STRASHNOW, Y., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, 76100, Israel
ELAD, Y., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, 76100, Israel
SIVAN, A., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, 76100, Israel
CHET, I., Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot, 76100, Israel

Under laboratory conditions, isolate TH–203 of Trichoderma harzianum was found to be tolerant of up to 20 000 ppm methyl bromide (MB) (v/v), whereas the plant pathogen Rhizoctonia solani was susceptible to a dose of less than 9000 ppm (v/v). Exposure to sub–lethal concentrations of MB had no effect on the in vitro antagonistic ability of T. harzianum. Soil fumigation with MB at the equivalent of a commercial dose of 500 kg/ha did not reduce the population of Trichoderma in soil and allowed rapid colonization of Trichoderma to develop in the soil. Under greenhouse conditions a combination of T. harzianum and a reduced dose of MB (equivalent to 200 kg/ha) completely controlled disease incidence of R. solani in bean seedlings compared with controls in untreated soils. Similar disease control was achieved with the recommended dose of MB. Under field conditions, the combination of 200 kg/ha MB and T. harzianum gave a significant synergistic effect on damping–off of carrot seedlings caused by R. solani, and had a similar effect on growth, yield and disease control to that of the recommended dose. T. harzianum was also able to prevent reinfestation by R. solani in fumigated soils. Copyright © 1985, Wiley Blackwell. All rights reserved