Combined application of dazomet and Trichoderma asperellum as an efficient alternative to methyl bromide in controlling the soil-borne disease complex of bell pepper

Bell pepper (Capsicum annuum) is an important greenhouse crop in central Europe. However, due to its monoculture cultivation soil-borne pathogens, especially Verticillium dahliae, are a significant yield-limiting factor. Apart from treatment with methyl bromide (MB) phytopathogens can be controlled by several alternative soil treatments. However, a universal control agent such as methyl bromide does not exist and there is crop specificity with respect to efficient treatments. Thus, the efficacy of chemical (dazomet), biological (Trichoderma asperellum) and combination of both treatments in the control of soil-borne pathogens of bell pepper in comparison with MB was examined. In 3 consecutive years six demonstration trials were conducted on commercial farms in Poland. In five of the six trials, the application of MB resulted in the best control of Verticillium wilt. However, there were no differences between the AUDPC values of MB and dazomet (DZ) alone or DZ combined with T. asperellum B35. Among tested alternatives, the most consistent effect on the yield, as well as on control of the root rot disease complex and Verticillium wilt, was observed for treatment with DZ in combination with Trichoderma asperellum. The average increase in yield induced by this treatment (40.1%) was similar to that of MB (41.4%). There was a correlation (r=0.790) between Verticillium wilt disease severity and root rot symptom scores at the end of the vegetation season. Verticillium wilt reduced fruit yield to a larger extent than the root rot associated with a complex of pathogenic soil-borne fungi (Colletotrichum coccodes, Fusarium spp.). Dazomet, combined with T. asperellum, provided the highest net marginal return and a higher return on investment than MB. The efficacy of T. asperellum applied alone was too variable (coefficient of variation 76%) to be accepted by the pepper growers.