Evaluation of non-chemical seed treatment methods for control of Alternaria brassicicola on cabbage seeds

Due to the lack of foliar fungicide use, the organic production of Brassica seeds free of Alternaria spp. is difficult. Therefore, effective seed treatments certified for use in organic farming are needed to eradicate or at least effectively reduce the seed-borne inoculum. We here report results of greenhouse and field experiments in which non-chemical seed treatments were tested for control of A. brassicicola on cabbage seeds naturally infested with the pathogen. In greenhouse experiments, significant improvements were obtained by seed treatment with some commercialised and experimental microbial biocontrol agents, an emulsion of thyme oil in water (0.1%) and by the tested physical seed treatments methods (i.e. hot water, aerated steam and electron seed treatment). Resistance inducers tended to increase the percentage of healthy plants, but the effects were statistically not significant. Generally the combination of physical treatments with the effective agents did not result in improved performance. Positive effects on crop establishment and yield by the same treatments were also observed in field tests. Overall the results indicate that several options for non-chemical control of A. brassicicola on Brassica seeds exist that are comparable in efficacy to the chemical standard Aatiram (active ingredient thiram) used in this study.