This report was presented at the UK Organic Research 2002 Conference. Soil samples containing resting structures of fungal crop pathogens (Verticillium dahliae, Sclerotinia sclerotiorum, Sclerotium cepivorum, Pythium ultimum), potato cyst nematodes (Globodera rostochiensis and Globodera pallida) and weeds (Chenopodium album and Agropyron repens) were treated with aerated steam in the laboratory at temperatures ranging from 50–80oC in a specially constructed apparatus. Steaming at 50 or 60oC for three minutes, followed by an eight-minute resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, fungi and nematodes. Low temperature/ short duration soil steaming could become a sustainable alternative to chemical or high-temperature steam soil disinfestation

Fielden, Nigel

Leifert, Carlos

Mullins, Chris E

Seel, Wendy E

Turbett, Yzanne

van Loenen, Mariska C A

Wilson, Michael J

English

Organic Eprints

  1 Low temperature/ short duration steaming as a sustainable method of soil disinfection   Mariska C A van Loenen, Yzanne Turbett, C E Mullins, Michael J Wilson,  Nigel Feilden, Wendy E Seel Department of Plant & Soil Science, Cruickshank Building, Aberdeen, AB24 3UU, Scotland, United Kingdom Carlo Leifert  Department of Agriculture, University of Newcastle, Newcastle Upon Tyne, NE1 7RU, England, United Kingdom  ABSTRACT  Soil samples containing resting structures of fungal crop pathogens (Verticillium dahliae, Sclerotinia sclerotiorum, Sclerotium cepivorum, Pythium ultimum), potato cyst nematodes ( Globodera rostochiensis and Globodera pallida) and weeds (Chenopodium album and Agropyron repens) were treated with aerated steam in the laboratory at temperatures ranging from 50–80oC in a specially constructed apparatus.  Steaming at 50 or 60oC for three minutes, followed by an eight-minute resting period in the steamed soil and immediate removal from the soil thereafter, resulted in 100% kill of all weeds, fungi and nematodes. Low temperature/ short duration soil steaming could become a sustainable alternative to chemical or high-temperature steam soil disinfestation.   Keywords:  soil disinfection, aerated steam, methyl bromide, soil-borne pests and diseases, weeds, solarization   INTRODUCTION  Increasing concern about the widespread use of pesticides in crops  has created an urgent need to develop new, more environmental friendly crop protection strategies. The use of soil fumigation in particular is based on highly toxic substances, which not only destroy soil-borne pests and diseases but also kill much of the saprophytic and beneficial microflora (Chen, 1991, Gamliel, 2000). Methyl bromide is a very poisonous but widely used soil fumigant that, because of its ozone-depleting properties, is being phased out by 2005 in industrialised countries and by 2015 in developing countries  (UNEP, 1998). Worldwide research is currently underway to find replacements for this compound (UNEP, 1998; UNEP, 2000).  Steaming  has been used for more than a century as a highly effective way of soil disinfection (Baker, 1962) and is under certain conditions a permitted practice in organic husbandry (Lampkin, 1998). However, the high temperature steam treatments (100-140oC) currently used  in horticultural practice have a range of negative side effects, in particular phytotoxicity caused by manganese and/or ammonium release from the soil as well as the creation of an ‘ecological vacuum’ due to eradication of most of the soil microflora (IKT-AT, 1992).  Low-temperature steam-treatments (60-80oC) are thought to avoid many of these negative impacts, but there is little information on the efficacy of low-temperature steam soil disinfection. We selected eight major soil-borne pests, diseases and w eeds:  fungal pathogens Verticillium dahliae (wilt disease), Sclerotinia sclerotiorum (white mould), Sclerotium cepivorum (onion white rot), Pythium ultimum (damping-off); potato cyst nematodes Archived at http://orgprints.org/8261  2 Globodera rostochiensis and  Globodera  pallida (eel worm) and  weeds Chenopodium album (fat hen) and Agropyron repens (couch grass). Agricultural soil samples containing resting structures of these organisms were exposed to aerated steam at a range of temperatures in a specially designed laboratory apparatus.   MATERIAL AND METHODS  Soils  Two contrasting field soils were used in experiments, i) soil D, a well structured loamy sand, organic matter (OM) 6%, available water (AW) 10-28% and  ii) soil W an un-stable, hard-setting, sandy clay loam,  OM 1.6%,  AW 7-13%.    Inserting target organisms in soil samples  The resting structures of  S. sclerotinia  and S. cepivorum  (sclerotia),  V. dahlia (microsclerotia), Globodera rostochiensis and G. pallida (cysts) and C. album (seeds) were inserted in small mesh bags. Soil sample holders, made of steel cylinders with an open top and steel mesh base, contained 1 litre of soil, at a  depth of  10 cm. Mesh bags and loose rhizomes of  A. repens were placed in the middle of the soil samples. One litre of P. ultimum inoculated soil was also placed in sample holders.    Moisture content of soil and target organisms  Soils were steamed at moisture level of approximately 70% field capacity, which was also the moisture content of  P. ultimum inoculated samples. Organisms in mesh bags were tested in a dry and  imbibed state. Imbibed organisms were soaked overnight.  A. repens rhizomes were tested after  overnight storage in moist soil. C. album and S. sclerotiorum  were additionally tested after soil moisture equilibration.  Steaming in steam-apparatus  Soil samples containing target organisms were inserted in sample holders and steam-treated in a steel test-rig, measuring ca. 2 x 0.3 x 0.3 m. Four sample holders were placed in a drawer and inserted in the central part of the apparatus. Water was heated electrically in a 50-litre tank. When at the required temperature fine water droplets were mixed with a stream of air (aerated steam) and directed towards the samples, which were steamed from the base upwards. Thermocouples interfaced with a computer and were inserted in the soil amongst the organisms. This enabled temperature readings during steaming procedure.  Organisms were steamed at 50, 60, 65, 70 and 80oC. Steaming lasted 3 minutes, after which soil samples were left inside the test-rig for an additional 7 minutes. The drawer was then withdrawn and the organisms removed for further assessment.   Assessment of organisms  Sclerotia of S.sclerotiorum and S. cepivorum were grown on PDA (potato dextrose agar). V. dahliae microsclerotia were plated out on a selective nutrient agar. Seeds of C. album were placed on moist filter paper and A. repens rhizomes were planted in a sandy compost.  Germination / growth of these organisms was established after 14 d. Cysts ( G. rostochiensis  and  G. pallida) were i mmersed in potato root diffusate, obtained from roots of potato plants (cv Désirée). They were incubated for 4 weeks, Archived at http://orgprints.org/8261  3 after which hatched juveniles were microscopically counted. Peas (cv Kelvedon Wonder) were grown in P. ultimum infected soil and germination counted after 14 d.   Data assessment   Each test involved four replicates of each organism. The numbers per replicate were: 20 seeds (C. album), 16 rhizome nodes (A. repens), 30 sclerotia (S. cepivorum), 20 sclerotia (S. sclerotiorum), 30 microsclerotia ( V. dahliae) and 10 cysts ( G. pallida  and  G. rostochiensis). The pea-bioassay was based on four separate P. ultimum inoculated soil samples. Control treatments consisted of the same number of organisms and replicates.   RESULTS  Some dry organisms required temperatures up to 80oC to be completely killed but all organisms in a moist state were killed at 50 or 60oC (Table 1). Temperatures were considered lethal when germination/hatching/growth was zero. Average control growth rates were:  C. album, 74%±3%;  S. sclerotiorum 100%;  S. cepivorum 71%±  5%;  V. dahliae 85%±5%; peas 72%±7%;  G. pallida and G. rostochiensis  57±8 and 159±26 juveniles per cyst respective and A. repens 6±0.2 shoots.   Table 1 . Minimum lethal steam temperatures of eight major soil-borne pathogens, pests and weeds. Organisms were steamed in two field soils at ca. 70% field capacity. Steaming lasted 3 minutes, followed by an 8-min ‘resting’ period before removal of organisms from the soil.  Minimum lethal temperatures  Soil D  Soil W Soil-borne  pathogens, pests  and weeds   dry1 imb2  s.m.e.3  dry1  imb2  s. m.e.3 S. cepivorum  50oC 50oC  nd  50oC  50oC  nd  V .dahliae  50oC 50oC  nd   50oC  50oC  nd  G. pallida  50oC 50oC  nd   50oC  50oC  nd  G. rostochiensis  50oC 60oC  nd   50oC  50oC  nd  C. album  65oC 60oC  60oC  65oC  60oC  60oC S. sclerotiorum  80oC 60oC  60oC  70oC  50oC  50oC A. repens.  nd  nd  60oC  nd   nd   60oC P. ultimum  nd  nd  60oC  nd   nd   60oC 1 dry = (air) dry organism 2 imb = imbibed organisms 3 s.m.e. = soil moisture equilibrated organism  DISCUSSION  It has been known for a long time that exposure to steam at 60oC for 30 min destroys most soil-borne pests and diseases and reduces problems of phytotoxicity and re-infestation that may occur after steaming at higher temperatures (Baker, 1962; Dawson  et a l., 1965). For this reason soil pasteurisation (70oC, 30 min) is the recommended method for steam disinfestation of glasshouse soils (IKC-AT, 1992). Despite this, steam practices such as sheet steaming, which tend to last much longer (6-7 h) and result in temperatures of 100oC in the top 25-cm of soil, are commonly used (IKC-AT, 1992). Also, because of the high costs involved, steam treatment is currently limited to a few high value horticultural and floricultural crops. However, our findings suggest that,  because major soil pests, pathogens and weeds are killed in steamed soil after only 10 minutes  at 50-60oC,  a smaller amount of energy may be needed to achieve soil disinfestation and costs of steaming soils could be reduced. Many soil borne pests, diseases and weeds have been controlled in Southern European and Mediterranean countries with low-temperature (45-60oC) ‘steam’ soil Archived at http://orgprints.org/8261  4 treatment, based on soil solarization (Katan and DeVay, 1991), apparently with little negative effect on chemical, physical or microbial soil properties (Chen et al., 1991). This relatively new disinfestation technique has been recognised as a non-chemical alternative to methyl bromide (UNEP, 1998) and is used by organic growers (Grinstein and Ausher, 1991; Bell and Laemmlen, 1991; UNEP, 2000). Solarization is however mainly suited to warmer climates. Low-temperature-short duration steam treatment of soil could become a comparable disinfestation method in cooler climates. Further investigations into soil properties with relation to steaming such as matric potential, nutrient content and microbial life are currently in progress.    ACKNOWLEDGEMENTS  This work was funded by the Department for the Environment and Rural affairs (DEFRA) under the UK Horticulture Link programme (project Hort216/HLO136LSF “Integrated use of Soil Disinfection and of Microbial Organic Amendments for the control of Soil Borne Diseases and Weeds in Sustainable Crop Production”: contact Chris Mullins, Aberdeen University). Consortium members including funders are : Bioquell Food Ltd, Berry World Ltd, East Malling Trust, E.S. Black Ltd, Horticulural Development Council (project CP6), Langmead Farms Ltd, The MicroBio Group Ltd, REGERO S.A., Tesco Stores Ltd, and TIO Ltd. Project Co-ordinator:  George Marston,  Lead P articipant: Tesco.  We are also grateful for the help from : Dr. D.L. Trudgill and Mrs. A. Holt, Scottish Crop Research Institute (SCRI), Dundee; Prof J.M. Whipps, Dr. G. White, Dr. E. Coventry and Dr. E.E. Jones, Horticulture Research International (HRI), Wellesbourne, and Dr. D.C. Harris and Ms. C. Lewis, HRI, East Malling.   REFERENCES  Baker KF (1962) Principles of heat treatment of soil and planting material. Journal of the Australian Institute of Agricultural Science 28:118-126 Bell CE and Laemmlen FF (1991) Soil Solarization in the Imperial Valley of California. In: Katan J and DeVay JE (eds.) Soil Solarization (pp  245-255). CRC Press London Chen Y, Gamliel A, Stapleton JJ and Aviad Y (1991) Chemical, physical and microbial changes related to plant g rowth in disinfested soil. In: Katan J and DeVay JE (eds.) Soil Solarization (pp 103-129), CRC Press London  Dawson JR, Johnson RAH, Adams P and Last FT (1965) Influence of steam/air mixtures, when used for heating soil, on biological and chemical properties that affect seedling growth. Annals of Applied Biology 56: 243-251  Gamliel A, Austerweil M and Kritzman G (2000) Non-chemical  approach to soilborne pest management – organic amendments. Crop Protection 19: 847-853 Grinstein A and Ausher R (1991)  Soil Solarization in Israel. In: Katan J and DeVay JE (eds.) Soil Solarization (pp. 193-204), CRC Press London  IKC-AT (1992) Stomen, technische handleiding bij het stomen van grond en substraat.   Informatie en Kennis Centrum Akker- en Tuinbouw, afd Glasgroente en bestuiving, Naaldwijk en afd. Bloemisterij, Aalsmeer, the Netherlands. 88 p Katan J and DeVay JE eds. (1991)  Soil Solarization. CRC Press London. 267p    Lampkin N (1993) Organic Farming. (p 637). Farming Press, Ipswich  UNEP (1998) Report of the Methyl Bromide Technical Options Committee (1998) Assessment of alternatives to Methyl Bromide. United Nations Environmental Programme. Nairobi, Kenya. 354 p UNEP  (2000) Case Studies on Alternatives to Methyl Bromide: Technologies with Low Environmental          Impact. United Nations Environmental Programme. Nairobi, Kenya. 77 p        From: Powell et al. (eds), UK Organic Research 2002: Proceedings of the COR Conference, 26-28th March 2002, Aberystwyth, pp. 211-214.       Archived at http://orgprints.org/8261

Low temperature/short duration steaming as a sustainable method of soil disinfection

Low temperature/short duration steaming as a sustainable method of soil disinfection

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