Grapevine Leaf Disease

Powdery Mildew

• Powdery mildew will appear in early to mid July. The disease will appear on the leaves as a white, powdery mildew. Powdery mildew infection will reduce the vine's hardiness through winter, and will stunt the vine's growth and reduce the plant's yield. French hybrids and European varieties are most susceptible to powdery mildew. Fungicide sprays are the most effective at controlling the disease.

Downy Mildew

• If you find that your grape leaves have yellow circular lesions on the leaves with a grayish mildew underneath, they probably have downy mildew. This fungus releases spores in the spring and spreads through wind and rain. Severe cases of downy mildew will turn leaves black and brown, and the leaves will fall off, exposing the fruit to sun scald.

Black Rot

• Black rot will appear on the leaves in small, reddish-brown circles on the lower leaves of the plant, usually in mid to late June. The circles will develop a black border and small pimples inside of the spots, and can infect any green tissue in the plant. Severe cases will spread to the grape, turning the berry a dark brown or black, and then they will dry and shrivel, devastating your plants and crop.

Phomopsis Leaf and Cane Spot

• Phomopsis leaf and cane spot shows up in mid June. The symptoms show up as small, angular dead spots, usually on the lower leaves first. The disease can then spread through the canes, tendrils, leaf petioles and eventually into the grape berries. This disease can reduce the vineyard crop by shaking berries off the vine before harvest by damaging the cluster stem. This disease is best controlled through fungicide.