Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: mandarins

Hot Mandarins. What to Look forward to After a Fire

Mandarins, also known as “zipper skins” and “easy peelers” can have very fragile peels/skins/rinds/exocarp that make them easily subject to more damage than most oranges and lemons. Some are a bit tougher skinned than others, but some are so fragile that any rough handling often prevents them from going through conventional packing operations.

These skins were recently put to the test in the recent fires in Ojai. There was a mix of different varieties - ‘Pixie', ‘Gold Nugget', ‘W. Murcott', ‘Yosemite Gold', ‘Tahoe Gold' and others. Some of them were more sensitive than others, some were closer to the fire, all were affected by smoke to some degree. In Matilija Canyon where smoke was present for many more days than in the east of the Ojai Valley and possibly more ash, the trees have started flowering sooner. That might be temperature difference, either cooler or warmer, so it is hard to say how much effect the smoke has had versus, the ash and/or heat. Smoke has many different gasses in it, one of which is ethylene which is a naturally occurring ripening agent. Smoke not only has gasses, but it occludes the sun so less or more or altered light might have an effect on these fruit. It's not a controlled experiment, so some little scientist is going to have to come along and wriggle out these different effects. Whatever. Fire and smoke have an effect on mandarins as we have seen in other crops, such as cherimoya, avocados and other citrus.


Heat damage. Fruit facing the fire.


Ash effects on fruit coloring. Fruit was covered with ash for several days until rain washed it off. Might be a pH effect (ash is alkaline), temperature effect, uneven light radiation, or other…….


Same sort of uneven coloring, that actually looks like an ashy color, but the ash has washed off the cluster by rain


And here's something interesting where fruit facing the fire is much lighter colored than fruit facing away from the fire. Here are two pieces of fruit, one from the side directly facing the fire, and the other from the other side of the tree. The side of that fruit facing the fire was also lighter colored. So, it had an effect through the canopy (small tree). The canopy was otherwise intact, unaffected heat or flames.


Oh yeah, and there is the characteristic fruit drop from either the heat, smoke gases, water stress or ….


And then there's the fruit that looks like it had actual embers on the skin.

If the tree survives and keeps its green leaves, sometimes the fruit is affected in ways that don't appear for a while. The peel may be affected, but in many cases the fruit is just as sweet as it could be. It just looks terrible. That might even be a selling point. "Here have a wonderous piece of history that braved the horror of the Ojai fires."

Posted on Wednesday, March 7, 2018 at 6:38 AM
Tags: abiotic (13), citrus (338), damage (24), fire (30), fruit (18), heat (6), mandarins (5), postharvest (4), smoke (2), stormy (1)

Satsumas and Navels - Too Late?

There have been some complaints about satsuma mandarin fruit having problems. These are prone to a rind/skin/peel breakdown when the fruit is not picked promptly. It's not clear what the cause is - wet winter, warm winter - but it is less of a problem if the fruit is picked when it is mature. A lot of the time in southern California, satsumas will develop good flavor and sweetness, but for lack of cool weather, they don't turn bright orange, a hallmark of the fruit. So growers will leave the fruit on longer, hoping for color, but the fruit becomes over mature, and more susceptible to breakdown. This weakening of the peel then opens it up to infection by fungi, such as Alternaria. In warm winters, the peel matures more rapidly and is more susceptible. Early maturing varieties like ‘Okitsuwase' are especially prone to breakdown later in the season, since their rind matures earlier. They end up being a mess, as can be seen in the photo below.

Navels can have a similar problem in these winters with erratic rainfall. Common wisdom is you don't irrigate in the winter, right? Wrong. With no, low and widely spaced rain events, the tree roots dry out, and rewet with rain. Navels are building their sugar in the winter and they become suction balls for water as the sugar increases. The fruit will continue to grow as the tree takes up water. When the roots run out of water, and then are suddenly rewetted during this period, the fruit can suck up water so rapidly that the skin cant expand fast enough and will split. So this is what happens with uneven irrigation or rainfall this time of year.  One of those abiotic problems in citrus.

satsuma rind breakdown
satsuma rind breakdown

split navels
split navels

Posted on Monday, February 26, 2018 at 7:10 AM
Tags: abiotic (13), citrus (338), mandarins (5), navel (11), orange (69), peel (2), rind breakdown (1), satsuma (2), skin (1)

Citrus Grower Meeting Coming Soon

Every year growers get together to learn what is being done in the citrus research world that could affect their operations. This June, University of California and the Citrus Research Board are bringing some good talks to three different growing areas. All growers are invited, but RSVPs are appreciated.


CRB-GrowerSeminar-Flyer 2017
CRB-GrowerSeminar-Flyer 2017

Posted on Friday, May 19, 2017 at 6:13 AM
Tags: ACP (86), alternate bearing (5), breeding (4), citrus (338), disease (57), fertilizers (6), grapefruit (27), huanglongbing (66), irrigation (80), irrigation (80), lemons (9), mandarins (5), nutrition (5), oranges (6), pests (25), tangerines (1)

The Citrus Research Board and Growers

Funding of the Citrus Research Board is an investment in pertinent research that supports the industry, making the information accessible to all within the industry from pest control advisors to packing houses to farm managers and others within the industry. The goal is to get the research done and then make sure it is used.  CRB represents both large and small growers throughout California.

CRB research programs are funded by grower assessments which attract both federal and state funding, funding which represents a third of the total budget. This funding is used to support such projects as, HLB-resistant citrus rootstocks; the development of effective, low-cost HLB early detection technologies to rapidly remove infected trees; improved biocontrol methods for specific insect control like Asian citrus psyllid, as well as others; pre-and post-harvest citrus research to maintain export markets, amongst many other research programs.

The Citrus Research Board also supports the Citrus Clonal Protection Program (CCPP) with the goal of insuring the safe introduction of citrus varieties, disease diagnosis and pathogen elimination of introduced varieties and the maintenance and distribution of introduced varieties. CCPP serves as the primary source of clean, disease-free budwood and new varieties from Florida. This work is a collaboration between the Citrus Nursery Board, the University of California and State and Federal Regulatory agencies.  The CCCP has become a major hub of the National Clean Plant Network for Citrus, resulting in the collaboration with 10 citrus centers in nine states and territories with multimillion dollar funding in support of CCCP's operations.

CRB research supports the California Citrus Quality Council (CCQC) with the primary objective of ensuring that California citrus meets domestic and international phytosanitary, food safety, food additive and pesticide residue regulations. CCQC ensures that California citrus growers have access to export markets for their fresh citrus fruit.  Exports represent a third of the California citrus grower profits.

CRB-funded research into the California citrus-breeding program has led to the development of the Tango mandarin, along with others. The core breeding program conducts yield trials throughout the state on all varietal types to give growers information on upcoming new varieties and rootstocks.  There is ongoing work to incorporate molecular tools to expedite breeding efforts to find plant materials resistant to HLB.

Along with CRB funding for cutting-edge projects for pest and disease control strategies, the CRB-funded CORE IPM Program led by Beth Grafton-Cardwell has responded to citrus grower needs for modifying existing spray schedule to treat Asian citrus psyllid. The program evaluates rotational sprays at appropriate times to avoid pesticide resistance to ACP.

Finally, this CRB-packaged information has been extended to growers through programs, including: The California Citrus Conference, Post-Harvest Conference and Seminar, and Regional Grower Education Seminars. CRB-funded research is compiled in Citrograph Magazine, the only magazine dedicated solely to the California citrus industry.

citrus and mountains
citrus and mountains

Posted on Wednesday, April 12, 2017 at 6:01 AM
Tags: ACP (86), Asian Citrus psyllid (57), citrus (338), citrus greening (13), extension (1), grapefruit (27), HLB (71), huanglongbing (66), kumquats (1), mandarins (5), ornages (1), research (3)

Area-wide Asian Psyllid Treatments in Ventura

On Aug. 30, Ventura County's citrus growers, pest-control advisers (PCAs) and pest-control operators (PCOs) embarked on the most ambitious program of Asian citrus psyllid suppression in commercial groves ever undertaken in California. The program involves coordinated pesticide treatments across more than 15,000 acres of citrus in the Santa Clara, Las Posas and Santa Rosa valleys. Hundreds of growers, PCAs, PCOs, grove managers and packinghouse field staff — aided by our county's two grower liaisons and the local ACP-HLB Task Force — are working together to pull it off.


This is the second cycle of area-wide management (AWM) treatments in Ventura County. The first was carried out from January through March in the east end of the Santa Clara River Valley. It involved eight of the county's 49 psyllid management areas PMAs and achieved good compliance, with 87 percent of the total acreage being treated (the rate within individual PMAs ranged from 80 percent to 93 percent).


The current cycle, however, involves 36 PMAs, vastly increasing the program's complexity. It also increases the workload for our PCAs and PCOs, and amplifies the consequences of any disruption in the timetable, which requires that all the citrus in each PMA be treated within a narrow two-week window.


And disruptions are precisely what the program has encountered. The extended periods of extreme heat that have cooked the county over the past two months have idled equipment and crews. At the same time, explosions of other pests — particularly broad mite, flaring under the unusually tropical conditions — have diverted resources to non-ACP treatments to avoid immediate economic harm from damaged fruit.


It remains to be seen whether the crews will be able to get back on track, and finish the fall AWM cycle by the end of November as planned. There is also the chance the applicator crews will encounter further delays, either in the form of extreme heat, Santa Ana winds or early rains associated with the strengthening El Niño condition in the Pacific.


As I have reminded members of Ventura county's citrus community numerous times since we began planning the transition to AWM, our program at this stage is a huge experiment with statewide ramifications.


We can't really draw lessons from areas outside California that are attempting area-wide suppression efforts (Texas and Florida) because their circumstances are so different. We have different weather and topography, for one thing. And Florida in particular did not even try to control ACP until most of the state was also infected with Huanglongbing (HLB) disease, so their program has struggled from the start. Our landscape is also quite different, with none of the giant citrus plantations of Florida and a much more complex pattern of intermingled smaller orchards and urban development than anything seen there or in Texas.


We also have little in common with the few other areas in California that are trying to implement AWM (mainly portions of Imperial and San Diego counties) because we have far more acreage and a much greater number of growers. Eventually, the San Joaquin Valley will find itself implementing AWM, at which point California will finally have an AWM program exceeding ours in scale. The very slow pace of ACP detections there, however, suggests that day is still well in the future.


For now, we have to figure out what works — and what doesn't — on our own. Trying to craft policies and protocols while also attempting to implement them is a bit like trying to build a race car while speeding down the track at 200 mph, but we have no other choice. Think of it as “adaptive management” on steroids.


There have been some very productive discussions among members of the Ventura County ACP-HLB Task Force and our hard-working PCA/PCO community, identifying data needs, logistical constraints and strategy options so we can continuously refine and improve the program. One of our chief challenges is adjusting for our equipment and spray crew limitations while still achieving effective ACP suppression, even when the weather and other pests refuse to cooperate.


One piece of very good news that has emerged at the midpoint of our fall AWM cycle is that the California Department of Food and Agriculture has been conducting timely treatments in urban yards within 400 meters of commercial citrus in each PMA. That did not happen last winter, and the result was swift re-infestation of commercial groves from ACP populations in neighboring landscape plants. At our request, and to CDFA's credit, the agency changed its policy and is no longer waiting to determine the level of grower participation before commencing those treatments.


Countering that, however, are scattered reports of growers refusing to participate — some even going so far as to switch packinghouses in order to avoid the policy instituted by responsible houses to suspend picking and packing fruit from an orchard during the PMA treatment window until the treatment has been conducted.


Evading the treatment requirement is irresponsible and fatally short-sighted. We know for a fact that HLB is less than 50 miles from us, and we also know for a fact that ACP from areas to the south — potentially even infected psyllids — is being transported into Ventura County in loads of bulk citrus. Just recently, a psyllid that tested “inconclusive” for HLB — neither positive nor negative — was collected in Piru. It may be a false alarm, and additional testing of psyllids at the same site will be conducted, but when clusters of such ACP have been found in the past, they have indicated locations where trees soon test positive for the disease.


Holdouts in the Ventura County citrus community must stop thinking of the ACP campaign as a battle against a bug, like so many other battles the industry has fought and won in the past. It is not. Ventura County citrus has never before confronted a tree-killing, insect-vectored disease epidemic, and the tools and strategies of conventional pest management will not stop or control it.


Save the date


To help Ventura County's citrus community better understand the nature of the epidemic — and the bitter lessons from Florida's failure to address it proactively — Farm Bureau and the ACP-HLB Task Force will host a workshop on Dec. 2. As speakers, we've invited three experts whose presentations were among the most compelling at last February's International Research Conference on HLB in Florida:

  • Mike Irey, director of research and business development for Southern Gardens Citrus (which farms nearly 15,000 acres of oranges in Florida), who will speak about conditions in his state and provide an industry perspective on what it's like to live with HLB for a decade;
  • Dr. David Bartels, an entomologist at the U.S. Department of Agriculture's Mission Laboratory in Texas, who will discuss his analysis of HLB survey data and what it can tell us about possible HLB infection sites throughout Southern California;
  • Dr. Neil McRoberts, an epidemiologist and associate professor of plant pathology atUC Davis, whose computer modeling and research into the economic and social factors affecting disease spread can help guide development of an HLB management strategy for California.


The workshop will be from 1 to 4 p.m. on Wednesday, Dec. 2, at the Museum of Ventura County, 100 E. Main St., Ventura. It's free, but RSVPs are required. Please contact us at or (805) 289-0155 if you plan to attend.


— John Krist is chief executive officer of the Farm Bureau of Ventura County. Contact him at

ACP nymph wax
ACP nymph wax

Posted on Tuesday, October 27, 2015 at 4:46 PM
  • Author: John Krist
Tags: grapefruit (27), huanglongbing (66), lemons (9), limes. psyllid (1), mandarins (5), oranges (6)
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