Abstract

Center rot of onion caused by Pantoea species can lead to substantial yield losses in the field and during storage. Growers rely on copper-based products or their combination with ethylenebisdithiocarbamate fungicides to manage center rot. Biocontrol agents (BCAs) are occasionally used alone or in combination with copper. The optimum intervals for alternate application of copper and BCAs have not been established and the efficacy of tank-mixing copper with BCAs over their solo applications remains largely understudied. We evaluated the ability of Bacillus subtilis QST 713 (Serenade ASO) or Bacillus mycoides isolate J (LifeGard WG) applied alternately or as tank mixes with copper (Nordox 75 WG) to manage center rot in onion leaves and bulbs. Alternating the application of BCAs with copper at longer intervals (10- or 15-d) could achieve a similar level of center rot control as their alternate treatment at shorter intervals (5-d). Under low disease pressure, two to three applications could be eliminated from the spray program without compromising disease suppression. We also found that B. subtilis QST 713 and B. mycoides isolate J strains from respective products were copper-sensitive at concentrations >250 ppm. Our concurrent study on the tank mix of BCAs with copper showed that standalone copper treatment had a similar level of disease control as their tank mix application. Frequent applications of copper may control disease relatively better than treatments lacking copper products but the integration of BCA with copper in spray programs may largely depend upon their compatibility and modes of action of the BCA products.