Grape Vine Diseases for Lenoir Grapes

Mildews

• Powdery mildew (Uncinula necator) is a common infection in grapevines, causing reduced or damaged fruit, stunted vine growth and interference with the plant's cold hardiness. Powdery mildew causes blotches on dormant canes and faded spots on foliage. The spores look like whitish powder and appear on leaves and berries. Fungicides may work best as protectants, since mildews may become resistant.

  Downy mildew (Plasmopara viticola) thrives in wet conditions, so make sure the grapevine's foliage has enough air circulation to dry after watering or rainfall. Lenoir grapevines may drop leaves and suffer reduced fruit production. The disease prefers cool, humid climates. Downy mildew causes yellow areas on the upper part of the leaf and downy growths on the underside. The leaves and stems may die, and infected fruit develops a white growth before failing. Begin using a fungicide before the Lenoir vine blooms. Make sure you know which mildew you are treating and use a product formulated for that disease. Follow application directions carefully.

Anthracnose

• Anthracnose is a fungal disease caused by Elsinoe ampelina. The infection causes circular spots with dark borders on the grapes that is often called "bird's eye rot." The fungus infects stems, leaves and shoots as well as the grapes. Anthracnose thrives in high humidity and overwinters in old lesions. Fungicides suitable for this disease are the same as those used to control black rot.

Black Rot

• Black rot (Guignardia bidwellii) attacks nearly all of the grapevine except the roots. Active in warm, humid climates, black rot causes small yellow spots on the leaves that enlarge and develop black borders and red centers. Eventually, tiny black specks appear on these areas. The specks are the spore-generating structures. Black rot may cause purple to black lesions on stems, shoots and tendrils, and eventually infect the berries, causing brown, soft spots. The fruit then shrivels, dries and turns hard, or mummifies. Destroy mummies and cut away diseased areas. Control weeds and make sure the plants get plenty of sun and air. Apply fungicides formulated to control black rot early in the season and continue applying every 7 to 10 days. Once the berries begin to change color on the vine, they should be safe from black rot.

Phomopsis Cane and Leafspot Disease

• Phomopsis cane and leaf spot disease (Phomopsis viticola) infects the main axis of fruit clusters (rachis), girdling the rachis and destroying the fruit. The fruit may also become infected, turning brown and shriveling. Spores reach the plants through splashing water from rain or irrigation and cause lesions on the shoots and leaves within three to four weeks of infection. Black lesions develop on shoots and canes and black fruiting bodies may appear on the basal region of the canes. On the leaves, brown or blackish spots develop, along with pimply-looking fruiting bodies. Leaves become distorted and yellow and may fall early. Remove infected canes and spurs while the vine is dormant and destroy the cuttings far away from the plant. A preventive fungicide in early spring may help avoid trouble. Choose a fungicide made to control phomopsis on grapes and apply according to label directions.

Preventive Measures

• Healthy vines are more resistant to diseases, so make sure the Lenoir grapevines have good air flow and sunlight, along with proper amounts of fertilizer and water. Make sure the plants have good drainage and enough space between each plant to grow comfortably. Sterilize pruning equipment between uses and do not practice overhead watering. Remove weeds and other plant debris and destroy it away from the vineyard.