Soil-borne bacterial pathogens pose a significant threat to organic onion production as there is a lack of effective pathogen control practices for both conventional and organic systems. Burkholderia cepacia (causal agent of sour skin) and B. gladioli pv. alliicola (causal agent of slippery skin) are prevalent throughout the onion growing regions of the U.S., including Georgia. Organic growers rely on cultural practices to combat soil-borne diseases, pests, and weeds. Plants in the Brassica family contain glucosinolates which undergo hydrolysis and produce isothiocyanate volatiles serving as a biofumigant. Biofumigation has shown to be successful at reducing diseases, but efficacy is dependent on pathogen, environmental conditions, cover crop biomass, and soil conditions. The objective of this study aims to determine biofumigation effect on soil-borne bacterial pathogens associated with Burkholderia spp. This study was conducted on organic certified land using B. juncea ‘Pacific Gold’ for mustards and A. cepa ‘Sweet Tule’ for short-day onion crop. Mustards were grown and terminated at flower initiation with biofumigation treatments including mustard incorporated into soil, mustard incorporated into soil and covered with polyethylene mulch, and a no mustard control. To evaluate effectiveness of biofumigation, measurements on weed seed germination and biomass, disease incidence/severity in bulbs, and onion yield were measured. Weed seed germination was evaluated before and after the incorporation of the mustards. Weed biomass was measured at multiple time points throughout the onion growing season. At harvest, onions were graded according to the USDA standards (Colossal, Jumbo, Medium, and Cull). Bulbs were evaluated for the presence of both diseases at harvest. Post-harvest evaluation of bulbs was also conducted. A 50 bulb sub-sample/plot/treatment was placed in storage (-2 °C, 70% RH) for a period of 90 days. After storage, bulbs were sliced, and disease incidence/severity was recorded. At mustard termination, dry biomass among all treatments averaged 4,540.5 lbs/acre. Eleven weeks after mustard incorporation, treatments with plastic mulch following mustard incorporation had significantly less weeds than the control treatments.
