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Oregon growers checking for heat damage to grapes, berries

Some plants shut down during lengthy hot spells, and may be slow to recover.
Eric Mortenson

Capital Press

Published on August 7, 2017 9:37AM

White drupelets on a late season raspberry are an indication of sun damage. Extended periods of high heat take a toll on wine grapes, blueberries and other crops.

Eric Mortenson/Capital Press

White drupelets on a late season raspberry are an indication of sun damage. Extended periods of high heat take a toll on wine grapes, blueberries and other crops.

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Oregon berry and grape growers are watching for damage caused by unusually hot weather that settled into Western Oregon and the Portland area.

Excessive heat can blister or sunburn wine grapes, which are still developing and won’t be harvested until September. Late season raspberries may develop white drupelets due to sun scald.

Blueberry harvest of mid- to late-season varieties is underway, and crop consultant Tom Peerbolt said mature berries may shrivel in the heat, while green berries may not reach full size.

“The plant can’t pump enough water, so it shuts down and interferes with sizing,” he said. “Fortunately a lot of the commercial folks have installed cooling systems, and they pay for themselves in an event like this.”

He said overhead misting systems cool plants in the field. With temperatures topping 100 in Portland and throughout Western Oregon the first three days of August, some growers ran the misters eight hours a day, Peerbolt said. He said the systems are a large infrastructure expense, but are intended to handle situations of extreme heat.

Climatologist Greg Jones, incoming director of Linfield College’s wine education program, said the current heat wave is unusual for its magnitude and length, and may turn out to be Oregon’s most extreme since 1981.

“Vineyards without irrigation might be able to handle the heat due to available soil moisture, but others will likely see some heat stress, potential sunburn on the fruit, and even leaf desiccation,” Jones wrote on a Linfield blog. “Also, one conundrum is that even though it is hot and it should facilitate ripening, it might actually slow it down as the vines often do not get fully back to 100 percent functioning for some time after a heat event like this.”

At King Estate Winery and vineyard outside of Eugene, Communications Director Jenny Ulum recounted the observations of Ray Nuclo, the company’s viticulture and winery operations director.

Ulum said Nuclo told her grapes don’t accumulate sugar during heat waves. “Over time that would be cause for concern, but grapes can weather a few days with no problem,” she said.

The degree of sun damage to grapes may vary with the type of trellis system used, Ulum reported. In a “hanging” trellis, fruit at the top of the trellis is exposed to the sun. Upright trellis systems provide more protection, with leaves trimmed on the east side so grapes will be exposed to morning sun, but left in place to shield grapes from the hotter midday and afternoon sun.

Ulum said Nuclo told her grapes that develop in sunlight tend to be more resilient to sun scald. Clusters that develop in the canopy shade and then are hit by strong sun tend to be more easily damaged.

Sun damage is less of an issue with Pinot gris grapes than with Pinot noir, Ulum said. Skins of the Pinot gris grapes are pressed off during the winemaking process, so any sunburned skins aren’t included in the wine.


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