- Author: Michael Hsu
Growers, UC Cooperative Extension researchers offer guidance on producing high-quality olives
Facing a deluge of lower-price products from Europe, the California olive oil industry is doubling down on its clear-cut competitive edge: the consistent and bona fide quality of its oil.
“Olive Production Manual for Oil,” a new book published by University of California Agriculture and Natural Resources, aims to help California olive growers maximize that advantage.
“It's a tough market to compete in, but I think the way to win for California is to compete on quality,” said book co-editor Selina Wang, a UC Cooperative Extension specialist in the UC Davis Department of Food Science and Technology. “The quality of California olive oil is unmatched, but you can't make good quality olive oil with bad fruit, so the goal is to get more fruit from the trees – and for the fruits to be high-quality fruit.”
The 273-page manual, available for purchase online, is the first of its kind in the U.S. While some parts of the book are specific to California (which grows nearly all of the olives for domestically produced olive oil), most of the material would be useful to producers in other states, Wang noted.
“Through our conversations with growers, it became clear to us that a manual like this – not a scientific publication but a manual that is easy to follow, written in language that is accessible, and with pictures and illustrations – would be really helpful to the growers,” she said.
Growth of California olive oil industry necessitated creation of manual
Aside from a book focused predominantly on table olives and another on organic olive production (by UCCE farm advisor emeritus Paul Vossen), there was no one-stop, comprehensive resource on the bookshelf for oil olive growers. The need for such a manual had become more acute as oil olives replaced table olives in California orchards during the last 20 years.
Whereas harvesting by hand was historically cost-prohibitive, the introduction of super-high-density planting systems in 1999 made oil olive production more economically feasible. Mechanical pruning and harvesting of new cultivars (Arbequina, Arbosana and Koroneiki) – specifically bred for these densely planted orchards – led to the rapid expansion of oil olives in the state. According to a U.S. Department of Agriculture report, California olive oil production jumped from 2 million pounds in 2006 to an average of 21 million pounds in 2021–23.
With about 37,000 acres of oil olives planted across California, the Olive Oil Commission of California saw the need to support the production of this manual. Championed by Dan Flynn, founder and executive director emeritus of the UC Davis Olive Center, Wang and co-editor Louise Ferguson outlined the contents of the book. They then sought out a mix of growers and industry professionals and UCCE advisors and specialists to write its chapters.
“Most of the information is data-based, from people who are working with the olives,” said Ferguson, a UC Cooperative Extension pomologist at UC Davis. “This is the first data-based olive oil production manual we've had.”
Manual infused with firsthand insights, practical recommendations
Hard-earned experience taught growers a valuable lesson that is conveyed in the book – the need to hand-prune. While mechanical pruning helps control the size of the trees, some hand-pruning is still required to allow light to filter to the leaves. Failing to do so leads to a dramatic decrease in yield.
“That happened in many of the orchards that were inexperienced in these new cultivars and new super-high-density planting systems,” Ferguson said.
She added that other key topics in the manual include irrigation management in a water-constrained state, nitrogen management, harvest timing and orchard site selection. Choosing a good spot for planting is crucial in this era of extreme climate volatility, Ferguson noted, as olive trees are significantly affected by temperature shocks in spring (fruit set) and fall (harvest).
For Wang, another overarching theme in the manual is the importance of testing. Testing the soil, water and leaves provides critical data that growers can use to adjust their inputs and production practices for optimal profitability.
“You may spend a couple hundred dollars on the lab work, but it will pay off, for sure – you're going to increase the health and productivity of your trees,” Wang explained. “Oil olive growers are paid based on the oil content in their fruit; you not only want to have a lot of fruit on the trees, you want to make sure that your fruit are accumulating oil.”
California oil olive growers, practices continue to evolve
Wang and Ferguson hope their book will help California producers compete more effectively in the global marketplace. Currently, about 90% of the olive oil consumed in the U.S. is imported from Mediterranean countries, due primarily to the lower price point. In that region, producers tend to harvest riper olives that produce oil at a greater volume but lesser quality.
In contrast, California growers harvest earlier and produce oil that is higher quality (with more flavor and more antioxidants) and far exceeds accepted standards for “extra virgin olive oil.”
According to Wang, California olive oil mills have nearly maximized their efficiency, and the growth opportunity for the industry is in the orchards: to optimize practices to produce more fruit, and to plant more trees. Wang said the new manual can help on both fronts.
“Just like for other crops, focusing on quality – while increasing efficiency and productivity, and therefore profitability – is the name of the game,” she said.
Ferguson also stressed that knowledge continues to evolve and urged growers to reach out to the editors and chapter authors with their experiences.
“Most of the authors are in California and they're working,” she said. “So if you start to notice things that are different, or you want more information or something is not clear, the authors are available.”
The manual can be purchased at https://anrcatalog.ucanr.edu/Details.aspx?itemNo=3559.
/h3>/h3>/h3>/h3>- Author: Penny Leff
Yesterday I was an agritourist. Pamela Marvel and Stuart Littell, owners of Grumpy Goats Farm, in the Capay Valley of Yolo County, invited me to be part of their annual olive harvest, joining the "friends and family" contingent and picking alongside a hired picking crew. Grumpy Goats is a twenty acre organic farm planted with multiple varieties of olives that are pressed into prize-winning extra virgin olive oil. For me, the day was an adventure. I got to enjoy a sunny fall day being part of an ancient rite of the season, and I got to spend a few hours with some people whose paths don't often cross my own.
Being a guest, I didn't arrive until 9:30 or so, after a beautiful drive through the surrounding farm land. Stuart was there to meet me, introduced me to the other friends and family, and offered me coffee and pastries. With my own picking basket strapped on, I started picking. The young trees were soft and kind, giving their fruit easily with a gentle pull. Even the lowest branches almost dragging on the ground bore olives to harvest. The rhythm was easy on the body - no ladders to climb and lots of trays close by to dump olives when the picking basket began to get heavy. The crew of men and women worked fast around me, and I learned by watching. The other family and friends guests and I tried to keep up, and talked as we picked.
After a few hours it was lunch time. Stuart and Pamela put on lunch for the "family and friends", while the crew gathered to eat by their vehicles or in the shade of the trees. We talked and ate and enjoyed the pleasant day, learning more about each others' lives. Then it was time to go back to picking. This time I joined in with the hired crew, trying not to get in their way.
I thought of the election earlier this week. I thought of our new president-elect and the fearful changes that might be coming for this kind woman and her family and her friends. I wondered what harvest day would be like for Stuart and Pamela next year, or the year after. This agritourism adventure connected me briefly to people whose kindness and friendliness I hope to be able to repay before too long.
UC Agricultural Issues Center has released two new studies on the cost and returns of growing olives in the Sacramento Valley. One study focuses on producing table olives with the Manzanillo variety. The other study focuses on establishing a super-high-density orchard and producing olives for oil, using the Arbequina variety.
The cost analyses are based on hypothetical farm operations of well-managed orchards, using practices common to the region. Growers, UC ANR Cooperative Extension farm advisors and other agricultural associates provided input and reviewed the methods and findings of the studies.
The authors describe the assumptions used to identify current costs for the olive crop, material inputs, cash and non-cash overhead. A ranging analysis table shows profits over a range of prices and yields. Other tables show the monthly cash costs, the costs and returns per acre, hourly equipment costs, and the whole farm annual equipment, investment and business overhead costs.
The new studies are titled:
- “Sample Costs to Produce Table Olives in the Sacramento Valley – 2016”
- “Sample Costs to Establish a Super-High-Density Orchard and Produce Olives for Oil in the Sacramento Valley – 2016”
Free copies of these studies and other sample cost of production studies for many commodities are available. To download the cost studies, visit http://coststudies.ucdavis.edu.
The cost and returns program is associated with the UC Davis Department of Agricultural and Resource Economics and the UC Agricultural Issues Center, which is a statewide program of UC Division of Agriculture and Natural Resources.
For additional information or an explanation of the calculations used in the studies, contact the UC Agricultural Issues Center at (530) 752-4651 or Jeremy Murdock at jmmurdock@ucdavis.edu.
About 16 years ago, well before I was a Master Gardener, I planted my first olive trees. My goal was simple. I wanted to block the view of a neighbor's collection of old non-working cars, trucks, boats and various other treasures.
My decision-making process was also simple. I was walking through Home Depot one day, saw nine Manzanilla olive trees in 15-gallon pots, thought olive trees were cool, so I bought them, took them home and planted them.
What have I learned from this experience? First, I'm a lucky person. All of my olive trees are alive and well despite being cared for by a former Midwestern with zero knowledge of olive trees. However, in the intervening years, I've learned a bit about them.
Did you know that some types require a pollinizer to produce olives? My Manzanilla trees did not produce much fruit until I planted two Picholine olive trees nearby.
Again, luck played a major role. I was strolling through the Napa Farmers' Market one day when McEvoy Ranch was selling olive trees. I bought two because I had room, and by chance they were Picholines, a pollinizer for Manzanilla.
Pruning slipped by me for the first 10 years or so. The trees grew tall and filled out, which I thought was the goal until I realized I had a jungle with fruit higher that I could reach with a ladder.
Folk wisdom says that olive trees should be thinned enough so that a bird can fly through them. A bird could do this in my little olive orchard only if it were carrying a chain saw.
For the last six years or so, I've been on a pruning rampage. I have reduced tree height to about eight feet, and it is now possible to walk between the trees.
Fortunately, olive trees are forgiving and can handle heavy pruning. Some fruit trees have a narrow window for pruning but not olive trees. I now do a heavy pruning in the winter and prune to shape and to remove suckers and water sprouts all year long. Someday I hope to witness a bird fly through my trees rather than over or around them.
It seems that all trees have an enemy or two, and olive trees are no different. I discovered early on that yellowed leaves with dark spotting and a halo around each spot were suffering from a fungal disease called peacock spot. This fungal disease causes partial defoliation, which weakens the tree and reduces fruit set. The fungus thrives when we get significant fall, winter and spring rain such as we had this past year.
The only preventive measure is to spray your trees with copper fungicide as early as possible after harvest. If you, like me, were lulled into a false sense of security by four years of drought and did not spray last year, there is nothing you can do now about peacock spot other than to hope it doesn't get worse. Note to self: spray this fall.
The major enemy of olive trees in our area is the olive fruit fly. An adult is only about a quarter-inch long, but these critters run in a gang and can ruin an entire crop. Three years ago, none of my olives was acceptable for curing or pressing. They all ended up in the garbage as they were not fit for compost either.
If you have any olive trees, you must take measures to combat the fruit fly even if you don't intend to harvest your olives. Doing nothing is akin to allowing an olive fruit fly hotel and spa to flourish before going on to your neighbors' trees where they will wreak havoc. If you want more information about control, you can find a wealth of information online.
I now have 22 olive trees. I have to say I enjoy them even when they present a problem or two. I find pruning to be therapeutic and the time spent harvesting in the fall most rewarding when I see those buckets of olives awaiting milling or curing.
Workshop: U. C. Master Gardeners of Napa County will hold a workshop on “Growing Olives” on Saturday, July 9, from 9:30 a.m. to 11:30 a.m., at Big Dog Ranch, 1020 Congress Valley Road, Napa. Learn what varieties to plant, where to plant them and how to maximize fruit size and yield. Presenters will also discuss drought tolerance, irrigation, harvesting methods and managing olive pests. On-line registration (credit card only) Mail-in/Walk-in registration (cash or check only).
Guided Tree Walk: Join U. C. Master Gardeners of Napa County for a free guided tree walk through Napa's Fuller Park on Monday, July 11, from 10 a.m. to 11:30 a.m. There is no charge for the walk but registration is recommended as space is limited. Meet at the corner of Jefferson and Oak Streets. Online registration or call 707-253-4221. Trees to Know in Napa Valleywill be available to purchase for $15 each. Cash or check payable to UC Regents. Sorry, we are unable to process credit cards.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
- Author: Jeannette E. Warnert
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.
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.