Fire blight, caused by the bacterial pathogen Erwinia amylovora, poses a major barrier to organic apple production. NOP standards no longer allow streptomycin and E amylovora has evolved antibiotic resistance. This project tested bacteriophages (viruses that consume bacteria), alone and with other biological controls (a Bacillus subtilis formulation Serenade Opti and the yeast-based Blossom Protect) against fire blight. Because phages are highly sensitive to solar UV, field applications were made in the evening and treatments included “sunscreen” adjuvants peptone (protease digestate of milk or meat) or kaolin clay.

Peptone and kaolin protected phages from UV in lab studies, but field trials showed inconsistent efficacy of biocontrols against fire blight and of sunscreens in protecting phage from UV. AgriPhage, a newer (2019) commercial product, outperformed two experimental phages and did not disrupt the flower microbiome. In Michigan, AgriPhage reduced fire blight 39% (similar to other biocontrols), which improved to 65% reduction when the AgriPhage was protected with 5 mg/mL peptone; however, AgriPhage proved ineffective in the North Carolina trial.