GROWING STRAWBERRIES, HEALTHY COMMUNITIES, STRONG ECONOMIES AND CLEAN ENVIRONMENTS:
WHAT IS THE ROLE OF THE RESEARCHER?

Marvin Pritts, Dept. of Horticulture, Cornell University, Ithaca, NY, USA 14853

Keywords: sustainable agriculture, fumigation, plastic, microorganisms, pesticides, biological control

Abstract

Strawberries are produced in much of the world with practices that many consider unsustainable. These include soil fumigation, the use of plastic, a high water requirement, and dependency on pesticides to produce high quality fruit. In addition, strawberry fruit quality is inconsistent in the marketplace, and the product is often unaffordable to poorer segments of the population. Many of the problems inherent in our production systems simply reflect an absence of design around certain guiding principles. No one set out to deliberately design an input-intensive, environmentally expensive production system for strawberries, it just evolved as growers and researchers responded to problems with short-term solutions. Researchers are now challenged to design and build strawberry production systems that follow certain guiding principles that include the use of renewable and recyclable resources, the use of products and practices that do not cause environmental damage, practices that do not harm communities of people, and systems that are economical. Eight critical questions are presented that, when answered, will help provide the building blocks for a more sustainable design. Our legacy as a worldwide community of researchers could be one of entrenchment as we fine-tune current production systems, or it could be one of creative design as we develop and introduce novel production systems that sustain soils, farms, communities, and the environment far into the future.

1. Introduction

Imagine a food production system that requires complete sterilization of the soil to be successful, uses large amounts of unrecyclable and nonrenewable plastic for controlling weeds and plant growth, requires a considerable amount of water to establish plantings, and depends on frequent applications of pesticides to produce acceptable fruit quality. In addition, imagine that the food from this system is considered to be among the most inconsistent items in the grocery store, and contains higher levels of pesticide residue than most other produce items. The price is sufficiently high so that poorer segments of society tend not to purchase the product, yet farm workers accuse growers of not paying a fair wage. Unfortunately, this description is typical of strawberry production in much of the world.

Has this situation arisen because those who work with strawberries are ill-intentioned? Do strawberry reseachers share the same agenda with multinational corporations who wish to sell products and dominate world markets? Have agricultural scientists no respect for environment and quality of life issues? I contend that the answer to these questions is "no." But if this is the case, how are we to explain to society why the production of one of nature's finest products, when under management of 21^st Century human beings, has such a large environmental impact and often negative reputation?

2. Guiding principles

Many of the problems inherent in our agricultural production systems simply reflect an absence of design around certain guiding principles. No one set out to deliberately design an input-intensive, environmentally expensive production system for strawberries, it just evolved as growers and researchers responded to problems with short-term solutions. How can we address replant problems? Fumigants can kill the harmful organisms. How can weeds be controlled? Black plastic can serve as a barrier. How can strawberry plants be made to fruit in warm climates? They can be transplanted from colder climates during the growing season and watered heavily until they establish themselves. As we solved problems to help move producers further down the road to profitability, we never paused to look where the road was leading. But what if we were to start over, at least conceptually, and begin to design a production system using certain guiding principles such as:

1. Benefits to the producer must exceed costs

2. Making money is NOT the sole guiding principle

3. Products used in the production of strawberries should be renewable or recyclable, not used faster than they can be regenerated, and not cause environmental damage during their manufacture

4. Products used in the production of strawberries should not cause environmental damage off-site after they are used

5. On-site environmental damage should be repairable at the time strawberry production ceases at that location

6. The production system should do no harm to local communities of people

What might a production system look like that attempts to follow these principles? Is such a conceptual production system impossible or impractical to realize?

Most of us work in concrete and steel buildings that use oil to warm them in the winter and oil to cool them in the summer. We also use oil to provide lights within our darkened offices on even the sunniest of days. Windows are frequently sealed for climate control, but this also seals in toxic fumes from furnishings, paints and treated fabrics causing some to suffer from "sick building syndrome." Our old carpets are taken to landfills, along with the tons of waste we generate annually from our buildings. Is that just the way it is, and the way it has to be? William McDonough, Dean of the College of Architecture at the University of Virginia, thinks not. He believes that we should marshal our intelligence to redesign our buildings to not create waste or use nonrenewable resources. He says that we need to re-imagine the world, and not just manipulate inputs and outputs within the constraints of a poorly designed system.

McDonough has designed buildings where grasses fed by storm water grow on a building's roof, thereby providing cooling in summer and a habitat for birds throughout the year. Night air sweeps under raised floors to cool the building's mass. Excess water from the roof feeds a strawberry field that, in turn, provides a healthy snack for the building's occupants. Special glass with light sensors allows a constant amount of natural light to enter, but traps heat that would otherwise escape. The carpets are recyclable, as are most of the building materials. Although such buildings are more expensive to construct, the long-term savings have been tremendous (Truppin 1999).

Can we re-imagine a strawberry production system that has similar characteristics to the building described above? Can energy inputs be reduced? Can solar energy conversion be maximized? Can fewer toxins be used? Can all the materials used in strawberry production be recyclable? Can the system be attractive in the rural landscape, and contribute to the life of the community?

One driving force leading to the situation that we find ourselves in is that we have been trained as discipline-oriented scientists and work within commodity boundaries, so we tend to define and address problems rather narrowly. We are often unaware of discoveries in other fields that could be useful in our own, or we tend not to consider solutions that lie outside our area of knowledge.

3. Critical questions

As biologists, we may not be able to address all of the social issues that surround the various concepts of sustainability. However, we can begin to answer a few questions that will be required to help us design and build a more sustainable strawberry production system.

1. How do we create and maintain a healthy microflora in the soil?

Our understanding of soil ecology in agroecosystems is very poor. We do not yet have an objective measure of soil quality or health, even though we can quantify nutrient concentrations in soils. We know, for example, that pathogenic organisms are frequently present in soils even when strawberry plants show no visible symptoms of disease (Wing et al., 1994). We know that annual fumigation eliminates most soil microflora and fauna, and keeps pathogen levels low. However, in perennial systems, fumigation is often associated with an increase in the pathogen populations. Speculation is that the elimination of competitive, beneficial organisms allows pathogens to thrive if they are not completely or regularly eliminated. In some cases, the addition of composts or certain fungi (e.g. Trichoderma, Gliocladium, Chaetomium) will suppress soil-borne pathogens, but in other cases, the addition of compost increases plant disease (Wing et al., 1994).

Robert J. Kremer, a microbiologist with the United States Dept. of Agriculture Cropping Systems and Water Quality Research Unit in Columbia, Missouri, finds that certain rhizobacteria, when provided with organic matter, keep weed seeds from germinating. By producing toxins and excessive concentrations of plant growth hormones, root cells of weeds rupture and leak, replenishing the organic matter for the rhizobacteria. Once weakened by the bacteria, weeds are less able to compete with other plants, and they become more vulnerable to other control measures. These bacteria seem not to affect crop plants. One of the most suppressive systems he examined was an organic strawberry field. Can we quantitatively determine how this field might differ from others that are not suppressive of weeds?

Agriculturists need a test to determine the relative health of the soil for sustaining strawberry production, and we need an understanding of mechanisms that increase beneficial and benign microorganisms that, in turn, suppress harmful organisms and improve nutrient cycling. Reliance on fumigation is a short-term solution to the problem of replant disease and poor soil health.

2. Can we use renewable products, such as cover crops, in place of plastic mulch, pesticides or other products that are toxic or not recyclable?

The disposal of plastic mulch is becoming a serious challenge in much of the world. Generally, this plastic is not recyclable, yet strawberry growers alone use enough plastic each year to circle the world more than 12 times with a sheet one meter wide (assuming 50,000 ha under cultivation with plastic (Hancock, 1999)). The environmental savings of substituting a renewable, degradable product for this plastic would be enormous.

Cover crops have many pest control properties that have not been fully utilized by strawberry producers; for example, suppression of weeds, nematodes, and soil pathogens (Grainge and Ahmed, 1988). In our own research, we have obtained benefits from using cover crop rotations as an alternative to fumigation, with some success. However, further work is required to identify appropriate mixtures and sequences for specific locations. For example, some cover crops are suppressive to certain species of nematodes, but not others. Obviously, most cover crops that grow well in one location will not perform as well in a different climate.

Currently-used cover crops were developed for agronomic or ornamental purposes, not for their suppressive effects on harmful organisms. What could we achieve, however, if cover crops were selected specifically for these effects? Could we develop a Brassica species sufficiently high in glucosinolates that nematodes and soil-borne pathogens would be eliminated after growing them on a site? Could we develop a cultivar of rye that would inhibit nearly all germination of weed seeds for several months, yet not affect strawberry plants that were set into the rye? Might we discover that certain undomesticated species have broad spectrum pest control properties with potential use in strawberry production?

The possibilities do not end with cover crops, but can extend to the breeding and selection of beneficial nematodes, mites and insects. Can predatory mites be selected for increased cold hardiness or other desirable traits? They have already been selected to tolerate high levels of pesticides (Kostiainen and Hoy, 1995). Also, races of fungi that are antagonistic to fungal pathogens have been selected and introduced into biological systems (Sutton, 1994). Of course, to implement these efforts will require an understanding of entomology, pathology, breeding and genetics, and strawberry production.

3. Can we breed varieties with characteristics that enable them to tolerate pests?

Traditional breeding programs have focused on fruit size and yield, and screening for pest resistance has mostly been limited to diseases where single-gene resistance is involved. Less attention has been given to breeding for tolerance against pests such as nematodes, arthropods or weeds that likely involve multigenic traits. Could strawberry plants, for example, be bred to resist weeds? Matted row plantings are established with few plants per hectare, relying on stolon formation to generate the appropriate density during the establishment year. However, such a system leaves a high percentage of soil exposed to sunlight and an opportunity for weeds to establish early. Strawberry roots typically are shallow, and plants do not compete well with weeds. A strawberry plant resistant to weeds might have rapid and deep rooting, rapid leaf expansion, and few stolons to facilitate a higher density planting. Weeds might have a more difficult time establishing themselves in such a planting, relative to the standard perennial matted row. Similarly, plants with vigorous root systems may be more tolerant to sublethal levels of root pathogens. Methods of identifying weed-tolerant or vigorously rooting genotypes must be developed before breeders can be expected to broaden their breeding objectives.

4. Can we identify, develop and implement dependable and effective biological controls for major pests?

Biological control offers several advantages over pesticide applications; one is that, theoretically, certain biological controls can be sustained over time (e.g. predatory mite populations). Too often, though, the search for biological controls is an attempt to replace one pesticide with an alternative, but the overall approach to pest management remains the same - treat the symptom. A truly sustainable pest management system uses the full complement of available defenses in a linked web of feedback loops, meaning that as one population grows beyond a certain boundary, levels are reduced through interactions with other organisms in the system. Historically, our approach to biological control has been one of importation followed by conservation. A sustainable system first tries to understand what makes an organism a pest, then attempts to maximize the effectiveness of indigenous populations of natural enemies or other factors that limit population expansion.

One potentially fruitful approach is habitat/landscape management. For example, strip-tilling cotton into a cover crop mixture of legumes has decreased significantly the need for pesticide sprays for armyworms and loopers because of increases in parasitoids (Lewis et al., 1997). Areas around strawberry plantings could be managed to provide refugia for natural enemies, as well as pollinators. This area of research has received little attention, but holds much promise.

Another approach is to remove the pest by introducing lethal genes into the population, rather than by applying pesticides. For decades, scientists have exposed harmful insects to radiation to create sterile males, which are then released to mate with females. This strategy is partially effective, but sterilized males are weaker than their unsterilized counterparts, and some fertile offspring are always produced. Scientists at Oxford University in England have used a similar approach, but have developed a dominant gene that kills females when they are not exposed to a particular chemical, an antibiotic in this case. When tetracycline is removed from the diet, females die. When antibiotic-dependent pests are released in a field, the males mate with females, and the female offspring die (because they have at least one dominant gene and are not exposed to tetracycline). Eventually all the females die and the population is severely curtailed (Thomas et al., 2000).

5. Can we produce plant material that requires less water to establish plantings?

Water is a limiting factor in many agricultural regions of the world, particularly those where strawberry production occurs on a large scale (e.g. California, Spain) (El-Farhan and Pritts, 1997). In fact, the International Water Management Institute recently concluded in a report on "Projected Water Scarcity in 2025" that water shortages will be the single greatest threat to food production and human health in the next 25 years (www.iwmi.org). The traditional method of establishing bare-rooted "fresh" strawberry transplants in plastic beds requires a great deal of water. In Florida, for example, beds are irrigated nearly continuously for two weeks following transplanting in October. The development of conditioned planting stock (where flower initiation has occurred as a result of short days and cool temperatures) in plug trays should have a major impact on reducing water requirements at planting (Poling and Parker, 1990). Such plugs need much less water to establish since their root systems are minimally disrupted upon transplanting. Widespread use of plug plants will require the reconfiguration of plant propagation facilities, but could result in plant production occurring close to fruiting fields, not only saving water but perhaps energy costs as well.

6. Can we breed productive plants with large, attractive, firm fruits that are also delicious?

An important factor in determining if a crop will be sustainable is a continuing demand for it in the marketplace. Most companies in today's global marketplace have recognized the importance of being "customer-oriented" and the value of repeat sales to long-term profitability. Few fruits can rival the flavor a fresh-picked, fully ripe Chandler, Elsanta or Earliglow strawberry. Why is it then that consumers (in the United States at least) rank strawberries (along with peaches and tomatoes) as one of the most inconsistent produce items in the grocery store? Unfortunately, it is because decisions about variety selection and harvest are often based on benefits that accrue to the grower or shipper as opposed to the consumer. For example, the variety 'Selva' produces attractive, firm fruit, is widely adaptable, is high yielding and produces over an extended period of time. Until recently, it was the most planted variety in the United States (Hokanson and Finn, 2000), but it lacks flavor. As a result, consumers did not increase their consumption of strawberries as much as they might have because of their disappointment with the product. Planting poorly flavored varieties and harvesting before fruits are fully mature to accommodate shipping practices reflect a lack of customer orientation, and ultimately affects the market for all producers. Since strawberry fruits are not an essential component of the diet and many substitutes exist, the eating experience must be of high quality to ensure that consumer demand will continue.

7. Can we breed low-chill varieties with improved tolerance to heat, water stress, and poor soils so they can be grown by farmers in developing countries?

Strawberries are a delicious food, high in nutrients, and have the potential to be grown in just about every country of the world. Strawberry consumption could potentially improve the diets of many people and provide a source of income for small farmers. Strawberries are having this impact today in countries such as China (Pritts et al., 1998). Most strawberry varieties, however, require relatively large amounts of water and nitrogen fertilizer for optimal performance. Few recent cultivars have high levels of resistance to pests. Today's varieties perform more poorly under stressful conditions than yesterday's varieties.

There are several reasons for our research community to develop at least some varieties tolerant to less-than-optimal conditions. One is to help provide a more diverse diet for malnourished people. A second is to provide an alternative crop for farmers in places such as Bolivia and Colombia where current income is derived from drugs such as cocaine. A third incentive is to develop a larger worldwide market for strawberries. The standard of living in many countries is improving, and as the standard of living improves, people purchase a higher percentage of their food. If people in countries such as China begin to incorporate strawberries into their diets, then the impact on world demand will be tremendous as the country develops further. Lastly, having a few stress-tolerant varieties available insures that strawberry production can still be an option should a water or fuel crisis develop.

8. Are there appropriate and politically acceptable uses for genetically engineered organisms in strawberry production systems?

The lack of customer orientation in agriculture has led to great suspicion regarding the use of genetically modified organisms (GMOs) in food production. With nearly all GMO foods introduced thus far, benefits of the technology accrue only to the producer or patent-holder, not the consumer. Contrast this with the nearly universal acceptance of pharmaceuticals, many of which are derived from GMOs, but where consumers derive significant direct benefits. Can there be uses of GMOs in agriculture that are acceptable to society? A place to start is not with the food itself, but with other components of the system. For example, might it be acceptable to transform a marigold (Tagetes) to have very strong nematode-suppressant properties, and use it as a rotational crop with strawberries? Wild Tagetes are generally not found in strawberry production areas, so gene escapes would not likely occur. The food itself will not have been altered, and pesticide use could be reduced. The drug-dependent flies described previously were developed, in part, with genetic engineering techniques. Should we dismiss GMO technology outright, or consider ways in which it can be used to benefit the consumer or environment, and that are consistent with the guiding principles discussed previously?

4. Concluding remarks

The goals of sustainable agriculture, as defined by the six guiding principles, are unlikely to be fully achieved, but we can certainly move closer to those goals than where we are today. It will require us to work in a more disciplinary mode, and outside of our commodity areas. It will require us to imagine where we would like to be, rather than solely address problems as they come along. To be a critic of agriculture is easy; the difficult and truly creative task is finding ways to do what is meaningful within the confines of fiscal, environmental, and community responsibility. Our legacy as a worldwide community of researchers could be one of entrenchment as we fine-tune current production systems, or it could be one of creative design as we develop and introduce novel production systems that sustain soils, farms, communities, and the environment far into the future.

References:

El-Farhan A.H. and Pritts M.P., 1997. Water requirements and water stress in strawberry. Adv. Strawberry Res. 16:5-12.

Grainge M. and Ahmed S., 1988. Handbook of plants with pest control properties. 470 pp. Wiley-Interscience, New York.

Hancock J., 1999. Strawberries. 237 pp. CABI Publishing, Cambridge.

Hokanson S.C. and Finn C.E., 2000. Strawberry cultivar use in North America. HortTechnology 10:94-106.

Kostiainen T. and Hoy M.A., 1995. Laboratory evaluation of a laboratory-selected organophopshate-resistant strain of Amblyseius finlandicus (Acari: Phytoseiidae) for possible use in Finnish apple orchards. Biocontrol Science and Technology 5:297-311.

Lewis W.J., vanLenteren J.C., Phatak S.C. and Tumlinson J.H., 1997. A total system approach to sustainable pest management. Proc. Natl. Acad. Sci. USA 94:12243-12248.

Poling, E.B. and Parker K., 1990. Plug production of strawberry transplants. Adv. Strawberry Res. 9:37-39.

Pritts M.P., Zhang J.J., Finn C. and Gao J., 1998. The strawberry industry in China. Adv. Strawberry Res. 17:1-6

Sutton J. C. 1994. Biological control of strawberry diseases. Adv. Strawberry Res. 13:1-11.

Thomas D.D., Donnelly C.A., Wood R.J. and Alphey L.S., 2000. Insect population control using a dominant, repressible, lethal genetic system. Science 287:2474-2476.

Truppin A. 1999. William McDonough, Designer of the Year. Interiors (January). BPI Communications, New York.

Wing K.B., Pritts M.P. and Wilcox W.F., 1994. Strawberry black root rot: a review. Adv. Strawberry Res. 13:13-19.

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