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Flooding As An Alternative to Pre-plant Methyl Bromide Fumigation
Flooding can be a viable alternative to methyl bromide as a preplant soil fumigation in flat, low-lying areas rich in mineral soils where there are seasonally high water tables (at least 4-6 feet from the surface) and abundant water supplies (e.g., Florida and in some parts of California). Approximately 66 percent of Florida soils have high water tables, of which an estimated 30 to 50 percent would be amenable to water table/flooding management practices (20 percent of all the land surface in Florida) (Buol 1973). Areas in Florida where flooding could be used as an alternative to methyl bromide include the Florida Peninsula (e.g., potatoes, tomatoes, bell peppers, and eggplants in Hastings and Bradenton, Florida) and east coast areas south of Vero Beach. Areas not suitable for flooding include northwest Florida and the Florida panhandle (Allen and Sotomayor 1996).
Flooding is believed to be as effective as methyl bromide for the control of some soil-borne pests and pathogens, particularly nematodes and non-aquatic weeds. Flooding also leaves no toxic residues. With the proper soil and water-availability conditions, flooding can be used to create anaerobic (little to no available oxygen) soil conditions which are followed by drainage to provide an aerated (available oxygen) root environment. This sufficiently will alter the soil environment in way that results in conditions which are unfavorable to pests. It will also conserve carbon in organic matter by slowing decomposition, increases the availability of certain micronutrients (e.g., magnesium and iodine) to crop plants, and changes the soil microflora to favor biological pest control (Snyder 1987). Flooding could be used in conjunction with other control practices, including organic soil amendments and soil solarization. As an added benefit, instead of leaving flooded fields fallow, it may be possible to grow cash crops (such as rice) on flooded fields (Allen and Sotomayor 1996).
In general, the flooding of soils significantly decreases soil oxygen supplies, causing an unfavorable environment for most pests, pathogens, and weeds (Maas 1987). Alternating anaerobic and aerobic conditions through periodic flooding, can cause a decrease in nematode populations (Dunn and Noling 1995, Wallace 1956), while longer periods of flooding have been found to be more effective in the control of weeds (Reddy and Patrick 1975 and 1976). Stover (1979) achieved nematode control by flooding and noted that for Florida organic soils, two weeks of flooding followed by two weeks of drainage, drying, and disking was as effective in controlling nematodes as continuous flooding for 9 months.
Flooding has been recognized as a viable means for controlling plant parasitic nematodes for more than 70 years. As early as 1907, Ernst Bessey (1911) observed control of root-knot nematodes on vegetables in flooded fields on islands which once existed in Lake Okeechobee (Synder 1987). More recent research indicates that proper water management and flooding practices can reduce nematodes and other pests in a variety of crops, including rice, bananas, corn, soybean, milo, sugarcane, tomatoes, bell papers, and eggplant (Hollis and Rodriguez-Kabana 1966, Rodriguez-Kabana and Hollis 1965, Muller et al. 1992, Muller and Van Aartrijk 1992). For example, flooding has been shown to be effective in the control of Panama disease and nematodes in bananas (Stover 1962, Maas 1969).
Many vegetable crops in Florida (e.g., eggplants, tomatoes) are grown in high water table soils that must be drained and managed to prevent anoxic rooting conditions. These high-value crops are produced in Florida during the fall, winter, and spring seasons. In the summer, however, fields are either fallowed or managed at a low scale because of seasonally heavy rainfall. This system of cropping followed by fallow may provide an opportunity for the development of specific management technologies during the summer off-season, including prolonged soil flooding (possibly with a water tolerant crop such as rice).
Current Research
Researchers at the USDA, Agricultural Research Service (ARS) in Gainesville, Florida are conducting experiments to assess the efficacy of soil water-logging for the control of root-knot nematodes (Meloidogyne arenaria) and purple nutsedge (Cyperus rotundus L.) populations. Specific issues being investigated regarding the effectiveness of flooding for the control of nutsedge include: 1) how water-logging affects sprouting of the nutsedge tuber, and 2) once the nutsedge is established, what becomes of it after flooding. Researchers are working to determine if tubers remain in a dormant, but viable stage during flooding (after which they can proliferate when appropriate conditions occur) or if the tubers die because of low soil redox potentials and unsuitable soil conditions resulting from flooding. Recent results indicate that purple nutsedge is suppressed in flooded rice fields. Additional research will be necessary to determine if nutsedge will still be suppressed during the subsequent cropping periods.
Because nematodes are aerobic organisms, they are controlled by asphyxiation in flooded fields, and by a build-up of H2S and other chemicals produced under anaerobic soil conditions that result from microbial fermentation reactions (Maas 1987, Hollis and Rodriguez-Kabana 1966). Other changes in soil ecology can occur that limit root-knot nematode reproduction or stimulate predation by beneficial soil organisms (Sotomayor and Allen 1996, Allen and Sotomayor 1996), however, additional research is needed to determine the exact response of nematodes to long-term flooding. Since high temperatures during flooding are more effective in controlling root-knot nematodes than lower temperatures (Stover 1979), combinations of treatments (alternate flooding, solarization, and high applications of fresh or composted organic matter) may prove to be more effective than long-term flooding alone in the control of nematodes.
Important Considerations for Flooding
When using flooding as a pest control measure, some basic processes should be considered (Snyder 1987):
- Time or Season of Flooding: In general, flooding is more effective at higher ambient air and soil temperatures. This places seasonal and geographic constraints on flooding. For example, flooding will require additional time to be effective at temperatures below 20 C (68 F) -- four to 6 weeks of flooding is effective in warm weather, while 6 to 10 weeks may be required to achieve effective control in cooler seasons.
- Alternate Flooding with Disking: Because some pathogens can survive flooding by persisting on plant debris in the soil-water interface or on the soil surface during draining; pests may be more easily eliminated if they are disked deep into soils before fields are reflooded.
- Water Depth: Most fallow flooding involves flooding to a depth of 10 cm (4 inches) to 40 cm (16 inches).
- Rice Culture: Because rice can be grown on fields flooded for pest and pathogen control, flooded fields can both generate revenue and provide opportunities for more efficient land/water use.
Costs
Flooding can be a viable and cost-effective alternative to methyl bromide in some situations. Flooding can be many times less expensive than methyl bromide fumigation, however, capital costs which may be necessary to achieve good pest control from flooding include those associated construction of retention/detention ponds, digging perimeter ditches and leveling fields, installing subsurface drains for reversible-flow drainage/irrigation/flooding water control, installing vertical barriers of low-density-polyethylene around the water management unit perimeters (i.e., land fill liners 3 to 5 feet below the soil surface to contain the flood waters), and installing power, pumps, and a pipe system (Allen and Sotomayor 1996). In considering the costs associated with this technique, it is also important to consider that water costs vary considerably from region to region. Regions with readily available water supplies will have lower costs, than areas where water must be pumped from wells or transported long distances.
| Costs | Flooding | Methyl Bromide |
|---|---|---|
| Capital | 60 | 54 |
| Labor/Operating | 4-39 | 436 |
| Materials
(Water/Chemical) |
0-41 | 1,936 |
| TOTAL | 64-140 | 2,426 |
Sources: Allen and Sotomayor 1996, Williams et al. 1992, Cooke et al. 1996, Gregory and Winn 1996, Giesler and Salassi 1995, Lagunas-Solar 1996, Onitsuka Greenhouse 1996.
References
- Allen, L.H.; Sotomayor, D., United States Department of Agriculture, Agricultural Research Service, South Atlantic Area Crop Genetic and Environmental Research Unit, Agronomy Department, Agronomy Physiology Laboratory, Gainesville, FL, personal communication, 1996.
- Bessey, E.A. Root-knot and its Control; United States Department of Agriculture; Bureau of Plant Industry Bulletin No. 217. U.S. Government Printing Office: Washington, D.C., 1911.
- Buol, S.W. Soils of Florida: Soils of the Southern States and Puerto Rico; South Cooperative Series Bulletin Number 174; joint regional publication of the Agricultural Experimentation Stations of the Southern States and Puerto Rico Land Grant Universities with Cooperative Assistance by the Soil Conservation Service of the United States Department of Agriculture; 1973, p 105 and map.
- Cooke, F.T.; Caillavet, D.F.; Walker, J.C. "Rice Water Use and Costs in the Mississippi Delta"; Bulletin #1039; Mississippi State University, Division of Agriculture, Forestry, and Veterinary Medicine, Delta Research and Extension Center: Stoneville, MS, 1996.
- Dunn, R.A.; Noling, J.W. 1995 Florida Nematode Control Guide. Institute of Food and Agricultural Sciences and Florida Cooperative Extension Service. IFAS Publications. University of Florida: Gainesville, FL, 1995; SP-54.
- Giesler, G.G., Salassi, M.E. "Projected Costs and Returns - Rice, Louisiana, 1995"; A.E.A. Information Series Number 131; Louisiana State University Agricultural Center, Louisiana Agricultural Experiment Station, Department of Agricultural Economics and Agribusiness: Baton Rouge, LA, 1995.
- Gregory, E.; Winn, J. "1996 Rice Production Guidelines"; Texas A&M University System D-1253. Texas Agricultural Extension Service: College Station, TX, 1996.
- Hollis, J.P.; Rodriguez-Kabana, R. Rapid kill of nematodes in flooded soil. Phytopathology 1966, 56, pp 1015-1019.
- Lagunas-Solar, M., University of California, Davis, CA, unpublished results, 1996.
- Maas, P.W.T. In Nematodes of Tropical Crops; Peachey, J.E., Ed.; Two Important Cases of Nematode Infestation in Surinam; Technical Communication 40; Commonw. Bur. Helminth, 1969, pp 149-154.
- Maas, P.W.T. In Principles and Practice of Nematode Control in Crops; Brown, R.H; Kerry, B.R., Eds.; Physical Methods and Quarantine; Academic Press: Orlando, FL, 1987.
- Muller, P.J.; Van Aartrijk, J. "Flooding Reduces the Soil Populations of the Stem Nematode Ditylenchus dipsaci in Sandy Soils"; Bulb Research Center: Lisse, Netherlands, 1992.
- Muller, P.J.; Van Beers, T.H.; DeRooy, M. "Flooding, a Non-chemical Soil Treatment to Control the Root-lesion Nematode Pratylenchus penetrans"; Bulb Research Center: Lisse, Netherlands, 1992.
- Onitsuka Greenhouse, Monterey, CA, unpublished results, 1996.
- Reddy, K.R.; Patrick, W.H. Jr. Effect of alternation aerobic and anaerobic conditions on redox potential, organic matter decomposition and nitrogen loss in a flooded soil. Soil Biol. Biochem. 1975, Vol. 7, 87-94.
- Reddy, K.R.; Patrick, W.H. Jr. Effect of frequent changes in aerobic and anaerobic conditions on redox potential and nitrogen loss in a flooded soil. Soil Biol. Biochem. 1976, Vol. 8, 491-495.
- Rodriguez-Kabana, R.; Hollis, J.P. Biological control of nematodes in rice fields: role of hydrogen sulfide. Science 1965, Vol. 148, 524-526.
- Snyder, G.H. Agricultural Flooding of Organic Soils; Technical Bulletin 870; University of Florida, Agricultural Experiment Station, Institute of Food and Agricultural Sciences: Gainesville, FL, 1987.
- Sotomayor, D.; Allen, L.H., Jr. Presented at the 1996 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions, Orlando, FL, November 1996; paper 97.
- Stover, R.H. "Fusarial Wilt (Panama Disease) of Bananas and other Musa Species"; Commonwealth Mycological Institute Phytopathology Paper: Kew, Surrey, 1962, Vol. 4, pp 1-117.
- Stover, R.H. In Soil Disinfestation; Mulder, D.J., Ed.; Flooding of Soil for Disease Control; Elsevier, Amsterdam, 1979, pp 19-28.
- Wallace, H.R. Soil aeration and the emergence of larvae from cysts of the beet eelworm, Heteroderma schlachtii schmidt. Ann. Appl. Biol. 1956, 44, pp 57-66.
- Williams, J.; Klonsky, K.; Livingston, P. "Sample Costs to Produce Rice in Sutter, Yuba, Placer, and Sacramento Counties - 1992"; U.C. Cooperative Extension: Davis, CA, 1992.
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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