Chris Caskey, The Union Democrat

An ongoing, multi-day cold snap could spell trouble for multiple crops in the Mother Lode, according to a local agricultural advisor.

Scott Oneto, the University of California Cooperative Extension farm advisor for the Central Sierra Nevada region, said grape vines, olive trees and fruit trees could all sustain damage with the bitter cold weather expected this weekend. But the extent of the damage is hard to predict.

"It's going to be a wait and see," Oneto said. "Unfortunately, there's not a whole lot (farmers) can do about it."

The West Coast cold front sent thermometers dropping earlier this week, with lows dipping into the 20s. The cold weather is expected to continue into the weekend. Foothill forecasts call for freezing rain and snow tonight into Saturday, with lows through the weekend dipping into the teens.

That will likely be a problem for young grape vines that have been planted within the past three years, Oneto said. While the wine grape harvest is over and the vines are dormant, he said the younger plants are susceptible to winter injury because they don't yet have mature bark to protect against the severe cold.

Oneto said that could lead to vines cracking, which will put those plants in harm's way for a bacteria known as crown gall, which damages the plants.

"Those are certainly going to see some injury," he said.

Fruit trees in the area, like apples and pears, could also see similar damage from the cold. And olive trees, which Oneto said take up hundreds of acres in the Mother Lode, could be in for problems as well.

Olives typically have leaves on the branches year round. Temperature dips this far below freezing will likely mean blackened leaf tips and, in some cases, leaves falling off altogether.

The olive trees are also vulnerable to a similar phenomenon as the grapes, as split bark will likely lead to a damaging bacteria called olive knot, which can hurt young and old trees alike.

"Because they are evergreen, with olive trees, even some of the mature trees we are going to see damage to them," Oneto said.

And like the other crops, it's difficult to predict how much damage the plants will sustain and what it will mean for next year's production. But Oneto also said the typical methods for protecting the plants through the cold - including wind machines or aerial irrigation - won't work when temperatures plunge this far below freezing.

"In this case, (increasing the plant temperatures) a couple of degrees isn't going to be enough," he said.