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

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

Treatment of soil borne pathogens Sclerotinia sclerotiorum, Sclerotium cepivorum, Verticillium dahliae and Pythium ultimum, potato cyst nematodes Globodera rostochiensis and Globodera pallida and weeds Chenopodium album and Agropyron repens with low-temperature/short duration steam and with ozone gas

Methyl bromide is a widely used soil disinfectant that, because of its ozone depleting properties, is being phased out in the EC by 2005.  Soil steaming is a well-established system of soil disinfestation and is increasingly seen as a viable option to methyl bromide replacement.  Traditional glasshouse steaming techniques create a number of problems because it involves treatment of soil with high-temperature (100-140°C) steam for up to eight hours or more.  This not only eliminates unwanted soil-borne pests and diseases, but also creates a ‘biological vacuum’, in which target pests and pathogens may quickly re-enter and luxuriate, perpetuating the need for regular disinfestation.   Soil steaming at lower temperatures, e.g. at 70°C, does not normally result in these unwanted side effects, because of the partial survival of the saprophytic microflora population. In this study agricultural soil samples, containing a range of important soil-borne pests and pathogens, were treated with steam in a specially designed laboratory steam-rig.  It was found that treatment at 60°C, for a duration of only 3 minutes plus eight minutes ‘resting’ (“low-temperature/short duration soil steaming”) was enough to 100% kill soil-borne fungal pathogens Sclerotinia sclerotiorum, Sclerotium cepivorum, Verticillium dahliae and Pythium ultimum;  potato cyst nematodes Globodera rostochiensis and Globodera pallida, and weeds Chenopodium album and Agropyron repens. When low temperature/short duration soil steaming was compared with a chemical soil disinfectant, using the fumigant dazomet (Basamid) at a rate of 760 kg/ha, both disinfestation methods resulted in 100% elimination of the above pathogens, nematodes and weeds and caused IGR (Increased Growth Response) of lettuce plants. In a further study, using four different soil types at three different matric potentials, it was found that efficacy of low-temperature/short duration steaming is dependent on soil type and soil moisture content, and that treatment of soil in a moist state is more effective than treatment in a dry state, especially when treating fine-textured sand and loam soils. Soil samples containing survival structures of soil pests were also treated with ozone gas in a specially designed ozone treatment chamber, but this did not result in elimination of target organisms.EThOS - Electronic Theses Online ServiceGBUnited Kingdo