Grape Diseases

Black rot is one of the most serious diseases of grapes in the eastern United States. Crop losses can range from 5 to 80 percent, depending on the amount of disease in the vineyard, the weather, and variety susceptibility. The fungus Guignardia bidwelli can infect all green parts of the vine. Most damaging is the effect on fruit.

Botrytis bunch rot, or gray mold, exists in all vineyards worldwide. This disease is caused by the fungus Botrytis cinerea and is commonly associated with the decay of ripe or nearly ripe grapes. Temperature and damp climates favor disease development. The bunch rot phase of the disease causes the greatest economic losses.

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. These galls are found mostly on the lower trunk near the soil line.

Downy mildew is caused by a fungus that can infect berries, leaves and young shoots. It occurs wherever it is wet and warm during the growing season. There is some variety resistance, with V. vinifera varieties being the most susceptible and V. rotundifolia being the most resistant.

Eutypa dieback is a fungal disease appearing as cankers on trunks and arms of infected grapevines. It is one of the most destructive diseases on the woody tissue of grapes. The fungus causing this disease has a wide host range, which includes at least 80 species in 27 botanical families. Most of its hosts are tree species that are common in natural forests.

Phomopsis cane, leaf spot, and fruit rot is one of two distinct diseases that used to be referred to as "dead arm" and is widely distributed in vineyards. The disease can weaken vines, reduce yields, and lower fruit quality.