- SCAB AND FIRE BLIGHT OF APPLE 381
The occurrence of streptomycin resistance inE. amylovorapopula-
tions in the Pacific Northwest states led to the development of the alter-
native antibiotic oxytetracycline for blossom blight control. However,
oxytetracycline is not bactericidal, functioning in the suppression ofE.
amylovoragrowth, and is not as effective as streptomycin for blossom
blight control (McManus and Jones 2004). Biological control materials
for blossom blight management include Serenade Optimum, a fermen-
tation byproduct of the bacteriumBacillus subtilis(Bayer CropScience),
the antagonistic bacteriumPantoea agglomerans(Bloomtime Biolog-
ical; Verdesian Life Sciences; Pasco, WA), and the antagonistic yeast
Aureobasidium pullulans(Blossom Protect; Westbridge Agricultural
Products; Vista, CA). However, in humid regions such as the midwest-
ern and eastern United States, these materials require up to four appli-
cations during apple bloom and have not been consistently effective in
controlling blossom blight (Ojiambo and Scherm 2006; Sundin et al.
2009). Other biological control materials under development include
the use of bacteriophage (bacterial viruses) and the use of antibacterial
peptides (Badosa et al. 2007; Kolozsvari Nagy et al. 2011; Badosa et al.
2014). While these efforts have shown promise in some cases under lab-
oratory, greenhouse, and limited field control experiments, commercial
products are currently not available as yet for fire blight control.
Copper compounds have shown some potential for blossom blight
control, but a confounding issue is that copper ions are also phytotoxic
to the apple host as well as broadly toxic to soil micro- and macro-fauna.
Copper phytotoxicity results in fruit russeting when copper sprays are
applied after the green tip growth stage of apple. Copper is a heavy
metal and soils containing more than 100 ppm of copper are recog-
nized as toxic to earthworms and other soil fauna (Streit 1984; Paoletti
et al. 1998). In addition, the low solubility of traditional “fixed” cop-
per compounds has limited the ability of these materials to rapidly kill
E. amylovoracells on flowers, a characteristic which would be most
desirable and similar to streptomycin. For example.E. amylovoracells
are highly sensitive to copper ions, which are bactericidal and can also
induce a viable but not culturable state of the pathogen (Ordax et al.
2006). However, if copper ions are not dissolved and available on flow-
ers, they will not affectE. amylovorapopulations rapidly enough to
effectively control blossom blight. Then, the fruit russeting aspects of
copper use overrides the potential benefits of blossom blight control.
A third antibiotic, kasugamycin, has been tested more recently as an
alternative to streptomycin that is more effective than oxytetracycline
(Adaskaveg et al. 2011; McGhee and Sundin 2011; Ngugi et al. 2011).
Kasugamycin (Kasumin; Arysta Corp., Cary, NC) was registered for use