Dick Hagerty: Central Valley cherry crop suffers from not enough chill hours

06/12/2014 6:40 PM

06/12/2014 6:41 PM

Cherry farmers are pondering the future of their $200 million annual Central Valley crop as this year’s harvest has come in at half or less of normal. In fact, a news report last week from Brentwood indicated 90 percent crop failure for this spring, and closer to home our local farmers are reporting harvest far below expectations.

“The consensus is that our warm winter is to blame,” said Joseph Grant, a UC Cooperative Extension pomology farm adviser in San Joaquin County. He went on to say that the weather left cherry trees short of the chilling hours they need to produce a full crop.

“This led to a very prolonged bloom and poor overlap between main varieties and their respective pollenizers,” he added.

So, what are these “winter chilling hours” all about?

Well, the short answer is that most of our local orchard varieties need a certain amount of hours during winter with sustained cool weather to create “dormancy.” That is, the tree goes into a type of hibernation, much like our Sierra bears, and the tree is better able to withstand harsh cold conditions as well as going through an expected cycle of rest and then being revitalized when the spring sun warms the tree and the earth.

Our Central Valley weather has been conducive to producing the very best crops of walnuts, prunes, cherries, peaches, nectarines, etc. The concentration of these crops in our area is no coincidence; it’s a clear expression of our cool winters and warm summers.

Ask 10 experts the exact temperature and time for chilling ,and you will likely get 10 answers. But the consensus of opinion rests in a range of under 45 or 50 degrees down to the freezing level.

The length of chilling is measured in hours, and the amount of chilling required varies by crop type and variety. Some “low chill” fruits and nuts require as little as 250 hours of chill while others may range 1,000 hours or more.

Traditionally, our cool, damp, foggy days and nights have produced ideal conditions. That is why our region is so popular and successful for the many varieties we grow. But in recent years, most of us have heaved a great sigh of relief at the lack of the all-present winter tule fog, while the farmers have become more and more concerned.

Some fruit varieties are able to produce with short chill seasons, but their production quantities and crop quality reflect those shorter chill times.

Several years ago, Bill Burchell and I traveled down to Hermosillo, Mexico, in the Sonoran Desert, to view peach orchards of varieties that had been developed here locally. Even though these varieties required the very lowest demand of chill time, the results were readily apparent. As we walked the tree rows in late spring the branches only held random quantities of developing fruit. Bill concluded and advised that it was highly unlikely that these conditions would be able to support a viable peach crop, given the prevailing warm winter weather.

The Modesto Rotary and the Burchell Nursery established a 14-acre fruit orchard at Rancho Santa Marta Orphanage in Baja California years ago. Even with careful selections for varieties with low chill needs, the orchard has continued to struggle.

Thus, added to the mounting crisis over shrinking water supplies, our local farmers are faced with another daunting situation that is clearly out of their control and at the total whim of Mother Nature. Is it possible our winters are just getting too nice?

Enjoy those cherries while we still have them. A few more warm winters and these crops will not be worth harvesting. Farmers will be challenged to find crops and varieties more suited to our changing climate.

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