Integrated Management of Bacterial Streak and Bulb Rot of Onion

Abstract

Significantly higher levels of bacterial streak and bulb rot of onion (BSBR), caused by Pseudomonas viridiflava, occurred in onions receiving excessive applications of fertiliser and were correlated with higher nitrogen content in plant tissues. Based on previous work that weeds, particularly cutleaf evening primrose (Oenothera laciniata), were the primary source of initial inoculum, oxyfluorfen was evaluated as a post-emergence herbicide after transplanting. The herbicide not only reduced weed levels as expected, but also reduced the incidence of BSBR. Lower levels of BSBR also occurred in plots treated with weekly applications of cupric hydroxide and maneb when compared to non sprayed plots, or plots treated only with the fungicide chlorothalonil. Harvesting onions with cutting shears contaminated with P. viridiflava increased the incidence of postharvest rots in onions clipped immediately after uprooting but not in onions allowed to cure in the field for 48 h. Finally, lower levels of postharvest disease occurred when onion bulbs were stored under controlled-atmospheric (CA) conditions (3% oxygen, 5% carbon dioxide, and 92% nitrogen) at 1degreesC. The various control procedures were combined into an integrated management strategy for the control of BSBR in Georgia.