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First Report of Resistance to Boscalid in Podosphaera xanthii, Cucurbit Powdery Mildew, in South Carolina

A. P. Keinath, G. Rennberger, and C. S. Kousik

August 2018


Resistance to boscalid, one of the older succinate-dehydrogenase inhibitors (SHDI) in Fungicide Resistance Action Committee (FRAC) code 7, was detected in Podosphaera xanthii, the cucurbit powdery mildew fungus, in South Carolina in July 2017. Resistance to the field rate (682 ppm) of boscalid was confirmed in greenhouse experiments and laboratory bioassays conducted on summer squash plants and cotyledons, respectively, that had been treated with a range of boscalid concentrations. This report is the first documentation of resistance to boscalid in P. xanthii in the southern United States.


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