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Help an oak tree tolerate severe drought

Mulch conserves water around the base of a tree.
National Arbor Day is April 24. With California's continuing drought, many trees are showing signs of water stress. UC Agriculture and Natural Resources tree experts have been hearing from homeowners who are concerned about the effects of the drought on valued oak trees in their landscapes.

“Concern has grown since severely stressed and even dead oak trees are becoming common observances,” said William Tietje, UCANR Cooperative Extension area natural resources specialist based inSan Luis Obispo County. “People are asking, ‘What can I do to help?'”

“Three options come to mind: deep water, mulch or do nothing,” said Tietje. Below, he and Steven Swain, UCANR Cooperative Extension environmental horticulture advisor for Marin and Sonoma counties, discuss the advantages and disadvantages of each option.

Deep Watering

Q: Should oak trees be watered?

If the soil under your oak 12 to 18 inches down is dry and crumbly, the oak is out of water. A deep watering will invigorate the drought-stressed tree. Perhaps it seems ill-advised to water an oak tree during a drought. But think about it a minute. If you lose the oak, you lose substantial aesthetic and property values. Also lost are the many ecosystem services provided by this “keystone” structure, such as shade, soil nutrients, wildlife habitat and biodiversity. These take a very long time to replace.

Q: How do I deep water?

Deep watering of the drought-stressed tree is accomplished by moving a hose under the canopy of the tree during the day for one or two days at a low flow or trickle, such that the water percolates into the soil. Do this once or twice during the summer to early fall with at least a month between watering to allow the soil to dry, reducing the likelihood that fungi will attack the tree roots.

Most any plant-based, commercially available mulch will work.

Q: Why mulch?

A prudent approach to the current drought and the maintenance of tree health is to conserve existing soil moisture as much as possible. Mulching under the tree helps to control moisture by keeping the soil cool and suppressing weed growth. Mulching also adds valuable soil microorganisms.

Q: Does mulch need to be composed exclusively of oak leaves and twigs?

A: No—Although the best mulch is the oak's natural leaf litter, other plant-based mulches can provide a similar benefit. In fact, there may be some advantages to having other plant components in the mulch.

Q: Can commercially available mulch provide the benefits of natural oak mulch?

A: Yes—Most any plant-based, commercially available mulch should be fine, especially mulches that are derived from multiple sources, such as municipal green-waste that has been composted. Composting allows some of the more reactive compounds that may be present in the mulch to be broken down by heat, chemical and biological means. There isn't necessarily a problem with using a single-source mulch (e.g., grape pressings, nitrolized sawdust [nitrolization allows nitrogen to remain available to the plant]), but because single-source mulches lack the variety of densities, chip sizes and nutrient compositions typically found in multiple-sourced mulches, there is a somewhat greater risk of problems using single-source mulches. Commercial compost may be listed as green-waste compost. The best recipe is 1 to 2 inches of compost overlain with 2 inches of coarsely chopped fir, redwood bark or wood, totaling 3 to 4 inches of mulch. Cover the area under the tree canopy at least up to the drip line. Don't mound the mulch against the tree trunk.

Q: Should mulch be mixed into the soil?

A: No—Although the oftentimes repeated advice that mixing mulch into the soil can cause a nitrogen shortage is mostly a myth, there are other reasons for not incorporating the mulch into the soil:

  • The process can cause root damage to existing plants
  • The process can degrade existing soil structure
  • Organic matter breaks down over time, and in the process causes the soils in which it has been mixed to eventually shrink in volume. This is fine in some instances, but it can spell disaster if one has incorporated mulch into soils that were placed beneath sapling trees, for instance. In this case, the soil under the tree will shrink in volume, and the tree will sink into the soil. Water then pools around the base of the tree, and the tree eventually develops root rot.

Because mulches are incorporated naturally into soils by earthworms, springtails, and microorganisms, the benefits of digging mulches into the soil are pretty much balanced by the liabilities. In short, save yourself the work. Put the mulches on the ground and let the earthworms do the work for you.

Q: Is there any mulch that is categorically unacceptable?

A: Common sense should prevail—Coarsely chopped bark, wood and leaves is probably the best composition for a mulch, and that same material composted is about as ideal as one can get. The very best are oak leaf mulches, which exist, but are quite pricey and are typically derived by stripping wild oaks of their natural mulch base. Even less-than-ideal source material, such as eucalyptus leaves or black walnut roots, can be safely used if properly composted.

Q: If oak trimmings and dead leaf fall from native oak trees are used for mulch, is the presence of termites or the spreading of oak bark beetles a concern?

A: No—Termites do not live (for long) in wood chips. They require contiguous, solid wood to form colonies. The spread of termites in wood chips, or even in small branches, is therefore a non-issue. Every spring, summer and fall, oak bark beetles actively hunt stressed oak trees in central coast woodlands, and will find them from miles away. Worrying about spreading any of the various bark beetles that can attack oaks is a little like worrying about getting salt spray at the beach. They've been here for millions of years before us, and they'll likely be here millions of years after we're gone. That said, you may not want to encourage large colonies in your back yard by, for example, stockpiling large amounts of beetle infested firewood right beneath an oak tree.

Doing nothing

If your tree appears healthy, with dense and green leaves over at least most of the canopy, it could be best to do nothing. In other words, “If it isn't broken, don't fix it.” Give proper considerations for the use of water during the current severe drought, and mandatory water-use restrictions, and deep water only if the tree shows symptoms of severe stress.

On the Central Coast, the predominant native oak trees are valley oak and blue oak, which drop their leaves in the winter, and the evergreen coastal live oak. Keep in mind that the two deciduous oaks, blue oak and valley oak, can respond to drought by undergoing leaf browning and leaf fall as early as July. This is a natural mechanism that the tree has evolved for water conservation. The tree is not dead and should be fine. All else considered, mulching that includes a green waste compost as described above could well be the most appropriate solution. Mulch conserves water as opposed to using water for deep watering, and mulching can improve important soil properties.

For more information, visit the UC Cooperative Extension San Luis Obispo County website http://cesanluisobispo.ucanr.edu and the UCANR oak woodland management website http://ucanr.edu/sites/oak_range.

Posted on Friday, April 24, 2015 at 11:11 AM

Can crickets be the new beef?

UC ANR's Mark Lundy says some of the sustainability claims on production of insects for human food have been overstated. (Photo: Kathy Keatley Garvey)
As the world strives to feed its growing population, some have suggested insects could be an environmentally friendly alternative protein source for people. However, research by UC Agriculture and Natural Resources experts on crickets found they don't have the potential to add much protein to the diet after all, reported Mandy Oaklander on Time.com.

For the study, published in the journal PLOS One, the researchers raised crickets on five different diets - corn, soy, grain, food waste and crop residue. They measured the crickets' size and how much edible protein they produced.

“I think the sustainability claims on this topic have been overstated given the current state of knowledge,” wrote UC ANR Cooperative Extension agronomy advisor Mark Lundy in an e-mail to Time. “I'm all for exploring alternatives, and I am impressed by the amount of innovation that has sprung up around insect cultivation and cuisine in the last few years. However, I also think we need to be clear-eyed about what the sustainability gains are and aren't, and focus our innovative efforts and limited resources to where they will have the most lasting impact.”

Lundy conducted the research and published the results with horticultural entomologist Michael Parrella, a professor and chair of the UC Davis Department of Entomology and Nematology. The story generated a great deal of news media coverage, including:

The environmental benefits of eating crickets vs. chicken: It's complicated
Brooke Borel, Popular Science, April 22

Humans Are Ready For Protein-Rich Crickets, But Are Crickets Ready For Us?
Rex Macadangdang, Tech Times, April 19

Crickets can't replace Meat in Human Diet: Study
Luis Georg, Perfect Science, April 18

Turns out, crickets may not be the solution to all of our problems
Lindsay Abrams, Salon, April 17

Crickets aren't ready to replace meat
Pat Bailey, Futurity.org, April 17

Crickets aren't the miracle source of protein
Kathy Keatley Garvey, Phys.org, April 16

Crickets Aren't the Superfood They're Cracked Up to Be
Alissa Walker, Gizmodo.com, April 16

Maybe crickets aren't the food of the future, after all 
Alexis Madrigal, Fusion.net, April 16

Crickets Alone Will Not Save You, Futurist Foodies Robbie Gonzalez, i09/We Come From the Future, April 20

Crickets Are Not a Free Lunch
Entomology Today, April 15

Posted on Friday, April 24, 2015 at 10:55 AM

New olive disease in Italy concerns California researchers

An olive orchard in Italy suffering from quick decline syndrome. (Photo: Rodrigo Krugner)
Olive farmers in southern Italy are dealing with a serious outbreak of olive quick decline syndrome, a new disease with symptoms that include leaf scorching, twig and branch dieback and, ultimately, tree death. In October 2013, the plant pathogen Xyllela fastidiosa was found for the first time ever in Europe and appears to be associated with the disease.

This has California researchers worried and baffled. The bacterium Xyllela fastidiosa has been present in the state for more than 100 years and can sometimes be found in olive trees. Trials conducted by USDA and UC researchers from 2008 to 2011 showed that strains of the bacterium found in California did not cause disease in olives.

“It's complicated,” said Elizabeth Fichtner, an olive and nut crop expert with UC Agriculture and Natural Resources (UC ANR). “The Italians found X. fastidiosa in sick trees, but the causal agent of the disease still remains to be identified by scientists.”

There are different subspecies of X. fastidiosa. In California, X. fastidiosa subspecies fastidiosa causes Pierce's disease in grapevines and almond leaf scorch disease. Another subspecies, multiplex, causes disease in almonds but not grapevines. A possible reason why California olive trees are unaffected by the bacterium is that the genotypes found in Italy belong to a different subspecies named pauca, a subspecies group not known to occur in the United States. Strains of X. fastidiosa subspecies pauca cause a serious citrus disease in Brazil and Argentina. The X. fastidiosa subspecies known from California do not cause disease in citrus.

Fichtner is working closely with USDA researcher Rodrigo Krugner of the USDA San Joaquin Valley Agricultural Sciences Center in Parlier to better understand the potential threat to California olives and keep California growers informed.

Symptoms of olive quick decline syndrome. (Photos: Rodrigo Krugner)
“Of course, we're concerned about diseases impacting olive trees in Italy,” Fichtner said. “From a standpoint of biosecurity, it's very important for us to be aware of the potential introduction of a new pathogen.”

Krugner traveled to Italy to view the olive trees with quick decline symptoms.

“They took me where it all started,” Krugner said. “Trees that were alive had scorched leaves, twig and branch dieback. I have been seeing olive trees in California with similar symptoms since 2008, but in Italy the disease is more severe. It's devastating.”

Surveys led by Krugner, dating back to 2008, showed that, among symptomatic ornamental trees in Southern California, 30 out of 78 were positive for X. fastidiosa.

“In the San Joaquin Valley, only 3 out of 121 were positive despite disease symptoms being the same between trees in the two regions,” Krugner said. “In greenhouse studies in which olive trees were inoculated with X. fastidiosa, the bacteria survived in the plants but produced no symptoms. In time, the bacteria disappeared.”

Krugner said he and Fichtner visited an olive orchard in the Fresno area where the trees were suffering from widespread leaf scorch symptoms and some dieback.

“The entire orchard had symptoms, every tree,” Krugner said. “But all samples were negative for presence X. fastidiosa by molecular tests and culturing.”

One possible explanation for the widespread and uniform distribution of the disease symptoms in the Fresno orchard was over watering and over working the soil, which may have damaged the roots facilitating the invasion of soil pathogens.

California olive growers and landscape managers with olive trees should be on the lookout for olive dieback symptoms. If new incidences of extensive dieback or scorch on olives are found, contact the local UC ANR Cooperative Extension farm advisor to facilitate early detection of potential new pathogens.

“Because of the regular movement of plants and plant materials across international borders, there is a constant flux of organisms,” Fichtner said. “We need to be aware of global trends in plant diseases and the establishment of insects that can spread disease.”

For more information about Xylella fastidiosa and olive quick decline syndrome in Italy, see an overview posted on the UC Berkeley plant disease page.

An initiative to manage endemic and invasive pests and diseases is part of UC Agriculture and Natural Resources Strategic Vision 2025.

Posted on Wednesday, April 22, 2015 at 11:13 AM

UC Irvine gets landscape tree help from UC ANR

UC ANR is helping UC Irvine deal with trees infested with polyphagous shot hole borer.
Hundreds of landscape trees on the UC Irvine campus have been infested with polyphagous shot hole borer, a pest introduced into California from Asia. UCI has assembled a team that includes UC Agriculture and Natural Resources experts to develop a management plan for identifying, removing, treating and replacing the ravaged trees, according to a UCI press release.

Polyphagous shot hole borer has been present on the campus for two to three years. The extent of the infestation  became apparent in the last few months when a significant number of trees began showing severe symptoms. UCI groundskeepers began to more closely examine a number of trees that appeared to be particularly distressed and worked with UC ANR staff to identify PSHB in early 2015.

A team of UCI staff qualified in tree management is receiving training from UC ANR (UC Riverside and UCCE) to properly identify and assess PSHB infestation. The team will monitor all trees on the UCI campus and, with input from faculty and students from UCI's Center for Environmental Biology, make the determination about which infected trees will be removed.

The news release suggests area property owners who suspect their own trees are infested with PSHB contact John Kabashima, UC ANR environmental horticulture advisor at the UC South Coast Research and Extension Center, 7601 Irvine Blvd., Irvine, CA 92618, pshb.ucce.oc@gmail.com.

Posted on Wednesday, April 22, 2015 at 9:27 AM

Fujimoto to receive Bradford–Rominger Agricultural Sustainability Leadership Award

Isao Fujimoto and his daughter, Esumi.
Isao Fujimoto, lecturer emeritus of Community Development and Asian American Studies at UC Davis, has been named the 2014 recipient of the Eric Bradford and Charlie Rominger Agricultural Sustainability Leadership Award for his commitment to California agriculture, rural communities, and social change.

The prestigious award, given each year by the Agricultural Sustainability Institute (ASI) at UC Davis, will be presented at a ceremony at UC Davis on April 23. UC Agriculture and Natural Resources, with its Sustainable Agriculture Research and Education Program, is a partner with ASI.

The keynote speaker at the awards presentation will be Navina Khanna, a UC Davis alumna and leader for food justice in California.

The Bradford–Rominger award honors individuals who exhibit the leadership, work ethic and integrity epitomized by the late G. Eric Bradford, a livestock genetics professor who gave 50 years of service to UC Davis, and the late Charlie Rominger, a fifth-generation Yolo County farmer and land preservationist.

Former students describe Fujimoto as a prophet and “energizer bunny of social change.”

“Isao began advocating for more socially just and environmentally sustainable forms of agriculture over 40 years ago,” said Mark Van Horn, director of the Student Farm at UC Davis. “At the time, it made him quite unpopular in some quarters, but he remained true to what he knew was right.”

In his early days at UC Davis, Fujimoto used the campus's signature red, double-decker buses to transport children of farm workers to school when public bus service was canceled. The incident sparked conversation about the need for the university to focus on California's rural communities, and led to creation of the Community and Regional Development Graduate Program at UC Davis in the mid-1970s.

Fujimoto was also instrumental in starting the Asian American Studies program on campus, and was mentor to many students who have become sustainable agriculture leaders in their own right. Throughout the 1970s, Fujimoto's home served as a local hub for community activism, with projects such as the Davis Food Co-op and the Davis Farmers Market starting out at his kitchen table.

“He has helped countless students understand the world around them and clarify their personal values and principles,” Van Horn said. “Most importantly, his actions have provided lessons and inspiration for those wanting to act upon their values and principles to bring about positive change in the world.”

Like Eric Bradford, Isao Fujimoto is a respected mentor and a consensus builder. Like Charlie Rominger, Fujimoto has consistently stood up for his beliefs, regardless of their unpopularity, and has done so with a kind heart and humble nature.

“The kind of commitment and sense of responsibility that Eric and Charlie had is a pretty remarkable trait,” Fujimoto said. “I find this award set up by the Bradford and Rominger families as a pretty significant marker of change in terms of broadening the scope of agriculture to include being conscious of the environment and using agriculture as a tool for building community.”

Past winners of the award include UC Agriculture and Natural Resource's advisor Rose Hayden Smith, specialist Ken Tate and advisor Mary Bianchi; and UC alumna Kelly Garbach.

Fujimoto will receive the award at the annual Bradford–Rominger Agricultural Sustainability Leadership Award Ceremony which begins at 5 p.m. in the Multipurpose Room at the Student Community Center at UC Davis. Khanna's keynote speech will address, “Claim Your Superpower: Meeting the Moment for a Winning Food Movement.” On April 24, Khanna will meet with UC Davis students to further discuss leadership in the food movement.

This event is free and open to the public. Students are encouraged to attend. Learn more about the award on the Agricultural Sustainability Institute's web site.

For more information, contact Aubrey White at 530-752-5299, abwhite@ucdavis.edu

Posted on Tuesday, April 21, 2015 at 1:47 PM

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