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Evaluation of oxathiapiprolin for management of downy mildew on sunflower
R. HUMANN (1), K. Johnson (2), T. Gulya (3), S. Meyer (1), J. Jordahl (1), A. Friskop (1), M. Wunsch (4), S. Markell (1). (1) North Dakota State University, Fargo, ND, U.S.A.; (2) DuPont Field Development, Grand Forks, ND, U.S.A.; (3) USDA ARS, Fargo, ND, U.S.A.; (4) NDSU Carrington Research Extension Center, Carrington, ND, U.S.A.

Downy mildew of sunflower is a yield-limiting disease caused by <i>Plasmopara halstedii</i>. Two tools are commonly used to manage the disease: fungicidal seed treatments and genetic resistance. The FRAC 4 fungicides, metalaxyl and mefenoxam, were effective until resistant <i>P. halstedii</i> isolates were identified in the late 1990s. Currently, only one seed care package containing the FRAC 11 fungicide azoxystrobin as the primary active ingredient, is marketed for use on sunflowers. The objective of this study was to evaluate the experimental fungicide oxathiapiprolin for management of downy mildew. Oxathiapiprolin has not yet been assigned to a FRAC group. Eight field research trials were conducted throughout 2012 and 2013, artificially inoculated with <i>P. halstedii</i> zoosporangia, and irrigated after inoculation. Incidence levels were determined by recording systemically infected plants four times throughout the growing season. In the six trials with measureable disease pressure, all treatments that contained oxathiapiprolin had significantly lower disease incidence than the non-treated checks. Similarly, all treatments containing oxathiapiprolin had disease incidence levels the same or lower than azoxystrobin treatments. Results indicate oxathiapiprolin could provide another management option for downy mildew.

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