Tests show winegrape growers can irrigate their vines less and later

Issue Date: October 7, 2009

By Steve Adler

Mark Greenspan, the founder of Advanced Viticulture LLC in Santa Rosa, has undertaken a two-part demonstration project at Hoot Owl Creek / Alexander Valley Vineyards in Sonoma County.

A demonstration project at the Hoot Owl Creek Vineyard in the Alexander Valley has confirmed two of irrigation expert Mark Greenspan's beliefs: North Coast winegrape growers can delay the start of their irrigation season until much later in the summer, and most farmers can save both water and money by changing the way they apply water to their grapevines.

Greenspan, the founder of Advanced Viticulture LLC in Santa Rosa, has provided expert consultation to winegrape growers for the past two decades. It is in that capacity that he has undertaken the two-part demonstration project sponsored by the Sonoma County Water Agency.

Working closely with Hoot Owl Creek / Alexander Valley Vineyards manager Mark Houser, Greenspan is examining several methods of drip irrigation, as well as the feasibility of using misters to cool vines on scorching summer days rather than utilizing overhead sprinklers that pump out considerably more water.

Regarding the first aspect of the demonstration, Greenspan said he is very pleased with what he has observed this year. As for the vine-cooling project, temperatures on the North Coast were cooler than normal during the summer, so results of his testing weren't as definitive. He said he hopes the water agency will sponsor the demonstration project for another year or more, so he can continue to accumulate data.

North Coast growers typically begin their irrigation season in June and some actually begin applying irrigation as early as May. But Greenspan has been able to demonstrate that by waiting until August, the vines did very well in setting a good crop of quality winegrapes. In fact, on one row of vines where there has been no irrigation water this year, the grapes cannot be distinguished from grapes growing on irrigated vines.

Cutting down on water use early in the season is important to farmers like Houser, who monitor their water use very closely.

"Saving water early in the season when the vines are young not only saves on water use, it cuts down on electricity, diesel and other things like that," he said. "And it is better for the vines. They aren't wasting water. You aren't wasting water. So it's a good farming practice."

Greenspan's demonstration project has sparked a lot of interest among North Coast winegrape growers. At two different field days this summer, more than 200 persons attended to observe what he has learned.

"There were some representatives in attendance from the larger operations, but it was primarily the smaller growers and maybe less experienced growers who were most interested in the project because most of them don't have that kind of expertise in house," he said. "On the other hand, I think a lot of people think they have it figured out. But I believe that many of them could improve their practices. There is always room for improvement."

Water use can be reduced in two ways without adversely affecting the vines, he said. Growers could delay their first application until later in the year, and they can cut back on the amount of water applied when they do irrigate.

"I've seen some growers start irrigating in May, but June is the trigger point for most of them. And that is what we are trying to encourage these growers not to do, because in our climate we have enough water," he said. "We want the growers to look at the vines, look at the shoot tips and wait as long as they can to irrigate. From wine quality and every aspect, waiting to irrigate is better because you are using more of the soil resources and you are able to get more nutrients out of the soil. It's not just water; it comes back to nutrients."

Greenspan explained that with drip irrigation, it is better to apply lesser amounts of water frequently rather than larger quantities less often.

"A lot of growers will put on one big application of drip over several hours and then come back in a week or two and do it again. They end up stressing the vines too much because they think they can just cut the water off at certain times," he said, adding that the practice also gives the vines more water than they need.

He explained that when he started the demonstration project, he was irrigating once a week, but he switched to twice-weekly applications when he noticed that the vines receiving the water were showing more signs of stress than vines that weren't being irrigated at all.

"This was interesting because what it told me is that the roots were getting modified because of the irrigation and they weren't picking up all of the available water that the non-irrigated vines were getting from the soil," he said.

It is important to put on small amounts of water each time—two gallons per vine per irrigation, which amounts to only about four gallons per week per vine. Many growers use a single, one gallon-per-hour emitter per vine, but Greenspan recommends two half gallon-per-hour drip emitters per vine. "Three is probably too many, and one is probably not enough," he said.

Greenspan also stressed that every vineyard is different and it is important for farmers to understand the particular soil profile of their site. He suggests that with existing vineyards, the growers dig some backhoe holes to check root depth and root patterns. With a site that is being developed as a new vineyard, the backhoe hole will reveal any limiting layers of subsoil and also indicate whether the soil profile can be modified.

He also recommends that farmers schedule their irrigations to target the weakest part of their vineyard.

"If you irrigate to the weakest part of the vineyard, you are keeping that part of the vineyard happy and you are keeping the rest of the vineyard happy, too. Ideally you are providing the same amount of water to every part of the vineyard because you want every vine to be the same size. If the vines are all the same size, they are all going to be using the same amount of water," he said.

Regarding the second aspect of the demonstration project, Greenspan pointed out that farmers can cut down considerably on water used to cool the vines in hot weather by switching to over-vine misters from higher-volume overhead sprinklers. While the practice of using the sprinklers is mostly found in areas of extreme heat like the Alexander Valley and Cloverdale, Greenspan said many growers opt for canopy management to shade the grape clusters.

Greenspan offers detailed guidelines for farmers on best management practices regarding irrigation and other aspects of vineyard health. Go to www.advancedvit.com and click on "Literature" to find a list of articles and tip sheets.

(Steve Adler is associate editor of Ag Alert. He may be contacted at sadler@cfbf.com.)

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