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March 2013 Issue of Wines & Vines
 
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Beating Mother Nature at Her Own Game

How growers can control environmental factors using high-tunnel technology

 
by Richard Carey
 
 
Click the photo above to listen to Dr. Eric Hanson with the Michigan State University Department of Horticulture discuss his experience building Haygrove High Tunnels for research into organic fruit farming in this video by Bonnie Bucqueroux.
 
Those of you who have followed my columns know that I usually discuss interesting and different ways to make better wines, more efficiently and more consistently. You may not have known that I came to winemaking as a plant physiologist. I became fascinated with the chemistry of wine in graduate school and proceeded to ferment anything I could in the course of getting my degree. So it is from the plant physiologist’s perspective that I am now writing about one of the most important aspects of winegrowing: how to get grapes to the best physiological maturity and at the highest sustainable yield. When that goal is achieved, growers make the most money and have the most incentive to give winemakers the best-quality grapes to make into wine.

I have been making wine on the East Coast for 17 years. I know that making high-quality, world-class wines from eastern fruit is possible. The challenge, however, is to make those wines in the East on a regular basis.

Haygrove High Tunnels are one growing method vineyard owners can employ to mitigate some of the environmental variations that are prevalent in the East. The eastern winegrape-growing environment is often characterized by late spring and early fall frosts or freezes, seasonal temperature changes that transition from too warm to too cold too quickly for the vines to adapt, a lot of rain (often occurring at inappropriate times), an abundance of cloudy days, less diurnal fluctuation in day versus nighttime temperatures and high humidity that allows many diseases to attack the vines.

Tunnels may also be increasingly important in the West as growers explore ways to combat the influences of global warming. Western growers can have more sun than they know what to do with, or have so little rain during the growing season that they get caught off guard when it does happen. Winter temperatures are not cold enough to moderate some diseases, and increasing average temperatures are changing the historic terroir of the wines.

In both regions, the overall basic concept is that uniformity of climate is important for fine wine production. This is the main theme of John Gladstones’ book, “Wine, Terroir and Climate Change,” and that general concept is also the underlying premise for new vineyard techniques that can be especially beneficial for high-value grape varieties grown in eastern climates.

Tunnel background
In my years on the East Coast I have observed that many of the tenets I thought were important from a West Coast winemaking perspective were not as true in the East. Vinifera grapes grown in the East make wines with considerably more acid than in the West, while western wines are usually higher in pH, alcohol, fermentable sugars and perceived tannins. While winemakers must approach the making of wines in each locale quite differently—and in some ways from opposite directions—all winemakers have the same goal: to make a balanced, good-tasting, high-quality wine.

With all of the environmental challenges to growing grapes, my plant physiology background suggested that the highest quality fruit should be produced in a growth chamber where the parameters could be controlled. A more practical solution landed on my doorstep several years ago, when the U.S. representative of Haygrove Inc., the producer of the Haygrove High Tunnel, came to me for assistance. As a result of that meeting, we jointly embarked on a research program to investigate first the utility of using the Haygrove tunnel system for growing high-quality grapes—and then, if it could be shown that tunnel-grown grapes produce equal or better wines, to determine the economic return on investment for using high tunnels.

Tunnels have been used for agricultural purposes for a very long time. Historically, there had been a lack of consistent design criteria to take financial advantage of the farming side of the equation until Haygrove developed their method of tunnel crop production in England in the 1990s. The company began to export to growers in other countries in 2001, and today there are more than 2 million acres of agricultural products grown under tunnels worldwide, with the largest acreage of tunnels being in China. Perennial and annual crops from strawberries and herbs to espaliered cherries can be commercially grown under tunnels.

The Haygrove tunnel system is a three-season greenhouse-type structure. Before the growing season begins, special luminescent polythene plastic is stretched over the steel hoop frame to create the tunnel that forms an in/out barrier. Doors can be installed on the ends of the tunnel to trap heat in the tunnel to protect against frost, or the tunnel can be left open. When frost is no longer an issue, the tunnel sides can be rolled up to vent the heat from the tunnel or rolled down to prevent rain coming in sideways. Tunnels range in size from 18- to 30-feet wide, between 10- and 18-feet tall (to accommodate commercial field-scale tractors) and are a minimum of 200 feet in length.

The experiment
In 2010 we planted 67 vines in four rows on a small plot of land behind Tamanend Winery in Lancaster, Pa. Approximately 66% of the plants were under the tunnel, with the balance outside the tunnel. The tunnel has an east-west orientation, which was in line with the prevailing winds. This orientation funneled winds through the tunnel, thereby reducing stress on the sidewalls. I chose Entave clones of Cabernet Sauvignon, Petit Verdot and Viognier, which have proven effective in producing some of the best wines in the East.

The tunnel is a single bay 24 feet wide by 60 feet long, and there are four rows of vines inset 24 inches from the pole line. Inter-row distance, as well as inter-plant, was laid out at 60 inches. The first row was planted with Cabernet Sauvignon, the second row was Petit Verdot, the third row was inter-planted alternately with Cabernet and Petit Verdot, and the fourth row was planted to Viognier. The inter-planting was chosen to distinguish any edge effec t of the plants on the outside rows. The plant density for this plot is approximately 1,500 vines per acre.

Water was delivered through a drip-irrigation line controlled by a home-style digital controller. The amount of water applied to the vines during the growing season was calculated to be the amount needed for ideal growing conditions. The outside plants were placed on the irrigation system for the first season to help them get established.

After the vines had been planted, we measured incident radiation at noon both inside and outside the tunnel on a clear day. Typically, noontime radiation is 1 watt per cm2, and this was the measurement at the site in June. In the tunnel, the incident radiation measured 0.75 watt/cm2. However, when the meter was turned off of perpendicular by just a few degrees outside, there was a dramatic drop in the incident radiation. In the tunnel, the fall off in radiation was much less. This indicated that the plastic was responsible for diffusing the incoming light and allowing the light to come into the grape canopy at many more and different angles.

It did not take long after planting for differences to show up between inside and outside vines. Cabernet and Petit Verdot vines under the tunnel grew faster, and the plants were stronger with more leaves that were darker green on the inside. The canopy for outside vines was more sparse, with less intensely green leaves. There were more shoots on the inside plants than outside. During this first year, the primary cane shoot on each vine was allowed to grow unimpeded until it reached the top of the trellis, which happened about mid-August. Shoots also budded out from this primary cane. It was a disorganized but very robust growth habit for the Cabernet and Petit Verdot. All fruit was stripped off.

The Viognier was quite different. It is a testament to the vigor of the Viognier vines that they survived to grow the next year. Unfortunately, the Viognier arrived very late in 2010 and did not get planted until about July 1. As a result, they suffered severely stunted growth. Compared to the vines planted earlier, the difference between the inside and outside Viognier plants was not as significant, and the canopy in both areas was sparse.

After the 2010 growing season, the Viognier produced less than one pound of pruning weight for both inside and outside plants. The Cabernet and Petit Verdot grown in the tunnel produced much higher weights: 2.1 pounds for Cabernet and 1.7 pounds for Petit Verdot, while the outside Cabernet produced 1.3 pounds and Petit Verdot 1.2 pounds.

In 2011 we did not train the vines into VSP until too late in the season for adequate cane selection for the cordon. This decision led to a second year of somewhat disorganized plant growth. The vines were just as robust as during the previous year, and pruning weights increased from the first year. The differential between outside and inside vines narrowed a small degree for each variety, but the total leaf area strongly favored the vines inside the tunnel.

During the 2012 growing season a traditional VSP training system was implemented. Based on the pruning weights from the 2011 season, we left 40 buds per plant. Buds began to swell noticeably in late February but then held constant until mid-March. The plastic was put up at the beginning of April. Because of the effects of putting up the plastic in 2012, we will install it in March this year.

During bud break, flowering and fruit set in 2012 there were weather events (rain and cool temperatures) that affected vines in both nearby vineyards as well as the outside plants in our research vineyard. By harvest, the yield on the outside plants was less than half the yield from the inside plants. Verasion occurred July 23, and harvest took place Sept. 26 (see table on page 64).

The inside plants for Viognier were harvested the second week in September, and the Cabernet/Petit Verdot was picked the last week in September. At the time of harvest for the grapes grown in the tunnel, the differences in chemistries were significant for the inside plants compared to the outside vines. The outside plants were scheduled to be harvested about two weeks later; however, birds decimated the outside crop before it could be picked.

An overall observation that was most impressive was the speed of establishment of the inside vines. The rate of vine growth and the increasing girth of the vines was about as fast as could be accomplished physiologically. The outside vines grew at reasonable rates, just not as fast.

The spray program was very simple. During the growing season, five or six fungicide sprays were applied to the inside plants. The outside plants had fungicides as well, but they were sprayed at the traditional rate of about every three weeks. In both plot areas there was no evidence of either powdery or downy mildew.

As indicated above, we wanted the vines to become firmly established as quickly as possible, so we chose to do very little pruning or vine training during the first two years of growth. In retrospect this was not necessary for the inside plants. In future plantings I would begin the process of pruning and training to get the VSP system established earlier. We have adopted a double Guyot vine-training system. Based on our observations, it is reasonable to expect full crops off inside plants that are well-balanced vines in the third year from planting.

In parallel to this experiment where inside and outside plants were compared, Ralph and Keith Cramer, the Haygrove Tunnel distributors in Mount Joy, Pa., installed a 230-foot tunnel on their property under our supervision in 2010. Four rows of vines were planted in the tunnel—two of Cabernet Sauvignon and two of Petit Verdot—with a plant density at the same 1,500 plants per acre as at the Tamanend site.

The tunnel at the Cramers’ property was planted because we determined that the experimental plot at Tamanend was too small to accurately extrapolate the data to full-scale production. The Cramers’ location is about 10 miles from our vineyard site and is similar in climate and aspect to our experimental plot at Tamanend Winery.

The production data presented in the table above is from the Cramers’ tunnel. In reviewing the data, it is apparent that significantly higher yields were obtained for these grapes than is typical for high-quality grapes grown on VSP in Pennsylvania. If the vines are capable of producing grapes at these rates, the question is: What is the quality of the wine tha t can be made from them? To the extent that tunnel-produced wine quality is at a higher level than that of wine produced conventionally, then that difference is the measure of the increased value a tunnel will provide and gives justification for a grapegrower to invest in a tunnel.

Wine quality
Grapes grown on a small research plot receive the TLC of hand-grown conditions, with the result that the fruit at harvest looks fantastic. The Cramer tunnel in Mount Joy is similar to the experience a commercial grower would encounter. In September 2012, we received grapes from that tunnel for fermentation at our winery, and I was amazed at how clean the fruit was. The uniformity of the crop was as good as could be expected, and the ripeness of the fruit flavors was excellent. The fruit chemistries were at ideal Brix levels of 24°, with picture-perfect total acidities and pH. Most importantly, the seeds were fully mature and ranged in color from medium brown to chocolate brown.

Fermentations were done with DV10 and were unremarkable. Malolactic fermentation was inoculated at 8° Brix with MBR 31. After fermentation, the juice color was deep ruby. The tannin structure was very pronounced but with roundness and fullness on the palate. At this stage of the wine’s development, I think these grapes have made some of the best wines I have experienced in the East.

No wine was made from grapes grown outside the tunnel due to decimation from birds. In coming years, all grapes will be net protected to avoid this problem. However, looking at the chemistries of those grapes before harvest, it is likely that those grapes were not as fully developed and might not have reached the highest levels of grape quality, even if allowed to ripen for an additional period of time.


References
I am grateful to John Gladstones for his prodigious body of work on grapes. He has performed a large amount of the basic research and given me source information that justifies many of the observations that I have seen about how grapes grow. When a researcher locates a compatriot who reports the same observations, he or she gains confidence that the research is real and important.

This article is the first in a series that will explore the means and potential for changing viticultural practices to enhance quality, consistency, value and sustainability. The next article will look at how tunnel technology can be scaled up for commercial grapegrowing in many different environments and regions. A subsequent article will discuss how grapevine physiology interacts with its environment, and how these environmental parameters lead to physiological maturity.

 
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