Chapter 20

Managing Vineyard Diseases

Fungal Pathogens

Eutypa Dieback

Eutypa (you-type-uh) dieback of grapes is caused by the fungus Eutypa lata and is one of the most destructive woody tissue diseases killing vascular cambium and adjacent vascular tissues. Eutypa dieback is abundant in regions of high rainfall.

Symptoms

Vegetative: Cankers are the earliest symptoms to develop that generally form around pruning wounds in older wood of the main trunk causing partial or complete dieback of cordon arms or entire vines. These cankers usually are difficult to see because they are covered with bark. One indication of a canker is a flattened area on the trunk.

Fruit: Inflorescences on stunted shoots are of normal size but if the shoot is severely infected they may shrivel and die. The fruit of infected vines do not exhibit many symptoms. Infected shoots have fewer and smaller fruit clusters, sometimes with a mixture of large and small berries.

Disease Cycle

The fungus survives in infected trunks for long periods. The fungus is generally present in older wood, such as vine trunks but generally not in younger wood, such as 1 or 2 year-old prunings. The fungus eventually produces reproductive structures (perithecia) on the surface of infected wood. Spores (ascospores) are produced in these structures and discharged into the air.

Disease Management

Cultural Practices: The primary control method is the removal of infected trunks from the vineyard and destroyed (either buried or burned) before the fungus spreads extensively in the infected vine. If the canker has grown below ground level, remove and replace the vine. An old infected stump left above the soil or trunk lying on the ground may continue to produce spores for several years. The spring is a good time to locate and mark the diseased vines.

Applying Control Materials: Chemical control is useful when retraining vines and making large trunk or cordon cuts. Sprays are directed onto cuts within 24 hours of pruning and followed up with a second application within 2 weeks, especially if weather conditions are consistently wet and/or rainy.

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