Tunnels Take Variability out of Grape Production

7/7/2012 7:00 AM
By Charlene M. Shupp Espenshade Special Sections Editor

MOUNT JOY, Pa. — One of the toughest parts of growing grapes is getting the climate right. An early frost, the crop could be damaged. Too much rain, the grape sugars are diluted.

And if the weather delays grape maturity, the vines do not harden in time, increasing the risk for winter damage.

Throw in the fact that Pennsylvania has a naturally wetter climate than the main wine-producing regions of the world, and you increase the difficulties of getting the dynamics of growing grapes just right.

And that’s proved especially true for producers trying to grow some of the higher-value grape varieties. Yet, it is those varieties that provide the bigger payoff.

One idea for solving this problem that is getting a look is the use of high tunnels, or unheated greenhouses, to better manage wine grapes.

Last week, growers had a chance to see high tunnels used with two grape varieties during an open house for the research projects at Cramer’s Posie Patch in Mount Joy.

The Cramers planted one-eighth of an acre of Petit Verdot and Cabernet Sauvignon under a high tunnel in 2010 to test the practicality of grapes under plastic.

So far, Keith and Ralph Cramer, and Penn State wine specialist Mark Chien have been pleased with what they have seen.

“The French call this cheating, but we call it new technology,” Chien said.

In addition to Pennsylvania, Chien said he has seen high tunnels used for grapes in Michigan and British Columbia.

The Cramers are quick to point out that they are not wine grape growers. Instead, they are passionate about high tunnels growing high-value flowers and vegetables to provide a jump on the growing season.

Chien said there has been scant data collected on the feasibility of high-tunnel grapes, but he sees potential.

The overriding problem for Pennsylvania wine-grape production is usually untimely, excessive rain.

In traditional wine-production regions, which have drier climates, grapes are irrigated. And when growers want the vines to switch to fruit production, they stop the irrigation.

High tunnels offer another way to provide water control for growers.

“High tunnels over high-value grapes become the insurance policy,” Chien said.

2011 was an example of a difficult wine-quality year. The cool, wet spring, dry summer and then the major storms of Irene and Lee hurt that year’s vintage.

So far, the Cramers have seen positive results from grapes in high tunnels.

Ralph Cramer said the vines are in full production one year earlier than normal. The grapes also ripen faster compared with their field counterparts. He said the vines benefit because they can be hardened off earlier to minimize winter damage.

Chien said the Cabernet Sauvignon is very cold sensitive, and “it doesn’t take much for it to sustain winter injury.”

This spring left its mark on grape production with an early warm-up, then a return to cooler weather and frosts, which are the main problem for grapes. Growers have reported losses of greater than 50 percent in parts of the state.

“Whether you believe in climate change or not, we have had earlier, warmer springs,” Chien said.

During years with difficult weather patterns, the grape crop is protected by high tunnels, which is where they could pay off with higher-value grapes.

Keith Cramer said the high-tunnel grapes have fewer wet season problems and require less spraying.

Chien said he is impressed with the quality of the grapes in the high-tunnel project and is looking forward to getting more data about grape performance.

He said he did not find any fungal diseases in the planting. However, now that the stand is in grape production, he is curious to see how bird and insect damage will compare with field damage.

The results have bolstered Keith Cramer’s enthusiasm for high tunnels. They might not give a big payoff every year, he said, but they can make a big difference in a difficult growing year.

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