![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Chloropicrin Applications for California Strawberries
Preplant soil treatment with chloropicrin (trichloronitromethane), alone, or in combination with other soil fumigants and pest control measures, can be used by strawberry growers as an alternative methyl bromide. Currently, there is widespread use of methyl bromide formulations that typically contain 33 percent chloropicrin for preplant fumigation treatments of strawberry nursery and production fields. These fumigation treatments are performed prior to planting and typically provide significant season-long control of a broad spectrum of soilborne pests, including a variety of fungal and nematode pathogens and weeds (USDA 1996).
The strawberry industry in California has favored the use of methyl bromide formulations that contain chloropicrin because of the synergistic effects of these two compounds. Tests and field experience have verified these effects and have shown that chloropicrin offers superior control of fungal pests, whereas methyl bromide is a better broad spectrum fumigant with efficacy against a wide range of pathogens, including weeds and nematodes (Liebman 1994, Wilhelm and Storkan 1990).
Recent interest in developing effective alternatives to the use of methyl bromide as a preplant fumigant in the California strawberry industry has led to design of experiments and field trials which test the effectiveness of chloropicrin in both nursery and field settings, alone, and in combination with fumigants such as Vapam® and Telone® . The results of field studies suggest that the use of chloropicrin will offer strawberry nursery and fruit producers in California a pest management tool for combating soil diseases caused by soilborne fungal pathogens (Duniway and Gubler 1996, Duniway et al. 1994, Coffey et al. 1994, Welch and Gubler 1994). Furthermore, in situations where soil fungi are the principle pests of concern, and other pests such as weeds and nematodes are controlled through other measures (e.g., alternative fumigants), it is possible that the use of chloropicrin will allow strawberry producers to effectively control soilborne fungal pathogens thereby promoting strawberry plant growth and crop yields similar to those achieved with methyl bromide fumigation.
The Importance of Fumigation to Strawberry Production in California
Finding alternative soil pest control measures has been a priority for the California strawberry industry because of its reliance on methyl bromide/chloropicrin fumigation to achieve superior yields and high quality fruit. California produces 75 to 80 percent of the nation's strawberries on less than half of the total U.S. strawberry acreage planted each year (Welch 1989). Average yields in California range from 24 to 40 tonnes per acre, values that are several times higher than those found in other parts of the country (i.e., Florida, Oregon, and North Carolina). In 1995, there were 23,600 acres of strawberry production in California yielding 1.19 billion pounds of strawberries with an average wholesale price of $46.30/100 lbs. Overall, the 1995 California strawberry crop was valued at $552 million (Hill 1996).
California's high strawberry yield can be attributed to the fact that California has adopted an annual planting system, developed highly productive strawberry cultivars, and has a cool climate to enhance strawberry production (USDA 1994). Because plants are grown as annuals, strawberry production in California occurs throughout most of the year (Welch 1989). Nearly all strawberry acreage in California is fumigated to control weeds, fungi, and nematodes, and use clear plastic mulch, irrigation, and fertilizers. Approximately 4.5 million pounds of methyl bromide are used annually in California for pre-plant fumigant of strawberries, representing roughly 35 percent of the total use of methyl bromide in California, 7 percent of United States use, and 4 percent of world use (DPR 1990-1992, NAPIAP 1993, UNEP 1992, EPA 1995).
In addition to its widespread use in fruiting fields, methyl bromide is considered to be a critical part of current produciton practices for strawberry nurseries to ensure the cleanliness of transplanted nursery stocks. Strawberry runners (transplants) are produced in nurseries and are then shipped to the fruiting fields throughout coastal and southern California each year where they are transplanted. All California strawberry growers depend on clean nursery stocks each year because there is a high risk that pathogens can be transplanted from the nurseries to the fruiting fields. In addition, researchers depend on nursery stock that has been produced using pre-plant fumigation with methyl bromide/chloropicrin (Larson 1996).
In California, fumigation with methyl bromide/chloropicrin is typically performed by contract applicators. Fields are covered with a clear plastic during the fumigant application process to hold the gas in the soil and increase efficacy (Voth et al. 1973). The tarp is removed after at least 24 hours and a clear polyethylene mulch is applied (usually in November) to warm the soil and promote early plant growth. Plants are then set into the planting beds in pre-moistened soil. If bed fumigation is used, the fumigation plastic remains in place for the duration of the crop cycle (USDA 1994).
Advantages of Chloropicrin
Chloropicrin currently appears to offer advantages as a soil fumigant because its use parameters are relatively familiar to applicators and its efficacy on economically important pests has been well documented. Despite the proven benefits of chloropicrin, the long-term effect of soil fumigation with higher dosages chloropicrin, community exposure concerns, and requisite dosages are still being evaluated.
Chloropicrin is a restricted use pesticide and is available in formulations with Telone® or as the sole active ingredient. Chloropicrin is typically injected six to eleven inches into the soil as a liquid 14 days or more before planting. It is a clear, colorless, nonflammable liquid with a moderate vapor pressure, and it rapidly diffuses through the soil profile and is toxic to common root destroying fungi. Chloropicrin is not considered to pose a threat to the ozone layer, it undergoes rapid degradation in sunlight, it is metabolized in soil to form carbon dioxide, and is not expected to accumulate in plant tissue. In addition, it is not soluble in water and therefore is not expected to pose a threat to groundwater. Finally, it is not expected to accumulate in animal cells. (USDA 1996).
Research on the efficacy of chloropicrin for strawberry production has been conducted and is ongoing. Chloropicrin is best known for its wide spectrum effectiveness in controlling soilborne fungi; however, it has particular effectiveness in controlling several genera, including Ceratobasidium, Colletotrichum, Cylindrocarpon, Fusarium, Idriella, Phytophthora, Pyrenochaeta, Pythium, Rhizoctonia, and Verticillium, all of which are known to cause root rot and/or wilt diseases in strawberries (Wilhelm and Westerlund 1993, Maas 1984). Chloropicrin may also have some degree of control of root destroying insects, slugs, snails, earwigs, root weevils, grubs and root lesion types of nematodes (Wilhelm and Westerlund 1993, USDA 1996).
Although some studies have shown that chloropicrin, when used as the sole active ingredient, is not as effective as methyl bromide/chloropicrin for fruit production or for the production of certified nursery stock (Shaw 1996, Larson 1996), a number of studies have indicated that strawberries treated with chloropicrin achieve yields similar to those attained with methyl bromide. For example, one California study demonstrated that strawberries planted in soil treated with 20 gallons chloropicrin per acre resulted in higher yields (6,428 trays/acre) compared to those grown with methyl bromide/chloropicrin (6,265 trays/acre) (Welch and Gubler 1994). Likewise, a similar study by Larson and Shaw (1994) found that approximately 100 pounds of chloropicrin applied produced higher yields (2,322 trays/acre) compared to that produced with methyl bromide/chloropicrin (2,303 trays/acre). The positive results of these studies support the findings that chloropicrin is an excellent fumigant for the control of soilborne fungi.
However, because the use of chloropicrin is not as effective as other compounds (e.g., Telone®) in controlling weeds and nematodes, research is now being conducted to further evaluate the effectiveness of chloropicrin when it is used in conjunction with other chemicals (Coffey, et al. 1994, Duniway and Gubler 1996). Results from these studies suggest that by combining chloropicrin treatments with other treatments, especially Telone®, control of many of the nematode and weed pests currently controlled with methyl bromide/chloropicrin fumigation treatments may be possible. In addition, the development of fumigant formulations that contain higher levels of chloropicrin may provide excellent pathogen control without requiring alterations to existing cultivation methods (USDA 1996).
Costs
Strawberries are among the most expensive crops to grow, with annual production costs as high as $24,600 per acre (attributed primarily to materials and harvesting costs) (Gliessman et al. 1990). Although profits and losses vary considerably depending on the size of the crop and fluctuations in market price, profits of $3,500 to $5,000 per acre or more have been reported (Gliessman et al. 1990, Webb 1994, Cochran 1994).
Although costs resulting from the need to perform additional pest control measures may be incurred (e.g., application of Telone®), the actual costs associated with applying chloropicrin (e.g., injection and tarping) will be similar to those for methyl bromide (Wilhelm 1995). However, one of the principle differences in the cost of chloropicrin versus methyl bromide/chloropicrin use in the California strawberry industry will be the material cost of the chemical (i.e., $675/acre for chloropicrin compared to $615/acre for methyl bromide/chloropicrin (67:33)). A material cost comparison is provided in Table 1 below:
| Material |
Chloropicrin/Telone®+
Chloropicrin (70:30) |
Methyl
bromide+
Chloropicrin (67:33) |
|---|---|---|
| Application Rate
(ai per acre) |
100 to 300 lbs./350 to 450 lbs | 300 to 375 lbs |
| Cost per Pound | $2.25/lb./$1.59/lb | $1.64/lb. |
| Total Material Cost
(per acre) |
$225 to $675/$556 to $715 | $492 to $615 |
Sources: Wilhelm 1995, Asgrow 1995, Coffey, et al. 1994, Duniway et al. 1994, Fowler 1996.
References
- Asgrow. 1995 (February 1). Personal Communication. Asgrow. Price Quote for Methyl Bromide.
- Coffey, et al. 1994. Evaluation of alternative soil fumigation methods for use in strawberry production in southern California. M. Coffey, A.O. Paulus, I. Schmitz, P. Rich, H. Krueger, M. Meyer-Podolsky, H. Forster, M. Vilchez, and F. Westerlund. In 1994 Annual International Research Conference on Methyl Bromide Alternatives and Emission Reductions: Conference Proceedings. Number 1. Kissimmee, Florida.
- Cochran. 1994. Personal Communication. J. Cochran. Swanton Berry Farms. Davenport, California.
- DPR. 1990-1992. Annual Pesticide Use Reports. Department of Pesticide Regulation, State of California Environmental Protection Agency. Sacramento, California.
- Duniway et al. 1994 (November 13-16). Evaluation of strawberry growth, fruit yield, and soil microorganisms in non-treated soil and in soil fumigated with methyl bromide/chloropicrin, Telone II/chloropicrin, chloropicrin, or Vapam in a California strawberry production system. J. Duniway, W. Gubler and N. Filajdic. In 1994 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions: Conference Proceedings. Number 16. Kissimmee, Florida.
- Duniway and Gubler. 1996. Evaluation of some chemical and cultural alternatives to methyl bromide fumigation of soil in a California strawberry production system. J. Duniway and D. Gubler. In 1996 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions: Conference Proceedings. Number 37. Orlando, Florida.
- EPA. 1995. Methyl bromide consumption estimates. U.S. Environmental Protection Agency, Stratospheric Protection Division, Washington, DC. August 7, 1995.
- Fowler. 1996. Price quote for Telone® and chloropicrin. Kirk Fowler, Tri-Cal, Hollister, California, December 10, 1996.
- Gliessman et al. 1990. Strawberry production systems during conversion to organic farming. S.R. Gliessman, S.L. Swezey, J. Allison, J. Cochran, J. Farrell, R. Kluson, F. Rosado-May, and M. Werner. Calif. Agric. Volume 44, pp. 4-7.
- Hill. 1996. Personal Communication. Howard Hill. National Agricultural Statistics, United States Department of Agriculture.
- Larson. 1996 (July, December). Personal Communication. Kirk Larson. University of California at Davis. Davis, California.
- Larson and Shaw. 1994. Evaluation of Eight Preplant Soil Treatments for Strawberry Production in Southern California. Larson, K.D. and D.V. Shaw. In 1994 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions: Conference Proceedings. Number 24. Kissimmee, Florida.
- Liebman. 1994 (July). Alternatives to methyl bromide in California strawberry production. Jamie Liebman. In The IPM Practitioner. Volume XVI, Number 7, pp. 1-12.
- Maas et. al. 1984. Compendium of Strawberry Diseases. J. L. Maas, ed., The American Phytopathological Society, St. Paul, Minnesota.
- NAPIAP. 1993 (April). National Agricultural Pesticide Impact Assessment Program. Biologic and Economic Assessment of Methyl Bromide. United States Department of Agriculture.
- Shaw. 1996. Analysis of chloropicrin efficacy for strawberry production. Unpublished study, Dr. D. Shaw, University of California, Davis. December 5, 1996.
- UNEP. 1992. Methyl Bromide: Its Atmospheric Science, Technology, and Economics. UN Ozone Secretariat, United Nations Environmental Programme. Nairobi, Kenya.
- USDA. 1996. Methyl bromide alternatives. U.S. Department of Agriculture, Washington, DC, Newsletter, July 1996.
- USDA. 1994. The U.S. strawberry industry. Economic Research Service, United States Department of Agriculture. Statistical Bulletin Number 914.
- Webb. 1994. Personal Communication. R. Webb. Driscoll Strawberry Research. Watsonville, California.
-
Welch. 1989. Strawberry production in California. N.C. Welch. University of California Cooperative Extension. Leaflet #2959, p. 15. - Welch and Gubler. 1994 (November 13-16). Soil fumigation experiment in strawberries in the central coast district of California. Norman Welch and Doug Gubler. In 1994 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions: Conference Proceedings. Number 17. Kissimmee, Florida.
- Wilhelm and Storkan. 1990. Large scale soil fumigation growth response. S. Wilhelm and R.C. Storkan. Phytopathology. Volume 49, pp. 530-531.
- Wilhelm and Westerlund. 1993. Chloropicrin - Soil Fumigant. Stephen Wilhelm, University of California and Frank Westerlund, California Strawberry Commission, California.
- Wilhelm. 1995 (February 1). Personal communication. John Wilhelm, Niklor Chemicals.
- Voth et al. 1973. Effect of tarp thickness and dosage on response of California strawberries to fumigation. V. Voth, D.E. Munnecke, A.O. Paulus, M.J. Kolbezen, and R.S. Bringhurst. Calif. Agric. Volume 27, Number 12, p. 14.
Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.
Back to Case Studies Volume 2 | Methyl bromide home