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Subject

Eutypa Dieback

Description

Wedge-shaped, darkened cankers develop in the vascular tissue.

Eutypa dieback, one of the most common canker diseases of grapevines in California, is caused by the fungal pathogen Eutypa lata. This pathogen requires wind-driven rain to disperse the ascospores to relatively fresh pruning wounds where infection takes place. Economic losses due to Eutypa dieback may be minor in early years but the most damaging effects are observed on older vines, which have large pruning wounds caused by drastic cutting to retrain them. Overall, the greatest loss is a shortened economic vineyard life.

The disease appears first in one or two spurs and spreads in the following seasons to adjacent spurs, eventually killing the arm or cordon. Shoots developing from below the affected arm are healthy the first year but may show symptoms in subsequent seasons. Unless a major portion of the vine's structural framework is involved, the affected shoots eventually may be covered by normal overgrowth from the vine's healthy portion. It is common to find one side of the vine dead, while the other side appears healthy. When the whole vine has been killed or is severely affected by Eutypa dieback, strong suckers often develop from the still healthy root system. Complete collapse and death of vines or arms in summer is uncommon; once shoots have emerged, they usually grow through summer and die the next winter.

An important diagnostic symptom of Eutypa dieback is the formation of pruning wound cankers. These dead areas surrounding large, old pruning wounds often can only be found by removing the rough outer bark. They are frequently located adjacent to the affected spurs. In advanced cases, the wood around an unhealed wound assumes a ridged and flattened appearance so that the trunk or cordon may be twisted and malformed. Older cankers show a marginal zonation, indicating successive annual attempts of the vine to overgrow the necrotic area.

Because E. lata is a wound parasite, infection invariably occurs through pruning wounds. The fungus has a long incubation period in the vine. Several growing seasons may elapse before visible cankers develop around an infected wound or before stunted shoot symptoms appear.

Because the spores are dispersed by rain, the chance for infection can be reduced by pruning the grapevines late in the spring when rains are not as likely to occur. Late pruning is also important in reducing the susceptibility of the wounds. Research has shown that vines pruned early in the winter, when they are dormant, do not heal as quickly and the pruning wounds are susceptible to infection for 4 to 5 weeks. When vines are pruned in late winter-early spring they are beginning to come out of dormancy and the period of wound susceptibility is reduced to 10 to 14 days because they heal faster.

In the long term, wound protection offers much better control prospects than eradication once the disease has become established. Pay special attention to wound protection if drastic retraining or changeover of the variety is contemplated or if the vineyard is located in an area known to have E. lata.