COMPOSTING & PLANT NUTRITION PRINCIPALS OF PEST MANAGEMENT; PESTS & SOIL DISEASE; PLANT & SOIL PESTS

The "Sunset Western Garden Book" says, "The notion of pest control - where control implies eradication - has been superseded by the concept of pest management. The management concept acknowledges that many of our perceived ‘problems' are indeed natural components of gardens: their simple presence doesn't necessarily spell trouble. In a diversified garden, most insect pests are kept in check by natural forces (such as predators and weather); only if the pests reach seriously damaging levels do you have an indication that natural controls are temporarily unbalanced - suggesting temporary intervention by the gardener."

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.

PEST MANAGEMENT

The principals of pest management are presented in six segments:
  1. The natural controls of the ecosystem;
  2. Protection of the garden environment;
  3. Pest and pathogens as organisms removed from their indigenous environment;
  4. The use of pesticides as a last resort;
  5. Issues of toxicity; and
  6. Pest Tolerance.

1. THE NATURAL CONTROLS OF THE ECOSYSTEM

The ecosystem is defined as "The way the community of all of the living things in a specific space interrelate with each other and with the physical and chemical environment that they share." The environment and those living things that impact on the various organisms regulate organism populations and are considered as natural controls. Organic gardening relies primarily on the natural controls for pest management.

The most important "natural controls" are: (See Olkowski)

An example of the way these natural controls manage pests:

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:

Note that the use of environmentally friendly pesticides is only one of a number of options. If environmentally friendly pesticides are to be used, they should be used only as materials of last resort. Pesticides, including those of natural origin and considered as "environmentally friendly," work because they are toxic to the target organisms. All of the pesticides are consistently toxic to other organisms and the ecosystem as well - those that are considered as "environmentally friendly" are, in reality, just "friendlier." Toxicity is relative.

5. ISSUE OF TOXICITY

There are a number of things that are involved in determining just how appropriate a material is for the garden. There are at least six major issues. The terms, "safe" or "environmentally friendly" are often used but that use is more promotional than descriptive. The main six issues are:
ENVIRONMENTAL FRIENDLINESS
If the options have finally come down to the use of a pesticide, it is important to use the one that will do the least amount of damage to the environment. It is seldom self-evident as to which material would be least damaging in the various situations. Nicotine, for example, is prohibited from use on certified organic crops by some certifying agencies because the material is so toxic and dangerous to handle. It is permitted for use by other certifying agencies because it breaks down so readily when exposed to sunlight and because it can be used in the garden without doing significant injury to bees.

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."

TREATMENT & PREVENTION OF PESTS & DISEASE

USE OF CERTIFIED MATERIALS

There are a number of certification standards that spell out what can and what cannot be used in the production of commercial organic crops. These standards are helpful to the home gardener as a general guide. All of the approved materials in the 1996 OCIA International Certification Standard are environmentally friendly, convenient to use and generally available for the home gardener.

PESTICIDES

Keep in mind that pesticides, including those that are permitted for use on certified organic crops, should be used as a last resort. These materials are destructive of the environment - those that are permitted for use on certified organic crops are just less destructive than those that are prohibited.

BOTANICAL PESTICIDES

Citrus oil, garlic, neem, pyrethrum and quassia are the only botanical pesticides that are allowed for use on certified organic crops by the OCIA. They are plant extracts that are relatively friendly to the environment. Nicotine, rotenone, ryania and sabadilla are also plant extracts but they are prohibited from use as a result of their high toxicity.

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.

MINERAL PESTICIDES

Bordeaux mixes, sulfur, lime sulfur, and suffocating or dormant spray oils are allowed for use on organic crops. Bordeaux is a slurry of copper sulfate and lime in water. It is effective in preventing and correcting a number of disease and mite problems on fruit trees and grapes but it also can burn the foliage and fruit. Bordeaux, sulfur, and lime sulfur are difficult to apply and over application can make the soil toxic. These materials are better suited for the commercial grower rather than the casual home gardener.

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.

ALTERNATIVE PESTICIDES

There are a number of insecticidal and herbicidal animal oil soaps on the market and they are permitt ed for use on certified organic crops. They are said to be reasonably effective, relatively nontoxic, and environmentally friendly. The materials bio-degrade. They are not particularly selective in their action and are a threat to the beneficial organisms.

SYNTHETIC PESTICIDES

All of the synthetic pesticides are prohibited from use on certified organic crops. The issue is their toxicity and their negative impact on the environment.

BENEFICIAL ORGANISMS & BIOLOGICALS

There is a whole army of beneficial organisms and biologicals available to the home gardener: pest predators, pest parasitoids, microbial inoculates, pheromones, etc. . They can be used effectively in many situations but they are also tricky to use. A separate class series on beneficial organisms and their use is planed for a later time.

TRAPS & BARRIERS

Traps and barriers are often overlooked in the home garden. Mostly, we just need to be reminded that they are a viable option. The problem with traps and barriers is that they tend to be "eyesores" ruining the look of the garden. The challenge is in coming up with devices or structures that work and blend in or contribute to the garden design. It can be done. It just takes some thought.

USE OF "HOME REMEDIES"

One of the problems with home remedies is that only some of them work. A spray of a 1% solution of baking soda in water will give good control of powdery mildew on roses. A drop of lemon oil does a fair job of cleaning up a cluster of mealy bugs. There was, however, a formula for an "organic RoundUp" being circulated a while back that was a mixture of battery acid and salt which would be an ecological disaster. This mix would be much more destructive of the garden environment than the product it was designed to replace.

Certainly, gardening is about trying new things. It's also about common sense.

READING