What Diseases Affect Grapevine Leaves?

Bacterial Diseases

Cutting tools should be sterilized before, during and after pruning grapevines.Brand X Pictures/Brand X Pictures/Getty Images

Crown gall is a disease caused by the bacteria Agrobacterium tumefaciens. Symptoms on the leaves present as wilted or stunted foliage. Irregular growths on the roots, stems or crown confirm the presence of this disease. There is no chemical control once a grapevine is infected. Prevent this disease by planting certified disease-free stock and ensuring that the vines are pruned using only sterile pruning tools to avoid spreading diseases.

Viral diseases on grapevines cannot be remedied by pesticides.Duncan Smith/Photodisc/Getty Images

Peach rosette mosaic, tomato ringspot and tobacco ringspot are three potential diseases of grape leaves caused by viral pathogens. RIngspot diseases present as yellow and smaller than usual leaves. The length of stem between leaves (internodes) is shortened with all three viral diseases. These viral pathogens are all spread by the activity of a microscopic worm known as a dagger nematode. There is no control for infected grapevines. They should be removed and the soil overturned by tilling. The soil should then be allowed to lay fallow for at least a season and be fumigated before replanting grapes.

Spots on grapevines are most often caused by fungal pathogens.Photos.com/Photos.com/Getty Images

Several fungal diseases can affect grapevines. Common ones are downy mildew, powdery mildew, black rot, phomopsis leaf spot and eutypa dieback. Spots on leaves, curled leaves, yellow leaves, brown leaves and leaves with a powderlike coating are all symptoms of fungal-induced diseases. Many fungal diseases are easily controlled and prevented with fungicides. Preventative sprays should be started at the first sign of growth in the spring and continued throughout the season at 10- to 14-day intervals. Sprays for treatment should occur every seven to 10 days.

Starting with healthy stock is the best defense against disease.Jupiterimages/Comstock/Getty Images

The best measure to combat potential diseases of grapevines lies in a proactive preventative strategy. Make sure to select and purchase stock from reputable sources only, and select disease-resistant cultivars only. Select a site appropriate for viticulture that drains well and receives plenty of sun. Making sure that your grapevines receive good air circulation by not planting near other trees or shrubs will help to control the incidence of many fungal diseases favored by humid conditions.