Black rot, caused by the fungus Guignardia bidwellii, is one of the most serious diseases of grapes in the eastern United States. Crop losses can be devastating, ranging from 5 to 80 percent depending on the amount of disease in the vineyard, weather, and cultivar susceptibility. The fungus can infect all green parts of the vine including, fruit, shoots, leaves, and tendrils. Most damaging is the effect on fruit.
Botrytis bunch rot or gray mold is a disease that exists in all vineyards worldwide. The disease is caused by the fungus Botrytis cinerea and is commonly associated with the decay of ripe or nearly ripe grapes. Temperature and cold, damp climates favor disease development. The bunch rot phase of the disease causes the greatest economic losses, especially on French hybrids and Vitis vinifera cultivars.
Crown gall occurs on over 600 species of plants. The disease is characterized by galls or overgrowths that form on the roots, trunk, and arms of grape vines. V. vinifera cultivars are more susceptible to crown gall than V. labrusca cultivars.
Downy mildew occurs wherever it is warm and wet during the growing season. There is some cultivar resistance, with V. vinifera cultivars being the most susceptible and V. rotundifolia being the most resistant. This disease is caused by the fungus Plasmopara viticola and infects berries, leaves, and young shoots.
Eutypa dieback is the name for the trunk and arm phase of what was once known as the "dead arm" disease. It is one of the most destructive diseases on woody tissue of grapes. The fungus causing this disease has a wide host range that includes at least 80 species in 27 botanical families. Most of its hosts are tree species that are usually common in natural forests.
Phomopsis cane, leaf spot, and fruit rot is widely distributed in vineyards. The disease can weaken vines, reduce yields, and lower fruit quality.
Powdery mildew, caused by the fungus Uncinula necator, can be found in most areas of the world where grapes are grown. The fungus affects all green tissues and can be found mostly on the leaves and fruit stems.