Trunk disease management in California

Three post-infection practices are available for symptomatic vines:

Vine surgery

There are two levels of vine surgery, depending on the percentage of symptomatic shoots and dead spurs on a vine.  If these canopy symptoms are restricted to one cordon, you can retrain a new cordon by laying down a healthy cane (Figure 12).  The newly retrained cordon should be treated like that of a young vine.  Adopting preventative practices (see Scenario 1) will ensure that the trouble of the retraining process is not squandered.

Figure 12

Figure 12

If more than one cordon has canopy symptoms, the entire vine can be retrained from a sucker at the base of the trunk (Figure 13).  Although it is costly, due mainly to labor costs for removal and retraining (approximately two years to complete), this approach allows a relatively rapid return to full production and quality, as it utilizes a well-established root system.

Figure 13

Figure 13

If a trunk sucker forms, it can be advantageous to train the new vine with the existing vine in place (Figure 14), a practice similar to ‘trunk renewal’, which is used in cold climates to replace trunks lost to winter injury.  In this way, there is still some fruit to harvest from the old vine as the new vine is trained; it is not a total loss of yields during the retraining process.  In mature vineyards, however, trunk suckers may not naturally grow from the base of every vine, so cutting off the vine just above the graft union can sometimes activate basal buds.  Furthermore, this aggressive approach removes the pathogen.

Figure 14

Figure 14

Vine surgery creates large wounds.  When retraining a cordon, the wound is located at the top of the trunk, infection of which can jeopardize both new and old cordons.  When retraining the trunk, the wound is located at the base of the trunk, infection of which can jeopardize the only remaining section of the vine that exists above ground.  To minimize the risk of infection, perform vine surgery in February or March and then apply a pruning-wound protectant.

The newly retrained vine should be treated like a young vine.  Adopting preventative practices (see Scenario 1) will ensure its productivity.

 

Sanitation

Figure 15

Figure 15

When it rains, trunk pathogens produce spores from infected/dead wood.  Therefore, removing or burning wood eliminates local sources of inoculum.  To further reduce the spread of trunk diseases within an infected vineyard, prune away dead spurs (Figure 15) or cordons with dead spurs/wood cankers, and then burn or remove this infected wood from the vineyard.  Sanitation creates large wounds.

As such, perform this practice in February or later and afterwards apply a pruning-wound protectant to all cuts that are made (Figure 16).  The efficacy of sanitation has not been evaluated experimentally.  We assume that it can reduce spore populations in the vineyard.  For many trunk pathogens (Eutypa lata is the exception), spores are spread by rain when it drops onto infected wood and then splashes over to a susceptible pruning wound.

Figure 16

Figure 16

Replanting

Figure 17

Figure 17

When the yield losses due to trunk diseases reduce revenue below management costs, its time to replant.  Replanting is not a management practice per se, but rather a consequence of not managing trunk diseases.  This can be done on a per-row basis, to avoid the huge expense of replanting the whole block at once (Figure 17).  That said, trunk diseases do not tend to be localized in sections of the vineyard or along rows; this recommendation is strictly for convenience.

 

Scenario 3 is a mature vineyard, 15-years-old (Figure 18).  There is a high percentage of vines with symptoms of trunk diseases, approximately 75% of vines in the vineyard.  Because disease incidence can vary according to factors other than vineyard age, disease incidence—in this case, 75%—is the most important factor to consider.

Figure 18

Figure 18

For scenario 3 (mature vineyard, 15-years old where 75% of vines in the vineyard are symptomatic), we recommend you retrain the trunks of the symptomatic vines (Figure 13) and/or replant rows (Figure 17).  The focus on retraining and replanting is based on the high disease incidence.  Most or all vines are infected at this point and you need to get rid of the infections completely.  It may be cost-effective to use this strategy, depending on the level of yield loss, rather than replanting the entire vineyard.

 

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