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QoI Resistance of Plasmopara viticola and Erysiphe necator in the Mid-Atlantic United States

A. Baudoin, G. Olaya, F. Delmotte, J. F. Colcol, and H. Sierotzki

February 2008


Of 20 Plasmopara viticola isolates from 4 locations in VA and northwest NC, 16 were resistant to QoI fungicides. The resistance factor was > 100, and label rates of formulated azoxystrobin and pyraclostrobin provided little or no control. Additional sampling revealed at least 15 additional vineyards with QoI-resistant P. viticola in Virginia, Maryland, and Pennsylvania. Of 22 isolates of Erysiphe (Uncinula) necator collected in 2005 from five Virginia locations, 20 isolates from 4 locations showed resistance to QoI fungicides. The G143A mutation for resistance was detected in several isolates of both pathogens. This is the first detection of this type of resistance in P. viticola in North America, and the second North American report of QoI resistance in E. necator.


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