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Poster: Biology & Disease Mgmt: Chemical Control


Kasugamycin mixtures with copper, mancozeb, or a thiadiazole improve bactericidal inhibition and efficacy of treatments against walnut blight
K. NGUYEN (1), H. Forster (1), L. Wade (2), J. Adaskaveg (3) (1) University of California Riverside, U.S.A.; (2) Arysta LifeScience, U.S.A.; (3) University of California Riverside, U.S.A.

Resistance to copper is common in Xanthomonas arboricola pv. juglandis (Xaj) populations in California walnut orchards making disease management difficult when applying copper alone. The use of mancozeb in mixtures with copper led to improved disease control. The risk of resistance development to both compounds, however, is high because this has occurred with other Xanthomonas spp. This stresses the need for new bactericides. Kasugamycin is an effective antibiotic against several bacterial pathogens (e.g., Erwinia and Pseudomonas spp.) but strains of Xaj often exhibit higher minimal inhibitory concentrations (MICs) than those of other species. Our goal was to improve the activity of kasugamycin by mixing with copper, mancozeb, or a thiadiazole. In in vitro spiral gradient endpoint and dilution plate testing with copper-resistant strains of Xaj, the average MIC for kasugamycin was 27.5 mg/L. When kasugamycin was mixed with copper, mancozeb, or a thiadiazole, average MIC values were reduced to 11.2, 6.1, or 12.8 mg/L, respectively. In field trials, treatments of kasugamycin mixed with either copper, mancozeb, or a thiadiazole reduced natural disease incidence by 84.2, 81.7, or 87.8%, respectively, whereas kasugamycin alone lowered blight by 50.3%, indicating the importance of using this antibiotic exclusively in mixed treatments for increased performance. Kasugamycin is currently under federal and California regulatory review for full registration on walnut.