Field evaluation in the Eastern United States of a biological control Blossom Protect for fire blight suppression efficacy, potential to cause fruit russeting, and compatibility with fungicides

Fire blight is a destructive disease of apple and pear, and its severity is intensified under humid conditions. Biological controls are important components of the integrated management of plant diseases; however, field trials in the eastern United States have shown that currently available bacteria- and bacteriophage-based biocontrols lack the consistency and efficacy needed to meet industry standards under humid conditions. Blossom Protect is a yeast-based biocontrol agent developed for fire blight and post-harvest diseases of apple. Although Blossom Protect has shown effectiveness in the Pacific Northwest under the arid conditions, its efficacy has not yet been tested at a large scale in the eastern U.S. In this study, we conducted a multi-location, multi-season field evaluation of Blossom Protect to determine its effectiveness in suppressing fire blight. Blossom Protect consistently suppressed blossom blight incidence, with an average disease suppression determined at 63.9%, which exceeded that of oxytetracycline (57.1%) but remained lower than that of streptomycin (79.3%). The disease-suppression efficacy of Blossom Protect was further enhanced by the use of a contact sterilant, Oxidate, in an integrated management program. Blossom Protect increased fruit russeting; however, russeting was limited to 6-10% of the fruit surface on average and did not increase the proportion of out-of-grade fruit. We also assessed compatibility with fungicides commonly applied during bloom, and found Blossom Protect to be incompatible with conventional multi-site and quinone outside inhibitor (FRAC M and FRAC11) fungicides, as well as OMRI-listed contact sterilants and sulfur-based materials.