Fungal Trunk diseases: a threat to aging vineyards?
Grapevine trunk diseases are often overlooked in Ontario due to their slow development relative to the more common and pressing disease targets of annual spray programs (powdery and downy mildews and bunch rot). Trunk diseases are caused by pathogens that grow only in mature wood and are almostalways associated with old, large pruning wounds which act as the point of entry for fungal spores. They subsequently grow, decay the wood and slowly kill the vines. Several fungi are known to cause trunk diseases in grapevine. Eutypa dieback is the main trunk disease problem of wine grapes grown in temperate regions and the one historically recognized as an occasional problem in Ontario vineyards, especially in vineyards over 10 years of age. Phaeoacremonium aleophilum and Phaeomoniella chlamydospora cause trunk diseases variously known as Esca, Petri disease, black measles, and "black goo". They are common and serious pathogens in California and parts of Europe. These fungi have previously been found in Virginia, Pennsylvania, and New York, although the extent of the problems that they might cause in the region has yet to be determined. A systematic survey of grapevine trunk diseases has not been conducted in Ontario.
A 2007-2008 survey conducted by Agriculture and Agri-Food Canada investigated decline problems in Okanagan vineyards (O'Gorman, Haag & Sholberg). The survey confirmed the presence of several fungal pathogens causing vine decline symptoms, including 2 pathogens associated with esca (P. chlamydospora and P. aleophilum). Closer to home, a survey of cankers from eighteen vineyards of V. vinifera, V. labruscana, and interspecific hybrids was conducted in 2007 in New York, Connecticut, Rhode Island and Vermont by Drs. W. Wilcox (Cornell University) and P. Rolshausen (University of Connecticut). In the cankers sampled, Eutypa lata was the most frequently isolated pathogen; it was recovered from 13 of the 18 vineyards sampled and from 20% of the diseased vines. This pathogen has long been recognized as a cause of grapevine trunk cankers in the Northeast United States and Ontario, and until recently was assumed to be the sole cause of these diseases. P. aleophilum and P. chlamydospora were associated with heavily symptomatic trunk-diseased vines in 12 out of 18 vineyards surveyed in four Northeastern states, suggesting that they may, indeed, be notable pathogens in that region and possibly in Ontario.
There are no chemical controls registered for control of most trunk diseases. Pruning out infected trunks and retraining trunks with new shoots is the only management option that can be exercised. Recommendations from elsewhere in the world suggest pruning as late as possible in the dormant season so that pruning wounds heal quickly and are not susceptible to infection by the pathogen for as long. It is also very important to remove infected trunks from the vineyard and burn them as they can act as a source of spores that can cause new infections.
As many newer vineyards age, it is likely that canker diseases will become increasingly important. The results from the northeast US survey suggest that such diseases are caused by a number of different organisms known to cause similar, often devastating symptoms in other parts of the viticultural world. The best strategy for minimizing the impact of trunk diseases is to assure vines that vines are as healthy and unstressed as possible, that pruning is done under ideal conditions for healing and that only clean nursery material is used when planting new vineyards.
Young vine decline in an Okanagan vineyard.
Springtime symptom of Eutypa dieback: stunted shoot growth,
sometimes occurring only on one side of the vine.
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