PANNA: Strawberry and Tomato Farming without Fumigants and Other Toxic Pesticides

Strawberry and Tomato Farming without Fumigants and Other Toxic Pesticides

by Lucius McSherry and Katherine Mills

One argument put forward by the pesticide industry for the continued use of high risk soil fumigants is that some crops simply can’t be grown without these dangerous chemicals. (1) However, many farmers are growing traditionally fumigant-dependent crops with safe and effective biological and cultural methods of pest control. Instead of introducing toxic chemicals into the air, these methods utilize beneficial plants and insects to control pests, rely on weeding and cultivation practices that use labor in place of pesticides, and locate fields with pest management in mind. Research and case studies abound that demonstrate successful and cost-effective less toxic alternatives for some of the most fumigant-intensive crops -- alternatives that don’t burden the environment and human health with the high-cost damage associated with fumigants.

Strawberries and tomatoes

Strawberries and tomatoes are two of the crops with the most intensive use of soil fumigants (2) because they are particularly vulnerable to several types of pathogens, insects, nematodes and mites that conventional farmers largely control with fumigants. These crops also use the greatest amount of the ozone depleting chemical, methyl bromide. In California alone in 2003, 3.7 million pounds of methyl bromide and 3.3 million pounds of chloropicrin were used to fumigate strawberry fields and 2.8 million pounds of metam-sodium were used on tomatoes. Yet other farmers have demonstrated that it is possible to farm strawberries and tomatoes in a cost effective way without the use of these harmful chemicals.

Economic comparisons between fumigated and non-fumigated fields

The University of California at Davis (UC Davis) studied two strawberry farms in the same growing region in California, a conventional farm using fumigants in 2004 and an organic farm using alternate methods to control the same problems in 2003 (see Table). (3,4) Organic strawberry farming produced higher yields per acre, but required more labor for hand weeding and disease control; therefore the organic farm’s cost per acre was higher. In the end, both methods were profitable and the relatively small profit difference (5.4%) between the two methods is far outweighed by the significant environmental and public health costs of releasing fumigants into the air. (5)

UC Davis conducted a similar comparison of organic and conventional tomato farms in California’s Sacramento Valley. (6,7) In this study, conventional yields were higher, but so were production costs. Overall net profits for organically grown tomatoes were only 10% lower than conventionally grown tomatoes. The study results for tomatoes were similar to strawberries -- both methods can be profitable and, again, the relative difference in profits should be evaluated in terms of both the price consumers will pay for cleaner production and the far greater costs of damage to the environmental and human health associated with the large-scale release of dangerous fumigants.

Alternative methods of weed and pest control

A number of approaches have been effective in strawberry and tomato cultivation to control the entire range of common pests without the use of dangerous fumigants; rotating crops in the fields, planting cover crops, and soil solarization to control pathogens and weeds; hand-pulling weeds to control detrimental plants in the fields; and using traps and predator species to minimize insect damage.

Crop rotation, the practice of planting different crops in a field in sequence over two or more seasons, aids in the control of soil-borne pathogens, weeds, and insects and can also increase the fertility of the soil. When one crop is planted season after season in the same field, pest populations are boosted by a constant source of the same nutrients. If different crops are rotated through the field, the life cycles of pests are interrupted and pest population growth is minimized. Crop rotation also significantly improves the health of the soil, as each crop interacts differently with the various components in the soil, allowing the exchange of different nutrients. When one crop is planted repeatedly, the soil continually releases the same nutrients and develops deficiencies that necessitate the use of fertilizers.

Cover crops are grown in between seasons of the regular crop to improve the soil and are plowed into the soil before planting of the desired crop. These crops are helpful in controlling nematodes or parasitic worms by interrupting the nematode food supply, while at the same time minimizing weeds and returning nitrogen and other nutrients  back to the soil. Farmers using cover crops reported better net returns than farmers growing tomatoes with conventional methyl bromide aplications, due to savings on the costs of methyl bromide and fertilizer. (8)

Tomato farmers in Florida have been successful in using soil solarization as an alternative to pre-plant fumigation. In this practice plastic is spread on the ground and is heated in Florida’s ample sunshine to a temperature that kills pathogens, weeds, and insects. A Florida study performed by the U.S. Department of Agriculture (USDA) showed that solarization, combined with deep disking prior to application of the plastic, produced yields 23% greater than adjacent plots fumigated with methyl bromide. (9)

In addition to crop rotation and solarization, the practice of hand-pulling weeds is effective. Although labor intensive, this close-up contact with the crop can also minimize fruit rot if the worker removes infected fruit during weeding. Fruit rot is caused by a fungus for which the only remedy is removal of the infected fruit. The UC Davis cost study reports labor time at 20 hours per month per acre for hand weeding strawberries at a labor cost of $201. The farms using fumigants to control weeds still incurred labor costs for hand weeding with 10.2 hours per acre each month at a cost of $102.51. In addition, the conventional farm spent $1,679 per acre each year for fumigation.

Several techniques control insect pests in strawberry and tomato fields without the use of harmful chemicals. Wasps and predatory mites are introduced to kill the species of mites and worms that feed on tomato plants, decreasing these populations significantly. Combinations of bug traps and vacuums have also been shown to work especially well on strawberries. In this technique a trap crop is planted on the border of the field, attracting pest insects to this sweeter and more appetizing crop (alfalfa is often used around strawberries, for example). A vacuum mounted on a tractor is then used to remove the insects from the border trap crop.

Other strategies for minimizing pests associated with strawberry and tomato farming include ensuring adequate water drainage in the field, carefully selecting the crop variety to suit the locality, and developing proper irrigation techniques. If the drainage system in the fields does not work adequately, pools of standing water can create an environment for insects, molds, and plant-and-root rot to thrive. Some varieties of strawberries and tomatoes are more resistant to pests than others; pathogen-resistant varieties grow better without fumigation than relatives not bred to be resistant to these pests. Finally, the type of irrigation system used is important for controlling mildew, especially on strawberries. Overhead irrigation systems can encourage mildew while drip irrigation, in which hoses drip water at the roots of the plants, will minimize certain types of mildew.

These are examples of just some of the cultural and biological methods that are currently being used successfully on strawberry farms in California and tomato fields in California and Florida. Farmers using these methods to control familiar pathogens, pests, nematodes and weeds associated with these crops are demonstrating that alternative pest control methods can be successfully employed on traditionally fumigant-dependent crops. Farms using these methods are turning a profit as well as setting a precedent for the wide-scale adoption of these techniques.

Raised on a farm in Florida, Lucius McSherry is a summer intern with PANNA. Katherine Mills is Assistant Scientist at PANNA.

Notes

1. One example put forward is the cultivation of tomatoes in Florida, where heavy reliance on fumigants has enabled the cultivation of a high-value crop in locations that are unsuitable. The other side of the argument is that careful crop selection is a necessity, not soil fumigation. See W.Rostov, A Schoenfied, Prospering Without Methyl Bromide: A Critique of USDA’s Analysis of a Methyl Bromide Ban, Pesticide Action Network North America, 1994, http://www.panna.org/resources/pestis/PESTIS.burst.382.html.

2. Florida used 6.1 million pounds on tomatoes in 1997, from National Pesticide Use Database, National Center on Food and Agricultural Policy, 1997, http://www.ncfap.org/database/default.php.

3. M. Bolda, L. Torte, K. Klonsky, J. E. Bervejillo. Sample Costs to Produce Organic Strawberries. University of California Cooperative Extension. 2003. http://news.ucanr.org/storyshow.cfm?story=597&printver=yes.

4. M. Bolda, Mark, L. Torte, K. Klonsky, R. L. De Moura. Sample Costs to Produce Strawberries. University of California Cooperative Extension. 2004.

5. Many studies address the external costs of pesticide use on the environment and public health. See, for example: by E. Tegtmeir, M. Duffy, External Costs of Agricultural Production in the United States, International Journal of Agricultural Sustainability,Vol.2, No.1, 1-20, 2004 on external costs of U.S. agriculture, and D. Pimentel et al., “Environmental and Economic Costs of Pesticide Use, “ BioScience, Vol. 42, No.10. American Institute of Biological Sciences, Washington, DC.

6. M., Gene, K. M. Klonsky, R. L. De Moura. Sample Costs to Produce Processing Tomatoes, University of California Cooperative Extension, 2001 (Davis, Calif.).

7. K. Klonsky, L. Torte, D. Chaney. Production Practices and Sample Costs for Organic Processing Tomatoes in the Sacramento Valley. University of California Cooperative Extension, 1993-1994 (Davis, Calif.).

8. A. A. Abdul-Baki, Cover Crops For Vegetable Production In Tropical Areas, American Vegetable Grower, March 2005.

9. D.O. Chellemi, 2001. Field Validation of Methyl Bromide Alternatives in Florida Fresh Market Vegetable Production Systems, in Global Report on Validated Alternatives to the Use of Methyl Bromide for Soil Fumigation, R. Labrada and L. Fornasari (eds). UN Fodd and Agriculture Organization, Plant Production and Protection Papers 166, 2001, Rome, http://www.fao.org/documents/show_cdr.asp?url_file=//DOCREP/004/Y1809E/y1809e00.htm.