Control of Soil-Borne Diseases in Tomato by Use of Steam and an Exothermic Reaction

Abstract

In 2005-2006 we tested pre-planting treatments applied using a self-propelled soil steaming machine designed for the release of steam after incorporation in the soil of a substance that causes an exothermic reaction able to heat it to a mild but effective temperature x time product. Experiments were conducted in open-field conditions by assessing the effectiveness of steam and potassium hydroxide (KOH) against Fusarium oxysporum f.sp. lycopersici and Sclerotium rolfsii on tomato plants. The combination of steam and exothermic reaction chemicals reduced the incidence of Fusarium wilt (93.4-94.8%) better than steam only (77.8-81.2%); control of Sclerotium rolfsii was likewise better with KOH (86.7-87.7%) than with steam only (65.0-71.0%). The effects of treatments on microbial density, plant growth and weed control were evaluated. Treatments caused significant reductions in the number of Fusarium oxysporum colonies compared to the untreated control, an increase in Trichoderma spp. and no significant effects on total fungus and actinomycete density. Significant reduction in weeds (above 82.5%) and drastic increase in plant growth was recorded with the use of steam/exothermic reaction. With a milder steam application, the exothermic reaction acts for a slight increase in Tmax and, most of all, on time in temperature x time product, obtaining a disease control similar to drastic steam treatments.