Sensitivity of Erwinia amylovora in Illinois Apple Orchards to Streptomycin, Oxytetracyline, Kasugamycin, and Copper.

In 2008 and 2009, severe fire blight (Erwinia amylovora) occurred in Illinois apple orchards, leading to speculation that streptomycin-resistant strains of E. amylovora might be present in some orchards. Statewide surveys were conducted in 2010, 2011, and 2012, and 117, 129, and 170, E. amylovora isolates were collected, respectively, from 20 counties. None of the 416 E. amylovora isolates tested were resistant to streptomycin (Agri-Mycin 17WP) at 50 mg/liter. Seven non-E. amylovora bacterial isolates were collected from E. amylovora-infected shoots that contained both a strA-strB streptomycin resistance gene and IS1133 on transposon Tn5393, which could be a potential source of streptomycin resistance for E. amylovora in Illinois in the future. Colony development of all 84 E. amylovora isolates tested was inhibited on Luria-Bertani medium amended with oxytetracycline at 50 mg/liter and kasugamycin (Kasumin 2L) at 100 mg/liter. Similarly, colony development of the 84 E. amylovora isolates was inhibited on casitone-yeast extract medium amended with copper sulfate at 0.16 mM. In 2011 and 2012, field trials were conducted to evaluate the efficacy of oxytetracycline (Mycoshield 17WP), kasugamycin (Kasumin 2L and ARY-4016-06), copper hydroxide (Kocide-3000 41.6DF), Bacillus subtilis (Serenade Max, QST713), and Pseudomonas fluorescens (Blight Ban A506) for management of fire blight in an apple orchard. Only kasugamycin (Kasumin 2L and ARY-4016-06) reduced blossom infection significantly. There was a significant interaction of kasugamycin (Kasumin 2L) with prohexadione calcium (Apogee 27.5DF) in reducing shoot blight incidence in the field in 2012.