FRESNO, Calif. — Warm temperatures during late winter and early spring may have hastened bloom and fruit development, but they also may have disrupted fruit trees’ normal winter slumber.

With some of the later stone fruit varieties still in bloom in late March, John Thiesen, division manager of The Giumarra Co., Reedley, said the crop appears 10-14 days earlier — depending on the variety — than historic dates.

Thiesen was quick to point out that the crop two years ago was extremely late. Last year, the crop was a few days ahead of 2012 but still later than the industry was used to.

“This year may be the new normal,” he said.

David Stone, owner of Valhalla Sales & Marketing Co., Kingsburg, said early stone fruit varieties appear to have a good fruit set, but the later varieties still had bloom at the end of March and it was too early to forecast set on those trees.

Bloom sprays this season were applied on the same date as last year, but Stone said degree days — a measure of accumulated heat — have been accruing faster this season than last.

“We’re gaining ground every day with those types of temperatures,” he said. Barring unforeseen cold snaps, Stone said the season could start five to 10 days early.

“That’s excellent,” he said. “That’s fantastic because it gets us started early and it gives us more marketing time on the tail end.”

Jeff Simonian, sales manager of Fowler-based Simonian Fruit Co., said in late March that crews had already begun thinning the early stone fruit varieties.

“It’s not a real heavy set, but a pretty good set on the stone fruit,” he said.

Although predicting harvest can be a “little bit of a crap shoot,” Simonian said it appeared the crop was five to seven days ahead of schedule.

Warmth, lack of fog affect bloom

What Thiesen said he had noticed was this year’s bloom was more erratic than usual and pointed to the winter as one possible reason.

Although the San Joaquin Valley probably received enough total chill hours during the winter, the timing of the cold weather may have disrupted tree physiology.

A hard freeze hit the region in early December, and temperatures during much of the remainder of the winter were above average.

“I think it’s manifesting itself in some of the odd things and odd blooms we’re seeing in certain varietal blocks,” Thiesen said.

One tree still may be in bloom, for example, while a neighboring tree is past bloom and already green with leaves, he said. In some cases, Thiesen said he’s seen the disparity on a single tree, with one branch in bloom and the remainder of the tree green.

The odd observations aren’t valley wide but are more spotty and tend to be variety specific, he said.

Kevin Day, a University of California Cooperative Extension farm adviser in Tulare, said he’d seen similar oddities this season and attributed part of it to the lack of overall chilling.

Trees grew well into the fall last year, so at least 100 hours didn’t count toward the 900-hour chill threshold, he said. Trees also started to move in January, lopping off another 400 hours or so.

In addition, Day said some scientific evidence discounts the contribution of temperatures below 32 degrees Fahrenheit toward chill hours.

“So there are a lot of things that contribute,” he said. “And few people recognize and appreciate the absence of fog.”

During a clear, sunny day with an ambient air temperature in the 40s, bark temperatures may rise to 50 degrees or higher, Day said.

But winter tule fog, such as what the San Joaquin Valley typically experiences, helps insulate tree tissue against the sun, keeping the trees in a winter sleep. This year, the valley saw little, if any, fog.