The Cabernet Sauvignon grapes on the right were treated with the kaolin clay product Surround. Photo courtesy of Ste. Michelle Wine Estates
A kaolin-based particle film used to control pests and sunburn in tree fruit may have application in wine grapes as well. Though some winemakers are concerned with residues on the grapes from the particle film, studies by university researchers have not found an adverse effect on commercial winemaking practices.
In two separate studies, both Dr. Christian Butzke, University of California Cooperative Extension enologist, and Philip VanBuskirk of Oregon State University reported that applications of the clay particle film sold as Surround, at recommended rates, don’t appear to have any significant impact on grape or wine quality. Butzke found no significant differences in fermentation performance of juices made from treated grapes versus a standard control. Buskirk, who studied the product for three years, also found no significant differences between wines made from control grapes and those from treated grapes.
VanBuskirk noted that his study results may have been somewhat skewed as the wines were made by three different winemakers during the three years of study. In 2000, a nonreplicated trial using Surround showed promising results, encouraging VanBuskirk and other researchers to study the material further and conduct a more in-depth trial.
From 2001 through 2003, the OSU trial was conducted in two locations using two varieties of red wine grapes. The replicated treatments were in a randomized block design. Rates of 50 pounds per acre and 25 pounds per acre were studied. In the first two years, initial application was made at veraison and repeated on a 14-day schedule for a total of three applications. In 2003, the first application was timed with the onset of 100-degree or more temperatures with the subsequent applications on the same 14-day schedule. Grapes from the different treatments were harvested separately, crushed, and evaluated before being made into wine.
Surround was effective in controlling grape leafhoppers and thrips, VanBuskirk said. They noticed that after treatment, insects were repelled and moved to adjacent untreated vines.
Depending on the year, some slight differences in grape and wine quality were apparent, he said, adding that the differences, which were not statistically significant, were likely related to year-to-year crop variation rather than the Surround treatments.
Surround sunburn trials are also taking place in Sonoma County vineyards that have been trained to a vertical-shoot-positioned trellis.
In Washington State, Dr. Russell Smithyman, director of research for Ste. Michelle Wine Estates, has worked with the material the past two years and is testing it again this season. Smithyman is interested in evaluating its sunburn protective qualities as well as efficacy on pests in organic vineyards.
As part of their Surround study, he applied the particle film to an under-performing Cabernet Sauvignon block for heat stress, but didn’t see a benefit in the ripening of the fruit from the material. However, they didn’t see any wine quality differences between the control and treated grapes when the grapes were made into wines.
“The kaolin clay is the same type of clay based-product—bentonite— that is used in fining white wines,” he said, though noting that red wines do not go through the same fining process as whites.
In another Ste. Michelle study, Smithyman explained that Surround was applied on the fruit before the leaves were stripped at the fruiting zone as protection in case high temperatures occurred after leaf removal.
“But again, the study was done in a low-performing block, and we didn’t attain desired sugar levels even with the material,” he noted. “But we didn’t have sunburn.”
Sunburn is not a “huge” issue for most Washington State growers, Smithyman said, adding that most growers prevent sunburn by canopy management. Sunburn usually shows up in stressed vines.
“In our whites, we have larger canopies, and there is little stress on the vines,” Smithyman added. “But with reds, we go the other way, and we want stressed vines, though still, I haven’t seen a lot of sunburn problems.”
This season, he plans to set up additional trials for sunburn in their Cold Creek Vineyard where they know quality fruit can be ripened and produced.
Smithyman is also studying the use of Surround in organic wine grape blocks for control of grape leafhopper. “It looks very promising as a treatment for leafhopper control.”
He believes there would be more interest in using the product for leafhopper control if it had both sunburn and pest control benefits.
The biggest question he hopes to answer from further research is the impact of Surround on winemaking. Although they haven’t recently compared wines made from treated and control grapes, he plans to revisit the wines made in their research winery to make sure there is no influence on the wines made from Surround-treated grapes.