Lemon Scions and Lemon Rootstocks Workshop & Field Tour
October 17, 2019
Visitors Center, Limoneira Co., 1141 Cummings Rd, Santa Paula, CA 93060 View map/directions here
Contact: Ben Faber, 805-645-1462, firstname.lastname@example.org
Which Way Lemon Industry?
What are Lemon Rootstock Choices?
What are Lemon Scion Choices?
How are they Complementary?
What are their Effects on Yield? Fruit Quality? Canopy Growth? Soil Compatibility? Tree Health?
HLB Tolerance? Maybe We Know a Little.
How do Scions and Rootstocks Compare in the Desert, Valley and Coast?
Come Learn this and more. Tour a Scion/Rootstock Trial
Mike Roose, UC Riverside Citrus Breeder
Tracy Kahn, UC Riverside Curator Citrus Collection
Glenn Wright, University of Arizona Citrus Extension Specialist
Ashraf El-Kereamy, UC Riverside Citrus Specialist
According to the latest USDA Foreign Agricultural Service GAIN Report (Global Agricultural Information Network), the European Union is still a major citrus producing area. EU citrus production is concentrated in the Mediterranean region. Spain and Italy represent the leading EU citrus producers, followed by Greece, Portugal, and Cyprus. For MY (October/September) 2018/19, Post expects overall citrus production to grow mainly in Spain due to favorable weather conditions. The quality of the fruit is forecast to be excellent and EU domestic consumption of citrus may stay flat in 2018/19.
EU lemon production is forecast to grow 10 percent and is stable compared with previous estimates. The overall growth is due to the strong production rise expected in Spain, the largest lemon EU producer. According to the latest data from the Spanish Ministry of Agriculture, Fisheries, and Food (MAPA), Spain's 2018/19 lemon production is forecast at 1.1 million MT, an increase of 19 percent compared to the previous year. Favorable weather conditions resulted in good flowering and fruit setting. In addition, in recent years Spain has increased its total planted area for lemons. Fruit quality is forecast to be excellent. ‘Fino' lemon is expected to increase by 14 percent due to the entry of new plantations over the last years. ‘Verna' lemon is expected to rebound; increasing by 90 percent as production of ‘Verna' lemon in the previous season was shorter than normal levels. Spain will continue to consolidate its leading commercial position in Europe with quality and phytosanitary guarantees. Following Argentina, Spain is the second largest lemon producer in the world but the first global exporter of lemons for fresh consumption. Spanish lemon production is concentrated in the regions of Murcia and Valencia, and the Provinces of Malaga and Almeria in Andalusia. ‘Fino' and ‘Verna' are the leading lemon varieties grown in Spain, accounting for 70 and 30 percent of the total production, respectively. The ‘Fino' variety is predominantly used for processing.
So far, Asian Citrus Psyllid and HLB are not a problem in the lemon producing areas of Spain and Italy. Read more about the citrus industry in the European Union – oranges, grapefruit, mandarins, fresh, processed, policy, export issues, MRLs and tariffs. Fascinating stuff and the potential impacts it has on California growers and production.
And what about what's going on in the Moroccan citrus world, right next door to Spain?
Voluntary Best Practices for Growers' Response to Huanglongbing
To provide California citrus growers with a strong toolbox of science-supported strategies and tactics to protect their orchards from Huanglongbing, the Citrus Pest & Disease Prevention Committee endorsed a set of best practices for growers to voluntarily employ in response to HLB in California.
The recommendations – which are grouped based on a grower's proximity to an HLB detection – represent the most effective tools known to the citrus industry at this time and are meant to supplement the California Department of Food and Agriculture's required regulatory response. They were developed by a task force consisting of growers from various regions across the state and scientists, including Dr. Beth Grafton-Cardwell and Dr. Neil McRoberts.
Growers are encouraged to use as many methods as feasible for their operation in order to limit the spread of the Asian citrus psyllid (ACP) and HLB, as the cost to manage the Asian citrus psyllid is far less than any potential costs or loss to the industry should HLB take hold throughout our state.
The Best Practices at a Glance
The complete best practices document, which includes the scientific rationale for the best practices, can be downloaded here. The following grid is intended to provide a brief, digestible format of the best practices.
What about Planting Lemons in Kern County?
By Craig Kallsen, UC Cooperative Extension Advisor, Kern County
Kern County is located at the southern end of the San Joaquin Valley of California. Over the past couple of years, I, as the citrus Farm Advisor for the University of California Cooperative Extension in Kern County, have received an increasing number of enquiries about the feasibility of growing lemons here. The answer is “yes” we can grow lemons here and according to the latest Kern County Agricultural Commissioner's Report (2017) we have 4010 acres of bearing and 10 acres of non-bearing lemons in the county. Those 10 acres of non-bearing lemons indicate that fairly recently someone decided lemons were the way to go.
These inquiries as to the feasibility of growing lemons are understandable. The price and demand for lemons in the U.S. and worldwide is increasing. Depending upon where you get your statistics the retail prices of lemons was something like $1.50 per pound from 2011- 2013 to something like $2 a pound from 2015 – 2017. The statistics show 2018 was even a better year for selling lemons. Consumption of lemons in the U.S. was less than 1 million metric tons in 2011 to about 1.25 million metric tons in 2017. Worldwide consumption has increased from about 4.5 million metric tons in 2011 to 5.5 million metric tons in 2017. If you add in other factors such as a heat wave, which, for example, hit Ventura County production hard in July 2018, or extreme winter freeze events, and sometimes-erratic supplies from other lemon producing areas of the world, prices can skyrocket 40% or more in a month. Being able to sell a carton of lemons for excess of $55 can be very attractive to prospective growers. Not surprisingly, if you compare the cost and returns of growing lemons with those of oranges, a person might wonder why anybody would choose producing navels over lemons (see https://coststudies.ucdavis.edu/ ).
Planting lemons is riskier. In the San Joaquin Valley, the major consideration is the greater frost sensitivity of lemons as compared most other citrus crops. Not only do lemons freeze at a higher temperature, so do its branches. A freeze, which can spoil orange or mandarin production for a year, can devastate lemon production for three years due to increased damage to the lemon canopy and the older branches of that canopy. If your tree freezes back to the major scaffold branches, you are out of business for a while. An important question is how often does it cold enough to destroy my lemon production capacity for three years or more? Industry wide, for the last 30 years we have had three freezes where lemon leaf canopies, even in the warmer areas of Kern County, were severely damaged – December 1990- January 1991, December 1998, and January 2007. Not to be an alarmist but, in looking at these dates, it would appear that we may be overdue for an extreme freeze. We flirted with one in early December of 2013. Over the years, I have noticed that as the time interval increases from the previous frost event, citrus orchards move further and further down onto the valley floor, only to retreat to higher ground after the next severe event.
Well, what about global warming? Shouldn't Kern County be getting to be a safer place to grow lemons? In answer, predictions can be difficult, and according to baseball legend Yogi Berra, this is especially so if they are about the future. Winter air temperatures have been climbing over the past 30 years in the southern San Joaquin Valley. With our Mediterranean climate in the SJV, most of our rain falls during the fall and winter. Drought years, which means drought winters, have become more common. The higher winter temperatures are good news for citrus growers, but the droughts have been bad news in that dry air in not conducive for fog formation. Fog, historically, is our winter blanket, that holds temperatures above freezing when conditions are ripe for rapid drops in temperature associated with clear, windless nights following cold fronts that move into the valley from Alaska and other points north.
The risk in growing lemons can be mitigated. As with any real estate endeavor, the three most important factors governing the value of a prospective lemon property are location, location and location. When we are talking about cold temperatures, we are talking about nighttime low air temperatures. Daytime winter temperatures, once we get into mid-morning, usually, are more than warm enough to keep lemons from freezing. The major mitigation factor under human control is to plant lemons in the areas of Kern County that have the warmest nighttime temperatures. These areas tend to be on the lower slopes of the foothills on the eastern and southern areas of the SJV. Cold air is much heavier than warm air and runs like a river downslope. Good cold drainage is necessary. If lemons are planted too far out onto the valley floor, they end up at the bottom of a lake of cold air during late fall and winter freeze events. The area where citrus is grown, often, is referred to as a belt along the lower foothills of the SJV. Not only is this belt characterized by more fog than higher up in the foothills, but also it is close to the atmospheric inversion layer that forms in the SJV during the winter. The SJV is at the bottom of a large deep bowl formed by surrounding mountain ranges, and the depth of this bowl makes the air more difficult to disturb by wind. This still air, on cold, clear nights during the winter, allows heat radiating into the sky from the ground to warm a layer of air, usually located from 500 to 1000 feet above the valley floor. The idea of using wind machines successfully is to move this layer of warm air down to the trees on the ground. If you are down on the valley floor, on most nights the warmer air is way too high up to bring it down to the ground with wind machines. If an orchard is 500 feet above the valley floor on the side of a foothill, you might already be in the inversion layer and won't even need to start your wind machines, or at worst, the inversion layer is close enough to bring that warm air down to the trees with wind machines. Unfortunately, the amount of land winter-warm enough for growing lemons in the foothills is very limited, and, currently, is occupied by other crops, probably citrus. We cannot grow lemons too high up in the foothills, because these areas are above the inversion layer and winter temperatures there will always be too cold for lemons. Kern County, in general, appears to be colder than its neighbor Tulare County to the north, and usually suffers more in terms of fruit and tree losses during extreme frost events.
Those bold enough to grow lemons appear to have more choices on which lemon to grow now than in the past. Some newer seedless or lower-seeded lemon varieties are available (https://citrusvariety.ucr.edu/ ). The Lisbon lemons, of which there are several selections, is an old Kern County standby, and appears to have better frost tolerance than the Eureka, commonly grown in the central and southern coastal areas. The Improved Meyer lemon is a hybrid, apparently, with citron, mandarin and pummelo heritage, and has excellent frost tolerance. However, the fruit does not hold up well on the tree, in storage or ship very well, and few commercial groves exist. It remains a very popular and successful backyard tree for homeowners.
With the threat of the Asian Citrus Psyllid (ACP) and the Huanglongbing disease it spreads, the feasibility of growing citrus under protective screens (CUPS) is under investigation. These protective screens, in addition to keeping ACP out, would likely provide additional frost protection as well.
The other obvious concern related to the number of enquiries I have received, is that even if lemons are not widely grown in Kern County now, worldwide demand suggests that there are likely many new acres of lemons in the ground now or in advanced planning stages in other locations in California, Arizona and the world. In the past, we have seen the acreage of a number of crop commodities rise and fall with the laws of supply and demand. We have planted and then pulled lemons in Kern County before based on market conditions. At some point, even unfrozen lemons will not sell if there are too many out there.
Figure 1. Frozen mature lemon trees in photo background, after the 1998 freeze in the Edison area of Kern County. Juvenile, undamaged navel orange trees in foreground (photo by Craig Kallsen).
One of the major challenges facing citrus integrated pest management (IPM) in California is the recent, sharp increase in the acreage of mandarins being planted. The current citrus IPM guidelines have been established from years of experiments and experience in oranges, with no specific guidelines for mandarins. In the absence of research into key arthropod pest effects in mandarins, the assumption that the pest management practices for oranges appropriately transfer for optimal production in mandarins has not been tested. We used a data mining or ‘ecoinformatics' approach in which we compiled and analyzed production records collected by growers and pest control advisors to gain an overview of direct pest densities and their relationships with fruit damage for 202 commercial groves, each surveyed for 1–10 yr in the main production region of California. Pest densities were different among four commonly grown species of citrus marketed as mandarins (Citrus reticulata, C. clementina, C. unshiu, and C. tangelo) compared with the standard Citrus sinensis sweet oranges, for fork-tailed bush katydids (Scudderia furcata Brunner von Wattenwyl [Orthoptera: Tettigoniidae]), and citrus thrips (Scirtothrips citri Moulton [Thysanoptera: Thripidae]). Citrus reticulata had notably low levels of fruit damage, suggesting they have natural resistance to direct pests, especially fork-tailed bush katydids. These results suggest that mandarin-specific research and recommendations would improve citrus IPM. More broadly, this is an example of how an ecoinformatics approach can serve as a complement to traditional experimental methods to raise new and unexpected hypotheses that expand our understanding of agricultural systems.