Influence of foliar sprays of Bacillus subtilis QST 713 on development of early blight disease and yield of field tomatoes in Ontario

Early blight is an economically important foliar disease of processing and fresh market tomatoes. The aim of this multi-year field study was to investigate the impact of weekly foliar sprays of dried and aqueous formulations of Bacillus subtilis QST 713 (Serenade and Rhapsody), alone or as tank mixes with copper hydroxide, on early blight disease development and fruit yields of tomato. Field plots were established in London, Ontario during the 2008-2010 growing seasons and disease conditions were created artificially by inoculations with spore suspension of the early blight pathogen. The tank mixes of copper hydroxide and chlorothalonil were included as a standard spray treatment. Late blight also appeared naturally in the plots late in 2009 and 2010 field seasons and affected fruit in both years, but more severely in 2009. Spray treatments had variable effects on tomato early blight and fruit yields depending on the level of disease pressure in the inoculated plots. The weekly sprays of biofungicide alone did not consistently reduce disease severity on tomato foliage or incidence on fruit, but in a tank mix with copper hydroxide, both formulations consistently reduced foliar disease severity even when disease pressure was high in plots. Under high disease conditions, copper hydroxide alone or as a tank mix with chlorothalonil also consistently reduced disease severity on foliage. The mixture of two fungicides also consistently increased total fruit yields in all 3 years. Plots sprayed with copper hydroxide alone and in tank mixes with chlorothalonil and the dried formulation of biofungicide consistently had less late blight-infected fruit. The combined effects of biofungicides and copper hydroxide or other fungicides should be further investigated for consistent disease management and yield improvement.