A mild January, followed by several days of 60-degree temperatures last week, could lead to the earliest arrival of pear blossoms in the Rogue Valley in nearly two decades.

A mild January, followed by several days of 60-degree temperatures last week, could lead to the earliest arrival of pear blossoms in the Rogue Valley in nearly two decades.

David Sugar, a plant pathologist at the Southern Oregon Research and Extension Center on Hanley Road, said the average date for Bartlett pear trees to reach full bloom is April 6.

"As of Tuesday we're 11 days ahead of average," said Sugar, who has tracked the pear crop for more than 30 years. "Last year, we were a week later than average."

January 2010 was the warmest on record in Medford, where records have been kept by the National Weather Service since 1911. If temperatures maintain their recent course, this would be the first spring since 2005 that the blossoms have come on early, and the earliest to bloom since the flowers arrived 12 days ahead of their average bloom time in 1992.

Whenever blossoms come early there is higher danger of losing fruit to frost.

"The earlier the bloom, the greater the risk of running into frosty nights," Sugar said.

"The bloom is the sensitive part of the tree. Trees themselves are very tolerant of (cold) temperatures, but blossoms are tender. The risk of a frosty night isn't over until Memorial Day. Early May frosts are not unusual, but the probability goes down as we go through April and May."

"The warm weather swelled the buds a little," said Associated Fruit Orchard Superintendent Luis Balero. "But the cold nights have been holding them down for a while. As long as cold weather keeps coming in, it will hold them down; but it's still kind of early for fruit buds. Frost control is what we're concerned about, and I'm a little nervous about it."

Phil Van Buskirk, also a member of the OSU experiment station staff, said there have been reports of some stone-fruit trees — plums and cherries — already blooming in the Rogue Valley.

"Once you have bloom, there is no turning back the clock. You have to protect the flower and small fruitlets or the crops are lost," Van Buskirk said.

Nightly lows have dipped below freezing several times during the past few clear nights.

"We can still have some pretty cool temperatures," Van Buskirk said. "I'm sure if there are some large blocks of stone fruits blooming, they're going to be protected, but the cost of protecting them is going to go up, because it's earlier in the year."

A mild winter followed by a cold snap can create mayhem for farmers, too.

Seven Oaks Farm in Central Point has winter onions in the ground that tend to send up seed heads when mild temperatures persist.

"When the weather switches back and forth, they don't know if they are supposed to go into seed mode or keep growing," said Doreen Bradshaw, one of the farm's owners. "When it gets warm and then goes cold, they think they have to hurry up and get seed going."

Strawberry crops, on the other hand, aren't as much of a concern for now.

"We don't have to worry about them at this point," Bradshaw said. "If it stayed super warm and they bloomed and then it frosted, that would be a disaster."

For that reason, tomato and pepper crops don't go in until mid-May, when the danger of a killing frost has largely passed. Prolonged late-winter warm spells bring on other issues.

"We don't like it to be this warm because it makes a better bug hatch," she said. "As long as they can find something to eat, they just keep coming. The other thing is that weeds are growing prolifically right now and the ground is too wet and soft to get out and cultivate."

Josh Cohen of Barking Moon Farm on Thompson Creek Road in the Applegate area said he plans to begin transplanting spring greens — such as salad mix, spinach, mustard greens and arugula — from a greenhouse to a fieldhouse on Thursday.

The farm produced about 600 pounds of carrots through the winter for delivery to the Ashland Food Co-op.

"That was at a time when everyone in the Willamette Valley was getting zapped," Cohen said. "We lost a lot in December, but we planted a lot."

Reach reporter Greg Stiles at 776-4463 or e-mail business@mailtribune.com.