Downy mildew, a fungal disease native to North America, attacks most species of wild and cultivated grape. The disease was inadvertently introduced into European vineyards in the late 1870’s where it devastated the European grape, Vitis vinifera, which is generally more susceptible to the disease than native American grapes. Today, the disease can be found on grapevines in most regions of the world that are wet during the growing season. The fungus causes direct yield losses by rotting inflorescences, clusters, and shoots, and indirect losses by prematurely defoliating vines which increases their susceptibility to winter injury and delays ripening of the fruit.