Seed treatments to eradicate Pyrenopeziza brassicae from infected mustard (Brassica juncea) seed. Poster presented at 2017 APS Annual Meeting

Light leaf spot of brassicas is caused by Pyrenopeziza brassicae, a new disease to the USA. The fungus can be seedborne and seed transmitted. A seed lot of ‘Caliente 199’ mustard (B. juncea) infected with P. brassicae was used to assess the efficacy of chlorine (1.2% NaOCl for 10, 20, 30, and 40 minutes), hot water (50oC for 15 and 30 minutes), steam (62.8, 65.6, 68.3, and 71.1oC), and 10 fungicide treatments to manage seedborne P. brassicae. Each seed treatment was compared to non-treated seed, and fungicide treatments were also compared to seed treated with a polymer colorant (seed coating) added to each product. All treatments reduced the incidence of seed infected with P. brassicae, from an average of 13.5% for non-treated seed to 0 to 4.3%, based on seed health assays. Likewise, all treatments, including the seed colorant control treatment, reduced seed transmission of P. brassicae from an average of 3.4% for non-treated seed to 0 to 0.4%. Seed transmission was not observed for the hot water, steam, and six of the fungicide treatments (azoxystrobin, fludioxonil, iprodione, thiabendazole, pyracostrobin + boscalid, and difenoconazole + fludioxonil + mefenoxam + sedaxane + thiamethoxam). The hottest steam treatment reduced seed germination from 98.0% for non-treated seed to 90.0 and 93.8% in Trials 1 and 2, respectively. The results demonstrate there are effective organic and conventional seed treatments for management of P. brassicae.