Efficacy of Bacillus subtilis QST 713 formulations, copper hydroxide, and their tank mixes on bacterial spot of tomato

• Field evaluation of Serenade biofungicide formulations on bacterial spot of tomato.
• Modest disease control on foliage with Serenade ASO [Bacillus subtilis QST 713].
• Good disease control on foliage with tank mixes of biofungicide & copper hydroxide.
• No consistent reduction of bacterial spot on tomato fruit.
• No consistent improvement in marketable and total fruit yields of tomatoes.

This study was conducted to investigate the effects of foliar sprays of wettable powder formulation (Serenade MAX or QRD 141) and aqueous suspension (Serenade ASO or QRD 145) of Bacillus subtilis QST 713, alone or as tank mixes with copper hydroxide, on bacterial spot disease and fruit yields of tomato. Field plots were established in London, Ontario Canada during the 2007–2010 growing seasons and disease conditions were created artificially by inoculations with cell suspension of bacterial spot pathogen. The aqueous suspension of biofungicide alone reduced the severity of bacterial spot on tomato foliage relative to water control in 3 of 4 years but in tank mix with copper hydroxide reduced disease severity on foliage in all 4 years. The wettable powder formulation of biofungicide alone did not consistently reduce bacterial spot severity on tomato foliage but in tank mix with copper hydroxide reduced disease severity on foliage in 3 of 4 years. Copper hydroxide alone also reduced the severity of bacterial spot on tomato foliage in 3 of 4 years. A consistent reduction in the percentage of diseased fruit was not seen with any of the biofungicide of copper hydroxide spray treatments. There was no consistent effect on marketable yield with any of the treatments. The wettable powder formulation of biofungicide in a tank mix with copper hydroxide increased total fruit yield during the first 2 years only, but the reason for this yield increase is not clear.The results suggest a moderate effect of biofungicide or copper hydroxide alone or in combination in reducing bacterial spot disease.