ENHANCING FLOWER COLONIZATION OF PSEUDOMONAS FLUORESCENS STRAIN A506, AND THE EFFICACY OF APOGEE AND SERENADE, FOR FIRE BLIGHT CONTROL IN THE SAN JOAQUIN VALLEY OF CALIFORNIA

B.A. Holtz, E.W. Hoffman, S.E. Lindow, B.L. Teviotdale
Fire blight is a serious disease of apple in the San Joaquin Valley of California because warm temperatures often coincide with bloom. Applications of streptomycin sulfate usually begin after 5% bloom and continue every five days until flowering is complete. In California, resistance to streptomycin occurs in Erwinia amylovora populations in at least 50% of apple orchards, and often the majority of strains in an orchard are resistant. Alternative fire blight control strategies were examined in 1999 and 2000 on apple cultivar ‘Pink Lady’. In 1999, fire blight was significantly reduced by Pseudomonas fluorescens strain A506 (Blight Ban A506) sprayed (150 ppm) at 20, 50, and 100% bloom, and early and late petal fall. The effectiveness of Blight Ban A506 to control fire blight was increased over three-fold when applied with low concentrations (0.05%) of an organo-silicon surfactant (Breakthru). Flower colonization by P. fluorescens A506 was significantly improved when combined with Breakthru, probably because the surfactant increased the amount of flower surface directly inoculated with the bacterium during spraying. Breakthru applied without Blight Ban A506 did not increase fire blight. In 2000, Bacillus subtilis QST713 (Serenade) was applied to ‘Pink Lady,’ ‘Fuji,’ and ‘Granny Smith’ apple trees during bloom at rates of 6.73 and 8.97 kg/ha. Serenade at 6.73 kg/ha significantly reduced fire blight when compared to streptomycin sulfate (Agrimycin) at 200 ppm, which in turn significantly reduced disease when compared to control trees. Serenade at 8.97 kg/ha rate did not reduce fire blight. In 1999 and 2000, applications of prohexadione calcium (Apogee) reduced rat-tail bloom on ‘Pink Lady’ trees and subsequently late season fire blight, but did not reduce early season infections. Applications at 2.5 cm of shoot growth significantly reduced shoot growth 7, 28, 56, and 84 days later.
Holtz, B.A., Hoffman, E.W., Lindow, S.E. and Teviotdale, B.L. (2002). ENHANCING FLOWER COLONIZATION OF PSEUDOMONAS FLUORESCENS STRAIN A506, AND THE EFFICACY OF APOGEE AND SERENADE, FOR FIRE BLIGHT CONTROL IN THE SAN JOAQUIN VALLEY OF CALIFORNIA. Acta Hortic. 590, 319-324
DOI: 10.17660/ActaHortic.2002.590.47
https://doi.org/10.17660/ActaHortic.2002.590.47
Blight Ban A506, Breakthru, organo-silicon surfactant
English

Acta Horticulturae