Subtropical Fruit Crops Research & Education
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Subtropical Fruit Crops Research & Education

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Huanglongbing Conference and the Forefront of HLB Research

The recent Huanglongbing Conference in Orlando, FL was chock full of people and ideas. Some of the ideas were still in the fermentation state and some were in practice on farm. One of the ideas that has been put into practice is the use of antibiotics, such as tetracycline and streptomycin to control the bacteria, Candidatus Liberibacter asiaticus (CLas), which causes HLB or citrus greening. This is somewhat disturbing since the rise of antibiotic resistant bacteria which affects humans has been affected by the wide-spread use in animal production facilities. This has led to some food companies to discontinue the sourcing of meat from animals treated with antibiotics for non-health reasons.

Antibiotics are molecules that limit the growth or reproduction of bacteria. They come under the umbrella of bactericides which include antibiotics, but also disinfectants like bleach and copper sulfate and antiseptics like peroxide, iodine and alcohol. Antibiotics when properly used will not harm human tissue and can be derived from bacteria, fungi and synthetically and will often act directly on the bacteria that is causing the disease. Some of these molecules can be simple assemblages of amino acids called peptides (etymology “to digest”)  or strings of peptides called proteins. And sometimes they do not work on the bacteria itself, but on steps that lead up to processes that make the bacteria effective at its job.

At the conference, several papers were presented that illustrated this type of antibiotic effect. One of these papers was presented by Robert Shatters for his group. The peptide they are looking at actually inhibits the movement of the CLas bacteria in the gut of the insect, reducing or possibly preventing the transmission of the bacteria to the host plant – citrus.

The following is an abstract from the paper.

Identification of gut epithelium binding peptides that reduce systemic movement of ‘Candidatus' Liberibacter asiaticus within the Asian citrus psyllid vector

Robert G. Shatters, Jr1, Dov Borovsky1, El-Desouky Ammar1, David Hall1, Kasie Sturgeon2, EricaRose Warwick2, Marc Giulianotti3, Radleigh G Santos3 and Clemencia Pinilla4

1USDA, ARS, USHRL, Fort Pierce, FL USA; 2University of Florida, CREC, Lake Alfred, FL USA; 3Torrey Pines Institute for Molecular Studies, Port St Lucie, FL USA; Torrey Pines Institute for Molecular Studies, San Diego, CA USA.

Non-Technical summary: The Asian citrus psyllid is the only known vector of the bacteriumthat causes citrus greening disease. This insect acquires CLas from an infected citrus tree while feeding as a nymph. Transmission to uninfected trees occurs when infected adults emerge and fly off and feed on uninfected trees. Our current understanding of the CLas-psyllid interaction suggests that adults become competent for transmission only after the bacterium moves from the insect gut into the hemolymph and then to the salivary glands. We have identified a set of small peptides that when fed to the psyllid, bind the gut membranes and reduce the ability of the citrus greening bacterium to move from the gut to the salivary glands. These peptides are now being tested to determine if they can be used as an effective way of reducing the spread of citrus greening disease.

This and other paper abstracts will soon be available at:

photo: HLB Symptoms

Posted on Friday, March 24, 2017 at 6:14 AM
Tags: antibiotics (1), antimicrobials (1), bactericides (1), citron (3), citrus (165), disease (35), grapefruit (9), lemon (34), mandarin (24), orange (29), peptides (1)

Carfentrazone-ethyl (Shark®) use in Avocados

Shark (carfentrazone) has been currently labeled for use in California avocados.   It's widely used in many tree and vine crops.  It's a Protoporphyrinogen oxidase (PPO) inhibitor. PPO is an enzyme in the chloroplast cell that oxidizes protoporphyrinogen IX (PPGIX) to produce protoporphyrin IX (PPIX).  PPIX is important because it is a precursor molecule for both chlorophyll (needed for photosynthesis) and heme (needed for electron transfer chains). Inhibitors of the oxidase enzyme, however, do more than merely block the production of chlorophyll and heme. The inhibition of PPO by inhibitors also results in forming highly reactive molecules that attack and destroy lipids and protein membranes. When a lipid membrane is destroyed, cell becomes leaky and cell organelles dry and disintegrate rapidly.

PPO Inhibitors have limited translocation in plants and sometimes are referred to as contact herbicides. PPO Inhibitors injure mostly broadleaf plants; however, certain PPO Inhibitors have some activity on grasses. PPO Inhibitors usually burn plant tissues within hours or days of exposure. PPO Inhibitors used in the United States belong to eight different chemistries. It is used in the same niche that Treevix, Venue, and the post rates of Goal are used although registrations vary among those of course (only Goal from that list is registered on avocado).

Carfentrazone is a broadleaf-only herbicide and is interesting in that it has a fairly narrow weed spectrum; it has some species that it is really good on, but misses some other broadleaves almost completely.  For example, it is excellent on bedstraw, but pretty weak on fleabane and marestail.  It can provide good an inexpensive top-burn of perennial weeds like field bindweed, but will not kill it.   Take a look at the label and, if the grower's weed spectrum aligns with some of the labeled weeds, it's worth checking out.  Just be aware that it is grass-only and doesn't get all broadleaves equally.

Injury symptoms can occur within 1 to 2 hours after exposure, appearing first as water-soaked foliage, which is followed by browning (necrosis) of the tissue. Symptoms will appear most quickly with bright, sunny conditions at application. Drift injury will appear as speckling on leaf tissue. The necrotic spots are sometimes surrounded by a reddish colored ring. Injury from soil applications or residues appears as a mottled chlorosis and necrosis.


 Fig. 1. Phytotoxicity of Shark herbicide on non-target leaf (above)

Phytotoxicity of Shark herbicide on non-target leaf. Since the droplets landing on the

Mixing the formulation depends on the growers sprayer calibration.  If applying 20 gal of water per acre, that would be 5 acres per 100 gal mix and would need 10 fl oz product.

For a “spot treatment”, there is a table on the Shark EW label with mix amounts “based on 1 gal of water evenly covering 1000 square feet”.  Take a look at Table 4 on this label: 



Posted on Thursday, March 23, 2017 at 6:20 AM
Tags: avocados (6), herbicides (7), phytoxciity (1), ucce (4)

Shoot and Twig Dieback of Citrus

Recently, an outbreak of shoot and twig dieback disease of citrus has been occurring in the main citrus growing regions of the Central Valley of California (Fig 1). The causal agents of this disease were identified as species of Colletotrichum, which are well-known pathogens of citrus and other crops causing anthracnose diseases. At this time, it is unclear how wide-spread the disease is in California citrus orchards, but surveys are being conducted to evaluate the spread of this disease in orchards.

The disease was first noticed in 2012 by several growers and nurserymen in various orchards in the Central Valley. Symptoms included leaf chlorosis, crown thinning, gumming on twigs and shoot dieback, and in severe cases, branch dieback of trees (Fig.2). The most characteristic symptoms of this disease are the gum pockets which appear on young shoots either alone or in clusters and the dieback of twigs and shoots (Fig.3). These symptoms were primarily reported from clementine, mandarin, and navel orange varieties. In order to determine the main cause of this disease, field surveys were conducted in several orchards throughout the Central Valley. Isolations from symptomatic plant samples frequently yielded Colletotrichum species.

            Field observations indicate that symptoms initially appear during the early summer months and continue to express until the early fall. Trees showing dieback and gumming symptoms characteristic of this disease are usually sporadic within an orchard and generally only a few twigs or shoots are affected within a tree. Morphological and molecular phylogenetic studies allowed the identification of two distinct species of Colletotrichum (Colletotrichum karstii and Colletotrichum gloeosporioides) associated with twig and shoot dieback. Interestingly, these Colletotrichum species were also isolated from cankers in larger branches. Although C. gloeosporioides is known to cause anthracnose on citrus, a post-harvest disease causing fruit decay, it has not been reported to cause shoot dieback of citrus. C. karstii however has not been reported previously from citrus in California and our laboratory is currently conducting field and green house studies to determine the pathogenicity of this species in citrus.

            At present, it is unclear how widespread this disease is in California orchards or how many citrus varieties are susceptible to this disease. Pest control advisors are advised to remain alert and monitor citrus trees for the presence of the disease in the Central Valley (particularly clementine, mandarin, and navel varieties) during the early summer months. Continuing research lead by Dr. Akif Eskalen (UC Riverside) in collaboration with Dr. Florent Trouillas (Kearney Agricultural Research and Extension Center), Dr. Greg Douhan (UCCE Farm Advisor Tulare County), and Craig Kallsen (UCCE Farm Advisor in Kern County) is focused on further understanding the biology of the fungal pathogens as well as factors influencing disease expression in order to develop management strategies against this emerging disease.

Shoot dieback symptoms on Clementine

Branch dieback symptoms on Clementine

Gumming symptoms on Clementine

(photos: A. Eskalen)


Posted on Wednesday, March 22, 2017 at 5:55 AM
  • Author: Joey Mayorquin, Mohamed Nouri, Florent Trouillas, Greg Douhan and Akif Eskalen
Tags: anthracnose (2), anthracnosis (1), blight (6), citrus (165), disease (35), drought (36), fungus (5)

Resistant Citrus Selections to HLB?

Three citrus trees that produce inedible fruit at the UC Lindcove Research and Extension Center in Visalia may be a game-changer for the citrus industry, reported Ezra David Romero on Valley Public Radio.

The trees are thought to be resistant to huanglongbing, a severe disease of citrus that has devastated the Florida industry and could become a serious problem in California. The citrus-saving potential of the three 34-year-old trees was outlined in an article by UC Agriculture and Natural Resources writer Hazel White in the most recent issue of California Agriculture journal.

UC Riverside citrus breeder Mikeal Roose collected seed from the trees and will test seedlings as soon as they are large enough. 

"So what (breeders) have to do is cross this with some edible varieties and eventually create something that has the gene for resistance, but also the genes for good fruit," said Beth Grafton-Cardwell, Lindcove director and research entomologist.

Huanglongbing disease has cut citrus production in Florida by more than half. It's been found in residential citrus trees in Southern California, but hasn't reached the state's vast commercial orchards yet. Grafton-Cardwell said she expects the disease will arrive in 4 or 5 years.


Posted on Monday, March 20, 2017 at 6:16 AM
  • Author: Jeannette E. Warnert
Tags: ACP (36), Asian Citrus Psyllid (24), bacteria (5), citrus (165), Citrus Greening (9), disease (35), HLB (22), host (1), Huanglongbing (31), resistance (8), tolerance (3), vector (2)

California State Soil - San Joaquin Series

Many states have a designated state bird, flower, fossil, mineral, etc. In California, the state bird is the California Valley Quail, the state flower is the Golden Poppy, the state fossil is the Sabertoothed Cat, and the state mineral is Native Gold. The state rock is Serpentine which contains chrysolite asbestos which is a carcinogen. It's a beautiful rock, though.

The state soil is the San Joaquin series. The series concept is that a given soil has certain properties like pH, depth, color, texture, etc. that distinguishes it from other “soils” or series. So wherever this soil is found it is given the same name. San Joaquin series is a soil that is found primarily along the foothills of the Sierras in the Central Valley. The name comes from where it is first described, in this case, San Joaquin, but it is found in other places. Yolo series is named after a soil on the campus at UC Davis in Yolo county, but it is also found in San Diego county, and in other states.

A description of the state soil can be found at the link below, as well as the state soils in other states:

Soils can be highly variable depending on the context in which they are found. Going to flat old Kansas which is actually flatter than a pancake (, the variability from spot to spot across miles can be minimal. But going to a place like Ventura, Santa Barbara, San Luis Obispo Counties of the Sierra foothills, you can't step on the same soil twice. That's because of the terrain and landforms. Where there is natural erosion (yes, it doesn't take humans to cause erosion) or accelerated erosion (this is where humans have often changed the landscape with roads, houses, removing ground cover) soil gets moved around and deposited in different positions and over time forms different soils with different properties. On large tracts of land that have not been altered much, such as avocado orchards, the naturally formed soils can be seen. In a housing tract where soil has been moved around to level and compact housing pads, it is often hard to find a natural soil because it is so highly disturbed. The soil can have been moved from one end of a 100 acres tract to the other with big equipment. It's all one big homogenous mix down to several feet at times depending on the slope.

In many cases, it is still possible to see the natural soils and knowing their series classification, it's possible to learn some of the properties and some of the problems that will be encountered when working with them. Knowing the pH prior to working it means that it could be adjusted before planting. It's a whole lot easier to adjust before planting than when the plants are in the ground.

You can see the soils in your area by going to the USDA-NRCS (Natural Resources Conservation Service) website - - and typing in the area code to find the soil at a given site. It probably isn't the state soil series, but it's your soil series.

For a great text on understanding soils, check out Soils: An Introduction by Michael Singer and Don Munns.

Posted on Friday, March 17, 2017 at 4:57 AM
Tags: dirt (2), earth (2), land (1), media (1), medium (1), series (1), soil (13), soils (3)

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