Thurston, H. David. 1992.
Sustainable Practices for Plant Disease
Management in Traditional Farming Systems.
Westview, Boulder, CO. 279 pp.
If plant pathologists and other agricultural scientists are to be effective in addressing the problems of food production in developing countries, the traditional farming systems in those countries must be thoroughly understood. This is essential so that researchers address appropriate problems in the context of farmers' systems, and so that efficient, proven techniques can be disseminated to other farmers. Traditional knowledge can be overvalued or romanticized, but that is better than despising or ignoring it. Far too many giant projects in developing countries costing huge sums have failed dismally and have caused serious ecological problems because they lacked sufficient understanding of traditional agriculture. Outside intervention is often misguided and irrelevant when it is undertaken without an understanding of traditional agriculture. Today there is serious concern about "modern agriculture" because it is so highly energy-intensive, its genetic base is narrow, and its goals of increasingly high yields and labor use efficiency lead to extensive monoculture and overproduction. Sometimes excessive erosion, pollution, and pesticide residues result. It is time to reexamine the potential for traditional agriculture to contribute to an improved, sustainable "modern agriculture."
Small farmers constitute a most important element in the agriculture of developing countries. Although figures vary somewhat, the following are typical. Data from the Food and Agricultural Organization (FAO) in 1970 indicated that holdings less than one hectare of land comprised 33% of all holdings in developing countries. The mean size of agricultural holdings in those developing countries reporting to FAO was 6.6 hectares. According to the National Research Council (1982), "Half of the world's population is engaged in agriculture, the vast majority in the tropics and subtropics." Goodell (1984) wrote that small farmers till 65% of the world's arable land, and Todaro (1977) stated that 70% of the world's poor live in rural areas and engage primarily in subsistence agriculture. Most of the farmers in many developing countries are women. Poverty and socio- economic insecurity characterize the lives of a large sector of the rural population, and these problems are exacerbated in the vast group of small or traditional farmers who often have few resources beyond the labor of their families.
What is meant by traditional agriculture? The term traditional is usually associated with primitive agricultural systems or preindustrial peasant agriculture. Traditional farming usually is based on agriculture that has been practiced for many generations. Teri and Mohamed (1988) note that peasant production practices result from a long-term process of adjustment to the environment. Most small farmers in the developing world utilize agricultural practices that are to some degree "traditional", but many small farmers could not be characterized as traditional. The agricultural activities of traditional farmers are associated closely with their culture, as Schultz (1974) explains:
|Among primitive and peasant societies, cultural values and attitudes, beliefs and behavior patterns often play an equal or greater role than economic considerations when deciding whether to accept or not new production practices. Kinship obligations, peer group pressure, fatalistic beliefs, negative social sanctions regarding accumulations or surplus, individuality, caste differences and constraints and the perpetuations of common traditional values through family socialization all represent serious challenges to the foreign change agent.|
Anthropologists, archaeologists, ethnobotanists, and geographersand to a lesser degree ecologists, economists, and sociologiststry to understand traditional agriculture. Unfortunately, plant pathologists and others in the so called "hard agricultural sciences" seldom take courses in these disciplines or read much of their literature, with the occasional exception of ecology and economics. Likewise, professionals in non-agricultural disciplines do not often read agricultural literature or take our courses in production sciences. Consequently each discipline develops a separate language, which is often all but unintelligible to outsiders.
Today the rhetoric in agriculture centers on "sustainability" (Edwards et al. 1990, Francis et al. 1990), LISA (low-input sustainable agriculture), and biotechnology. Although these terms are vague and all-encompassing, they strongly affect current funding and research directions. Some economists, strongly advocate continual growth in the world's economy, and others, more ecologically minded, believe that sustainable development should be the goal. Brown and Shaw (1982) stated: "In a world where the economy's environment support systems are deteriorating, supply-side economics with its overriding emphasis on production and near blind faith in market forces will lead to serious problems." Rapid economic growth rarely can be achieved without jeopardizing ecological sustainability. Some economists (Daly 1980) argue for a steady state economy rather than an expanding one. Schultz (1964), in his classic study Transforming Traditional Agriculture, suggests that a country dependent on traditional agriculture is inevitably poor. More recently Ruttan (1988) commented:
|Traditional agricultural systems that have met the test of sustainability have not been able to respond to modern rates of growth in demand for agricultural commodities. A meaningful definition of sustainability must include enhancement of agricultural productivity. At present the concept of sustainability is more adequate as a guide to research than to farming practice.|
Do such conclusions by eminent economists suggest that nothing is to be gained by a study of traditional agriculture? I think not, and I doubt if such a conclusion is intended. If modern scientific agriculture is to have a role in the amelioration of world hunger and starvation, in part caused by population pressure resulting in environmental degradation, sustainable agricultural practices of traditional farmers in developing countries must be thoroughly understood and compared with alternative, new practices. If changes in traditional systems are necessary or needed, a thorough understanding of these systems is imperative as a first step before changes are initiated. Sustainable educational institutions of high quality with interest in and respect for traditional systems should be a high priority in future development funding. Traditional practices often provide effective and sustainable means of disease management. Traditional practices and cultivars (landraces) have had a profound effect on "modern agriculture," and most of our present practices and cultivars evolved from these ancient techniques and plant materials. Traditional systems and their disease management practices are in danger of being lost as agriculture modernizes; therefore, those practices should be studied carefully and conserved before they disappear.
Wilken (1974) suggests several additional reasons why the agricultural activities of traditional farmers are worthy of study. First, some traditional farming systems have excellent records in resource management and conservation. He suggests that those systems, which have lasted for thousands of years, surely justify serious study, although not all of the practices and strategies developed by traditional farmers are always successful. As Eckholm (1976) writes: "The littered ruins and barren landscapes left by dozens of former civilizations remind us that humans have been undercutting their own welfare for thousands of years." Perhaps we can learn from previous mistakes. In today's world a study of successful systems is especially important as petroleum, water, and other resources are becoming scarce.
Second, Wilken notes that although many traditional practices are labor-intensive, this aspect may be important and attractive to some societies having an abundance of labor and chronic unemployment. He writes that although traditional technology may be of little interest to scientists and Western businessmen, it represents the labor of millions of humans and the management of millions of hectares, and even small improvements would be significant for the world as a whole. For planners in developing countries, traditional methods have some advantages over modern agricultural techniques. For example, capital and technological skill requirements of traditional technologies are generally low, and adoptions often require little restructuring of traditional societies.
Finally, Wilken suggests that since modern agriculture has developed primarily in temperate regions the adoption of practices that are acceptable in these countries may have unexpected and undesirable impacts in developing countries, especially in the tropics.
To illustrate how lack of training in international agriculture can lead to errors in judgement when working with traditional systems in developing countries, I will use an example from my personal experience. In June l954 I went to Colombia, South America as an assistant plant pathologist with the Rockefeller Foundation. My knowledge of the country was essentially zero. I had to look up Colombia's location in an atlas and knew not one word of Spanish. Because of my lack of experience and training, I knew essentially nothing of the agriculture, customs, traditions, history, religion, or sociology of Colombia. I had seen Andean peasants only in picture books and had no inkling that thousands of years of agricultural trial- and-error, observation, and selection were behind what appeared to me to be haphazard or "primitive" farming systems.
I was hired by the Rockefeller Foundation to work in their agricultural program with the Colombian Ministry of Agriculture, specifically with potatoes. Fortunately, I did know something about potatoes, as I had received a M.S. degree in plant pathology from the University of Minnesota and had done my thesis on late blight of potatoes, a disease of worldwide importance. After a few months in Colombia, during which I had experienced a severe case of culture shock, but also had time to see how potatoes were grown and to travel a bit, I decided that almost everything the farmers were doing relative to growing potatoes was wrong. They planted whole tubers rather than cut seed as was done in Minnesota, they used very small tubers for seed (often 3- 4 tubers per hill) rather than a single 30-40 gram seed piece of optimal size as was done back home, and they planted seed so there would be 50-60 cm between plants rather than the 20-30 cm recommended in Minnesota. Rows were l50 cm apart rather than the 90 cm row spacing Minnesota growers used.
The fungicides used for disease control were ineffective, herbicides were not used, storage procedures were inadequate, and so forth. Almost all cultural procedures were "a mano", i.e. done by hand. On steep hillsides (where I eventually realized that the vast majority of Colombian potatoes were grown) that was understandable, but in the level land of the Sabana de Bogot , where our experiment station was located, I reasoned that large tractors and machinery such as that used in Minnesota were appropriate. Thus, I ordered a huge potato harvester, which simultaneously dug two rows of potatoes and put them directly into a truck. In retrospect, the machine was the most useless thing one could imagine for Colombian potato farmers and their conditions. Labor was less than $l.00 (US dollars) per day, and thus obtaining inexpensive labor for harvesting was not a major problem. The machine lasted barely two years before it broke down and became useless for lack of spare parts. By that time I had come to realize that perhaps it was not "appropriate" technology for Colombia.
Another order was for a 300-gallon, l4-row, John Bean potato sprayer. Insects and late blight of potatoes (caused by the fungus Phytophthora infestans) are serious problems in Colombia, and potatoes had to be sprayed frequently in order to obtain economic yields. The sprayer was useful for fungicides tests on our experiment station; we grew up to 100 hectares of potatoes on level ground, but it was not appropriate for most Colombian conditions. It took some time for me to realize that only a small percentage of the potatoes in Colombia could be sprayed with such a machine because of the steep slopes where most were grown. At that point we began using portable backpack sprayers for our fungicide tests, as most growers in the country used them, and the data we obtained using them was much more meaningful to Colombian growers than that obtained with a 300- gallon sprayer few of them could afford.
Almost all growers in the Andes of South America plant whole potato seed (tubers) rather than cut seed, which is commonly used in the United States. It is well known that cutting seed is an excellent way to spread pathogens (especially bacteria and viruses), but in the US we are able to use cut seed because of excellent seed certification programs and sound sanitation practices. Nevertheless, serious problems due to the use of cut seed still cause serious losses in the US. With my temperate zone mindset in l954, I believed we should use cut seed as growers in Minnesota did, especially so we could use the tuber- unit method for reducing viruses. This is a method whereby a tuber is cut into four pieces and planted with a space between it and other tubers. This practice greatly facilitates field removal or roguing of virus-infected plants and in the l950s was considered essential in the US to a good seed certification program. In l955 the potato program of DIA (Division of Agricultural Research of the Colombian Ministry of Agriculture), in cooperation with the Caja Agraria (a semi-official agricultural bank in charge of seed production for DIA), began to increase supply of the improved variety Monserrate, which held great promise for potato culture in Colombia because of its high productivity, high degree of general resistance to Phytophthora infestans, adaptability, and other excellent agronomic characteristics (Estrada et al. 1959). Incidentally, Monserrate's high level of general resistance to P. infestans is still evident today (Parker 1989).
By l959 a total of 700 tons of Monserrate seed was available for use by farmers. Almost all multiplication was accomplished using cut seed pieces, although customarily whole tubers were used in Colombia for planting. During the second growing season of l959, about 30 hectares of Monserrate were planted by the Caja Agraria on the farm "Valmaria" near Bogota at an elevation of 2620 meters. This planting represented about 50% of the Monserrate seed available for the entire country for the coming season. At harvest time approximately 30% of the tubers were infected with Pseudomonas solanacearum (the bacterium that causes bacterial wilt of potatoes). The disease, although common on potatoes in many countries at lower elevations, had been reported only a few times at high elevations in Colombia. This loss was a severe blow to the potato program of DIA, since the infected seed from this farm had to be discarded or sold for human consumption. Similar seed in the hands of several growers who cut their seed, following DIA recommendations, produced fields with l00% infection by P. solanacearum.
As a result of these losses from bacterial wilt, growers and the Caja Agraria became convinced that Monserrate was highly susceptible to the disease and demand for seed declined drastically. In fact, the Caja Agraria almost terminated its national seed multiplication program. In subsequent years, when whole seed pieces were planted in the same fields, no detectable infection occurred. Our research program reverted entirely to using only whole seed, and subsequently we never had another problem with P. solanacearum on our station (Thurston l963). We researchers finally came around to using a practice traditional farmers knew was practical for their conditions. Colombian farmers probably had discovered over the centuries that cut seed would not produce a crop. We scientists had to rediscover what the traditional peasant farmers of Colombia already knew. Many, although not all, of the practices of Colombian potato farmers had sound reasons for their existence, which we could not initially discern.
This example illustrates that because of lack of education or experience relative to traditional farmers and traditional agriculture in Colombia, my judgment on technology recommendations and appropriate areas of research in my first years there was initially poor. I spent a total of 11 years in Colombia and am proud of my association with DIA, ICA (Colombian Agricultural Institute), and the Rockefeller Foundation. In subsequent years, I believe I became useful and productive as regards the Colombian agricultural program, especially after I gained respect and appreciation for the knowledge of small farmers and the basic soundness of their farming systems.
Many projects intending to improve the lot of small farmers have failed due to a lack of understanding of how and why traditional agriculture works. I wish to emphasize that we in the temperate regions (our governments, universities, and private organizations) are still sending agricultural scientists to the tropics or into difficult, complicated environments with the same lack of training and experience I had initially. Often scientists who are sent have almost no understanding of or sensitivity to the agronomic and socioeconomic problems of the tropical regions; often they have the same mindset I originally had, i.e. that the only way to make progress is to do it like it was done back home. Not only the US, but most temperate countries of North America, Europe, and Asia are doing the same to some degree. Because of similar training, agricultural scientists trained in the leading agricultural universities of many developing countries encounter similar problems when they try to work with traditional farmers in their own country or other areas of the developing world.
Traditional farmer knowledge is often impressively broad and comprehensive. A few examples can illustrate this. Conklin (l954) described the agricultural knowledge of the Hanunóo, a mountain tribe of Mindoro in the Philippines. On some aspects of agriculture their knowledge is amazingly wide, accurate, and practical. They distinguish l0 basic and 30 derivative soil and mineral categories and understand the suitability of each for various crops as well as the effects of erosion, exposure, and over-farming. They distinguish over l,500 useful plant types, including 430 cultigens, and they discern minute differences in vegetative structure.
Mayan Indians in Mexico have their own comprehensive plant classification system. Berlin et al. (l974), describing the Mayan (Tzeltal) taxonomic system, state that "471 mutually exclusive generic taxa were established as legitimate Tzeltal plant groupings."
Bentley (1989) found that traditional farmers in Honduras, in addition to considerable general knowledge about plants, had an impressive knowledge of growth stages (phenology) of crops, especially maize and beans. Unfortunately, many farmers did not recognize plant diseases or pathogens. Bentley (1989) noted: "Traditional Central American peasant farmers know more about some aspects of the local agroecosystem than about others. In general farmers know more about plants, less about insects, and still less about plant pathology."
Much of the literature on traditional agriculture is anecdotal rather than experimental, much to the distress of scientists who believe that only information obtained by scientific methods is of real value. Also, traditional agriculture often includes a mixture of superstitious, religious, and magical beliefs (Casas Gaspar 1950). Some beliefs are of no obvious practical value, but others may constitute sound agricultural practices. Huapaya et al. (1982) interviewed Ayamara Indians near Lake Titicaca in Peru regarding their knowledge of plant disease management. They believe that plant diseases are caused by halos around the sun, certain phases of the moon, drought, hail, lightning, excessive humidity, fog, frost, dew, and the use of horse or cattle manure. The entrance into a field of animals in heat, pregnant or menstruating women, drunk men, or people or animals when dew is on the ground was also thought to cause disease. Indians dust their crops with ashes, spray them with fish water, place branches of muña (Minthostachys spp.a traditional insect repellent) between plants, and rogue diseased plants. To manage diseases they practice careful seed selection, crop rotation, and don't plant when the moon is full or the sun has a halo. People and animals are not permitted in fields when dew is on the ground. Several of the above practices would reduce disease incidence, but clearly their activities are a mixture of useful and useless practices.
Archeologists believe that humans began crop production perhaps 10,000 years ago. Some ancient societies developed sustainable agriculture practices that allowed them to produce food and fiber for thousands of years with few outside inputs; other traditional strategies were not so successful. Many of their successful practices have been forgotten or abandoned in developed countries, but are still used by many traditional, subsistence, or partially subsistence farmers in developing countries. Although considerable evidence shows that traditional farmers experiment and innovate (Chambers et al. 1990), most useful traditional methods of agriculture probably were developed empirically through millennia of trial and error, natural selection, and keen observation. These practices often conserve energy and maintain natural resources. Traditional farming systems, especially in the tropics, frequently resemble natural ecosystems. This, and their high level of diversity, appear to give them a high degree of stability, resilience, and efficiency. Teri and Mohamed (1988) state: "widespread plant disease epidemics in traditional agriculture are either rare, undocumented, unnoticed or all three." Traditional farmers are not always interested in the highest yields, but are concerned more with attaining stable, reliable yields. They minimize risks and seldom take chances that might lead to hunger, starvation, or loss of their land.
Most practices for disease management used by traditional farmers in developing countries are cultural practices. Yet little information is available in an easily accessible or understandable form on the cultural practices used in traditional systems. Palti's (1981) Cultural Practices and Infectious Crop Diseases is an excellent source of information on cultural practices for the management of plant diseases, but emphasizes primarily "modern" agriculture. Some practices of traditional farmers are these: altering of plant and crop architecture, biological control, burning, adjusting crop density or depth or time of planting, planting diverse crops, fallowing, flooding, mulching, multiple cropping, planting without tillage, using organic amendments, planting in raised beds, rotation, sanitation, manipulating shade, and tillage. Most, but not all, of these practices are sustainable in the long term. The disease resistance of traditional cultivars or landraces selected over millennia also is most important. Landraces are usually genetically diverse and in balance with their environment and endemic pathogens. They are dependable and stable in that, although not necessarily high yielding, they yield some harvest under all but the worst conditions. Pesticides are generally used in small amounts by traditional farmers, primarily because of their expense.
A major question regarding traditional agricultural practices is: are they sustainable? Can a practice be continued for a long period of time without environmental degradation, serious reduction of crop productivity, and the addition of heavy fossil-fuel inputs? The information in Table 1.1 strongly suggests that most traditional practices are sustainable. However, note that some of the practices require high external inputs, and many practices have high labor requirements. The various practices in Table 1.1 have been characterized according to my own knowledge and perceptions, recognizing that exceptions to some classifications might be made.
|TABLE 1.1. Sustainability, External Inputs Needed, and Labor Requirements of Selected Plant Disease Management Practices of Traditional Farmers.|
|adjusting crop density||Yes||Low||Low|
|adjusting depth of planting||Yes||Low||Low|
|adjusting time of planting||Yes||Low||Low|
|altering of architecture||Yes||Low||High|
|biological control (soil)||Yes||High||High|
|planting diverse crops||Yes||Low||Low|
|planting in raised beds||Yes||High||High|
|using organic amendments||Yes||High||High|
|a Under high population pressure the slash and burn system is neither stable nor sustainable.|
In Table 1.2, a number of traditional agricultural systems are considered for their productivity (crop yield or income produced), sustainability (ability to maintain the system in existence over a very long period of time even when subjected to stress), stability (obtaining consistent and reliable yields in both the short and long run), and equitability (relative distribution of wealth in a society). Conway (1985, 1986) discussed and defined the above terms. My classifications are obviously subject to considerable discussion, and exceptions might be made to some the classifications. Table 1.2 illustrates considerations important to planning agricultural development.
|TABLE 1.2. Productivity, Sustainability, Stability, and Equitability of Selected Traditional and Modern Agricultural Systems of the Tropics|
|Traditional Tropical Systems||Productivity||Sustainability||Stability||Eq uitability|
|Home gardens (Indonesia)||High||High||High||High|
|Slash and burn||Low||High a||High||High|
|Tapado, beans (Costa Rica)||Low||High||High||High|
|Modern Tropical Systems||Productivity||Sustainability||Stability||Eq uitability|
|Banana for fruit||High||Intermediate||Intermediate||Low|
|Rubber (Hevea in Asia)||High||High||High||Intermediate|
|a Under high population pressure the slash and burn system is not stable nor sustainable.|
Finally, systems should be analyzed for their yield per unit of land, capital, labor, and energy (other than human). Again, the classifications are generalizations I have made primarily for illustrative purposes. Table 1.3 gives insights into why traditional farmers make the decisions they do relative to their choice of farming systems.
|TABLE 1.3. Yield Per Unit of Land, Capital, Labor, and External Inputs of Selected Traditional Agricultural Systems|
|Yield per Unit of|
|System Inputs||Land||Capital Labor||External|
|Home gardens (Indonesia)||Intermediate||High||High||High|
|Plantain s (Uganda)||High||High||High||High|
|Slash and burn||Low||High||Inter||None|
|Tapado beans (Costa Rica)||Low||High||High||None|
Alternative agriculture, organic agriculture, ecological farming, and sustainable farming are among 16 terms used to describe a complex and interdisciplinary movement gaining rapid acceptance in recent decades, especially in the developed countries of the world (Merrill 1983).
Organic farming is perhaps one of the oldest farming systems in the world and has been practiced for millennia in Asia (King 1926). Significant portions of Chinese agriculture still use organic farming systems. Before World War II most agriculture in the corn belt of the US was essentially a crop and livestock system. Rotations were of 3-6 years duration, animal manure was applied to the soil, and rotations usually included legumes. The system has given way to open, cash grain systems (Thomason and Caswell 1987) in which rotations, if practiced, are of short duration and fertilizers are inorganic. An Amish farmer in New York described this system to me as "mining the soil." The cash grain system is not a sustainable model in the long term and is inappropriate for most developing countries. It is hoped that this book will contribute to a better understanding of traditional systems.
Cultural practices are often forgotten or barely mentioned in the modern plant disease literature, even though many farmers have successfully managed plant diseases for thousands of years, primarily with cultural practices. Most of these practices are sustainable, and, although some are highly labor-intensive, this is not necessarily undesirable in settings where land, energy, and capital are more limiting than labor. It is important to integrate traditional cultural practices into pest management systems for developing countries, especially those for management of plant diseases, to a greater degree than has been done in the past. If, as Boserup (1965) suggests, "population increase leads to the adoption of more intensive systems of agriculture in primitive communities, and an increase of total agricultural output," then efforts must be made to better understand the agricultural systems and practices of traditional farmers if the serious errors and failed projects of agricultural development efforts in recent decades are to be avoided. At the very least, these traditional practices are points of departure that will lead to the development of appropriate and acceptable improved practices.
Traditional agricultural practices deserve more respect than they receive. Traditional farmers' knowledge regarding many aspects of agriculture is often broad, detailed, and comprehensive, although this is not always the perception among agricultural scientists and development workers. Norgaard (1984) wrote:
|Traditional knowledge has been viewed as part of a romantic past, as the major obstacle to development, as a nonissue, as a necessary starting point, and as a critical component of a cultural alternative to modernization. Only very rarely, however, is traditional knowledge treated as knowledge per se in the mainstream of the agricultural and development and environmental management literature, as knowledge that contributes to our understanding of agricultural production and the maintainence and use of environmental systems.|
Although traditional farmers may not know what fungi, bacteria, or viruses are, in many cases they have effective, time-tested practices for managing pathogens. Traditional agricultural practices must be understood and conserved before they are lost with the rapid advance of modern agriculture in developing countries. Plant pathologists and other agricultural scientists can learn much from traditional farmers to elucidate principles and practices useful in the future management of plant diseases.
Detailed studies should be made to learn the effects of pathogens on existing traditional agricultural practices and the effects of traditional agricultural practices on pathogens. Scientists need to learn the role and importance of the practices developed during the last ten millennia. A study of methods of pest management in traditional agriculture, and research on improving their use, would provide a sound basis on which to initiate realistic improvements in systems of traditional agriculture. It is also probable that such studies will provide lessons and information of value to modern agriculture (Glass and Thurston 1978). After all, by using various cultural controls, resistant varieties, and biological control, traditional farmers have been practicing integrated pest management for centuries. The remarks of Haskell et al. (l981) summarize the complexity and challenge of traditional agriculture:
|It is now becoming recognized that any attempt to import technological change in ignorance of, even in defiance of, the socio-cultural background of small farmer practice is a recipe for disaster. The basic reason is simple; traditional peasant systems of agriculture are not primitive leftovers from the past, but are, on the contrary, systems finely tuned and adapted, both biologically and socially, to counter the pressures of what are often harsh and inimical environments, and often represent hundreds, sometimes thousands, of years of adaptive evolution in which the vagaries of climate, the availability of land and water, the basic needs of the people and their animals for food, shelter, and health, have been amalgamated in a system which has allowed society to exist and develop in the face of tremendous odds.|