What can be done to limit damage from the November freeze?

The cold weather that blasted the Pacific Northwest during mid-November is causing worry among many growers.

Some areas are reporting damage to trees and vines that still had leaves and didn’t have time to accumulate significant cold hardiness.

Temperatures in a number of areas, including Oregon’s Hood River, The Dalles, and Dufur, and Washington’s Red Mountain and Walla Walla Valley, reached single digits or were low enough to have caused some bud and tissue damage.

Growers and cooperative extension agents in The Dalles and Hood River have already found damage to flower buds and vegetative buds, spurs, shoots, and limbs, with some being killed outright, according to recent reports.

Although the full extent of damage will not be known until later next spring, disease and other problems, like bacteria canker in cherries, infection of cytospora in pome and stone fruit, and crown gall in grapes, often follow winter injury.

Most disease symptoms can be seen in the spring. Management tactics for diseases from winter injury focus on prevention, because once the disease takes hold, little can be done to cure the trees or vines.

Oregon State University Extension educators Lynn Long and Jay Pscheidt developed recommendations for growers to follow in the aftermath of the November freeze. (Read the PDF) While there is nothing that can be done to correct freeze injury, OSU Extension offers advice on pruning and pest management to prevent the spread of diseases.

Removing damaged and diseased wood this winter during pruning is the best course of action and may help trees recover and slow or stop the spread of disease, say Long and Pscheidt.

They also encourage growers to consider summer pruning in diseased blocks. Grape growers will need to assess damage by cutting buds and canes in their vineyard before pruning.

Once the extent of damage is determined, a pruning strategy can then be developed. Washington State University scientists have developed a model for grapes to help predict cold hardiness.

Information about grapevine cold hardiness can be found at: http://wine.wsu.edu/research-extension/weather/cold-hardiness/