|Authors: ||K.B. Johnson, V.O. Stockwell, T.N. Temple|
|Keywords: ||fire blight, antibiotics, integrated control, resistance management |
The aminoglycoside antibiotic, kasugamycin (Kasumin), was evaluated for fire blight suppression in inoculated pear and apple orchard trials in 2007. The antibiotic standards, oxytetracycline and streptomycin, and the biological control agents, Pantoea agglomerans C9-1S and a protease-deficient Pseudomonas fluorescens A506 (A506 AprX-), were included as components of the experimental treatments.
In previous experiments, when compared to two applications of oxytetracycline alone, we have a shown consistent enhancement in blossom blight control with an ‘integrated strategy’, which consists of biological control agents sprayed at 70% bloom, followed by an oxytetracycline application at full bloom.
After two applications of kasugamycin (100 ppm), the relative incidence of blossom blight in pear and apple was reduced to 7 and 23%, respectively, compared to 30 and 53%, respectively, with oxytetracycline (200 ppm). One application of oxytetracycline preceded by an application of the biocontrol agents showed a relative disease incidence of 18% in pear and 56% in apple, whereas for the integrated strategy with kasugamycin, relative disease incidence was 15% in pear and 36% in apple.
At 7 to 9 days after the pathogen inoculation, the incidence of recovery of Erwinia amylovora was 40% from flowers that received the integrated strategy with oxytetracycline but only 7% from those that received kasugamycin.
The incidence of recovery of C9-1S and A506 AprX- from flowers inoculated with these bacteria and then oversprayed with oxytetracycline was 77 and 70%, respectively.
Flowers that received kasugamycin as the second treatment, the incidence of recovery of the biocontrol agents were 56% for C9-1S and 50% for A506 AprX-. Kasugamycin shows promise as a control agent for fire blight in integrated programs, but it may interfere with the growth of biological control agents.
An integrated biological and chemical strategy involving kasugamycin requires further investigation to determine the feasibility of selecting biological agents with greater tolerance to this material, and within the chemical component, to evaluate mixtures of antibiotics where kasugamycin is applied at a lower rate.
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