APS Homepage

POSTERS: Chemical control

Zinc oxide as an ultraviolet light protectant for natamycin in pre-havest management of gray mold and powdery mildew of strawberry
Daniel Chen - Department of Microbiology and Plant Pathology, University of California. Helga Förster- Department of Microbiology and Plant Pathology, University of California, Kevin Nguyen- University of California Riverside, Jim E. Adaskaveg- Department of Microbiology and Plant Pathology, University of California

The biofungicide natamycin is sensitive to ultraviolet light and degrades quickly in sunlight, limiting its field use. Zinc oxide (ZnO) and ferulic acid were evaluated as pre-mixtures with natamycin (provided by registrant) or in tank mixtures with natamycin against the pre-harvest pathogens Botrytis cinerea (gray mold) and Podosphaera aphanis (powdery mildew) of strawberry. In a field study with two strawberry cultivars, 4 weekly applications of natamycin 500 ?g/ml + ferulic acid (50,000 ?g/ml) or + ZnO (50,000 ?g/ml) treatments were done. Fruit were harvested 7 days after the last application, inoculated with B. cinerea, and evaluated for gray mold incidence after 5 days. For both cultivars, the natamycin-ZnO formulation was significantly more effective than the natamycin-ferulic acid formulation or natamycin alone. In a greenhouse study with powdery mildew, natamycin 1000 ?g/ml or a natamycin 1000 ?g/ml + ZnO 10,000 ?g/ml tank mixture were applied to plants. Inoculum was provided by diseased plants placed among experimental plants. After 18 days, leaves were rated for disease severity (based on % diseased area). The natamycin-ZnO treatment was significantly more effective than natamycin alone. Natamycin and ZnO are naturally occurring compounds and efficacious in mixtures. Because viable resistance in filamentous fungi has not been reported to natamycin after decades of use in the food industry, this mixture may be important in fungicide resistance management.