The researchers asked growers if they used either of several treatments known to prevent grape vine canker diseases from spreading. Depending on the group, the proportion of growers applying these treatments ranged from as few as 25 percent to as many as 80 percent.

Recently, the researchers released results of the findings from their survey of 67 grape growers in the southern San Joaquin Valley, mostly Fresno County raisin growers. The survey focused on two types of trunk disease treatments: Delaying pruning until late in the dormant season and painting pruning wounds with a chemical protectant immediately after pruning.

Between 50 percent and 60 percent of these growers reported never or rarely using these practices in the past five years. In the same period, less than 20 percent reported always using them.

When asked the typical age of a vineyard when they first started using delayed pruning and pruning-wound protectants, about 40 percent of growers reported usually starting when the vineyards were older than 13 years. “A sizeable minority of growers likely start to use the preventive practices after infection has already occurred,” the researchers report.

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Often, vines don’t shown signs of the diseases until they are eight years or older, the researcher note, even when infection occurs much earlier. Among these growers, roughly 20 percent start delayed pruning when the vineyards are between 4 and 7 years old. A little under 30 percent begin applying pruning-wound protectants to vines at that age.

 In terms of how well each practice maintained adequate yields or how cost-effective it was, growers rated both delayed pruning and pruning-wound protectants as mildly effective, the researcher notes. At the same time, they rated pruning-wound protectants slightly more positive than delayed pruning.

These findings are described in more detail in the Research Brief, Trunk Disease Survey in Fresno: Preliminary Results, published by the Center for Environmental Policy and Behavior at the University of California, Davis.