California accounts for 85% of strawberry (Fragaria ×ananassa, Duch.) production in the United States and ≈20% of worldwide production [U.S. Environmental Protection Agency (USEPA), 2009a]. Most of the 16,107 ha under strawberry cultivation in California is in the southern and central counties along the coast, where the climate favors year-round production and harvest [U.S. Department of Agriculture–Economic Research Service (USDA-ERS), 2005, 2010]. High land prices often make it economically difficult to implement crop rotation with strawberry cultivation, resulting in high pest pressures (Duniway, 2002a). Since the 1960s, strawberry producers in California have depended on a mixture of two soil fumigants, methyl bromide (MB), and chloropicrin (Pic) for weed and pathogen control. MB fumigation in strawberry fields has been among the largest uses in California (USDA-ERS, 2000).
MB has been classified as a Class I stratospheric ozone-depleting chemical. Under the Montreal Protocol, the use of MB for fumigation in the United States after 2005 is permitted only through critical use exemption (Anbar et al., 1996; USEPA, 1993). For California strawberries, technically and economically feasible alternatives to MB are needed for control of pathogens such as Verticillium dahliae, Pythium spp., Rhizoctonia spp., and Phytophthora spp., root-knot (Meloidogyne spp.) and sting nematodes (Belonolaimus spp.), and weeds such as nutsedge (Cyperus spp.) and winter annuals (USEPA, 2009a). In 2008, a 14% reduction in gross revenue was estimated for California strawberry growers using alternatives vs. those using MB (USEPA, 2009b). Alternative fumigants to MB include Pic, 1,3-dichloropropene (1,3-D), metam sodium, and methyl iodide (Duniway, 2002b). Each of these fumigants has their advantages and disadvantages, and none is a complete replacement for MB (Shaw and Larson, 1999). Besides their inability to provide the spectrum of pest control achieved by MBPic use, these fumigants have to comply with ever increasing regulations. These regulations prohibit the use of fumigants on acreage sufficiently close to “sensitive sites” such as schools and houses, limit application methods and timing, restrict total annual fumigant use, and restrict the use of a specific fumigant in a geographical area, among other restrictions. In addition to direct effects on fumigant use, compliance costs are increasing, reducing growers’ net returns.
Solarization is a non-chemical approach widely used in tropical regions to treat infested soils. The potential of solarization for pest control in temperate and subtropical regions, including Arizona, California, Florida, North Carolina, and Texas in the United States, has also been examined, but its efficacy is found to be variable in these regions and not always effective as MB fumigation (Chellemi et al., 1994; Hartz et al., 1993; Ristaino et al., 1991). Solarization may not control all pests and its pest control efficacy is likely to decrease with increasing soil depths (Hartz et al., 1993; Stapleton et al., 2000). Soil solarization is initiated by covering the soil with clear film for a period of 4 to 6 weeks. The best season to practice solarization is summer, which corresponds to the period between May and September in the Central Valley in California and between May/June to August/September in coastal California (Elmore et al., 1997). Pathogens such as Verticillium spp., Rhizoctonia solani, Fusarium oxysporum, and Sclerotium rolfsii can be controlled through solarization (Katan, 1984). Solarization controlled common purslane (Portulaca oleracea L.), hairy crabgrass [Digitaria sanguinalis (L.) Scop.], and pigweeds (Amaranthus spp.) in Central Greece and has potential to control other annual weed species (Hartz et al., 1993; Vizantinopoulos and Katranis, 1993). Perennial weeds, bulbous weeds, and those with a hard seedcoat are difficult to control through solarization (Linke, 1994). In coastal California, the effect of solarization on soil pests is inconsistent as a result of the presence of a marine fog layer and low summer soil temperatures.
Steam has long been used in nursery and greenhouse crop production systems to control soilborne pests, and studies have shown that most plant pathogens, insects, and weeds will die when moist soils are heated to maintain temperatures of 65°C or greater for 30 min (Baker and Roistacher, 1957). Pullman et al. (1981) found a linear relationship between soil temperatures and time needed to kill most soil pathogens. Subbarao and Hubbard (1996) showed that constant temperatures of 35°C for 45 d reduced V. dahliae microsclerotia numbers by 70%. Steam applications have been also been performed in orchards and in forests (Moyls and Hocking, 1994; Norberg et al., 1997). However, steam application over large areas is limited by its high fuel costs, slow speed, and amount of labor required (Melander and Jørgensen, 2005). To minimize fuel costs during steam operation, we hypothesized that a combination of solarization with steam may have beneficial additive and synergistic effects on pest control than steam or solarization used alone.
The objectives of this study were to: 1) test the efficacy of steam in controlling soil pests in strawberry production; 2) to determine if combining solarization with steam in coastal California would achieve greater pest control and higher yields compared with steam or solarization used alone; and 3) to determine the economic feasibility of steam and solarization treatments relative to MBPic fumigation.
Anbar, A.D., Yung, Y.L. & Chavez, F.P. 1996 Methyl bromide: Ocean sources, ocean sinks, and climate sensitivity Global Biogeochem. Cycles 10 175 190
Baker, K.F. & Roistacher, C.N. 1957 Baker K.F The U.C. system for producing healthy container-grown plants California Agr. Expt. Sta. Ext. Serv. Manual 23.
Bolda, M.P., Tourte, L., Klonsky, K.M. & De Moura, R.L. 2010 Sample costs to produce strawberries: Central coast region, Santa Cruz and Monterey Counties Univ. of California Coop. Ext. ST-CC-10 21 p.
Chellemi, D.O., Olson, S.M. & Mitchell, D.J. 1994 Effects of soil solarization and fumigation on survival of soilborne pathogens of tomato in northern Florida Plant Dis. 78 1167 1172
Dahlquist, R.M., Prather, T.S. & Stapleton, J.J. 2007 Time and temperature requirements for weed seed thermal death Weed Sci. 55 619 625
Daugovish, O. & Fennimore, S.A. 2008 Weeds 115 133 Strand L.L. Integrated pest management for strawberries 2nd Ed Univ. of California Integrated Pest Mgt. Davis, CA
Duniway, J.M. 2002a Non-chemical alternatives used in the USA on horticultural crops Proc. Intl. Conf. on Alternatives to Methyl Bromide. 18 Nov. 2011. <http://ec.europa.eu/clima/events/0039/crops_alternatives_en.pdf>.
Elmore, C.L., Stapleton, J.J., Bell, C.E. & DeVay, J.E. 1997 Soil solarization: A non pesticidal method for controlling diseases, nematodes, and weeds Univ. of California, Div. of Agr. and Natural Resources Publ 21377.
Hartz, T.K., DeVay, J.E. & Elmore, C.L. 1993 Solarization is an effective soil disinfestations technique for strawberry production HortScience 28 104 106
Jäderlund, A., Norberg, G., Zackrisson, O., Dahlberg, A., Teketay, D., Dolling, A. & Nilsson, M.C. 1998 Control of bilberry vegetation by steam treatment—Effects on seeded Scots pine and associated mycorrhizal fungi For. Ecol. Mgt. 108 275 285
Linke, K.H. 1994 Effects of soil solarization on arable weeds under Mediterranean conditions: Control, lack of response or stimulation Crop Prot. 13 115 120
Luvisi, A., Materazzi, A. & Triolo, E. 2006 Steam and exothermic reactions as alternative techniques to control soil-borne diseases in basil Agron. for Sustainable Dev. 26 201 207
Monterey County Agricultural Commissioners’ Office 2009 Monterey County Agricultural Commissioner's Rpt: 2009 Salinas, CA
Moyls, A.L., Hocking, R.P., Neilsen, G.H. & Hogue, E.J. 1994 Apple tree growth response in greenhouse pot tests using heat-treated replant soil versus orchard replanted trees with in situ heated soil Acta Hort. 363 57 64
Norberg, G., Dolling, A., Jäderlund, A., Nilsson, M.C. & Zackrisson, O. 2001 Control of heather [Calluna vulgaris (L.) Hull] by steam treatment: Effects on establishment and early growth of Scots pine New For. 21 187 198
Norberg, G., Jäderlund, A., Zackrisson, O., Nordfjell, T., Wardle, D.A., Nilsson, M.C. & Dolling, A. 1997 Vegetation control by steam treatment in boreal forests: A comparison with burning and soil scarification Can. J. For. Res. 27 2026 2033
Peters, J. 2000 Tetrazolium testing handbook Contribution No. 29 to the Handbook on seed testing. Assn. of Official Seed Analysts, Ithaca, NY.
Pullman, G.S., DeVay, J.E. & Garber R.H. 1981 Soil solarization and thermal death: A logarithmic relationship between time and temperature for four soilborne plant pathogens Phytopathology 71 959 964
Rainbolt, C. 2011 Steam as a methyl bromide alternative in California cut flower production MS thesis California State Univ.–Fresno Fresno, CA
Ristaino, J.B., Perry, K.B. & Lumsden, R.D. 1991 Effect of solarization and Gliocladium virens on sclerotia of Sclerotium rolfsii, soil microbiota, and the incidence of southern blight of tomato Phytopathology 81 1117 1124
Samtani, J.B., Ajwa, H.A., Weber, J.B., Browne, G.T., Klose, S., Hunzie, J. & Fennimore, S.A. 2011 Evaluation of non-fumigant alternatives to methyl bromide for weed control and crop yield in California strawberries (Fragaria ananassa L.) Crop Prot. 30 45 51
Shaw, D.V. & Larson, K.D. 1999 A meta-analysis of strawberry yield response to preplant soil fumigation with combinations of methyl bromide–chloropicrin and four alternative systems HortScience 34 839 845
Subbarao, K.V. & Hubbard, J.C. 1996 Interactive effects of broccoli residue and temperature on Verticillium dahaliae microsclerotia in soil and on wilt in cauliflower Phytopathology 86 1303 1310
Tanaka, S., Kobayashi, T., Iwasaki, K., Yamane, S., Maeda, K. & Sakurai, K. 2003 Properties and metabolic diversity of microbial communities in soils treated with steam sterilization compared with methyl bromide and chloropicrin fumigations Soil Sci. Plant Nutr. 49 603 610
U.S. Department of Agriculture–Economic Research Service (USDA-ERS) 2000 Economic implications of the methyl bromide phase-out Info. Bul. 756. 18 Nov. 2011. <http://www.ers.usda.gov/Publications/AIB756/>.
U.S. Department of Agriculture–Economic Research Service (USDA-ERS) 2005 Fruit and tree nuts outlook 18 Nov. 2011. <http://www.ers.usda.gov/publications/fts/jul05/fts317.pdf#page=15>.
U.S. Department of Agriculture–Economic Research Service (USDA-ERS) 2010 U.S. strawberry industry 18 Nov. 2011. <http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1381>.
U.S. Environmental Protection Agency (USEPA) 2009a Methyl bromide critical use renomination for preplant soil use (open field or protected environment) 18 Nov. 2011. <http://epa.gov/ozone/mbr/cun2009/cun2009_StrawberryFruit.pdf>.
U.S. Environmental Protection Agency (USEPA) 2009b Methyl bromide critical use nomination for preplant soil use for strawberry fruit grown in open fields 18 Nov. 2011. <http://www.epa.gov/ozone/mbwr/CUN2011/CUN2011Strawberry.pdf>.
Webster, T.M. 2003 High temperatures and durations of exposure reduce nutsedge (Cyperus spp.) tuber viability Weed Sci. 51 1010 1015
Yamamoto, T., Ultra, V.U. Jr, Tanaka, S., Sakurai, K. & Iwasaki, K. 2008 Effects of methyl bromide fumigation, chloropicrin fumigation and steam sterilization on soil nitrogen dynamics and microbial properties in a pot culture experiment Soil Sci. Plant Nutr. 54 886 894
Zackrisson, O., Norberg, G., Dolling, A., Nilsson, M. & Jäderlund, A. 1997 Site preparation by steam treatment: Effects on forest vegetation control and establishment, nutrition, and growth of seeded Scots pine Can. J. For. Res. 27 315 322