This session is about the principals of pest management and the various ways to treat or prevent serious or significant problems with pests or disease in the home garden.
The most important "natural controls" are: (See Olkowski)
In Southern California, aphid populations build to high numbers in early Spring and early Fall when there is an abundance of fresh, new foliage rich in nitrogen. The buildup of aphids is sharp and dramatic. This buildup of aphids then triggers a build up of those organisms that feed on the aphids. Generally, this means a buildup of lady beetles in about two weeks as it takes them about that long to build a viable population. The lady beetles then become the predators and the aphids become the prey. Once the bulk of the aphid population has been consumed or reduced by the lady beetles, most of the lady beetles move on searching for a richer supply of aphids elsewhere and the system returns to a few aphids and a few lady beetles here and there which is normal. The garden needs a small aphid population to maintain a small number of lady beetles for the sake of the natural control system.
Notice that the event that started these regulating steps was the
change in the season and the basic dynamic is that organisms build-up
populations in response to an increased food supply. The aphid
"problem" was, in reality, a temporary condition of an increased
population caused by a change in the season. The natural controls, an
integral part of the ecosystem, returned the aphid population back to
more conventional levels without intervention by the gardener.
2. PROTECTION OF THE GARDEN ENVIRONMENT
Olkowski comments on the ability of the housefly to grow from being an
egg to being an adult capable of reproduction in as few as six days
and adds that a female housefly can lay up to 600 eggs at one time.
The authors then project that a single mating pair and their progeny
could produce a layer of flies over the entire surface of the earth in
a single summer. In context, Olkowski makes the point that the
ecosystem uses these natural controls to regulate populations and that
the natural controls are exceptionally efficient.
The natural controls are also fragile and the use of toxic materials
in the garden can and does cause them damage. Had the gardener used a
pesticide like malathion to kill the aphids in the example, the
application would have also killed the lady beetles plus a whole
battery of other beneficial organisms.
"Rodale's Color Handbook of Garden Insects" by Anna Carr says,
"If you were to spend an afternoon sifting through the soil and
examining the plants in one square yard of your garden, chances are
you'd find well over 2000 insects, ranging from microscopic
spring-tails to larger beetles and butterflies. Very few of these
would pose any threat to the health and productivity of your garden.
The fact is, most insects are directly beneficial to man and all are
useful and necessary to the economy of nature."
3. PESTS AND PATHOGENS AS ORGANISMS REMOVED FROM THEIR NATIVE
ENVIRONMENT
Just as weeds are problem plants because they were moved away from
their native environment and separated from their natural controls, at
least some of the pests seem to be problem organisms because they were
moved from their native settings and separated from their natural
controls as well. This dynamic also seems to apply to at least some of
the pathogens. It may be that this dynamic applies to all of the pests
and pathogens but that's strictly a guess.
Olkowski cites the Japanese beetle, the Mediterranean fruit fly and
the gypsy moth as examples of organisms that are problem pests because
of their separation from their natural controls and cites the
organisms that cause Dutch elm disease and chestnut blight as examples
of problem pathogens for the same reason.
4. THE USE OF PESTICIDES AS A LAST RESORT
Basic good gardening usually prevents and/or corrects most of the pest
or disease problems encountered in the home garden. In those cases in
which pest or disease problems still persist, there are a number of
additional techniques or materials that can be used as supplements for
pest management. The OCIA's International Certification Standard, for
example, lists a variety of materials that are approved or prohibited
for use in the production of certified organic crops. These standards
are also appropriate for the home garden and they are helpful to the
home gardener as a guide.
The approved pest management techniques or materials listed include:
One of the public gardens that promotes the avoidance of pesticides, uses Malathion for the control of thrips on roses. Thrips leave their shelter from inside the buds to mate at first light. Malathion evaporates so rapidly that it is almost a poison gas. The gardener's thinking is that the use of Malathion at first light would "get" the thrips without hurting the bees who show up later in the day. This approach, however, would also "get" those many beneficial organisms who "sleep over."
On a practical basis, use only those pesticides that are approved for
use on organic crops by the OCIA. Their list of approved materials
seems the most appropriate for the home gardener. It is based
primarily on environmental friendliness.
ACUTE TOXICITY
Most of the commercial pesticides are classified on the basis of their
acute oral toxicity - the number of milligrams of the test material
that will kill 50% of the test animals in a very short time. The test
material is force fed to the test animals and the results are
projected to milligrams of test material per kilogram of body weight
for the test animals. These projections are the LD50 numbers for the
various materials. The lower the number, the more toxic the material.
Pyrethrum, a natural derivative from pyrethrum daisies, is a relatively safe material with an acute oral LD50 of 1500. Diazinon, a synthetic material, is significantly more toxic with an acute oral LD50 of 300. Just because something is from natural sources doesn't mean that it is necessarily low in terms of acute toxicity. Nicotine, for example, has an acute oral LD50 of 55.
Pesticides are usually labeled on the basis of their acute oral LD50.
The testing procedures are relatively inexpensive and the test results
are relatively reproducible. Class I pesticides carry the label,
"Danger" and they have an LD50 rating of up to 50; Class II pesticides
carry the label, "Warning" and they have an LD50 ranging from 51 to
500; Class III and Class IV pesticides carry the label, "Caution."
Class III pesticides have LD50 ratings ranging from 501 to 5000 and
Class IV pesticides have LD50 ratings over 5001.
CHRONIC TOXICITY
There are problems in measuring the effects of long term exposure to
the various pesticides. There is no recognized testing standard. There
seems to be too many variables and the test results are too dependent
on interpretation. The long term effects can be carcinogenic (causing
cancer), mutagenic (causing genetic changes) or teratogenic (causing
birth defects).
The full effects of DDT didn't show up for years. This may or may not
be true of other materials as well.
TARGET SPECIFICITY
Olkowski makes the statement, "The best materials [pesticides] are
species-specific; that is, they effect just the group of animals or
plants you are trying to suppress. Avoid broad-spectrum materials
because they are non-selective and can cause resurgence and secondary
pest outbreaks in the long run. Where broad-spectrum materials must be
used, apply them in as selective a way as possible."
In practice, target specificity is very relative. Virtually any
material that is highly toxic to one organism will be at least mildly
toxic to the other organisms. Target specificity works well when the
control agents are biological and not just toxic agents. The use of
beneficial organisms or virile inoculates like BT can be very specific
which is a decided advantage.
PERMANENCE
Some of the synthetic pesticides of the 1940's and 1950's have left
toxic residues that are still with us today. There are massive
deposits of DDT, for example, sitting on the ocean floor off the coast
from Southern California left over from the days when the area had
significant agriculture.
In the U.S., most of the residual chlorinated pesticides have been outlawed by the EPA but there is still a host of pesticides that cause significant damage to the environment and many of these materials have a long term presence. RoundUp, for example, is promoted as being environmentally friendly because it is relatively low in terms of both acute and chronic toxicity and because it is said to break down readily after application. The claim of rapid break down seems more promotional than factual. RoundUp binds very tightly onto clay soil particles and it can remain in the soil for a long time.
It is realistic to assume that any toxic material that you might use
in your garden will be there for some time.
SYNERGISM
The dictionary defines synergism as, "The simultaneous action of
separate agencies, which, together, have greater total effect than the
sum of their individual effects: said especially of drugs." The lethal
combination of heroin and alcohol is an example of synergism.
Piperonyl butoxide, (PBO), is a natural insecticide derived from
sesame. It is relatively nontoxic. It is used primarily as a synergist
to increase the toxicity of a number of botanical products such as
pyrethrum or rotenone. The consumer may think, for example, that a
certain formulated pyrethrum product is safe and environmentally
friendly because it contains only "natural ingredients". . . But if
that formulation includes PBO, the product could well be relatively
toxic and destructive of the environment. PBO is prohibited from use
on certified organic crops by the OCIA.
6. PEST TOLERANCE
A friend made the statement that the greatest gift the parent could
give to the child was the ability to cope with the ambiguities of
life. For the gardener, the ambiguities of life means putting up with
a few bite marks or blemishes on the garden products. An aphid or
grass hopper has a legitimate presence in the garden. They are mostly
a problem when there are just too many causing too much damage.
Christopher Lloyd, the great English gardener, says, "The gardener must train his eye not to see those things he doesn't want to see."
Neem oil is an interesting material. It is extract from the neem tree. It has been in use as an insecticide, fungicide, and bactericide for centuries in Asia and Africa. It is in the process of becoming registered and cleared for use by the various regulatory agencies in the U.S. It is relatively nontoxic, environmentally friendly, and can be use more or less selectively against many pests without doing serious damage to many of the beneficial organisms. It seems to be generally effective. The down side is that neem oil is expensive.
Suffocating or dormant spray oils, however, are convenient materials for the home gardener and they are very handy for spot treatment of white flies, mealy bugs, aphids, scale, a variety of mites plus a variety of plant diseases should outbreaks occur. One part oil is cut with 50 parts of water, shaken and applied as a spray to the point of runoff. They can be washed off by the rain and repeated applications at weekly intervals may be required. They work by suffocating the target organisms rather than being toxic, per se, and if used in moderation, they don't seem to pose any real threat to the environment. The materials bio-degrade. They should be used in cool weather to avoid foliage burning. "Eco-Oil" from "Gardens Alive," @ (812) 537-8650, is a favorite brand because it causes less leaf burn at elevated temperatures.
Certainly, gardening is about trying new things. It's also about common sense.