From the UC Blogosphere...
Think of the ABCs: almonds, blueberries and cherries. Then think of watermelons and pumpkins. All those crops will be...
Rising temperatures appear to be reducing the number of hours tree crops in the San Joaquin Valley are subjected to chill during the winter, a critical factor in producing a profitable yield, reported Ezra David Romero on Valley Public Radio, KVPR-FM.
Pistachios, for example, require temperatures between 32 and 45 degrees for about 700 hours each winter, but for the past four years have had less than 500 chill hours.
UC Davis researcher Hyunok Lee recently published a study about climate change impacts on agriculture in UC Agriculture and Natural Resources' peer-reviewed journal California Agriculture. The study found that winter temperatures are increasing more than any other time of year. Her modeling looks at the year 2050 in Yolo County.
“Our agriculture will continue,” Lee said. “But if you look at . . . like 20 years or 30 years. The pattern may change a little bit, crops may move a little bit north.”
Romero spoke to UC Cooperative Extension farm advisor Craig Kallsen, who holds the UC Cooperative Extension Presidential Chair for Tree Nut Genetics. Kallsen is conducting trials aimed at finding pistachio varieties with novel nut, tree growth and yield characteristics, and varieties that produce a high yield even under low-chill conditions.
"We're trying to use the other species of pistachios actually to see if we can come up with something that has a low chill requirement. It's pretty hypothetical at this stage,” Kallsen told Romero. “We made quite a few crosses this spring and we actually hope to put a trial in a low chill area.”
David Doll, UC Cooperative Extension farm advisor in Merced County, is studying other tactics to improve winter chill, such as using overhead sprinklers to cool the trees and painting them white with liquid clay to reflect sunlight.
"So this is something that could impact a lot of farmers over the next 10, 20, 30 to 40 years,” Doll said. “And in fact it's already impacting farmers on random given years across the state."
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Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
Help Desk Client: My mature 40 foot redwood trees seem to be showing signs of stress from the continuing drought. While it gets just as much water from my garden irrigation as it did pre-drought, I now am noticing that various branches are showing needle die-back. Can you tell me what's wrong? Is it the drought or something else affecting the tree? And if it's something else, what is it and what should I be doing to correct it and bring back the trees to full health?
We have completed our research. The symptoms are consistent with the types of water stress we are seeing on redwoods in the central parts of the county where redwoods are not well-adapted. Under the microscope, there also appeared to be some fungus, but not the aggressive type that would cause a serious problem in your trees. More likely the fungus, in an opportunistic way, came into the needles that were already dying from the drought stress. No treatment is advised or necessary, other than good cultural care of the trees.
The best course of action is to follow the advice you received while visiting us last week: making sure that you water the trees out at the dripline and beyond during the warm, dry summer and fall months prior to the rainy season. Avoid watering near the trunk which can predispose the trees to rot. Redwood trees will compete with each other if planted closer that 7 feet apart, increasing their water needs. Water stressed trees should not be fertilized. As long as the needles are green and growing during the spring and summer, fertilizer is probably not needed.
Also, as noted above, during the drought, the MGCC Help Desk has fielded many questions and concerns about redwood trees. A previous blog responded to many of your and others' concerns, especially with advice on irrigation, at http://ccmg.ucanr.edu/HortCoCo/?blogpost=19256&blogasset=12496. Your perusal of the advice and recommendations should help you determine the necessary steps to make your redwood trees healthy again.
I hope that your trees will become healthier ithis spring after all this good rain we are having along with the possibility of supplemental irrigation over the non-rain periods. Please let us know if you have any more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (JL)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).