Load cells automatically detect tension differences in grapevine trellis wires.

Load cells automatically detect tension differences in grapevine trellis wires.

For the last seven years, U.S. Department of Agriculture researchers at Prosser, Washington, have studied technology that provides grape growers with real-time data on vine development, a tool that could make crop estimation of juice and wine grapes easier. Funding is winding down on the project in Washington State, with hopes that a commercial entity will partner with the USDA.

Dr. Julie Tarara, research horticulturist for USDA’s Agricultural Research Service, has been the lead investigator of the trellis tension monitor project, an automated system that uses load cells to detect tension differences in the trellis wire that supports grapevines in the vineyard. Data loggers capture the measurements every 5 seconds, with averages calculated for each 15-minute period.

"The trellis tension monitor gives us information that we never had before," said Tarara, adding that growers have never been able to follow vine growth continuously during the season in an automated fashion. "Before, the best we had was a snapshot at different stages." Tarara thinks the technology has many applications, from identifying lag phase to better managing activities like crop thinning. As the trellis tension monitor shows instantly when the crop has been thinned, a grower could use the data to determine if the desired amount was thinned.

When combined with historical data collected on crop growth, it could help growers build their own vine-growth curves and compare crop differences between years, she said.

The idea is to get added value from your trellis system, said Paul Blom, research biologist for the U.S. Department of Agriculture at the Prosser research station. Blom has worked with Tarara on the trellis tension monitor for the last five years. The system has been studied in research plots and commercial Concord and wine grape vineyards.

"The concept is simple," Blom said, addressing the Washington State Grape Society’s annual meeting in Grandview last fall. He explained that it’s based on measuring the tension changes in the trellis wire during the season as the vine grows. "It’s a way to get a lot of information out of your trellis investment."

The data must be periodically downloaded to a computer or personal digital assistant device like a PalmPilot. Data could also be sent by telemetry to a central ­computer.


"While I presented this as a simple concept, there are still a lot of devilish details that make it difficult," Blom said.

Each vineyard installation is essentially a unique entity, he noted, which makes it difficult to generalize the data for a model applicable across sites and locations. There are year-to-year variations in tension changes, daily temperature effects, and the occasional unexplained anomaly that Blom and his research colleagues must account for.

Blom said that part of product commercialization would include development of basic software to smooth some of the background noise in the data and interpret the resulting curves. When the data are downloaded, they must be processed with custom algorithms to eliminate some of the noise, he explained. The most important noise is daily temperature fluctuation in wire tension from the cordon wire stretching and contracting during the day and night. A measurement of wire temperature is incorporated to correct for this effect.

Potential uses

Although originally the technology was developed with the idea of using it to better estimate the size of the crop, Blom thinks the system has other potential uses as well. "The tool is probably a better package for monitoring the crop throughout the season," he said. "For crop estimation, we have had variable results, from very large errors to ­estimates that are dead on."

Blom, who is employed as a postgraduate scientist, will be spending the coming year writing scientific papers describing the results of the project. Minimal field work will be conducted in Washington vineyards in 2008.

Tarara has shared research information with interested wineries in Australia, the E & J Gallo Company from California, and several individual growers in the western United States. She will be cooperating with Gallo in 2008 as they work with the technology in two California vineyards.

Entities that are interested in the project see potential for using the technology to identify grape phenological stages, including grape maturity. It may have value showing when berries begin to lose mass as they hang on the vine and maturity advances.