Trunk disease management in California

Applications of pruning-wound protectants

Fungicides that prevent infection of pruning wounds are labeled for dormant-season use in California:

  1. Thiophanate-methyl (Topsin M WSB; United Phosphorus, Inc., King of Prussia, Pennsylvania)
  2. Myclobutanil (Rally; Dow Agrosciences LLC, Indianapolis, Indiana)

In addition, there are other non-fungicidal materials that form a toxic or physical barrier to infection:

  1. Figure 7

    Figure 7

    Boric acid (Figure 7; Tech-Gro B-Lock; Nutrient Technologies, Inc., Dinuba, California)

  2. VitiSeal (VitiSeal International LLC, San Diego, California)

**For more details on pruning-wound protectants, please refer to the Eutypa dieback section of the UC Grape Pest Management Guidelines (http://www.ipm.ucdavis.edu/PMG/r302100611.html, which is applicable to all trunk diseases).

All pruning-wound protectants must remain continuously active for 30 days if vines are pruned in December or January, during the period of high risk of infection. Reapplication may be necessary, depending on the protectant used and the timing of its first application with respect to rain. Rain triggers spore production and washes protectants off pruning wounds, so try to schedule applications before rain, maybe more so than immediately after pruning.

 

Figure 8 (click for larger view)

Since thiophanate-methyl (Topsin) has been extensively studied, relative to other protectants, we use it here to illustrate an important point regarding the early adoption of preventative practices in young vineyards (Figure 8).  This example uses figures for an acre of Cabernet Sauvignon vines in San Joaquin County, California (aka Lodi, Crush District 11).  We show the cumulative net returns expected over the course of 25 years.

The healthy vineyard featured in this graph is a best-case scenario, but it is atypical.  In our experience, all vineyards become infected by trunk diseases; we do not expect to find a vineyard in California without some level of yield loss.  Nonetheless, the simulated, healthy vineyard provides an optimum reference for our economic simulation.  The infected vineyard is a worst-case scenario, in which neither Topsin applications nor other management practices are taken.  In this simulated, infected vineyard, taking no action to manage trunk diseases results in losses of $39,662 per acre over 25 years.  Thus taking no action in young vineyards is a poor investment decision, given that it can take up to 10 years to break even on the high vineyard establishment costs.

If we assume a very modest level of disease control efficacy— 50%—the cumulative net returns from adopting Topsin applications are significantly higher than taking no action.  Starting Topsin applications in years 3 or 5 can result in a positive return on investment ($12,784 and $5,787 per acre, respectively); whereas initiating Topsin applications in year 10 results in net losses (-$19,624 per acre), although is not as costly as taking no action (-$39,662).

Results of simulations evaluating the effects of delayed pruning or double pruning or the effects of these practices in different growing regions can be seen at our economics of trunk-disease management website: http://maxnorton.github.io/kaplan-model/

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