Metam Sodium as an Alternative to Methyl Bromide for Fruit and Vegetable Production

Background

First discovered in 1950, metam sodium, also sold under the trade names Vapam, Busan, and Sectagon II, degrades rapidly to methylisothiocyanate, the product's primary bioactive agent (Budavari 1994). Used as part of an Integrated Pest Management system, metam sodium is a broad spectrum soil fumigant that can be used to control nematodes, weeds, and fungi affecting a variety of economically important fruit and vegetable crops. Overall, metam sodium is considered a cost effective, technically viable alternative to methyl bromide for controlling soil pests affecting high value fruit and vegetable crops in Florida and California.

Metam sodium is a readily available, moderately toxic, versatile pesticide product. For over three decades, metam sodium has been used in a variety of experimental and commercial applications. By using metam sodium to treat soils prior to planting, fruit and vegetable growers can control tough annual weeds, reduce nematode populations, and control soil-borne pathogens. In California, because of the low cost, ease of application, safety, and effectiveness in controlling soil pests, over 8 million pounds of metam sodium were used in the production of melons, peppers, tomatoes, potatoes, strawberries, nurseries, ornamentals, cut flowers, container plants, forest tree seedlings, citrus, grapes, almonds, artichokes, asparagus, and carrots (CDPR 1995). In general, metam sodium reduces competition from soil pests, promotes healthier crops and higher yields, provides early uniform crop maturity and fruit ripening, and allows growers to greatly increase economic returns by achieving maximum early season yields (ICI 1992).

Benefits of Metam Sodium

Cost-effective method to control tough annual weeds, reduce nematode populations, and control soil-borne pathogens prior to planting fruits and vegetables.
Versatile product used for over three decades. Has been shown to reduce competition, improve plant growth, and increase yields.

Commercially Viable Alternative to Methyl Bromide

Many researchers have cited metam sodium as a potential alternative to methyl bromide fumigation, and metam sodium's low cost and wide-range of control makes it a strong candidate for fumigation on many crops (Braun and Supkoff 1994, Noling and Becker 1994, Yarkin 1994). Metam sodium is registered for use in controlling a wide array of soil-borne pests. It can be used to control weeds (e.g., bluegrass, bermudagrass, chickweed, dandelion, ragweed, henbit, nutsedge, and wild morning glory), nematodes, and soil diseases caused by species of Rhizoctonia, Fusarium, Pythium, Phytophthora, Verticillium, Sclerotinia. Metam sodium is also useful in Integrated Pest Management systems, as metam sodium can be used in conjunction with resistant varieties, improved sanitation techniques, biological control agents, and soil pasteurization (i.e., solarization, hot water, or steam) (Noling and Becker 1994). Overall, metam sodium use could be expanded across a wide range of fruit and vegetable crops including tomatoes, strawberries, and peppers which currently account for nearly 60 percent of domestic methyl bromide consumption (EPA 1994).

Improved growth responses and yield increases have been experimentally and commercially documented (Larson and Shaw 1994, Olson and Noling 1994, Cook and Keinath 1994, ICI 1992). In the production of carrots and tomatoes, metam sodium has been used to significantly reduce populations of stubby root (Paratrichodorous sp.) and root-knot nematode (Meloidogyne sp.) prior to planting (ICI 1992).

A fresh market tomato study comparing metam sodium and methyl bromide fumigation to an untreated control reported that yields and fruit quality obtained with metam sodium were equivalent to those achieved with methyl bromide fumigation (Cook and Keinath 1994). Also, results of a study performed by Dr. Noling and Dr. Olson of the University of Florida investigating the use of metam sodium on tomatoes indicated that yields achieved with metam sodium were 85 percent of the methyl bromide yields (Olson and Noling 1994). Additionally, in two strawberry field trials, metam sodium was applied at 75 gallons per acre through sprinkler system; methyl bromide/chloropicrin was applied at 325 lbs per acre. Overall, during the early part of the season, yields achieved with metam sodium were 26 percent greater than those obtained with methyl bromide. Although methyl bromide yields for the overall season were 14 percent greater than yields achieved with metam sodium, because metam sodium treatment costs were one third less than methyl bromide costs and higher early season yields achieved by metam sodium received significantly higher prices, economic returns with metam sodium were greater than those achieved by using methyl bromide (ICI 1992).

Successfully Applying Metam Sodium

Although growers have historically been frustrated with metam sodium's soil distribution characteristics and variations in pest control, research and advances in application techniques have the potential to increase the consistency and efficacy of metam sodium as a soil fumigant. Effectively using metam sodium to control pests currently treated with methyl bromide will require some low-cost modifications of cropping systems, including the adoption of drip irrigation systems, narrower bed widths, multiple drip tubes per bed, and planting practices which place plants closer to drip tubes (Noling and Becker 1994).

To effectively use metam sodium, the applicator must follow the recommendations provided by the product label, including considerations of the soil conditions, methods of application, application rates, and the factors influencing the release rate. In most cases, 25 to 100 gallons of metam sodium are applied per treated acre as a liquid and then incorporated into the soil through tilling and irrigation (Braun and Supkoff 1994). An important consideration for ensuring effective application is placement of the material in the soil profile. Metam sodium is most effectively applied through drip tape if it is applied no more than 6 inches off center and 2 to 3 inches deep. Metam sodium can also be applied through sprinkler or flood irrigation. The release rate of metam sodium depends on several factors including soil temperature, texture, moisture and pH. Prior to application the seedbed must be prepared by ensuring that it is free of clods and by receiving a preplant fertilizer treatment. Additionally, soil moisture must be at least 50 to 75 percent of field capacity, and soil temperatures must be between 40 F and 90 F in the top 2 to 3 inches (ICI 1992).

Cost Effective Alternative to Methyl Bromide

Metam sodium is not a restricted use pesticide, and does not have to be applied by a certified applicator. In addition, because metam sodium is water soluble and has low volatility, it is the only soil fumigant that can be applied through irrigation systems (ICI 1992). In addition, although metam sodium has a high aquatic toxicity rating, in general, the environmental and health risks posed by metam sodium are lower than those posed by methyl bromide. One of the greatest advantages to the use of metam sodium, however, is the low cost. Although supplemental pest control activities may be required and would increase the total application costs, metam sodium is safer and easier to use than methyl bromide and it costs less. The attached table compares the costs of metam sodium and methyl bromide for soil fumigation treatments. The average cost of metam sodium ranges from $5.40 to $7.40 per gallon (Asgrow 1994), with typical application rates ranging from 75 to 100 gallons per acre (Braun and Supkoff 1994). Total application costs can average between $750 to $1,000 per acre. By comparison, methyl bromide application costs are estimated to range from $1,200 to $1,500 per acre. Overall, because of its familiarity, availability, effectiveness, and low cost, metam sodium is possibly one of the highest profit alternatives to methyl bromide for the production of fruits and vegetables in the United States (Yarkin 1994).

Relative Costs of Methyl Bromide and Metam Sodium Fumigation

Metam sodium

Cost Per Unit ($): $5.40 - $7.40 per gallon
Units Per Acre: 75 - 100 gallons
Additional Costs: Labor/Tarp
Estimated Cost Per Acre: $750 - $1,000

Methyl Bromide

Cost Per Unit ($):$1.12 - $1.64 per pound
Units Per Acre: 180 - 400 pounds
Additional Costs:Contract Fumigation
Estimated Cost Per Acre:$1,200 - $1,500

Source: Asgrow 1995, Lykes Agrisales 1995, Tjosvald 1995.

References

Asgrow 1995. Price Quote. Active Ingredient Prices for Vapam® and Methyl Bromide. Asgrow Chemical, Immokalee, FL.
Braun and Supkoff 1994. "Options to Methyl Bromide for the Control of Soil-Borne Diseases and Pests in California with Reference to the Netherlands". Adolf Braun and David Supkoff, Pest Management Analysis and Planning Program, California Environmental Protection Agency, Department of Pesticide Regulation, Sacremento, CA. July 1994.
Budavari (ed.) 1989. The Merck Index. Merck & Co. Rahway, NJ
Cook and Keinath 1994. Metam sodium as an alternative soil fumigant to methyl bromide in fresh market tomatoes, 1993. F&N Tests 49:160.
CDPR 1995. California Department of Pesticide Regulation, Sacremento, California California Pesticide Use Report, University of California, Davis, CALLIPM, Pesticide Use Summary Database, April 1995.
EPA 1994. Methyl Bromide Consumption Estimates. U.S. Environmental Protection Agency, Stratospheric Protection Division, Washington, D.C. May 3, 1994.
ICI 1992. Vapam® Product Guide. ICI Agricultural Products. Wilmington, DE.
Larson and Shaw 1994. "Evaluation of Eight Preplant Soil Treatments for Strawberry Production in Southern California". 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL.
Lykes Agrisales 1995. Price Quote. Active Ingredient Prices for Vapam® and Methyl Bromide. Lykes Agrisales, Lake Placid, FL.
Noling and Becker 1994. "The Challenge of Research and Extension to Define and Implement Alternatives to Methyl Bromide". Supplement to the Journal of Nematology, Vol 26, No. 4s, pp. 573-586.
Olson and Noling 1994. "Fumigation Trials for Tomatoes and Strawberries in Northwest Florida". 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL. November 1994.
Tjosvald 1995. Personal Communication. Steve Tjosvald, Monterey County Cooperative Extension Service, Watsonville, CA. ICF Incorporated, Washington, D.C. April 1995.
Yarkin 1994. Methyl Bromide Regulation: All crops should not be treated equally. Cherisa Yarkin, David Sunding, David Silberman, and Jerry Siebert, University of California, Davis. California Agriculture, Volume 48, Number 3. May-June 1994.

More information on this material is available from the Metam-Sodium Task Force Product Stewardship Committee .

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.

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