When Ryan Schilperoort decided to convert his juice grape vineyard from rill irrigation to drip one year and from hand pruning to machine the next, he asked Washington State University for help.
In return, viticulture researchers asked if they could monitor a few control patches to study the differences in outcome, and a private-public experiment was born.
About 15 years ago, Schilperoort’s drastic changes would have been considered impossible to the point of heresy. That thought changed with the 2015 drought, when Roza Irrigation District customers received only 46 percent of their usual water allotment.
“It makes it a little tough to irrigate 100 acres with half your water,” Schilperoort, a third-generation grower in Sunnyside, Washington, told the crowd assembled at the university’s Viticulture Day in August, where researchers shared their latest findings and offered tips on everything from plant nutrition to soil health monitoring. The event was co-hosted by Washington State University and the Washington State Grape Society.
He installed drip irrigation in 2016 and cut his water use by half. The next year, he converted from hand pruning to mechanical pruning, which leaves the vines taller, with more vegetative growth on the top and a heavier crop.
Worried about narrowing his rootzone and growing more vine at the same time, he asked for help from Markus Keller, a WSU viticulturist at the Irrigated Agriculture Research and Extension Center in Prosser.
“So, not only are you supplying suddenly much less water potentially but on a very narrow zone, but now you’re building up your vine size on top of that just a year later,” said Keller, whose team helped with soil moisture monitoring and left a few portions hand pruned as controls. The work is ongoing.
But the biggest news is that nothing really happened. Vines kept up production. Fruit ripened on time. Weeds didn’t invade. He never had much chlorosis, and the changes didn’t lead to any. And the whole operation didn’t spiral into a biennial bearing cycle.
“It doesn’t look like a crashed crop to me,” Keller said, pointing to a verdant and uniform canopy throughout Schilperoort’s rows.
If anything, production with mechanical pruning increased by 30 percent to more than 14 tons per acre, compared to 11 tons per acre in the hand pruned control plots.
Everything else stayed the same — berry weight, berries per cluster, sugar per fruit — except now there are more fruitful shoots on the top of the canopy and, therefore, more clusters on the vine.
“We never missed a beat,” Schilperoort said.
Meanwhile, the roots seemed to have adjusted to drip irrigation just fine. In 2016, when the Bonneville Power Administration insisted on creating access to its utility poles that stand in Schilperoort’s vineyard, the roots they pulled up had more live fine roots than he expected.
He was surprised at how much new root growth he saw just one year after converting to drip.
He has used the drip irrigation system to chemigate and fertigate, allowing him to cut his nitrogen inputs in half.
He also drastically reduced his equipment use and labor, because he could accomplish with a turn of a valve what he used to do with a sprayer. Plus, he gets more uniform irrigation from the new system. With rills, the uphill vines always got more water than the downhill areas. He also gets fewer weeds from drip irrigation.
Drip irrigation and mechanical pruning aren’t new to Concord grapes. Many growers made the switch to drip from overheads or rill after earlier droughts. He estimates he spent about $1,400 per acre to install the system, including both labor and materials. Prices may have gone up by now, he said.
And, Schilperoort was actually pretty late to the mechanical pruning party, he said. “I was one of the last guys to hand prune … but it is nice to put some science behind what we’re doing out here.”
Schilperoort’s pruning regimen still involves some hand follow-up work, though Keller has been advising minimal pruning.
They typically cut by hand up to the bottom wire and instruct workers to keep moving through the rows quickly, not worrying if they miss a vine or two.
Meanwhile, Keller’s team has been operating a test vineyard at the Prosser research center and has logged the same mechanical pruning production increase of 30 percent.
The experiment station also has tested different watering rates at different timings. Keller watered a control plot at 100 percent. For one treatment, he irrigated at 50 percent volume from fruit set to veraison. In another treatment, he irrigated at 50 percent from veraison to harvest. For the third treatment, he boosted irrigation by 50 percent.
The only consistent significant difference was this: 50 percent less water between fruit set and veraison led to 10 percent smaller berries and therefore 10 percent lower production. The sugar levels remained constant, he said.
This means growers can cut water use in half during fruit ripening as long as they provide enough water earlier, before veraison.
The news prompted him to reflect back to when he started at the experiment station in 2001. He was new to Concord grapes.
Industry leaders told him it was impossible to drip irrigate juice grapes, impossible to manage a cover crop and impossible to machine prune without triggering a biennial bearing cycle.
But he did all three at the station’s research vineyard and, today, the industry routinely does all three commercially. He has yet to see a biennial crop.
“Sometimes in order to get to the next level of production, you have to do things that are not possible,” said Keller. “Turns out, they’re all possible.” •
Watch: Easy method to evaluate soil textures
Margaret McCoy, a graduate student at Washington State University’s viticulture and enology program, demonstrates a “quick and dirty method” to test soil texture in August 2018, at the university’s annual Viticulture Day in Sunnyside, Washington. Learn more about estimating soil texture by using a flowchart developed by WSU at http://bit.ly/wsusoiltexture
—by Ross Courtney
An earlier version of this story did not note that the Viticulture Day event was co-hosted by Washington State University and the Washington State Grape Society.