Managing Grapevine Trunk Diseases in California's Southern San Joaquin Valley

Most California vineyards are eventually attacked by one or more grapevine trunk diseases (Esca or Botryosphaeria-, Eutypa- and Phomopsis diebacks). These fungal pathogens cause chronic infections of the wood, which are slow to develop. The symptoms that follow can take years to become obvious. Prevention is an efficient approach, but requires adoption before symptoms appear. To encourage early adoption of preventative practices, economic analyses simulated their benefits in the table grape cultivar Crimson Seedless. Adoption of delayed pruning or pruning-wound protectants was compared in a young, healthy vineyard (years 3 and 5) versus in a mature, diseased vineyard (year 10). A survey of table and raisin grape growers in California's southern San Joaquin Valley revealed their usage and perceptions of preventative practices. Also, to help growers with mature vineyards, the economic benefits of vine surgery (also referred to as "trunk renewal") between years 11 and 15 were examined. Our economic simulations showed prevention is cost-effective, if adopted in young vineyards. However, in spite of acknowledging the impact of trunk diseases, only 25 to 30% of growers use preventative practices, and only half of such growers adopt in young vineyards. Further, growers who use prevention and adopt early also perceive preventative practices as more cost-effective. Therefore, an outreach strategy to convince non-adopters must emphasize the long-term economic benefits of early adoption of preventative practices, given the inevitable appearance of symptoms at vineyard maturity. Despite the high one-time cost of vine surgery, our economic analyses suggest its adoption is a cost-effective complement to prevention, and thus, it should be integrated into management recommendations for table grape vineyards at 11 to 15 yrs.