I’m studying for a wine exam and came across this chart on viral, bacterial and fungal diseases of the vine on The Society of Wine Educators Wine Academy site. Chances are this might be more than you want to know about what can go wrong out in the field, but I’m finding it quite handy.
| Viral Diseases | Description |
| Leaf Roll | A viral infection that is responsible for the lovely gold and red leaves in the vineyard come autumn. This colorful display is coupled with the downward rolling of the leaf blade, hence the name, leaf roll. Pigments that were to develop in the grape end up staying in the leaf, thereby delaying ripening. Crop yield is also affected. The only known remedy is vine removal. The disease is spread by insect vector (often mealy bugs) or by propagating new vines from clippings that are infected with the virus. |
| Fan Leaf | A viral infection that is responsible for unusual growth patterns in the vine: short internodes, abnormal branching, malformed leaves that look like fans, small clusters, poor fruit set and shot berries. A vine infected with Fan Leaf has a truncated life span. Fan leaf is spread by insect vector (generally nematodes) or by propagating new vines from clippings that are infected with the virus. |
| Bacterial Diseases | Description |
| Pierce’s Disease | A bacterial affliction that results in premature leaf fall and eventual vine death. First, large dead areas appear on the leaves and expand until the entire leaf falls from the vine. Robbed of a way to manufacture nutrients, the vine eventually dies. The disease is spread by insect vectors like leafhoppers. Disease pressure is highest in the southern United States with outbreaks occurring wherever vineyards border streams or wetlands with marsh grasses. Recently, however, Pierce’s Disease has begun to spread north from Mexico on a new vector, the Glassy Winged Sharpshooter, and is now threatening vineyards previously thought to be safe from the disease. |
| Crown Gall | A bacterial affliction that causes large tumors or growths to appear on the trunk of the vine. These tumors girdle the vine, strangling the portions above it so that the vine withers and dies. |
| Fungal Diseases | Description |
| Esca/ Black Measles |
A fungus that thrives in warm climates and can kill a vine suddenly when hot weather arrives. Typically, leaves fall off and berries develop spots. |
| Eutypa Dieback/ Dead Arm |
A fungus that stunts vine shoots and cups leaves by releasing a toxin into the plant. The affected cane or canes eventually die, hence the name, “dead arm”. This fungus is common to Mediterranean climates and is believed to enter the vine through pruning wounds. |
| Powdery Mildew/ Oidium |
A mildew native to North America that attacks the entire vine with white cobweb-like filaments. If an infection takes place before flowering, yields are reduced. If the clusters are infected by oidium, they will not reach full size or achieve maximum pigment development and the fruit will have undesirable flavors. Although native American vines are immune, Vitis vinifera is highly vulnerable to it. |
| Downy Mildew/ Peronospera |
A mildew native to North America that attacks the green portions of the plant. In its beginning stage, a vine leaf looks as if it has oil spots. Then, spores germinate and spread outward in white, cottony filaments. A severe infection will cause the vine to lose its leaves, effectively delaying ripening. Threat of Downy Mildew is highest in warm, humid weather, but a copper-sulfate spray known as “Bordeaux Mixture” is effective in preventing an outbreak or curtailing an existing one. |
| Botrytis Cinerea | A mold of many synonyms…Edelfaule, Pourritre Noble, Noble Rot, Botrytis attacks healthy white grapes, concentrates their sugars and adds a honeyed note to their flavor profile. Botrytis is responsible for creating some of the finest sweet wines in the world. The fungus germinates and spreads when humidity is at least 90 percent and the weather is warm (59-68° F). These moist, warm conditions must be followed by dry, warm conditions or Botrytis will quickly degenerate into Gray Rot, a rot which will ruin the fruit. |
A Thirsty Spirit 