California -- Using horticultural oils to control powdery mildew and suppress grape leafhopper, mite, scale and mealybug is becoming a popular tool of integrated pest management (IPM) in vineyards, but Laura Breyer of Breyer's Vineyard IPM Service in Windsor says that questions have been raised about the oil’s impact on grape ripening, yield and quality. “Some winemakers have become reluctant to allow their growers to use oils because of these concerns,” she says. But she participated in two recent reports -- one from the Central Coast and the other from the North Coast -- that seem to dispute those fears.