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Metam Sodium as an Alternative to Methyl Bromide for Fruit and Vegetable Production and Orchard Replanting
This is an update of a July 1995 EPA report (Alternatives to Methyl Bromide, Ten Case Studies) entitled "Metam Sodium as an Alternative to Methyl Bromide for Fruit and Vegetable Production". Additional information on this materials, including new data from field tests, is reported here. This report contains information on the use of this pesticides in the production of crops where methyl bromide is currently used.
First marketed in the 1950's, metam sodium is a soil pesticide that has been sold under the trade names Amvac Metam Sodium®, Busan®, Metam CLRTM 42%, Sectagon 42®, and Vapam®. Once in the soil, this pesticide degrades rapidly to methylisothiocyanate (MITC), the product's primary bioactive agent (Budavari 1994). Metam sodium is a broad spectrum soil fumigant that can be used to control plant parasitic nematodes, weeds, germinating weed seeds, and soil-borne plant pathogenic fungi affecting a variety of economically important fruit and vegetable crops. This pest control tool can be a cost effective, technically viable alternative to methyl bromide for controlling soil pests affecting high value fruit, vegetable, and orchard crops.
Metam sodium is registered and available to growers. It has no effect on the stratospheric ozone layer, and with current use patterns there are no residues left on crops. For over four decades, metam sodium has been used in a variety of experimental and commercial applications for the control of annual weeds, reduce nematode populations, and control soil-borne pathogens. In California, over 15 million pounds of metam sodium were used in 1995 for 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 1997).
However, it should be noted that metam sodium has a reputation with some growers of being unforgiving and unreliable if not used carefully. Growers that have used this material note that correct application procedures are critical to insure success in the control of pest, especially nematodes and fungi. Current methyl bromide users should bear this in mind as they consider future utilization of this material.
Commercially Viable Alternative to Methyl Bromide
Table 1 compares methyl bromide and metam sodium soil fumigation use for grapes, peppers, tomatoes, processed tomatoes and strawberries for California in 1995 (CDPR 1997). As indicated in table 1, methyl bromide is not used in processing tomatoes --- this crop is shown in this report to show a successful and established use pattern, not to imply substitution in this or any other crop.
| Crop | Methyl Bromide | Metam Sodium |
|---|---|---|
| Grapes | 575,000 | 15,500 |
| Peppers | 49,000 | 7,600 |
| Tomatoes | 266,000 | 243,000 |
| Processed Tomatoes | -0- | 2,888,000 |
| Strawberries | 4,200,000 | 30,000 |
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, and can be used to control weeds (e.g., annual bluegrass, bermuda grass, chickweed, dandelion, ragweed, henbit, nutsedge, and wild morningglory.), nematodes (e.g. root knot, lesion, dagger, lance, needle, pin, reniform, stunt, stubby root, sting, spiral), and soil diseases caused by species of Rhizoctonia, Fusarium, Pythium, Phytopthora, Verticillium, Sclerotinia. Metam sodium is also useful in Integrated Pest Management systems, as it 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). It is possible, based upon current metam sodium use patterns, to see expanded across a wide range of fruit and vegetable crops including tomatoes, strawberries, and peppers which currently utilize methyl bromide for soil pest control.
Fruit and Vegetable Production
Note that not all the crops listed in this section currently utilize methyl bromide in their production. However, a description of metam sodium efficacy is provided to illustrate the kind of pest control that can be acheived with this material. While this document assumes that such pest control efficacy is transferrable to crops that use methyl bromide, this must be established with field trials where applicaiton methods and production timing can be established. This is especially important with metam sodium, where application techniques are absolutely critical to success.
Carrots
In comparisons with methyl bromide, metam sodium has shown good growth responses and yield increases (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). Application through drip irrigation on California tomato and carrot beds before planting significantly reduced nematodes in the soil as well as root gall ratings at mid-season and harvest and increased yields in most cases (Roberts et. al. 1988). In Florida, use resulted in improved plant vigor and stand, reduced root-knot nematode damage and increased yields (Johnston et. al. 1991).
Tomatoes
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). In the production of tomatoes in southwest Florida, Fusarium crown and root rot has been the most prevalent soilborne disease. Metam sodium has been demonstrated to significantly reduce crown rot incidence and when combined with solarization, control was equivalent to methyl bromide + chloropicrin (McGovern et. al. 1996).
Strawberries
In California strawberry production, methyl bromide and metam sodium are rated comparable in chemical effectiveness to control annual and perennial weeds (UC 1996). Field experiments conducted by the UC Cooperative Extension over a three year period on broccoli, cauliflower and strawberries demonstrated that metam sodium will effectively control several annual weeds common in these crops (Agamalian 1990).
In two registrant-supported strawberry field trials, Metam sodium was applied at 240 lbs 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% greater than those obtained with methyl bromide. Although methyl bromide yields for the overall season were 14% greater than yields achieved with Metam sodium, because metam sodium treatment costs were 1/3 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).
Weed Control
Hairy nightshade (Solanum sarachoides Sendter) and black nightshade (Solanum nigrum L.) are widespread major weed problems in California processing tomatoes causing severe economic loss to growers. This loss amounts to greater than $68 million due to hand hoeing costs and yield reductions. A three year study of Solanum species control in processing tomatoes conducted by University of California Cooperative Extension Farm Advisor, Mullen, show metam applied preplant subsurface can be effective for control of Solanum and other weed species (Mullen). It must be noted that processing tomatoes do not currently use methyl bromide. Reference to this crop is to establish metam sodium as a good weed control tool, with the broad (and very likely) assumption that such effective weed control will be transferrable to other cropping situations.
Nematode Control
A statewide investigation into the potential of various nematicidal materials for controlling root-knot nematodes (Meloidogyne spp.) on processing tomatoes was conducted in California during 1985. Metam sodium applied via drip irrigation at both 64 and 128 pounds active per acre significantly reduced root galling throughout the season and had significantly reduced numbers of root-knot nematode second stage juveniles in soil assessed at planting time. These two treatments gave the highest yields in these experiments (Roberts and Matthews 1985). Again, it must be noted that processing tomatoes do not currently used methyl bromide, and reference to this crop establishes metam sodium as a good nematode control agent, with the assumption that such control may be transferrable to other cropping situations, such as those where methyl bromide is currently used.
Plant Disease Control
Metam sodium applied at rates of 10 to 40 gallons per acre greatly reduced pythium and Fusarium soil levels and root infection in processing tomatoes. Metam sodium also significantly reduced the "corky-root like" banded lesions on roots in midseason. It was concluded that the control of these common soil fungi by metam sodium may have contributed, along with nematode control, to the overall plant growth increase and yield increase that occurred in most of these experiments.
Fusarium oxysporum causes serious losses in yield and quality of celery. It attacks the fibrous root system and spreads through the xylem into the crowns. The initial symptom is a retardation of growth, usually followed by yellowing of the foliage. Field evaluations conducted during 1989 in California revealed that fumigation of soil with metam sodium promoted early plant growth and increased yield in fields infected with this disease (Becker et. al. 1990). Very little celery production currently uses methyl bromide, so here again, reference to this crop establishes the pesticidal effects of metam sodium, with the assumption that such control will be transferrable to cropping situations where methyl bromide is currently used.
In 1990, Johnston and Phillips evaluated soil fumigants for control of Phytophthora and Pythium blight of peppers. The incidence of Pythium blight was high in this test and this test was considered definitive. Metam sodium applied via drip irrigation at 160 to 320 pounds active per acre provided significant reduction in Pythium blight and a significant increase in total yield (Johnston and Phillips 1991).
Orchard Replant Sites
Pathogenic soil organisms present in the soils of most mature orchards often reduce root growth of young fruit trees when the site is replanted. Poor root development leads to reduced vegetative growth and poor fruit yields throughout the life of the replanted orchard. While many soil fumigants, fungicides, fertilizers and soil amendments have been tested for effect on the orchard replant disease, only three have shown long-term growth and yield benefits in Washington orchard trials: methyl bromide, metam sodium, and fumigants containing chloropicrin (WSU 1996).
To evaluate control of southern blight in apples, UC Farm Advisor Joseph Grant and Greg Browne, USDA-ARS are evaluating alternatives to methyl bromide + chloropicrin. In year one of the experiment, metam sodium performed as well as the methyl bromide/chloropicrin mixture for control of the disease at tree replant sites (USDA 1996).
Trials conducted to evaluate the use of methyl bromide alternatives on orchard replant sites demonstrated that metam sodium can provide comparable control as methyl bromide (McKenry 1994). However, the study also noted that metam sodium does not always penetrate deep roots, and thus may not control nematodes in old roots if the proper soil conditions are not present. A vineyard with root lesion and root knot nematodes was replanted to strawberries. Results of this trial revealed that soil drenching replant sites with 300 lbs of metam sodium gave equivalent nematode control for 24 months. A 20 year old plum site, with root lesion and ring nematodes, was replanted to nectarines. Soil drenching with 330 lbs of metam sodium gave equivalent nematode control for 24 months. At another site, soil drenching a 15 year old peach and plum orchard, infested with root lesion and citrus nematode, with metam sodium gave comparable nematode control. Additionally, at an old almond orchard, infested with root lesion and ring nematode, replanted to grapes was treated with metam sodium at 327 lbs. Results showed comparable nematode control and plant growth when compared to methyl bromide.
Successfully Applying Metam Sodium
Although some growers have 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, in some cases, 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 use metam sodium effectively, 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. 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).
In most cases, 80 to 320 pounds active 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).
Metam sodium can also be applied through sprinkler, flood or drip irrigation. Research trials indicate that application of metam sodium through overhead irrigation water may be a more effective way to obtain uniform distribution than by injecting with chisels (Adams and Johnson 1983, Adams et. al. 1983, Ben-Yephet and Frank 1984). Additionally, University of Georgia researchers demonstrated that metam sodium was more effective against Rhizoctonia and Pythium when applied through overhead sprinkler irrigation than when injected with chisels in a fall experiment (Sumner and Phatak 1988).
University of Georgia researchers demonstrated that proper placement through adequate water is important for the efficacy of metam sodium (Sumner and Phatak 1988). Metam sodium moves in the water phase (opposed to methyl bromide which moves in the air phase) so adequate watering is essential. Failure to appreciate this fact is one of the major causes of inconsistency in metam sodium application. These trials demonstrated that the application of metam sodium in 2.5 cm of water was more effective in controlling root diseases in deep-rooted vegetables such as okra than in 1.3 cm of water. Application in 0.6 cm of water were ineffective. 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.
Cost Effective Alternative to Methyl Bromide
An advantage to the use of metam sodium is the low cost. Although supplemental pest control activities may be required under certain circumstances and may increase the total application costs, metam sodium is considered by many to be safer and easier to use than methyl bromide. Table 2. compares the costs of metam sodium and methyl bromide for soil fumigation treatments. The average cost of metam sodium ranges from $0.41 to $0.88 per pound active (Johnson Mercantile Co. 1997, Western Farm Service 1997), with typical application rates ranging from 240 to 320 pounds active per acre (Braun and Supkoff 1994). Total metam sodium costs can average between $141 to $282 per acre. In comparison, the average cost of methyl bromide ranges from $3.13 to $4.25 per pound (Shore Chemical 1997, Helena Chemical 1997, Cal Ag Industrial Supply 1996). Methyl bromide co-sts are estimated to range from $560 to $1,700 per acre.
| Fumigant | Cost Per Unit | Units Per Acre | Cost Per Acre |
|---|---|---|---|
| Metam sodium | $0.41 - $0.88 per lb. | 240 - 320 lbs. | $141 - $282 |
| Methyl Bromide | $3.13 - $4.25 per lb. | 180 -400 lbs. | $560 - $1,700 |
References
- Adams and Johnston 1983. Factors Affecting Efficacy of Metam Applied Through Sprinkler Irrigation for Control of Allium White Rot. Plant Disease, 67:978-980.
- Adams et. al. 1983. Application of Metam Sodium by Sprinkler Irrigation to Control Lettuce Drop Caused by Sclerotinia minor. Plant Disease 67:24-26.
- Agamalian 1990. Evaluation of Calcium Cyanamide for Preplant Weed Control in Horticultural Crops. Proc. Weed Sci. Soc. 43, 1990.
- Becker et. al. 1990. Effect of Rhizobacteria and Metham-Sodium on Growth and Root Microflora of Celery Cultivars. Phytopathology, Vol. 80, No.2, 1990.
- Ben-Yephet and Frank 1984. Optimization of the Metham-Sodium Dose in Controlling Verticillium dahliar in Potato. Phytoparasitica, 12:203-205.
- 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, Sacramento, CA, July 1994.
- Budavari (ed.) 1989. The Merck Index. Merck & Co. Rahway, NJ.
- Cal Ag Industrial Supply. Price Quote. Active ingredient price for methyl bromide. Cal Ag Industrial Supply, Hollister, CA. 1996.
- California Agriculture 1994. Soil Fumigants provide multiple benefits; alternatives give mixed results. California Agriculture, Vol. 48, No. 3, May-June 1994.
- 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 1997. California Department of Pesticide Regulation, Sacramento, California California Pesticide Use Report, University of California, Davis, CALIPM, Pesticide Use Summary Database, April 1997.
- EPA 1994. Methyl Bromide Consumption Estimates. U.S. Environmental Protection Agency, Stratsopheric Protection Division, Washington, D.C. May 3, 1994.
- EPA 1996. Methyl Bromide Consumption Estimates. U.S. Environmental Protection Agency, Stratsopheric Protection Division, Washington, D.C.
- Helena Chemical Company 1997. Price Quote. Active ingredient price for methyl bromide. Helena Chemical Company, Kerman, CA. 1997.
- ICI 1992. Vapam® Product Guide, ICI Agricultural Products, Wilmington, DE.
- Johnson Mercantile Company 1997. Price Quote. Active ingredient prices for metam sodium and methyl bromide. Johnson Mercantile Company, Hamilton, NC.
- Johnston and Phillips 1991. Evaluation of Soil Fumigants, Fungicides, and a Surfactant for Control of Phytophtora and Pythium Blights of Peppers, 1991 F&N Tests 47:104.
- Johnston et. al. 1991. Evaluation of Fumigants and Nematicides for the Control of Root-Knot Nematodes on Carrot, 1991. F&N Tests 47:158.
- Larson and Shaw 1994. "Evaluation of Eight Preplant Soil Treatments for Strawberry Production in California". 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL.
- McGovern et. al. 1996. Reduction of Fusarium Crown and Root Rot of Tomato by Combining Soilsolarization and Metam Sodium.
- McKenry, Buzo, Kretsch, Kaku, Ashcroft, Lange, Kelly. 1994. "Soil Fumigants provide multiple benefits; alternatives provide mixed results." California Agriculture. 48:22-28.
- Mullen. A Three Year Study of Solanum Control in Processing Tomatoes. Robert Mullen, Farm Advisor University of California Cooperative Extension, San Joaquin County.
- 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 Emission Reductions. Kissimmee, FL. November 1994.
- Roberts and Matthews 1985. Report on 1985 Nematicide Trials. Nematologist and Research Associate, Kearney Agricultural Center, Parlier, CA.
- Roberts et. al. 1988. Effects of Metam Sodium Applied by Drip Irrigation on Root-Knot Nematodes, Pythium ultimum, and Fusarium sp. in Soil and on Carrot and Tomato Roots. Plant Disease, Volume 72 No. 3. March 1988.
- Shore Chemical 1997. Price Quote. Active ingredient prices for methyl bromide. Shore Chemical, Turlock, CA. 1997.
- Sumner and Phatak 1988. Efficacy of Metam-Sodium Applied Through Overhead Sprinkler Irrigation for Control of Soilborne Fungi and Root Diseases of Vegetables. Plant Disease, Vol. 72, No. 2 Feb. 1988.
- UC 1996. Strawberry Integrated Weed Mangement. Strawberry Pest Mangement Guidelines. April, 1996.
- USDA 1996. Technical Reports: Research on Alternatives to Methyl Bromide for Control of Soilborne Pests of Grapevines and Tree Fruits and Nuts. U.S. Department of Agriculture: Methyl Bromide Alternatives, October 1996.
- Western Farm Service 1997. Price Quote. Active ingredient price for metam sodium and methyl bromide. Western Farm Service, Fresno, CA. 1997.
- WSU 1996. WSU-TFREC Orchard Management Forum: Orchard Fumigation. Washington State University, 1996.
- Yarkin 1994. Methyl Bromide Regulation: All crops should not be treated equally. Cherisa Yarkin, David Sundling. David Silberman, and Jerry Siebert, University of California, Davis. California Agriculture, Volume 48, Number 3. May-June 1994.
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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