The management of Sclerotinia stem rot of soybean caused by [Sclerotinia sclerotiorum (Lib) de Bary] integrates several tactics that may include biological control. However, the successful incorporation of biocontrol agents into the management program might be hindered by agrochemical application. To determine the compatibility of potential biocontrol agents with agrochemicals, growth of Trichoderma asperellum, T. gamsii and Coniothyrium minitans was tested with selected chemicals on agar plates. Effects of selected agrochemicals on C. minitans growth and biocontrol activity were also tested in soil and in water. On amended agar media, Trichoderma spp. and C. minitans were insensitive to the herbicide lactofen and were inhibited to varying degrees by some of the tested fungicides. The survival and the biocontrol activity of C. minitans in the soil was not impaired by propamocarb HCl, tetraconazole or lactofen treatments. When mixed in a water suspension, none of the selected the herbicides or a biofertilizer affected C. minitans population in the suspension over a 4 h period, suggesting that they can be applied in a tank mix. Under field conditions, Trichoderma spp. and C. minitans reduced the disease severity and viable sclerotial population of S. sclerotiorum, but their efficacy varied across years and location. Co-application with lactofen enhanced the efficacy of disease suppression and yield in some cases but reduced the efficacy in others. The effect of the biological control agents or chemicals evaluated on yield during three years of trials was inconsistent.
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