt of this add:
limestone meal, colloidal phosphate, • 1 cup greensand
• 5 lb blood meal and green sand mixed • 1 cup colloidal phosphate
together in equal parts) • 1½ to 2 cups crabmeal, or
• 1 bucket soil blood meal
• 2 buckets compost • ½ cup lime
Sources: For the blocking and organic potting mixes, Coleman’s The New Organic Grower: A Master’s Manual of Tools and Techniques for the Home and
Market Gardener. For the vegetable transplant recipe, Rynk’s On-Farm Composting Handbook. (See Additional Resources.)
1 This mix is heavier than modern peat mixes but still has good drainage. Compost promotes a healthy soil mix that can reduce root diseases.
Vermiculite or perlite can be used instead of sand. Organic fertilizer may be added to this base.
2 Standard 10-qt bucket.282 • Organic Gardening Chapter 18
environment than their synthetic coun- the mulch. Direct-seeded crops such as
terparts. Organic management of weeds, root vegetables and lettuces can be planted
insects, and diseases integrating cultural, through a thin layer of mulch and still
physical/mechanical, and biological con- emerge. To promote crop emergence while
trols is discussed below. minimizing weeds between the crop rows,
you also can mulch with a thicker layer
Weeds around the planting furrow and leave the
furrow exposed.
Cultural controls for preventing weeds Straw mulch is commonly used in
include home gardens, and it is effective in con-
• crop rotation and spacing trolling weeds and conserving moisture.
• physical barriers on the soil However, if it’s not clean, straw may import
• bringing into the garden only materials weed seeds and create more weeds than
that you know to be free of weed seed it reduces. Mulches and hay and manures
• not allowing existing weeds to go to seed from animals eating them can contain her-
Crops and cover crops planted in tight bicide residue, but most herbicides break
succession compete with weeds for light, down rapidly in the environment. However,
nutrients, and water. The more these picloram, clopyralid, and aminopyralid do
resources are in use by crop plants, the less not break down quickly, and, in concentra-
available they are for weeds. tions as low as 1 ppb (parts per billion), they
In addition, planting vigorous transplants can be lethal to sensitive garden plants such
on relatively tight spacing closes the plant as peas, beans, lettuce, spinach, tomatoes,
canopy rapidly, helping crop plants out- and potatoes. These herbicides are used
compete weeds for light, water, and avail- to control broadleaf, persistent weeds
able nutrients. Techniques such as French such as Canada thistle in pastures, under
biointensive gardening (Jeavons, 2004) and power transmission lines, and in hay and
square-foot gardening (Bartholomew, 2005) wheat crops. They are used because they
emphasize close plant spacing and arrang- are long-lived, effective, and low in toxicity
ing plants by vertical size to produce a to humans and other animals. They can,
dense canopy that maximizes crop produc- however, persist in the garden for several
tion and minimizes weed pressure. years. If you are buying hay or straw mulch
from a local farm, you can avoid bringing in
Mulches and Other Physical Barriers contaminated mulches by asking whether
Physical barriers such as mulches, plastic, the field in which the crop was grown has
landscape fabric, and even cardboard block been sprayed with picloram, clopyralid, or
light to germinating weeds. They greatly aminopyralid in the past two to three years.
reduce weed emergence and also conserve These herbicides are sold under the follow-
water. When these barriers are plant-based, ing trade names:
they add organic matter to the soil as well. • Picloram: Tordon, Access, Surmount,
Typically, a 1-to-2-inch layer of straw or hay Grazon, and Pathway
mulch, with some additional hand weed- • Clopyralid: Curtail, Confront, Clopyr
ing, will suppress weeds for much of the AG, Lontrel, Stinger, Millennium Ultra,
season. More mulch can lead to outbreaks Millenium Ultra Plus, Reclaim, Redeem,
of fungal and bacterial disease in warm, wet Transline
years. To minimize diseases, keep mulches • Aminopyralid: Milestone, Forefront,
off crop plant stems. Also, on long-season, Pharaoh, Banish.
disease-sensitive crops such as tomatoes
and peppers, remove lower leaves touchingChapter 18 Organic Gardening • 283
Figure 4. Specialty garden hoes. light weeding in tight garden spaces or in
fine seed beds, use a colinear hoe. It is a
small, light tool that is dragged along the soil
grub hoe surface or slightly below it to kill weeds. For
larger weeds or larger areas, a standard gar-
den hoe is most commonly used. A stirrup
hoe, or “hula hoe,” is an alternative to the
garden hoe. It has a spring-steel blade that
cuts in both directions for high efficiency.
Unlike a fixed-blade garden hoe, the head of
collinear hoe stirrup hoe
a stirrup hoe has a limited swivel joint at the
top that allows the blade to remove weeds
by pushing and pulling the hoe without
having to lift the hoe. The ability to move
Weeding techniques the hoe back and forth without having to
Once weed pressure begins to mount— lift the hoe has also led to stirrup hoes also
and it generally does—physically removing being called “scuffle hoes.” The stirrup hoe
weeds is the organic gardener’s only option. can work the soil deeper than a garden hoe
No consistently effective, approved organic in loose and light soils. To chop out larger or
herbicides are available at this time. The fol- deeply-rooted weeds, a “chop” or “grub” hoe
lowing methods are most commonly used. is an aggressive tool that quickly unearths
Hand weeding—The oldest method of weeds. Although grub hoes are effective,
weed control is hand weeding, and it is still they can be heavy and physically demand-
the most effective for commonly occurring ing to operate.
weed species in Kentucky. Hand weed- Mechanical cultivation—Mechanical
ing is particularly effective for removing cultivation is generally used in large gardens
annual weeds with shallow root systems. that have wide spacing between rows. On a
With hand weeding, you can remove weeds large scale, it can be much faster than hand
growing in the row without harming grow- weeding. Garden tillers are set at as shallow
ing crop plants. If you regularly hand-weed a depth as possible to so nearby crop plants
while performing other gardening tasks, won’t be damaged and soil disturbance at
you can do so rapidly and keep weed pres- deeper depths will be minimized. Extensive,
sure low. Hand-weeding is also the easiest regular mechanical cultivation destroys
method to use when weeding in garden soil structure and leads to increased
beds with mulches. However, if you’re breakdown of soil organic matter and
weeding on a large scale or have high weed organic amendments such as composts and
pressure, you may need to use tools. manures. Mechanical cultivation should
Hoeing—Hoeing can be both efficient be conducted under proper soil moisture
and effective for removing small weeds or conditions to help minimize damage to soil
chopping out larger ones. It is most effective structure. Soils that are too wet will stick
for weeding between rows of crop plants to tillage implements and “smear” the soil
that have a wide spacing between plants and create compacted conditions when the
so the crop plants won’t be damaged. Hoe soil dries. In general, soil moisture can be
shallowly near plants so you do not damage estimated by taking a handful of soil and
their roots; hoe deeply when you need to forming a ball by gently squeezing it. If the
unearth roots of persistent weeds such as ball readily holds it shape, it may be too wet
curly dock, Johnson grass, nut sedges, etc. to till. Soils that crumble gently but still have
A sharp hoe makes hoeing much easier, as some tangible moisture are in better condi-
does having the right hoe for the job. For tion for tillage.284 • Organic Gardening Chapter 18
Insects for whiteflies and other insects but are best
used for monitoring for insect pressure, not
Insect control in the organic garden control. Japanese beetle traps, which rely
begins with growing healthy plants. Weak on a synthetic lure or a sex pheromone to
plants, which have nutrient deficiencies, attract the beetles, are also available in gar-
tend to be the first to succumb to insect den shops. These traps are highly effective,
pressure. Nutrient excesses (particularly even from long distances. However, beetles
nitrogen) can lead to outbreaks of insects may linger and feed on crop plants, doing
such as aphids. Soil testing and proper fer- more damage than would have occurred
tility management can help minimize both without the traps. For that reason, these
nutrient deficiencies and excesses. traps are not widely recommended. Instead,
Timing is also important. For pests you might consider removing beetles and
that increase throughout the season, such other insects by hand.
as corn earworms, tobacco hornworms, Trap crops are grown to lure pests away
cucumber beetles, etc., early plantings can from more desirable crop plants. For exam-
minimize pest pressure. For pests such as ple, flea beetles will feed on giant mustard
flea beetles that subside with onset of sum- over kales and other Brassica crops, and
mer heat, delaying plantings of eggplant and blue hubbard squashes are used as traps for
other summer crops that are sensitive to cucumber beetles, which feed on a variety
flea beetles can minimize their damage. of cucurbit crops. Insect pests on the trap
Row covers of lightweight fabric can be crop can either be left alone or destroyed by
used as insect barriers to exclude insect hand picking or with an organic insecticide.
pests from crop plants. When using row if you have to use pesticide to get rid insect
covers in the summer, the fabric should be pests, trap cropping helps limit how much
of “insect-barrier” thickness so that temper- you have to spray in addition to protect-
atures under the fabric don’t get too hot and ing crop plants. For a summary of effective
maximum light penetrates the fabric. The trap crop studies, see http://www.oisat.
fabric can be removed after the threat of org/control_methods/cultural__practices/
pest damage has passed. For crops that bear trap_cropping.html
fruit, the insect barrier should be removed
during flowering to allow for pollination. Beneficial Insects
Row covers are particularly effective in pre- Beneficial insects, or “natural enemies,”
venting imported cabbageworms and cab- are used in the organic garden to con-
bage looper moths from laying their eggs on trol pests biologically. A number of spe-
Brassica crops. Use wire hoops, which are cies of beetles, parasitic wasps, flies, and
available commercially, or homemade PVC nematodes are predators or parasitoids
frames to support row covers during the of pest insects. (Parasitoids are organisms
summer. Both hoops and frames will allow that lay their eggs or larvae in the body
air to circulate around the plants. These of a host [pest] organism. The immature
supports can also be used with thicker parasitoid feeds on the body fluids and
fabrics and/or plastic to extend the grow- organs of the host and evenutally emerges
ing season into spring or fall. Avoid pinning and kills the host.) A number of ben-
plants to plastic mulches, where they can be eficial insects are available commercially.
damaged by excessive heat. Sources can be found online and in the UK
A wide variety of traps can be made or Cooperative Extension publication Vendors
purchased. For example, slugs and snails of Beneficial Organisms in North America
can be attracted to a shallow container filled (ENTFACT-125) at http://www.ca.uky.edu/
with beer and buried level with the soil. entomology/entfacts/ef125.asp. Common,
The slugs and snails drown in the beer. (The commercially available beneficial insects
beer must be changed every several days, as and the insect pests they control are listed
the trap fills and/or becomes foul.) Prepared in Table 4.
sticky traps are available in garden shopsChapter 18 Organic Gardening • 285
Table 4. Guide to insects as biocontrols.
Beneficial Insect Pest Insect Controlled
Green lacewing (Chrysoperla rufilabris)1 Aphids, mealybugs, immature scales and white-
flies, thrips, spider mites
Lady beetle Aphids, Colorado potato beetles (egg stage), and
other insect pests
Beneficial nematodes (various species) Root knot nematodes, flea larvae, grubs
Praying mantis (Tenodera aridifolia sinensis)1 Foliar feeding insects
Mealybug destroyer (Cryptolaemus montrouzieri) Mealybug larvae
Trichogramma wasp Over 200 species of moth eggs, including tomato
hornworm, loopers, etc.
Spined soldier bug (Podisus maculiventris)1 Larvae of Mexican bean beetle, European corn
borer, corn earworm, cabbage looper, cabbage-
worm, Colorado potato beetle, and flea beetles.
1 These beneficial insects are general predators, shown with the pest insects against which they are particularly
effective.
In general, you can expect a delay scouting and removal while you take care of
between the time of beneficial insects’ other garden tasks. Physical removal is less
release and effective control of the pest. effective for small or fast-moving insects,
Effective control can be difficult if you which will likely require some of the other
release them after you notice a major pest techniques explained above.
outbreak, because a sufficient population Although organic insecticides, which are
has to build up to control the outbreak. You derived from botanical or mineral sources,
should release a large number of them at do not persist as long as their conventional
the first sight of the pests. Most importantly, counterparts, a number of them are used
you should create a habitat in which the in organic gardening. In general, an organic
beneficial insects can overwinter and per- insecticide requires that the pest insect
sist in your garden or yard. Ideally, a year- ingest it directly or at least come in contact
round habitat for beneficial populations will with it. For example, organic gardeners can
limit outbreaks of pest insects. Typically, use Bacillus thuringiensis (Bt) to control cat-
perennial vegetation, woody shrubs, crop erpillars. It should be applied as a spray or
residues, and even boards will provide over- powder every three to five days as needed
wintering habitat for beneficial insects and during periods of caterpillar pressure.
their offspring. Several general insecticides, such as pyr-
The most reliable way to control insect ethins, are approved for organic production.
pests is to physically remove them from These insecticides should be sprayed just
the plant by hand and drop them into a before sunset, when pest insects are active
container of soapy water. Adding a squirt but pollinators are not, in order to prevent
of dish soap to an empty quart jar then contact with bees and other pollinators.
adding water creates a solution that effec- Examples of insecticides approved for
tively traps insects placed in the jar. The organic production and the organisms they
soap breaks the surface tension of the water, control are listed in Table 5. Organically-
which prevents the insects from gaining approved insecticides are available at some
traction and climbing out of the jar. This garden supply stores but are also available
method works particularly well for beetles online in home garden quantities from
and caterpillars, which can generally be commercial organic nursery and horticul-
controlled at the garden scale by daily tural suppliers (see Additional Resources).286 • Organic Gardening Chapter 18
Table 5. Insecticides approved for use in organic production.
Active
Ingredient Origin of Active Ingredient Pest Insects Controlled
Bacillus thuringi- A toxin produced by the soil bacterium Bacillus Caterpillars, such as cabbage looper, hornworm, imported
ensis (Bt) thuringiensis cabbageworm, corn ear worm, etc.
Diatomaceous Fossilized remains of diatoms, algae with a silica- Particularly effective on soft-bodies insects but also deters
earth based hard shell beetle, flea, and ant activity on plants
Insecticidal soaps Salts of fatty acids derived from coconut and other Soft-bodies insects such as aphids, thrips, whiteflies, etc.
oils
Kaolin clay A naturally occurring clay mineralogy ground into a Numerous. Kaolin clay is sprayed on crop plants, deterring
fine powder pests from landing, feeding, and depositing eggs.
Neem The neem tree (Azadirachta indica), an evergreen Gypsy moths, leaf miners, whiteflies, thrips, loop-
native to the Indian subcontinent ers, caterpillars, and mealybugs (disrupts feeding and
development)
Pyrethrins Chrysanthemum (Dendranthema grandiflora) Numerous. Pyrethrins are general insectides and affect
flowers beetles, caterpillars, and various sucking insects.
Sabadilla Seeds of a tropical lily plant Schoenocaulon offici- Sap-feeding insects, caterpillars, and thrips.1
nale, native to Central and South America
Spinosads Soil actinomycete, Saccharopolyspora spinosa Numerous. Disrupts nuerotransmittors and feeding pat-
terns in moths, caterpillars, leaf miners, thrips, Colorado
potato beetles, and fire ants
Sulfur The mineral sulfur Spider mites, psyllids, and thrips
1 Highly toxic to honeybees, so application at sunset is recommended.
Diseases region are key to proper cultivar selec-
tion. It should be noted that treated and/or
Cultural controls are the best way to genetically modified seeds are prohibited in
prevent disease in organic gardening, USDA-certified organic production.
since few options exists for biological Disease organisms are spread by moving
control of diseases. Gardeners can best infected materials from plant to plant. To
control diseases from the outset through help avoid such spread, remove diseased
cultural practices that deter buildup of plants when leaves are dry and place them
disease organisms. Crop rotation is espe- in sealed plastic bags. This practice will help
cially important in controlling diseases of prevent bacteria or fungal spores spread-
Solanaceous crops (tomato, pepper, potato, ing to healthy plants. To minimize disease
etc.) as bacterial and fungal diseases are transfer between plants, avoid harvesting
particularly problematic when these crops or pruning tomato plants while the leaves
are produced organically. It is also best to are wet. Use a bleach-treated cloth to wipe
avoid composting residue of diseased plants down pruners between working tomato or
of any Solanaceous crops so that disease tree crops, which will also help minimize
organisms won’t build up in the compost disease spread.
pile. Instead, dispose of residue of diseased Many diseases spread by insect vectors—
plants or any Solanaceous crops in sealed insects transporting disease from plant
garbage bags and burn it or throw it away to plant as they feed. In Kentucky, bacte-
with municipal garbage. rial wilt of cucurbits is a classic example
It’s also important to select disease- of this method of disease spread. Spotted
resistant cultivars. There are a number of and striped cucumber beetles carry bacte-
sources for high-quality, untreated and/or rial wilt of cucurbits between cucumbers
organic seed. Knowing disease issues that and other cucurbit plants as they feed.
are problematic in your garden and in yourChapter 18 Organic Gardening • 287
Therefore, this disease is controlled through
the beetle vector, not the bacteria (Erwinia
Additional Resources
tracheophila) that causes the disease. This Bartholomew, Mel. 2005. Square Foot
example highlights an important principle Gardening: A New Way to Garden in
for the organic gardener: knowing the root Less Space with Less Work. Rodale Press,
cause of a disease or other problem in the Emmaus, PA. 352 pp.
garden requires understanding the entire Boyhan, George. E. 2009. Growing
garden as a system. One might view the dis- Vegetables Organically. University of
ease as the problem because it may be the Georgia Cooperative Extension Bulletin
final fatal blow to the plant. However, if the 1011. Athens, GA. 10 pp. http://www.
root cause is insect or soil related, treating caes.uga.edu/applications/publications/
the disease is ineffective if the underlying files/pdf/B%201011_4.PDF
condition or cause is not resolved. Caldwell, Brian. 2005. Resource Guide
Very few sprays are designed to control for Organic Insect and Disease
diseases organically. Copper-based products Management. New York State
are considered synthetic but are allowed in Agricultural Experiment Station,
USDA-certified organic production with Geneva, NY. 169 pp. http://www.nysaes.
certain restrictions. These products are cornell.edu/pp/resourceguide/index.php
restricted because they can accumulate in Coleman, Eliot. 1989. The New Organic
soil and create copper toxicity problems; Grower: A Master’s Manual of Tools and
are highly toxic to fish; and can also harm Techniques for the Home and Market
bees, beneficial soil bacteria and fungi, Gardener. Chelsea Green Publishing,
and earthworms. Copper-based products White River Junction, VT. 340 pp.
have been shown to somewhat effective in Gershuny, Grace, and Deborah L. Martin
controlling downy and powdery mildews, (eds). 1992 (Revised Edition). The Rodale
bean anthracnose, and tomato early blight. Book of Composting: Easy Methods for
Bordeaux mix (a blend of copper sulfate Every Gardener. Rodale Press, Emmaus,
mixed with hydrated lime) is considered PA. 278 pp.
a synthetic substance and is restricted in Jeavons, John. 2004 (Sixth Edition). How to
organic production due to its long residual Grow More Vegetables (and Fruits, Nuts,
activity and high toxicity to bees. Sulfur Berries, Grains and Other Crops than
that is mined (elemental sulfur) rather than You Ever Thought Possible on Less Land
extracted through manufacturing/power than You Can Imagine). Ten Speed Press,
generation can be used in certified organic Berkeley, CA. 240 pp.
production. In addition to serving as a trace Kuepper, George. Potting Mixes for
mineral, sulfur has fungicidal effects. Certified Organic Production. 2010
Research and development of organi- (reviewed edition).
cally-approved disease controls is occurring ATTRA Publication #IP112. National
rapidly. Up-to-date information and new Sustainable Agriculture Information
products can be found eXtension’s eOr- Service, Butte, MT. 20 pp. http://attra.
ganic website (http://www.extension.org/ ncat.org/attra-pub/potmix.html
organic_production) as well as Caldwell’s Lowenfels. Jeff, and Wayne Lewis. 2006.
Resource Guide for Organic Insect and Teaming with Microbes: A Gardener’s
Disease Management listed below. Guide to the Soil Food Web. Timber
Press, Portland, OR. 196 pp.288 • Organic Gardening Chapter 18
National Sustainable Agriculture Organic Materials Review Institute. www.
Information Service (also known as omri.org.
ATTRA). An excellent source of infor- Riotte, Louise. 1998. Carrots Love
mation on all kinds of sustainable and Tomatoes: Secrets of Companion
organic agricultural practices, marketing, Planting for Successful Gardening. Storey
etc. www.attra.org. Books, North Adams, MA. 224 pp.
Online Information Service for Non- Rynk, Robert. 1992. On-Farm Composting
Chemical Pest Management in the Handbook. Natural Resource,
Tropics. Trap Cropping. Hamburg, Agriculture and Engineering Service.
Germany. http://www.oisat.org/control_ Stephens, James M. 2003. Organic
methods/cultural__practices/trap_crop- Vegetable Gardening. Florida
ping.html Cooperative Extension Service Circular
Oregon State University Extension Service. 375. University of Florida, Gainesville,
Organic Gardening Fundamentals. FL. 12 p. http://edis.ifas.ufl.edu/pdffiles/
10-Minute University Series. http:// VH/VH01900.pdf
extension.oregonstate.edu/extension/ United States Department of Agriculture
mg/metro/sites/default/files/Organic_ Agricultural Marketing Service. The
gardening.pdf National Organic Program. http://www.
Organic Gardening Magazine. Published ams.usda.gov/AMSv1.0/nop. Last modi-
by Rodale Press since the 1940s. Now fied: 11/09/2010.
available online at: www.organicgarden-
ing.com.
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Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, M. Scott Smith, Director of Cooperative Extension
Programs, University of Kentucky College of Agriculture, Lexington, and Kentucky State University, Frankfort. Copyright © 2012 for materials developed by University of
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