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PLANT ECOLOGY: A NEW APPROACH TO PESTS IN AGRICULTURE

By Eliot Coleman
For presentation at NCAMP's 11th National Pesticide Forum

This is a radical paper. I make no apologies because I know from practical experience on my farm that what I am about to present is valid. I propose that our current pest control thinking in agriculture is 180 degrees backwards. It is almost as if there is an embroidered tapestry of the natural world hanging from the rafters. The conventional pest control mentality is standing on the back side of the tapestry. From that perspective the pest controllers see difficulties, confusions, insoluble problems, and loose ends. If we could stand on the front side of the tapestry we would have a clear picture of how the natural system functions. And what is apparent from the front side of the -tapestry is a new understanding of plants and pests where pesticides are as mistaken as any of the other rejected theories that humans have held and discarded over the centuries.

There are many examples of such 180 degree reversals. We now forgive Galileo for expressing the Copernican view that the earth revolves about the sun rather than the once prevalent Ptolemaic opposite. Except for a few Flat Earth societies the round earth is acknowledged. A number of modern examples have arisen recently. Back when wolves were considered bad, confusion reigned over whether it was better to shoot, trap, or poison them. Now a totally pew understanding of their benefit as predators in the system is commonplace. The attitude on forest fires has reversed from seeing them as something totally negative to understanding that they serve an important positive role. Some brave thinkers in Yellowstone took a lot of flack for pursuing that new policy.

The 180 degree radical agricultural idea in this paper suggests that it is a more successful approach to enhance the insusceptibility of plants rather than to kill insects. This view sees insects and disease in agriculture as indicators of plant stress rather than as enemies to be destroyed. Insects and disease are bringing us a message and since it is a message we haven't understood, we have tried to kill the messenger. If we pay attention to the message we can learn to prevent pest damage from occurring and pesticides become unnecessary.

I have often been asked what qualities are required to be a successful organic grower. My semi-joking reply has been, "just one, a thick skin." I realized as soon as I started 25 years ago that my chosen field made me an instant odd-ball. Conventional farmers, fertilizer salesmen,extension agents and a majority of the general public all treated me with the type of scorn that our society reserves for the "reality challenged". My first act of self protection was to stop using the word organiciand substitute the word biological - biological agriculture - the same as the word "biologique" that the French use. At an international agricultural conference a French friend asked me why I had made that change. "Organic is a buzz word," I told him. "It alarms people. Whenever I,say organic I can see people's eyes begin to cloud over and they start looking at their watch." "Quel coincidence," he said. "What a coincidence. That is just what happens in France when I say biologique."

Despite my occasional discomfort at being considered an odd-ball, I was not unaware of the reasons why. First, I was espousing a theory in disagreement with popularly accepted thinking. And, second, I could produce very little, if any, scientific data to support my case. The only proof I had was my farm. People could come there and see that it worked, as my customers did when buying produce. But the nay-sayers hadn't seen it. And even if they had seen it' my successes were merely anecdotal evidence and, consequently, not acceptable to Science with a capital S. I learned to live with that situation and figured it would change in the future as more scientific studies about organic farming were published.

But there is one subset of organic growing about which extensive scientific evidence does exist - the relationship between plants and pests. Although almost none of this research directly specifies organic agriculture, its subject matter - the effect of cultural practices on the resistance of plants to insects and disease - has a long history of scientific investigation. It also ties in with a casually stated tenet of organic farming that healthy plants aren't bothered by insects. Or, put more scientifically, that plants are inherently insusceptible when properly grown and only become subject to insect and disease problems when they are stressed by unfavorable growing conditions. The best defense, therefore, is to optmize the growing conditions with organic matter, minerals, crop rotations, green manures, soil aeration, soil drainage, irrigation and other cultural practices.

But no one had ever attempted to pull all the evidence together in order to establish the bows and whys. Thus, many years ago, I began spending evenings in the periodical stacks of the nearby university library reviewing the literature on the subject. The evidence was impressive. For example, an industry financed survey of the literature on just one small segment of the subject, the influence of potassium on plant health (Perrenoud, 1977), cited 534 references and noted that since 1950 the number of new references available has doubled every decade. A paper by White (1984) specifically exploring one theory about the relationship between plant stress and insect abundance cites more than 300 references and has itself been cited almost 200 times in subsequent studies. That isn't to say that everyone agrees on this subject but rather that a great deal of work has been and is being done.

Let me give some examples: Benepal and Hall (1976) at Kansas State investigated the relationship between an imbalanced supply of the major plant nutrients on squash plants and insect infestation by the squash bug. Plants grown in cultures deficient in either phosphorus, potassium or sulphur showed an increase in the non-protein free amino acid level in the leaves compared with plants grown with full nutrition. The more imbalanced the nutrition, the higher the free amino acid level. They observed a direct correlation between the increased free amino acid levels in the leaves and the increased number of insects feeding on the plant. The more imbalanced the nutrition, the higher the number of insects. When plants were grown with balanced nutrition insect feeding was negligible or non-existent.

White (1984) in Australia found similarly that plants under a wide variety of environmental stresses become a better source of food for invertebrate herbivores because the stress causes an increase in the amount of nitrogen available in their tissues. And, further, that the degree of the disruption of the metabolism of a plant necessary to induce these physiological changes may often not be sufficient to produce visible signs of stress in the plant. The only indication is the presence of invertebrate herbivores feeding on the crop.

In a study of rice crops from 970 sites in Brazil, Primavesi et al (1977) stressed the importance of minor element nutrition in protecting paddy rice from the disease, rice blast. They determined from field experiments that plant infection, even under conditions especially favorable to the development of the disease - such as susceptible variety, unsuitable soil, infected seed, heavy nitrogen fertilization, and climatic conditions favorable to the fungus - it could be prevented if sufficient levels of important minor nutrients, in this case principally manganese and copper, were available to the plants.

Van der Lann (1956) in Holland carried out trials on the specific influence of organic manuring on nematode infestations. The nematodes caused only minor damage on the organic manure plots. He accounted for the difference as follows: (a) organic matter improved soil structure and moisture holding capacity and many parasites are known to cause less damage in improved soil; (b) organic matter increased soil micro-organisms and the nematodes may have been killed by their natural enemies; (c) organic manuring is known to affect the morphological structure of the plants and their roots and these changes may have made the plant more resistant to nematodes; and (d) physiological changes within the plant tissue also occurred which added to the resistance of the plant.

Thiem (1938) in Germany, refers to both an absolute and a relative immunity to pests. The former he calls genetic immunity and the latter pheno-immunity. He considers plants to be genetically immune when their resistance is such that a specific pest can never propagate and develop on them. Pheno-immune plants, on the other hand, are those whose degree of resistance is such that they will be susceptible or resistant depending upon outside influences. If the resistance of a pheno-immune plant is to be adequately maintained then cultural conditions affecting soil structure, its physical and chemical make-up, and its biotic life must be carefully considered. Thiem further contends that even an agricultural practice such as large scale monoculture, often considered a causative factor of insect multiplication, will present no problem if cultural practices succeed in assuring pheno-resistance.

A few quotes from the conclusions of other studies will complete the picture: Lees (1926) "... perhaps in the future more reliance will be put on correct cultural conditions than on spraying, and the conditions of the host plant be more closely watched than the presence of the insect parasite." Wittwer and Haseman (1945) "possibly the continuing need for the creation of new insecticides to hold in check greater and more destructive ravages in insect pests is aggravated by the gradual but general decline in soil fertility from year to year." Van Emden (1966) "There is ample evidence that the nutrient status of the host plant has major effects of economic importance on phytophagous insects." Johnson (1968) "the evidence supports the idea that plant condition as affected by water or nutrient stress be a primary factor influencing the population dynamics the insects feeding on the plant." Leath & Ratcliffe (1974) "One cannot help but be impressed by the extent and diversity of the research on the plant disease-fertility relationship Evidence shows both direct and indirect effects of fertilizer applications on (1) pathogens in the soil and in the host, (2) the pathogenicity per se of an organism, as well as (3) the structural and physiological changes in the host that contribute to disease resistance, tolerance or escape." Chaboussou (1976) "To sum up, the results already obtained seem to show that the search for improvement in the plans 'c resistance through its physiology is not just Utopian but quite practical."

Even the USDA in its 1957 Yearbook of agriculture has this can of to say: "Well fed plants usually are less susceptible to soil borne organisms than are poorly nourished plants. Good fertility may so enhance the resistance of the (host) plant that the parasite cannot successfully attack the roots." And in one of the few studies specifically relating to organic farming, Culliney and Pimentel (1986) conclude: "Whatever the cause(s) for the significantly fewer insects in the organic treatments, the results support the proposition that organic fertilizers can promote crop-plant resistance to attack by insect pests."

Every one of these studies confirmed what I was seeing on my farm. So I assumed that if I began speaking about the theory that unstressed plants have inherent resistance to pests I would no longer be considered "reality challenged". I would now be able to cite scientific research to confirm the practical success I was having in growing pest free crops. Boy, was I surprised. The information was just as poorly received as previously. But the reaction had changed I no longer encountered clouded eyes and furtive glances at watches. I had moved beyond that. I was an even odder-ball. The new response was the "Brooklyn Bridge look." The one that goes, "Un huh, and if I believe that I suppose you'll tell me that you have a bridge in Brooklyn to sell." Feel free to indulge. I'm used to it by now.

But the fact is that this concept works not only on my farm but on organic farms all across this country and around the world. In preparation for this talk I sent out a questionnaire to 50 of the best commercial organic vegetable growers. I asked them if they had observed on their farms a correlation between healthy, unstressed plants and reduced incidence of pests and diseases. All but one said yes. I asked them what percentage of potential pest problems they expected to avoid entirely through growing healthy, unstressed crops. The average response was 75 percent. If you realize that these growers have achieved that level of success with no other resources than their own determination the 75 % figure is particularly impressive. Even more impressive if you realize that what they are doing is impossible according to conventional agricultural thinking. If these commercial organic growers are doing 75 ~ of the impossible one would expect great interest in this idea and the beginning of a concentrated effort to seriously investigate it.

I haven't seen it yet. The idea meets enormous resistance. When I suggested to the organizers of a couple of recent conferences on alternative pest control that they include at least one paper introducing an outline of this theory, the suggestion was politely but firmly rejected. I suspect they thought a theory that weird would jeopardize the legitimacy of the entire conference. They were right, but for the wrong reason. The idea is only weird when one merely fiddling with the fine tuning of the status quo. What I am proposing is a revolution. This theory deals in realities that are Outside the present framework of accepted entomological thought. My suggestion to the conference organizers was rejected because I was asking what I call an unanswerable question. Let me give an example. I have many times been involved in conversations with entomologists where I have requested that they pause for a moment in their discussion of alternative pest control. I have then asked them if they are aware of the fact that I and many other organic vegetable growers seem to have been able to establish systems where pest control, as they view it, is not the issue; that we have learned to view pests as indicators of plant stress rather than as enemies; that we deal with the situation by focusing on correcting the cause of the problem, inadequate growing conditions, rather than focusing on treating the symptom, the pest. After I ask that question they smile politely, thank me for my input, and return to their discussion of pest control. In this case I have asked an unanswerable question. They ignored me because the only way to deal with the issues I raised would have been to question the very assumptions at the basis of their thinking. A major impediment to understanding this concept is not entomological but rather etymological. Because of our unfamiliarity we have no word for this concept. And we can hardly consider an idea if we have no word with which to refer to it. For example, everyone is familiar with Departments of Plant Pathology, but does any university have the opposite, a Department of Plant ? What would the word be? Plant etiology. Plant ethology. We are all familiar with the phrase "pest control", but who ever hears about "plant enhancement". Since I love words I have often played with creating a combination such as eu-crasio-trophic: A well state of the physical constitution through nourishment. I suspect plant etiology or plant ethology may be the simpler term. The Department of Phyto-eu-crasio-trophy doesn't exactly trip off the tongue. But the fact remains that without a word we can not even begin to consider the concept. Another major resistance to the idea comes from humal, fear of powerlessness if we don't arm ourselves against our supposed ene es. This is obvious from the words we use in writing and speaking about agriculture. Pests "attack" the plant. They "ravage" the crop. We do "battle" with them in order to "defeat" or "conquer" the "enemy". We use bug "killer" in a spray "gun" to "blast" them. Van den Bosch (1978) paints a compelling verbal picture of the modern pesticide applicator portrayed as a swaggering, macho, Western gunslinger "pumping the lethal load of his Colt .44" into the bad guy. Our primary view of the biological world and natural systems of agriculture is one of fear and mistrust. Only rarely do we consider the improved relationship that could result from investigating, analyzing, understanding, and cooperating.

Despite the surface appearance of a natural approach in the importation and dispersal of predatory insects, the practice is based on the same enemy thinking as is the use of pesticides. It is similar to the situation towards the end of the Vietnam war when we began to think that it was wrong for occidentals to kill orientals and we instituted a policy called Vietnamization so that orientals could kill orientals. Bringing in mercenary bugs is still an enemy philosophy, still treating the symptom, still killing the messenger.

I have pondered a lot about the reasons for our attitude. I think we have difficulty in accepting the idea of a benevolent nature with elegant systems because we have made nature in our own warlike image. We see natural processes as if they are projections of our own actions and thought patterns. Thus we see malevolence in the relationship of one organism to another and in nature's relationship to us. We don't notice the beneficial balances between predator and prey that are maintained throughout the natural world. We miss the obvious logic of tipping that balance in our favor by creating optimum growing conditions for the plants. All we can see are the temporary agents who inform us of the imbalance (the pests) as threatening forces to be battled and defeated. We need to look again. It is a refreshing mental exercise to look at something familiar from a different perspective; to reappraise nature as a system that is not malevolent but benevolent; to see pests as helpful signals or indicators, not enemies; to see the relationship between predator and prey as natural management rather than violence; to understand that when we work against the system by doping up sick soil and killing pests we are contributing to the problem. The farmer's aim is not to protect sick plants but to enable healthy ones. You enable plants to attain their natural insusceptibility by removing plant stress. You remove plant stress by working to optimize all the agronomic factors involved in plant well being.

In closing let me give a short summary of my argument. If we can modify our thinking to realize that pest problems in agriculture are symptoms of a deeper problem, we can learn from them to search for their causes. The extensive literature on the subject strongly suggests that the cause lies in the physiological dysfunction of the plant as a result of imbalanced nutrition or unsuitable growing conditions. One effect on the plant of this physiological dysfunction is to increase its susceptibility to disease and enhance its suitability as a source of nourishment for insects. In consequence, to resolve the problem rather than only to mask the symptoms, the practices of the farmer must begin from a cause correction thought pattern. For those farmers wishing to attempt such a shift, general experience has shown that practices which stimulate the biological activity of the soil such as adding organic matter, mineral balance, near neutral pH, soil aeration, moisture level, and crop rotation to name a few, are the most widely effective and least expensive in enhancing the pest resistance, the yield, and the biological quality of the produce. In twenty five years of market growing I have never found any need for pesticides once I succeeded in creating growing conditions that optimized the physical well-being of the crop. Those conditions are not the same for all crops. I have had to experiment and observe. But in no case did the creation of those ideal conditions require more than the minimal resources of a small farm or more than a reasonable understanding of soil science and agronomic principles. What it did require was a thought pattern that approached the problem from the point of view of cause orrection rather than symptom treatment. For too long organic farming has been presented as an answer to the pesticide problem without any real understanding of how it functions or how well it could function. It was held out as something akin to a fairy godmother. I'm reminded of the two customers who walked up to my market stand next to the asparagus fieldione August. The asparagus fern was beautiful and green and about six feet tall. They had obviously been discussing the merits and demerits of organic agriculture because as they came in view of the asparagus field one grabbed the other's arm and said, "There, I told you organic farming was sensational. Look at that dill!" It wasn't dill but it was sensational.

Galileo realized that he would have "to mold anew the brains of men" in order to change the prevailing view of cosmic patterns. The change I am proposing - from a preoccupation with pest destruction to a concentration on plant construction - requires a similar remolding. But it is one that will allow us to seriously research and quantify the successes of organic growers and make them understandable and accessible to all farmers. This is a biologically-oriented thinking that sees our agricultural efforts as participatory rather than antagonistic vis--vis the natural world. It isn't a question of whether pesticides are undesirable or not. The fact is that they are superfluous. They were devised to prop up an agro-industrial framework that was misconceived from the start. When you abandon that framework, you can abandon its negative thinking pattern. We need to begin studying the natural systems of agriculture from the point of view of aiding and abetting and enhancing the positive factors rather than our present focus on killing the negative factors. The published research and the experience of organic farmers demonstrates clearly that when we accentuate the positive, we simultaneously eliminate the negative.

REFERENCES

BENEPAL, P.S. and HALL, C.V. 1976. The influence of mineral nutrition of varieties of Cucurbita pepo L. on the feeding response of squash bug Anasta tristis De Geer. Am. Soc. Hortic. Sci. 90, 304-312.

CHABOUSSOU, F. 1976. Cultural factors and the resistance of citrus plants to scale insects and mites. pp. 259-280. In Fertilizer Use and Plant Health. Proc. 12th Colloquium of the International Potash Institute, Worblaufen-Bern, Switz.

COLEMAN, E.W. AND RIDGEWAY, R.L. 1983. Role of stress tolerance in integrated pest management. pp. 124-142. In Sustainable Food Systems. D. Knorr (Ed.) AVI, Westport, CT.

CULLINEY, T.W. and PIMENTEL, D. 1986. Ecological effects of organic agricultural practices on insect populations. Agric. Ecosystems Environ. 15, 253-266.

JOHNSON, N.E. 1968. Insect attack in relationship to the physiological condition of the host tree. N.Y. State Agric. Exp. Stn., Cornel University, Ithaca, N.Y.

LEATH, K.T. and RATCLIFFE, R.H. 1974. The effect of fertilization on disease and insect resistance. pp. 481-503. In Forage Fertilization. D.A. Mays (Editor).Am. Society of Agronomy, Crop Science Society of America and Soil Science Society of America, Madison, WI.

LEES, A.H. 1926. Insect attack and the internal condition of the plant. Ann. Biol. 13, 506-515.

PERRENOUD, S. 1977. Potassium and plant health. International Potash Institute, Worblaufen-Bern, Switz.

PRIMAVESI, A.M., PRIMAVESI, A., and VEIGA, C. 1972. Influences of nutritional balances of paddy rice on resistance to blast. Agrochimica 16 (4-5), 459-472.

THIEM, VON H. 1938. Uber bedingungen der massenvermehrung von insekten. Abr. Physiol. Angew. Entomol. Berlin-Dahlem 5 (3), 229-255.

VAN EMDEN, H.F. 1966. Plant resistance to insects induced by environment. Sci. Hortic. 18, 91-102.

VAN DEN BOSCH, R. 1978. The pesticide conspiracy. Doubleday, Garden City, NY.

VAN DER LAAN, P.A. 1956. The influence of organic manuring on the development of the potato root eelworm, Heter dera rostochiensis. Hematology 1, 113-125.

WHITE, T.C.R. 1984. The abundance of invertebrate herbivores in relation to the availability of nitrogen in stressed food plants. Oecologia (Berlin) 63, 90-105.

WITTWER, S.H. and BASEMAN, L. 1945. Soil nitrogen and thrips injury on spinach. J. Econ. Entomol. 38 (5), 615-617.

Copyright 19-- Eliot Coleman. All rights reserved.


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