Integrated control of pink root (Pyrenochaeta terrestris) of onions by dazomet and soil solarization

Abstract

At Frankston in southern Victoria in 1984-85, dazomet applied at 750 kg/ha either alone or in combination with solarization, reduced disease incidence and severity of pink root, increased yields by at least 100% and improved storage quality of onions. Solarization for 6 weeks delayed the development of pink root, but had no effect on either the disease incidence or severity at harvest. Solarization, however, did increase yields by 23% at harvest compared to untreated soils.A bioassay of 0-10 and 10-20 cm layer of soil after treatment showed that dazomet applied alone or in combination with solarization reduced the number of plants infected by P. terrestris to less than 5% in both layers. Untreated and solarized plots had more than 86% of the plants affected. A similar bioassay taken 3 months later just before sowing showed that the number of plants infected with pink root had increased in the 0-10 cm layer of plots treated with dazomet, indicating that some reinfestation had occurred. There was no reinfestation in the combined treatment.Fusurium spp. were isolated from almost 100% of roots sampled, and although more than 70% were pathogenic under controlled conditions in the glasshouse, they did not appear to cause disease in the field or significantly affect yields.Cultivation of soils after harvest in 1985 and remoulding seedbeds prior to sowing the next crop apparently caused reinfestation of soils, and there was no residual benefit from treatments applied in 1984.