Powdery mildew of Grapes
Powdery mildews are generally host-specific. Uncinula necator is the pathogen that causes powdery mildew on grape and linden. The most susceptible hosts of this pathogen are members of the species Vitis. The signs of powdery mildews are widely recognizable and easily identifiable. The majority of them can be found on the upper sides of the leaves; however, it can also infect the bottom sides, buds, flowers, young fruit, and young stems. A gray-white, dusty, fungal growth consisting of mycelia, conidia and conidiophores coat much of the infected plant. Cleistothecia, which are the overwintering structures, present themselves as tiny, spherical fruiting structures that go from white, to yellowish-brown to black in color, and are about the size of the head of a pin. Symptoms that occur as a result of the infection include necrosis, stunting, leaf curling, and a decrease in quality of the fruit produced.