- Author: Ben Faber
Citrus: UC IPM Pest Management Guidelines
|Publication Number: 3441
Copyright Date: Rev. 2017
Length: 234 pp.
Inventory Type: PDF File
|This is a free publication if you access it as a web page or downloadable PDF document.
These official UC-approved guidelines for pest monitoring techniques, pesticide use, and nonpesticide alternatives for agricultural crops are essential tools for anyone making pest management decisions in the field. This 124-page guideline covers citrus fruit.
Updated August 2015.
A hard copy version of these guidelines can be purchased as Publication 3441P.
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- Author: Georgios Vidalakis and Greg Douhan
Department of Plant Pathology and Microbiology, University of California, Riverside, CA 92521-0122, USA. and University of California Cooperative Extension, Tulare County, Tulare, CA 93274-9537
The Citrus Clonal Protection Program (CCPP) has its roots in the 1930s, when Professor H. Fawcett of the University of California (UC), Citrus Experiment Station in Riverside, discovered the graft-transmissible and viral nature of the citrus psorosis disease. In 1956, following a request from the California citrus industry, UC Riverside established the “Citrus Variety Improvement Program” which in 1977 became the CCPP. Today, the CCPP stands as a cooperative program between the United States Department of Agriculture (USDA), the California Department of Food and Agriculture, and the citrus industry of California as represented by the California Citrus Nursery Board and the Citrus Research Board.
Since 2009, the CCPP has also been part of the National Clean Plant Network (NCPN) for specialty crops. The purpose of the CCPP is to provide a safe mechanism for the introduction into California of citrus varieties from any citrus-growing area of the world for research, variety improvement, or for use by the commercial industry of the state or any citrus hobbyist and enthusiast. This comprehensive mechanism includes disease diagnosis and pathogen elimination, followed by maintenance and distribution of true-to-type citrus propagative material. The potential problems resulting from the introduction of pathogens into a country or citrus area cannot be overemphasized. Likewise the need for pathogen-tested citrus propagative materials is recognized as basic to the establishment and maintenance of a sustainable and profitable citrus industry. The presence of graft-transmissible pathogens such as viruses, viroids or bacteria in citrus propagative materials can be deleterious to tree survival and fruit production for both existing and future citrus plantings.
Realizing that the availability of pathogen-tested, true-to-type propagative materials are critical for citrus and other vegetatively propagated crops, three USDA agencies (Animal and Plant Health Inspection Service, Agricultural Research Service, and National Institute for Food and Agriculture) came to an understanding in 2005 to create a national network to support the use of clean propagative materials. The NCPN, came into being in 2008 with the mission of "providing high quality asexually propagated plant material free of target plant pathogens and pests that cause economic loss.”
Incorporation of citrus into the NCPN began in 2007 and a charter was adopted in March, 2010 for a "Citrus Clean Plant Network" (CCPN). The CCPN currently has centers in California, Florida, Arizona, Texas, Louisiana, Alabama, Hawaii, Maryland, and Puerto Rico. In a typical year, NCPN Citrus centers conduct over 75,000 diagnostic tests, distribute over 600,000 pathogen-tested plant materials, perform therapeutics on hundreds of plants, and maintain hundreds of foundation plants.
NCPN Citrus has established and enhanced quarantine, germplasm, and extension and education programs in all of the major and minor citrus producing regions. This has facilitated the importation, testing, therapy, and release of pathogen-tested citrus to nurseries, growers, and the public both regionally and globally.
- Author: Rock Christiano
Citrus Clonal Protection Program Lindcove Research & Extension Center, University of California
When I started working at the Citrus Clonal Protection Program (CCPP) in 2012 (Fig. 1), citrus budwood was distributed three times per year (i.e. January, June and September) and there was a minimum order limit for 36 buds per order. In July of 2013, CCPP began monthly budwood distribution and essentially removed the budwood order limit offering as little as one budstick (6 buds). This was a game changer. In the following three years of monthly budwood distribution, the amount of requested buds has increased by almost 50% (Fig. 2), and most importantly, the orders placed by citrus hobbyists has increased by almost 80%. Citrus hobbyists are growing citrus for non-commercial purposes. Many of the hobbyists have a small “citrus forest” in their backyards, typically of diverse varieties, and they are very proud of their trees. They are typically not interested in purchasing grafted citrus trees, they want to graft their own citrus trees. It is hard to understand the citrus hobbyists' deep affection for their trees! I grew up in a citrus family farm and for me, citrus was as any other crop, a plant for profit. However, after interacting with the citrus hobbyists over the past several years, I have gained a level of respect and understanding that the passion citrus enthusiast have.
I had always been taught that citrus hobbyists are a threat to the citrus industry and their capacity to propagate citrus should be limited or denied. This line of thinking has resulted in some citrus production areas to restrict citrus budwood access for non-commercial use. Today, I see that ignorance is the true threat to the citrus industry. People usually don't understand or comprehend that smuggling plants or plant parts can disseminate diseases and cause severe economic damage to the farmers. Restricting the desire to propagate a citrus variety may force someone to smuggle it. A sad example is Huanglongbing (HLB) in California. This imminent threat to the California citrus industry was first found in a back yard citrus tree that had 23 grafts of unknown budwood origin.
The California HLB/Asian Citrus Psyllid prevention campaign is doing an excellent job of educating the public. Also the University of California Cooperative Extension is teaching Master Gardeners about the dangers of smuggling plants. On the Internet, there are individuals, such as the pomologist-writer “Fruit Detective” and the citrus hobbyist-blogger “Fruitmentor”, educating people on the correct way to propagate citrus and providing information regarding the threat of importing budwood that that may contain pathogens that could effects citrus production locally. Thanks to this multi educational effort, many citrus hobbyists are now part of the solution and they are actively engaged in the effort to protect the California citrus.
CCPP has over 300 citrus varieties available to anyone interested in propagating citrus trees for commercial or personal use. Orders can be as small as 6 buds (one budstick) per variety at $ 4.50. Therefore, the CCPP offers the incentive to use inexpensive-easily purchased- tested budwood over smuggled or exchanged “dirty” citrus budwood.
Despite all of the above, I still strongly recommend to purchase grafted trees at local stores or online (e.g.
www.fourwindsgrowers.com). Grafting citrus is not as easy as it may look. It requires skill, another citrus tree to be used as a rootstock, and a controlled environment (especially
temperature and water). However, if you are going to do it yourself, make sure the material your using is disease free!
To learn more about the CCPP, go to www.ccpp.ucr.edu and remember: CCPP is the place for starting citrus correctly.
Panoramic view of the Citrus Clonal Protection Program foundation block operations at the Lindcove Research and Extension Center, Exeter, California. Photo: E. Grafton-Cardwell.
- Author: Ben Faber
When reviewing possible problems your citrus might have, it's easy to jump to the conclusion that it is a virus. That's because viruses are a major problem around the world in citrus and the effects can be slow, chronic and debilitating or fast and deadly. Images get posted on the web, and if those symptoms look like something your tree has, then by golly you have a virus. Well, actually viruses are everywhere and in most plants, so you probably do have a virus or viruses, but not plant debilitating one. California, has had a pretty thorough nursery inspection procedure in place for many years and the likelihood of a virus causing a problem is less likely here than in many parts of the world.
In most cases viruses are difficult to eradicate in practice, so it is best to remove them before they get out in the field. The Citrus Clonal Protection Program (http://www.ccnb.info/page.php?s=2&c=3) weeds out citrus viruses before they get to wholesale nurseries and into the trade. That does not mean that we don‘t have debilitating viruses in the California industry. We do. Tristeza is in some of our orange orchards and that can lead to significant yield reductions and tree death (http://www.ipm.ucdavis.edu/PMG/r107101311.html.). Tristeza is spread by the melon aphid and is hard to control without good control of the aphid. In many older orchards there is exocortis and psorosis http://www.ipm.ucdavis.edu/PMG/r107100100.html; http://www.ipm.ucdavis.edu/PMG/r107100511.html). These are graft transmissible and why it is not good, in fact unlawful, to propagate trees with uncertified budwood.
In most cases in California if you are having symptoms of unhealthy in your trees it's most likely due to an irrigation problem (too much, too little, poor timing), a nutrient deficiency and possibly a fungal disease (most likely a root one such as armillaria or Phytophthora). Or in this day, it could be the start of Huanglongbing vectored by Asian Citrus Psyllid (http://www.ipm.ucdavis.edu/PMG/r107304411.html). Before jumping to the conclusion that there is a virus in your trees. Check out the most common problems for California citrus first (http://www.ipm.ucdavis.edu/PMG/C107/m107bpleaftwigdis.html). There are enough of those anyway.
- Author: Robert R Krueger, John A Bash, Richard F Lee
The UC Riverside Citrus Variety Improvement Program (CVIP), the forerunner of the Citrus Clonal Protection Program (CCPP), began indexing candidate varieties in 1958. At that time, the full range of indicator plants that is utilized today was not known. In the early 1960s, the usefulness of ‘Dweet’ tangor as an indicator for Citrus Concave Gum Virus as well as other psorosis-like viruses was demonstrated. Consequently, starting in 1963 over 150 varieties not previously indexed on ‘Dweet’ were indexed on that indicator.
One of the results of this re-indexing was that a ‘Cleopatra’ mandarin (CRC 270, which had been indexed as VI 92) produced a leaf mottle resembling but distinct from that of psorosis or concave gum. The source tree showed no evidence of decline due to this virus, although it did show twig die-back, produced very small fruits, and was not vigorous. The trunk did not exhibit any discoloration or pitting. Because there were other selections of ‘Cleopatra’ available in the CVIP, this particular selection, which had been introduced from Florida in 1914, was eliminated from the program. Types of citrus other than ‘Dweet’ produced no symptoms but could act as carriers. This presumptive virus did not provide any protection against psorosis-like viruses and so was considered a distinct virus. Because this virus produced symptoms only in ‘Dweet’, it was named ‘Dweet Mottle Virus’ (Roistacher and Blue, 1968).
Dweet mottle virus remained a rather obscure virus. It was not observed to produce any losses in economic situations and was not reported to occur in commercial production. In fact, it was detected in the CCPP indexing program only one time after 1963. This was in a mandarin type introduced from New Zealand in the late 1990s.
In the mid 1980s, the Spanish group at the Instituto Valenciano de Investigaciones Agrarias (IVIA) reported a graft-transmissible disease that caused a bud-union incompatibility between ‘Nagami’ kumquat and ‘Troyer’ citrange (Navarro et al, 1984). The ‘Nagami’ in question (SRA-153) had been introduced from the Station des Recherches Agrumicoles in San Giuliano, Corsica. In addition to the incompatibility, the presumptive virus caused
vein-clearing in sweet orange and some other indicators and stem pitting in citron. After shoot-tip grafting, some of the plants produced were compatible with ‘Troyer’ and did not cause veinclearing but did pit the citrons, suggesting that there was more than one virus involved.
A later report (Galipienso et al, 2000) demonstrated that this virus caused bud-union creasing with ‘Nules’ clementine and ‘Eureka’ lemon on ‘Troyer’, whereas the same was not observed with ‘Pineapple’ sweet and ‘Marsh’ grapefruit on ‘Troyer’. The budunion problems were similar to those caused by Citrus tatterleaf virus. However, the pathogen did not act like CTLV in symptom expression in indicators or in mechanical transmissibility in herbaceous hosts. This report further strengthened the evidence that more than one virus was involved. All sources of the virus used in the reported experiments produced a chlorotic blotching in ‘Dweet’ tangor and stem pitting in citron. However, the bud union crease and vein-clearing in ‘Pineapple’ sweet orange were not observed in some shoot-tip grafted plants or from ‘Marsh’ grapefruit or ‘Pineapple’ sweet orange pre-inoculated with tissue from SRA-153 ’Nagami’.
The same group partially purified and characterized the apparent causal agent, and gave it the candidate name Citrus leaf blotch virus (Galipienso et al, 2001; Vives et al, 2001, 2002). These papers also indicated that CLBV was detected in trees in Spain and introductions from Japan and Florida. They also reported the development of probes usable for RTPCR as well as other molecular detection methodologies (Galipienso et al, 2004).
Luís Navarro of IVIA, in conversation with one of the authors (RRK) and Chet Roistacher in 2001, revealed that CLBV might be similar to Dweet mottle virus, based upon the symptom expression in ‘Dweet’. Consequently, we sent him tissue of the Dweet mottle positives maintained at the CCPP. This allowed the Spanish group to compare DMV and CLBV. They recently reported that the symptom expression of the two putative viruses is somewhat different: CLBV from SRA-153 induced bud-union crease of ‘Nules’ on ‘Troyer’, vein-clearing in ‘Pineapple’ sweet, chlorotic blotching in ‘Dweet’, and stem-pitting in ‘Etrog’, whereas DMV induced only the chlorotic blotching in ‘Dweet’ and stempitting in ‘Etrog’. Furthermore, they reported that the nucleotide identity between CLBV and the two California sources of DMV was over 96 %. They interpret these results as indicating that at the least DMV and CLBV are closely related. Dweet mottle may be caused by CLBV, with another virus being present in SRA-153 ‘Nagami’ causing the bud-union crease and vein-clearing (Vives et al, 2004).
The overall status of CLBV in California is unknown at this time. The recent report of seed transmission of CLBV (Guerri et al, 2004) makes it a concern for the citrus nursery industry. It is possible that more attention will need to be paid to the phytosanitary status of seed source trees than in the past. It should be noted that recently Citrus Variegated Chlorosis was also reported to be seedtransmitted (Li et al, 2003). In addition, there are anecdotal indications that certain individuals in Spain have alleged that CLBV was introduced into Spain in C-35 seeds from California. Furthermore, the recently reported bud-union problems between ‘Fukumoto’ and ‘Beck’ navels and certain citrange rootstocks resemble the bud-union problem associated with CLBV (as well as CTLV).
Consequently, we have recently assayed all rootstock varieties, kumquats, and ‘Fukumoto’ navels in the CCPP Foundation Block at Lindcove Research and Extension Center utilizing RT-PCR (Galipienso et al, 2004) with our local DMV positives and a CLBV positive from Florida DPI (received via RF Lee) used as positive controls. Whereas the positives consistently produced a positive result from the RT-PCR, none of the FB trees did so. We have also tested all trees maintained in the Repository Protected Collection (the other source of clean citrus propagative material in California) in the same manner and to this point have detected no positives. If any positives are detected either at CCPP or NCGRCD, they will be re-sanitized.
The fact that all C-35 in California is derived from trees in the FB means that, given that the FB trees are apparently free of CLBV, other C-35 seed source trees should also be free of CLBV. However, ‘Troyer’ was introduced to California before indexing began, and it is possible that there are some seed-source ‘Troyer’ that do not derive from the FB trees. Therefore, clean FB ‘Troyer’ would not necessarily mean that all commercial ‘Troyer’ are also clean. A similar situation exists with the navels of interest. All ‘Fukumoto’ in California derive from the FB trees and freedom of these trees from CLBV would also mean that other trees are also free. However, ‘Beck’ navels have never passed through the CCPP and are not maintained in the FB, so nothing can be conjectured about ‘Beck’ at this point.
The close identity of CLBV and DMV has probably prevented CLBV from becoming introduced to California. All introductions of new citrus germplasm are indexed into ‘Dweet’ tangor (among other indicators). This would detect CLBV, which gives a reaction in ‘Dweet’ tangor, even if the actual identity of the virus was not known at the time of the index. Any apparent positives of this sort, even if misidentified, would have been eliminated by thermal therapy or shoot-tip grafting before release. Thus, probably CLBV and/or DMV are probably not present in California or, if present, have very low incidence.
It should be noted that our experience with CLBV is just beginning. Conversations with L Navarro and J Guerri of IVIA during the recent 2004 meeting of the International Organization of Citrus Virologists suggest that detection of CLBV is not always straightforward. The Spanish researchers told us that CLBV appears to be distributed irregularly in the trees. Detection is variable even in small greenhouse trees, and sometimes leaves from the same tree give variable results. We are thus continuing to assess the reliability of the RT-PCR test under our conditions. We are also currently observing the reaction of our DMV positives in indicators other than ‘Dweet’ in order to assess whether the reaction under our conditions is the same as that reported from Spain. If any growers or extension personnel have questions or concerns regarding DMV or CLBV, we invite them to contact us.
(Robert Krueger is the Curator at the USDA-ARS Citrus Germplasm Repository, Riverside; John Bash is a Staff Research Associate at U.C. Riverside; Richard Lee is the Director of the USDA-ARS Germplasm Repository, Riverside)