The Citrus leaf miner has four life stages

My name is Warner and Im with Warner's tree surgery today I would like to talk to you about your citrus trees. You might think there all right, but you need to take a closer look at the leaves.

The Citrus leaf miner has four life stages: egg, larva, pupa, and the adult moth.

It repeats this cycle up to 8 times a season infecting the entire tree Leaf damage reduces your trees vigor affecting fruit production and making it susceptible to soil fungus,citrus blight and other diseases.

 

Citrus Leaves Curling

 

The Asian Citrus Leaf Miner

 

Tree Disease Basics playlist

 

Whiteflies in Temp AZ

Arriving here in 2011 and breeding up to 15 times a year, the Asian Citrus Leaf Miner was in every citrus tree I looked at for several years.

The population grew unchecked well into the summer of 2019,. So for at least 8 years, the leaves on your citrus trees have been producing far less energy than normal.

Because of this the reserve cells are dangerously low. Biologically speaking, your citrus trees have run out of gas.

Because it has no natural predator in Arizona there was nothing to keep it in check. However now it competes with the Ash Whitefly.

It takes years but eventually a citrus trees reserves will be drained to the point that it can no longer defend itself against any insects or soil born fungus.

That’s where we come in, if it’s not too late we can get you started on a program to restore the energy reserves of your trees.

Watch the videos on this page to learn more.

I have included a link to a tool developed by the Department of Agriculture among others to help people world wide to idrnyafy and treat citrus diseases. To keep your citrus trees healthy, call us at Warner’s Tree Surgery at (480) 969-8808 and schedule a time to talk to our Tree Doctor.

Ash Fly

common name: ash whitefly
scientific name: Siphoninus phillyreae (Haliday) (Insecta: Hemiptera: Aleyrodidae: Aleyrodinae)

Introduction - Synonymy - Distribution - Description and Biology - Host Plants - Natural Enemies - Selected References

Introduction (Back to Top)

The ash whitefly, Siphoninus phillyreae (Haliday), is a pest of numerous ornamental and fruit crops, including citrus. It causes severe damage to pear and apple in Europe. Most ash whiteflies in California were found on pomegranate, ash tree, pear, apple, loquat and citrus. Heavy infestations cause leaf wilt, early leaf drop and smaller fruit (Bellows et al. 1990).

Discovered in Florida in 2010, if it becomes established it could become a pest of ornamental plants and possibly other crops.


Several life stages of the ash whitefly, Siphoninus phillyreae (Haliday), on fallen Bradford pear leaves.

Figure 1. Several life stages of the ash whitefly, Siphoninus phillyreae (Haliday), on fallen Bradford pear leaves. Photograph by Lyle J. Buss, University of Florida.

Synonymy (Back to Top)

The ash whitefly, Siphoninus phillyreae, was described as Aleyrodes phillyreae by Haliday (1835), on Phillyrea latifolia collected in Dublin, Ireland. It has several synonyms listed in Mound and Halsey (1978).

Distribution (Back to Top)

Native to Europe, the Mediterranean and northern Africa, the ash whitefly is found in numerous countries, including:

Africa: Cameroon, Egypt, Ethiopia, Libya, Morocco, Sudan

Asia: India, Iran, Israel, Pakistan, Saudi Arabia, Syria

Europe: Austria, Corsica, Czech Republic, Cyprus, England, France, Germany, Hungary, Ireland, Italy, Poland, Romania, Spain, Switzerland, Yugoslavia

North America: United States (California, Florida)

Oceania: Australia (New South Wales, South Australia, Queensland and Victoria)

(Mound and Halsey 1978, Bellows et al. 1990, Raymond Gill personal communication, Chris Baptista personal communication, Stocks and Hodges 2010). 

In the United States, ash whitefly was first collected in Los Angeles County, California in 1988, and then spread to other counties. It was later discovered in Arizona, Nevada and New Mexico. It appeared in Raleigh, North Carolina in 1993. It is also reported from Arizona, Georgia, Nevada, New Mexico, South Carolina and Texas. A successful biological control program using a parasitic wasp reduced infestations to undetectable levels (western states) or possibly eliminated the infestion (North Carolina). In 2010, it was discovered in central (Lake Buena Vista) and northwestern (Panama City) Florida (Stocks and Hodges 2010).

Description and Biology (Back to Top)


 

Adult: The adult appears much like a typical whitefly with a light dusting of white wax. Depending on temperature, females live from 30 to 60 days, while males live an average of nine days. This rapid development time, without the presence of the parasitiod, initially produced numerous generations per year in California, whereas only two to three generations were reported in Egypt. Plus, the ability of all life stages to overwinter on non-deciduous hosts allows a rapid build-up in population at the start of the season (Stocks and Hodges 2010). Winged females lays eggs on the underside of the leaves. When the nymphs emerge, they rarely move far and feed on the plant sap until pupation (Gillespie 2000). 

Adult ash whiteflies, Siphoninus phillyreae (Haliday).

Figure 2. Adult ash whiteflies, Siphoninus phillyreae (Haliday). Photograph by Lyle J. Buss, University of Florida.

Pupa: On first observation, the pupal case appears similar to the white armor of a male snow scale. Closer observation with a hand lens reveals a whitefly pupal case with two longitudinal tufts of white wax. The vasiform orifice is surrounded by dark brown derma (inner, thicker layer of the cuticle), with the anal area appearing as a dark brown spot. Lateral areas of the pupal case are light beige. Depending on the age, lesser or greater amounts of white wax will be present. The dorsal surface has 40 to 50 long glassy tubercles similar to the cornicles found on aphids. These tubercular structures produce a droplet of glassy wax and this gives the pupal case an unusual appearance. The longitudinal white tufts of wax obscure some glassy tubercles (R.J. Gill, personal communication). The pupal case size is 0.8 to 1.0 mm long by 0.55 to 0.7 mm wide and is tan or beige in color(Mound 1966, Stocks and Hodges 2010).

Pupal stage of the ash whitefly, Siphoninus phillyreae (Haliday), showing glassy, wax droplets

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Figure 3. Pupal stage of the ash whitefly, Siphoninus phillyreae (Haliday), showing glassy, wax droplets. Photograph by Lyle J. Buss, University of Florida.

Puparia (3 tan-colored individuals) and juveniles (translucent nymphs) of the ash whitefly, Siphonius phillyreae (Haliday), on pomegranate.

Figure 4. Puparia (3 tan-colored individuals) and juveniles (translucent nymphs) of the ash whitefly, Siphonius phillyreae (Haliday), on pomegranate. Photograph by Lyle J. Buss, University of Florida.

Host Plants (Back to Top)

European Insect Arrives In Arizona

Staff Writer Gardeners have a new insect pest to worry about this spring. The ash whitefly (Siphonium phillyreae) from Europe arrived in Phoenix and Tucson last November by way of California. We should expect to see its appearance in Cochise County in late April.

The gnat-sized ash whitefly infests and seriously damages a variety of landscape trees and ornamentals. In California it has attacked apples, pears, pomegranates, apricots, peaches, citrus, olive, ash, and other, shade trees. The whitefly has apparently not affected any native desert plants, but infestations appear to be spreading to more host plants than are normally attacked in its native European range from Ireland to Egypt.

Ash whiteflies can kill full grown trees by repeatedly destroying all of the tree's leaves.

I have witnessed this myself

Warner

Leaves affected by the whitefly turn yellow, curl, and drop prematurely. In addition, whiteflies excrete a sugary honeydew that attracts sooty mold fungi, further damaging the tree. Infestations of flying adult ash whitefly have been compared to a light snow flurry in appearance. They are multivolting, producing more than one generation per year, and do best at temperatures around 77 degrees.

Experiments in California have shown that common pesticides are completely ineffective against the ash whitefly. However, laboratory experiments with two biological controls indicate that the whitefly's natural European predators may be used successfully in the U.S. to control the insect. Field studies are currently under way using a small parasitic wasp, Encarsia Formosa, and a ladybird beetle, Clitostethus arcuatus, both imported from Europe. The ladybird beetle has not cleared quarantine yet, but the wasp has recently been released. Serious infestations of ash whitefly generally do not occur in Europe because of the presence of these natural predators. It will take some time to develop a suitable biological control program in the U.S.

Concerned growers can contact Dr. David Byrne, University of Arizona entomologist, for more information.

Author: 
Jackie Dillon-Fast
Issue: 
February, 1990

See Also

University Of California, Riverside
Center for Invasive Species Research
 

The ash whitefly is a polyphagous species found on several plant families, (modified from Bellows et al. 1990) including:

Aleo See OREGON DEPARTMENT OF AGRICULTURE FACT SHEETS AND PEST ALERTS

Alternaria brown spot

Originally alternata was described as Alternaria citri Elli & Pierce or A. alternatapv. citri

Other common names

 

Alternaria brown spot (ABS), alternaria brown spot of mandarins, brown spot

 

Disease cycle 

Alternaria is spread by airborne spores. Rain events or sudden changes in relative humidity also favor spore release. Sporesare produced on older lesions formed on wilted twigs and mature leaves. Some spores come from fruit lesions but they are not a major inoculum source. Even the leaf contributes to the inoculum. Although the spores are airborne and carried by winds, alternaria brown spot is often spread among groves on nursery stock transported by humans. 

Symptoms 

Leaf - initial foliar lesions occur on young tissue as small brown to black spots that develop prominent yellow halos. Lesions expand into irregular or circular necrotic areas which can involve large portions of the leaf, especially on highly susceptible cultivars like 'Minneola'. A fungal toxin is produced that can cause necrosis and chlorosis along the veins extending from lesionsLesions are flat and visible on both sides on the leaf. Older lesions have a brittle paper-like texture in the middle of the lesions.

Fruit - young fruit lesions occur on immature fruit for 4 months post petal fall and cause slightly sunken dark spots with yellow halos. On more mature fruit, lesionscan vary from small specks to large pockmarks. The fruit rind responds to infection by forming a barrier of corky tissue that erupts from the surface. In the later stages of the disease, the corky tissue can fall out, forming craters or pockmarks on the surface of the fruit. Early fruit drop is common, especially if infection has occurred shortly after petal fall. Alternaria fruit lesions can crack around the outer edge, giving a moat-like appearance. During the packing process, the tops of alternaria lesions may be lopped off, making visual identification difficult.

Host range

 

Dancy tangerine hybrids ['Minneola' tangelo ('Honeybell'), 'Orlando' tangelo, 'Sunburst', 'Nova,' and 'Lee'] and 'Murcott' ('Honey' tangerine) frequently have fruit infections of alternaria brown spot. Grapefruit and lemons may also be affected.

Distribution

 

Has been reported from Argentina, Australia, Brazil, Columbia, Greece, Iran, Israel, Italy, Peru, Spain, South Africa, Turkey, the United States, and Uruguay. The disease is likely found in other countries that produce susceptible cultivars.

Easily confused with

 

Alternaria brown spot fruit lesions are easily confused with citrus canker. Alternaria is extremely common on certain cultivars of tangerines while citrus canker is uncommon on tangerine cultivars.

Chimera

Leaf - the mutation produces variegated leaves, misshapen leaves, or leaves that are completely white. May also produce multiple bud growth resulting in a witches' broomsymptom. Restricted to one section of a tree.

 

 

 

Fruit - overall fruit appearance can be changed or sections of the rind can appear striped and/or green. 

Host range 

All citrus may exhibit chimeras.

Easily confused with 

Huanglongbing (HLB)

Fruit - overall fruit appearance can be changed or sections of the rind can appear striped and/or green.

Citrus bacterial spot

 

 

 

 

Scientific Name

[Bacterium] Xanthomonas alfalfae subsp. citrumelonis (syn. Xanthomonas axonopodis pv. citrumelo)

Other common names 

CBS, this however may lead to confusion since citrus black spot uses the same abbreviation.

 

Disease cycle 

Citrus bacterial spot is only known to occur only under nursery conditions. There are three groups of isolates based on laboratory assays considered aggressive, moderately aggressive, and weakly aggressive. Only aggressive isolates were historically spread in field nurseries naturally by wind-blown rain and overhead irrigation. All strains can be mechanically moved from tree to tree under normal nursery operation. When infected trees are transplanted into groves, the bacterium rapidly dies off and the disease becomes undetectable in a few months. The activity of the citrus leaf miner exacerbates citrus bacterial spot.

 

Symptoms 

Leaf - the symptoms of citrus bacterial spot are very similar to those of citrus canker, but the lesions are flat and not raised. Foliar lesions show necrotic centers that often can crack or drop out and are surrounded by water-soaked margins. Lesions produced by aggressive strains have more pronounced water-soaked margins than those of citrus canker. Budtake and growth on infected rootstocks, especially Swingle, can be infected.

Fruit - fruit infection is rare and has only been reported on Flying-dragon trifoliate.

Host range 

Citrus bacterial spot can affect common scion and rootstock species and is most severe on Swingle citrumelo, trifoliate orange rootstock, and grapefruit scions

Distribution 

Only known to occur in Florida.

Easily confused with 

Citrus canker

It should be noted that citrus bacterial spot was initially regulated in Florida similarly to citrus canker, however, the low disease potential in groves was realized and the disease was deregulated. Care must be taken to differentiate between citrus bacterial spot and citrus canker.

Citrus black spot

Often abbreviated as CBS. This however may lead to confusion since citrus bacterial spot uses the same abbreviation. Many of the common names for black spot are based on observed symptom types but all refer to the same disease which can be confusing. The symptom based names are: hard spot (shot-hole spot), false melanose (speckled blotch), freckle spot, lacy-spot, cracked spot and virulent (spreading or galloping) spot.


Disease cycle
As in many diseases, timing is important for black spot to occur. Inoculum in the leaf litter needs to be available during the period when the host is susceptible and the environment is favorable for infection. Fruit are susceptible from fruit set until 5-6 months later, when they become age resistant.

Both the ascospores (sexual spores) and the conidia (asexual spores) of G. citricarpa are able to infect susceptible tissues.

Ascospores are found in microscopic fungal structures embedded in the leaf litter. They are the most important source of inoculum, in some regions causing nearly all infections. Ascospores have never been found in fruit lesions or lesions on attached leaves. Spores are released when the leaf litter is wetted by heavy dew, rainfall, or irrigation and can be carried by air currents over long distances.

Dark brown or black pycnidia, structures that produce conidia, are formed on fruit, fruit pedicles and leaf lesions. They are also abundant on dead leaves. Conidia are not wind-borne, but may reach susceptible fruit by rain splash. These spores are not considered a significant source of inoculum in climates with dry summers; however, in climates with frequent summer rains, conidia play a larger role in the epidemic when there are multiple fruit ages present on trees simultaneously. Often late hanging fruit with lesions remain on the tree and spores can be washed onto young susceptible fruit.

Citrus canker

Different strains of citrus canker have been reported throughout the world. The Asiatic strain (A-strain) is the most widespread and severe form. Strains can be differentiated by molecular tests and host range.

Other common names
Asiatic citrus canker

Disease cycle
Citrus canker is not vectored by any organism but is spread by wind-driven rain. However, wounds caused by feeding of the Asian citrus leaf miner (Phyllocnistis citrella Stainton) may serve as an entry point for the bacterium if citrus canker inoculum is present.

Symptoms
Leaf - typical citrus canker lesions on leaves will range from 2-10 mm in size and will have raised concentric circles on the underside of the leaf. Frequently lesions will be surrounded by a water-soaked margin and a yellow halo. As a canker lesion ages, it may lose it palpable roughness, but the concentric circles will still be visible with a hand lens (on the underside of the leaf). The yellow halo eventually changes to dark brown or black and the water-soaked margin surrounding the lesion may diminish. The middle of the lesion (on underside of leaf) will be corky in texture with a volcano or pimple-like point. With the exception of very young lesions, lesions always penetrate through both sides of the leaf. In the presence of damage, the lesion may follow the contours of the damage and therefore may not be circular. In older lesions, a saprophytic white fungus may grow over the center of the lesion. The center of a lesion may fall out producing a shot hole appearance.

Fruit - typical citrus canker lesions on fruit will range from 1-10 mm in size. Larger lesions usually penetrate a few millimeters into the rind. Fruit lesions may vary in size and may coalesce. Fruit lesions consist of concentric circles. On some varieties these circles are raised with a rough texture on other varieties the concentric circles are relatively flat like the surface of a record. The middle of the lesion will be corky in texture with a volcano or pimple like point. The center of a lesion may crack and has a crusty material inside that resembles brown sugar. Frequently on green fruit a yellow halo will be visible; however it will not be visible on ripened fruit. Lesions may have a water-soaked margin and the water-soaked margin is especially evident on smaller lesions. In the presence of damage the lesion may follow the contours of the damage therefore not being circular. In older lesions a saprophytic white fungus may grow over the center of the lesion.

Citrus chlorotic dwarf virus

Disease cycle
Vectored by bayberry whitefly (Parabemisia myricae (Kuwana)). It is transmissible by grafting on infected buds, slash inoculation from extracts of infected leaves and bark in phosphate buffer.

Citrus whitefly

Bayberry whitefly was first discovered in the U.S. by California agriculture officials in 1978, and in Florida by agriculture officials in early 1984. Early dense populations caused defoliation in California citrus (M. Rose, pers. comm.), but this has not happened in Florida. The early finds in Florida were under natural biological control by hymenopterous parasites, including Eretmocerus sp. Apparently, the parasites were introduced with the whitefly. According to Mike Rose (pers. comm.) the Eretmocerus species present in Florida is the same as that found in California.



Symptoms
Field symptoms consist of chlorotic flecking on young leaves, warping, crinkling, inverted cupping, spoon-shaping and variegation on leaves. Strong chlorosis and dwarfing of leaves are also observed. Grapefruit, lemon, mandarin and sour orange develop more severe symptoms than sweet orange. Diagnosis is made by grafting on rough lemon and Citrus macrophylla preferably in warm conditions

Citrus scab

Conidia are produced on the surface of scab pustules. These spores spread to new susceptible tissue. There are two kinds of spores, clear oval shaped and colored spindle shaped (found in Florida and Brazil). The clear oval shaped type are spread by splashing rain and perish as soon as they dry, while the spindle-shaped form remain viable for a short time and are dispersed by wind for short distances.

Symptoms
Leaf and fruit - early scab pustules are a mixture of fungal and host tissue. These pustules are slightly raised and pink to light brown in color. Young foliar lesions superficially resemble young citrus canker and may have a slight water soaked margin. As fruit and leaf pustules develop, the small elevated pink spots become more defined and may form conical depressions nearby. As the pustules mature, they become warty and crack. Pustule color may progress to yellowish brown and eventually to a dirty grey. On lemons, tangerines, and sour orange, the growths are relatively raised. In contrast, on grapefruit the growths are flatter.

Host range
Citrus scab is only a serious problem on some varieties. It is severe on rootstock seedlings of rough lemon, sour orange, Rangpur lime, and Carrizo citrange, and scions of Murcott tangor, Temple tangor, and other tangerine hybrids. It is occasionally found on grapefruit.

Distribution
Present in most humid citrus producing areas.

Easily confused with
Young citrus canker

Citrus stubborn disease (CSD)

CSD is caused by Spiroplasma citri, a phloem-limited, cell-wall-less bacterium. S. citri is transmitted in a propagative, circulative manner by several leafhoppers including Circulifer tenellus and Scaphytopius nitridus in citrus-growing regions of California and Arizona and C. haematoceps (syn. Neoaliturus haematoceps) in the Mediterranean region. The pathogen multiplies in the vector but no transovarial transmission occurs.

Spatial and temporal analysis of CSD incidence indicate only primary spread occurring and no or very limited secondary spread (citrus to citrus). Scaphytopius can develop on citrus but the population remains low to negligible throughout the season. C. tenellus and C. haematoceps have a wide host range which includes many natural hosts of S. citri but citrus is a non host of these leafhoppers. Citrus becomes infected when inoculative Circulifer vectors feed temporarily on citrus during migratory flights.

S. citri is graft-transmissible with side grafts but rate of bud transmission is very low due to low pathogen titer. Seed transmission does not occur. S. citri is phloem-restricted where it multiplies and moves slowly through the tree. CSD has a long latent period of months to years after inoculation. Detection varies with season with highest titer being in hot summer months, concomitant with most pronounced symptom expression.

Symptoms
Leaf - symptoms can vary with season and variety but typically include small size with upright position; some mottling resembling nutritional deficiencies; shortened stem internodes leading to bunchy-type growth. Symptoms on mildly-infected trees are often localized within a sector of a tree.

Fruit - symptoms are variable but include small size, lopsided, with immature acorn-shaped fruit and stylar-end breakdown or greening. Fruits exhibiting blue albedo have been reported. Fruit drop is common but extent depends on horticultural management. Internal fruit development can be imperfect with thinner rind on one side and thicker on the other. Severely-affected fruit can be insipid or bitter flavored. Seeds produced are often aborted.

Whole tree - symptoms and growth habits of affected trees varies. Some infected trees may not appear different from non-infected trees and remain unnoticed for several years. Field diagnosis is complicated with freeze and insect damage, poor nutrition and other diseases. Trees with obvious symptoms include: fruit drop; mildly-infected trees may be normal in size but severely-affected trees are stunted with thin canopy often with a flattened top and tip dieback. Irregular flowering is common resulting in various-sized fruit with different maturities. Fruit production can be greatly reduced.

Host range
Citrus scab is only a serious problem on some varieties. It is severe on rootstock seedlings of rough lemon, sour orange, Rangpur lime, and Carrizo citrange, and scions of Murcott tangor, Temple tangor, and other tangerine hybrids. It is occasionally found on grapefruit.

Distribution
CSD occur in citrus grown in the Coachella Valley and interior valleys of central and southern California and Arizona. It is present in the Mediterranean region inducing Israel, Syria, Turkey, Morocco, etc. The disease is prevalent in temperate regions with arid or semi-arid climates where citrus is grown with irrigation. These areas have limited seasonal rainfall but enough to support rapid germination and growth of natural weed hosts of S. citri and competent leafhopper vectors. Because infected leafhoppers remain infectious for life, this pathosystem presumably sustains S. citri and only limited primary spread occurs in citrus. CSD is not known to occur in tropical or sub-tropical regions

Citrus tristeza virus (CTV)

Tristeza is vectored by several species of aphid the most efficient being the brown citrus aphid Toxoptera citricida (Kirklady). Where T. citricida does occur, Aphis gossypii (Glover), the cotton/melon aphid, is the primary vector. The aphid can acquire the virus after feeding on infected plants for 5-60 minutes; but loses the ability to transmit the virus after 24 hours.

CTV is also graft-transmitted, but not transmitted through seed. The virus exists in many forms known as strains that vary in the type and severity of symptoms manifested in host plants. Some strains are mild and produce no noticeable symptoms however; other strains are severe causing decline and death of the tree or deep pits in the trunk and stem. CTV is phloem-limited and the largest of the known plant viruses.

Symptoms
There are three distinct syndromes of CTV infection: quick decline, stem pitting, and seedling yellows. The most notorious is quick decline (QD) and is associated with the name Tristeza. It is a three-component malady consisting of a sweet orange variety used as a scion grafted onto sour orange rootstock and infected with a quick decline strain of CTV.

In this case, the virus affects the cambium layer right below the bud union and prevents the normal development of cambium cells (that mature into xylem and phloem cells). As a result, the flow of photosynthetic products from the upper portions of the tree down to the roots and water and nutrients adsorbed by the roots and transported up the tree are blocked. The decline may not occur for several years, or it may occur rapidly after a heat and/or water stress event, leaving fruit shriveled on the tree and leaves brown and dehydrated. When the decline is slow, often a bulge occurs above the bud union when a window is cut in the bark (inner flap).

Severe strains of CTV cause symptoms such as stem pitting (SP) and seedling yellows (SY), regardless of the rootstock. Grapefruit varieties are most susceptible to stem pitting strains, but these strains can be severe for many other citrus varieties. When the bark is peeled away, pits in the wood can be observed ranging from short and narrow to elongated and deep; gum is sometimes associated with the pits. Trunks may be so severely impacted that they have a ropey appearance. Severely affected trees are chlorotic, stunted, and generally have a low yield of poor quality fruit. Citrus macrophylla or alemow is most susceptible to SP strains.

Seedling yellows (SY) is typically not seen in field situations with the exception of topworking SY-infected trees with grapefruit or lemon budwood. It affects primarily young seedlings, and nursery workers rogue out affected plants. The SY reaction is frequently used to describe field collected isolates of the virus in bio-characterization experiments performed under controlled greenhouse conditions. A severe strain often causes the SY symptom in sour orange, grapefruit and lemon host indicator plants.

Leaf - chlorotic leaf flecking, vein clearing, leaf cupping, corking of leaf veins, and stem pitting.

Fruit - reduced fruit size.

Whole tree- the symptoms are similar to root injury. These symptoms include thinning of foliage, twig dieback, retardation of growth and possibly tree collapse.

Trunk - inside of the bark a honeycomb or stem pitting appearance can be detected with the unaided eye. In the trunks and limbs of larger trees, there sometimes is a bumpy or ropy appearance caused by the pitting.

Host range
The host range of this pathogen is very complex as it varies with rootstock and scion combinations, CTV strain, and environmental conditions. In general, the tristeza virus infects almost all species, cultivars and hybrids of Citrus in addition to other genera in the Rutaceae such as Aegle, Microcitrus, and Passiflora. Some pummelo genotypes and Poncirus trifoliata are resistant to most isolates. Most trifoliate orange clones and their hybrids are tolerant to most isolates and are widely used as rootstocks. Sour orange and alemow are highly susceptible. Mandarins are typically tolerant.

Distribution
CTV occurs in every citrus producing area throughout the world; however not all have severe isolates. The virus primarily spreads by the sharing of infected budwood. Most countries counteract with activity by the implementation of budwood certification programs which include the testing of budwood for graft-transmissible pathogens, budwood-clean-up through thermal therapy and shoot-tip grafting, and distribution through certified nurseries

Citrus variegated chlorosis (CVC)

CVC is a systemic disease that only survives in plant xylem or within its vector. X. fastidiosa has been shown to move from seed to seedling in sweet orange. CVC has a latency period of 9-12 months before symptoms occur.

Natural spread of X. fastidiosa occurs by several species of sharpshooter leafhoppers in the order Hemiptera. At least 11 species of sharpshooter have been shown to vector CVC. Some of these species currently occur in the United States. Sharpshooters are xylem feeders and acquire X. fastidiosa within two hours of feeding. Sharpshooters have a high rate of feeding and retain infectivity indefinitely. Sharpshooters do not pass X. fastidiosa onto the next generation. Sharpshooters have an extensive host range and may undergo one to several generations per year.

Symptoms
Leaf - foliar symptoms of CVC are very similar to nutrient deficiency and other diseases; therefore, it is difficult to rely on foliar symptoms alone for identification. Early leaf symptoms resemble zinc deficiency with interveinal chlorotic areas on the upper surface. Early symptoms may be limited to a single branch. As the leaf matures, gummy lesions become visible on the lower leaf surface corresponding to chlorotic areas on the upper surface of the leaf. The chlorotic areas gradually enlarge toward the leaf margin, and the lesions on the underside of the leaf may become dark brown or necrotic. Leaves may be smaller than normal. Leaf symptoms are most pronounced on mature leaves (behind the new flush).

Fruit - blossom and fruit occur at the normal time, but fruit thinning does not occur. This results in clusters of 4-10 early maturing fruit. Fruits of infected trees may exhibit sunburn damage because of defoliation at branch terminals. In addition, fruit may change color early, have hard rinds, lack juice, and have an acidic flavor. Fruit symptoms of CVC are more easily recognized from a distance.

Whole tree - affected trees may exhibit reduced vigor and growth, and show abnormal flowering and fruit set. Newly affected trees may only exhibit symptoms on one limb or branch, and then symptoms may spread to the entire canopy. Older trees may only show symptoms on the extremities of the branches. Severely diseased trees frequently posses upper crown branches with defoliation at terminal twigs and small leaves and fruit.

Host range
Xylella fastidiosa can infect most of the citrus cultivars, species and hybrids, yet the severity of symptoms is variable. Sweet oranges are the most susceptible. Grapefruit, mandarins, mandarin hybrids, lemons, limes, kumquat and trifoliate orange are moderately susceptible, showing less severe symptoms. Rangpur lime, citron, and pummelo are less susceptible.

Distribution
CVC is found throughout South America.

greasy spot

The major source of inoculum for greasy spot are wind-dispersed sexual spores (ascospores) produced during periods of wetness on decomposing fallen leaves. The disease cycle of this pathogen is unusual because most of the infection occurs on mature leaves. In areas with high temperature and high rainfall the disease cycle continues year round and infection may occur at any time.

Symptoms
Leaf - foliar symptoms first appear as yellow spots on the upper leaf surface, with a corresponding slightly raised, pale orange to yellowish brown blister on the lower surface. Later the symptoms on both surfaces become darker brown or black and show a more 'greasy' appearance.

Fruit - fruit exhibit necrotic specks in the epidermis between the oil glands.

Host range
Greasy spot affects all commercial citrus cultivars. It is most severe on grapefruit, lemon, tangelos and early season sweet oranges.

The fruits and leaves of grapefruit are highly susceptible.

Greasy spot is also known to affect the leaves of other rutaceous genera closely related to citrus, such as Aeglopsis, Fortunella, Murraya, and Poncirus.

Distribution
Greasy spot is found in parts of Asia, Central and South America, the Caribbean, Texas, and Florida.

Other Mycosphaerella spp. have been found in California, Australia, and the Mediterranean, but do not cause greasy spot symptoms.

Easily confused with
Citrus varigated chlorosis (CVC)

Huanglongbing (HLB)

Huanglongbing (HLB) is presumptively caused by a phloem limited bacteria. In citrus there are three forms of concern, the Asian, African and American forms. The Asian form of HLB expresses symptoms in both cool and warm conditions. The African form of HLB expresses symptoms only in cool conditions (20-250 C, 68-770 F).

Both isolates can be vectored by the Asian citrus psyllid Diaphorina citri (Kuwayana) and by the psyllid Trioza erytreae (Del Guercio). The American form was identified in Brazil in 2004 and is transmitted by D. citri there.

HLB can be graft transmitted but transmission rates are variable because of irregular distribution of bacteria within the host plant. Seed transmission may be possible but studies are not yet conclusive and if it occurs it is only at very low levels and the disease does not seem to persist beyond early seedling stages. The most important method of disease spread occurs by the two species of psyllids that serve as vectors. HLB can be acquired by both nymphs and adults, which can maintain and transmit the disease throughout their 3- to 4-month lifespan. HLB is systemic and has an incubation period of three months to multiple years before symptoms are visible.

Symptoms
Leaf - although symptoms differ according to citrus variety, common symptoms may be described. The most characteristic symptom of HLB is a blotchy mottle. This mottling is distinct from nutrient deficiency in that HLB induced mottling usually crosses the veins and is asymmetrically displayed on the leaf blade. Mottling is most frequently found on newly mature hardened-off leaves but fades with leaf age. The blotchy mottle will be visible on both sides of the leaf and have multiple hues of yellow and green. Dark green areas can sometimes be reduced to small circular dark green dots that contrast with the light yellow/green background. This symptom is referred to as green islands and had been occasionally observed on sweet orange. In addition to blotchy mottle, infected leaves may be thicker and leathery and have raised corky veins. It is common to observe foliar symptoms that resemble nutrient deficiency similar to zinc patterned deficiency. A tree affected by HLB may exhibit yellow shoots and or deficiency symptoms that are on one or many branches randomly arranged in the canopy. This contrasts with a true nutrition deficiency that is exhibited uniformly throughout the canopy. On severely infected branches leaves may form "rabbit ears" that are small upright shoots with compressed internodes.

Fruit - fruit may be small and lopsided. Cut fruit may have a curved axis and the vascular columella can be stained orange-brown. Seed abortion is also common. Fruit may ripen backwards with the stylar end remaining green as the fruit colors. The fruit symptoms with major economic impact are the reduction in fruit size, premature fruit drop, low content of soluble acids in the juice and a bitter or salty taste of the juice

Whole tree - the irregular distribution of symptoms on the tree corresponds with the irregular distribution of the bacteria in the tree. On severely infected trees, foliage may be sparse with the top third of the canopy being thin. Eventually the tree may go into a complete decline, collapse, and die. Trees with a prolonged infection appear stunted when compared to healthy trees.

Regulatory information
The most current regulatory information can be found at:

Regulation documents

Quarantine map

Host range
HLB can infect all citrus cultivars and hybrids and some relatives. Other Genera in the Rutaceae that can harbor HLB include: Atalantia, Balsamocitrus, Calodendrum, Clausena (Wampi), Fortunella (Kumquat), Microcitrus, Murraya (orange-jessamine), Poncirus (trifoliate-orange), Severinia (Chinese box-orange), Swinglea, Toddalia and Triphasia (trifoliate limeberry).

Distribution
The Asian form is found in Asia, the Middle East, South America, Central America, The Caribbean and the Southeast United States.

The African form is found in Africa and the Middle East.

The American form is found only in Brazil.

Leprosis

Citrus leprosis virus (CiLV) is transmitted by the false spider mites in the genus Brevipalpus (Acari: Tenuipalpidae). Brevipalpus mites occur on citrus around the world but do not alone cause significant damage unless the mite population is extremely high. Multiple species of Brevipalpus mites may transmit the virus; however, there has been misidentification of the mites found in association with the virus. Brevipalpus obovatus, B. californicus, and a closely related species of B. phoenicis (which has not been identified at this point)have been associated with CiLV. All three species have been collected from citrus in the United States. The disease only spreads when both infected trees and the vector is present. The virus does not appear to move systemically in the host plant with the exception of short distances along the mid-vein or secondary veinlets.

All active life stages of the mite are equally able to transmit the virus, yet there is no transovarial transmission of the virus (virus moving from female to offspring). Newly hatched mites must feed on infected plant tissue in order to acquire the virus. The virus multiplies in the mites; therefore the mite may spread the virus throughout its life.

Symptoms 

Leaf - foliar lesions are shallow but visible on both sides. Each lesion is produced in association with the feeding by the mite vector. Symptoms appear 1-2 months after inoculation. Typical lesions are circular with a dark-brown central mite feeding spot. The overall lesion size may vary from 10-30 mm with the central mite feeding spot ranging 2-3 mm in diameters. The feeding spot is surrounded by a chlorotic halo with 1 -3 concentric rings. Lesions may coalesce to form larger erratically shaped lesions. Under high temperature conditions the center of the lesion may crack.

Fruit - fruit lesions only affect the outer rind. Lesions appear as flat or depressed spots 10-20 mm wide with a necrotic center. It is common for a single fruit to exhibit up to 30 lesions covering a significant portion of the rind. Lesions on green fruit initially appear as yellow circles with a central mite feeding spot. Over time the lesion becomes brown or blackish, sometimes depressed. Infected fruit tend to change color early and become susceptible to various rots. CiLV also induces premature fruit drop which greatly reduces yield. Infected trees may have copious amounts of fruit on the ground.

Stem - on young stems, symptoms appear as small, chlorotic, shallow lesions that become darker brown or reddish. On bark and twigs lesions become corkier as they age and may progress into conspicuous scaling bark symptom. Lesions may coalesce which may lead to girdling of the stem and result in die back.

Regulatory information 

This disease does not occur in the United States.

Host range 

Hosts of the Citrus leprosis virus (CiLV) are only known to occur in the genus Citrus. Recorded hosts include Mexican lime, sour orange, rough lemon, Persian lime, lemon, citron, mandarins, mandarin hybrids, sweet oranges and grapefruits. Sweet oranges and grapefruits are considered the most susceptible; other listed varieties exhibit various levels of resistance and may not show conspicuous symptoms.

Distribution 

As of publication Citrus leprosis virus exists in Argentina, Brazil, Colombia, Uruguay, Paraguay, Venezuela, Panama, Honduras, Guatemala, Costa Rica, Nicaragua, El Salvador, and Mexico. Leprosis was found in Florida in the 1920's but no longer occurs in Florida and is considered an exotic disease throughout the United States.

Easily confused with 

CiLV leaf symptoms may be confused with measles, pesticide injury or insect damage. CiLV fruit symptoms may be confused with citrus canker. On the trunk CiLV bark scaling symptoms can appear similar to citrus psorosis. However, the psorosis virus causes wood staining while CiLV does not.

Lime anthracnose

The epidemiology of this disease has not been completely studied. Lime anthracnose survives year to year on dead twigs and in lesions on mature leaves. It only infects young tissues following spore dispersal by water splash. The constant leaf flushing of key limes together with the large amount of innoculum that can be produced on these tissues, make lime anthracnose difficult to control.

Symptoms 

Leaf - foliar symptoms are visible as necrotic spots that may produce a shot-hole effect if the necrotic areas fall out. In severe infections the leaves and entire young shoots can become totally blighted and drop. In addition shoot tips may die back and leaf distortion may occur.

Fruit - infection of young fruit usually results in premature fruit drop. Late infections produce lesions that are often large and deep and accompanied by fruit distortion.

Host range 

Key/ Mexican lime (Citrus aurantifolia) is the only known host.

Distribution 

Lime anthracnose occurs in humid regions of the Americas as well as Zanzibar (Africa).

Mal secco

Conidia are produced in pycnidia found on withered twigs and from hyphae growing on exposed wood or debris, including branches, leaves, and fruits. Most probably the pathogen can also be transmitted to other trees through contaminated pruning tools. Twigs and leaves lying on the soil may be a source of inoculum for infection through wounded roots. Leaves infected by the fungus fall to the ground during autumn and spring, and the fungus within the leaf tissue are able to sporulate at temperatures ranging from 10 to 25°C (55 to 77°F).

Under natural conditions, the inoculum can be dispersed by wind and rain; P. tracheiphilapenetrates the host through wounds via both conidia and mycelium. Infection usually occurs during the winter. Although the optimum temperature for pathogen growth is about 25°C (77°F), optimum temperature for symptom expression and xylem colonization is 20 to 22°C (68 to 72°F). Infection occurs between 14 and 28°C (57 and 82°F), whereas at temperatures above 28°C (82°F), fungal growth ceases and symptoms are not expressed. A unique characteristic of this fungus is its ability to produce a- sexual spores called phialoconidia. These are spores formed on the mycelium in the plant xylem released into the transpiration flow. When a spore reaches a location where it can germinate it forms new hyphae causing disease.

Symptoms 

Typical symptoms include veinal chlorosis, leaf wilt; red coloration of the xylem and dieback of twigs and branches; in many cases dieback is sectorial. The pathogenproceeds slowly downward from the infected young shoots to the branches and main limbs; when the trunk and roots become infected, the tree dies. When the fungus infects the base of a trunk or the roots, a phenomenon can occur known as – mal fulminante. In these cases, the tree usually dies quickly.

Host range 

The principal host of mal secco is lemon. The disease is highly destructive on lemon, and citron (C. medica L.), lime (C. latifolia Tan.), and bergamot (C. bergamia Risso) also have been reported to be very susceptible to natural infections. Different degrees of resistance are shown by other species and hybrids. Sweet orange (C. sinensis (L.) Osbeck), grapefruit (C. paradisi Macf.), clementine mandarin (C. clementina Hort.), tangerine (C. reticulateBlanco), and mandarin (C. deliciosa Tenore) are affected sporadically by the disease and are considered tolerant. Among rootstocks, sour orange (C. aurantium L.), the most widespread lemon rootstock in Italy, Greece, and Turkey, rough lemon (C. jambiri Lush.), Volkamer lemon (C. volkameriana Ten. & Pasq.), and alemow (C. macrophilla Wester) are very susceptible. Reports on the degree of susceptibility of citrus species to mal secco are sometimes contradictory, especially for rootstocks. Sour orange, for example, is considered to be very susceptible in Italy, but only moderately affected in Israel. It can be stated that almost all citrus species are susceptible to P. tracheiphila when artificially inoculated by wounding.

Distribution 

Mal secco is present in all the citrus producing countries in the Mediterranean and Black Sea areas with the exception of Spain, Portugal, Morocco, and some areas of the Arabian Peninsula. The disease is not known to occur in the citrus-growing countries of the Americas or Oceania, even though there is no obvious climatic or cultural factor limiting the establishment of mal secco disease in non infested areas.

Easily confused with 

Citrus blast (Pseudomonas syringae pv. syringae)

Measles

Disease cycle 

Measles can be graft transmitted.

Symptoms 

Leaf - numerous pale yellow spots on leaves that can be seen on the upper leaf surface and appear tan to brown on the lower surface.

Whole tree - often a single branch or limb exhibits symptoms.

It should be noted that: Measles occurs on rare occasions. It tends to only occur on a few trees in a grove.

Host range 

Measles has been observed on multiple sweet orange varieties.

Distribution 

Measles has occurred in Florida and Brazil. Larger scale outbreaks have been reported in Brazil.

Easily confused with

Citrus varigated chlorosis (CVC), leprosis, and psorosis

Melanose

Melanose is a saprophyte that completes its lifecycle on dead twigs. The disease severity is determined by the amount of inoculumon dead wood in the tree canopy and the duration of wetting periods following rainfall or overhead sprinkler irrigation. Around 18-24 hours of wetting are required for infection to occur and severe infection is favored by long periods of continuous wetting. Spores cause problems when there are significant amounts of dead wood on trees, on the ground or in piles of brush left in the grove. 

Symptoms 

Leaf - about one week after infection foliar symptoms appear as small brown discrete spots. These spots become impregnated with a reddish-brown gum and are raised above the leaf surface. Early pustules on leaves are surrounded by a yellow halo. However, this halo quickly disappears leaving only small corky pustules. The numerous small pustules give the leaf a rough sandpaper texture. Distortion and dieback of young shoots are associated with severe infections.

Fruit - fruit symptoms can vary depending on the age of the fruit at the time of infection. Early infections, soon petal fall, will show relatively large pustules and when in large numbers they may coalesce to form extensive areas that often crack to produce a pattern described as "mudcake melanose". Infections during later stages of fruit development produces small discrete pustules distributed by spore-laden rain or dew which flows over the fruit surface creating the "tear-stain melanose" pattern. These injuries to the fruit rind are superficial and are not important if the crop is processed. If copper fungicides are applied for control, stippling, copper fungicide damage, may occur, which can resemble the disease and is often called star melanose.

Host range 

All citrus cultivars.

Distribution 

Present in most citrus producing counties.

Nutrient deficiency

Nutrient deficiencies have a wide range of symptoms that will not be fully covered in this key. Things to look for are how symptoms are distributed throughout the tree and throughout the grove. Nutrient deficiencies tend to be more uniformly distributed in the tree than the diseases they are commonly confused with. A nutrient deficiency may express itself on the whole tree level causing twig die-back, long thin branches, yellowing, and reduced or abnormal growth. Nutrient deficiencies may alter fruit characteristics such as shape, hardness, peel thickness, and peel texture. Nutrient deficiencies may manifest on leaves resulting in chlorosis, enlarged or shrunken leaves, raised veins, unusual leaf patterns and changes in leaf coloration. For example, zinc deficiency will appear on new foliage throughout the tree in contrast to early HLB symptoms which are restricted to a single or a few shoots.

Host range 

All citrus is susceptible to nutrient deficiency.

Easily confused with 

Huanglongbing (greening), citrus varigated chlorosis (CVC), psorosis

Phytophthora

Phytophthora is a water mold (Class Oomycetes, formerly a fungus-like protist) that is found throughout the world. Under favorable conditions (high moisture and temperature) it produces large numbers of motile zoospores that can swim in water for short distances. These zoospores are the infective agents that may be transported in rain or irrigation to the roots. When zoospores contact roots they encyst, germinate and enter the root tip resulting in rot of the entire rootlet.

Foot rot or gummosis occur when zoospores splash onto a wound or bark crack around the base of the trunk. Additionally, there is an association of Phytophthora root rot when roots are damaged by citrus root weevils, particularly Diaprepes abbreviatus.Root stock susceptibility depends on which Phytophthora species are present and the presence of favorable soil, water and environmental conditions.

Symptoms 

Leaf - yellow foliage and shoot die-back. If citrus weevils are present adults may feed on leaves causing notching.

Fruit - reduced fruit size and yield.

Trunk - infection of the trunk by Phytophthora results in dark water soaked areas in the area of active infection. Lesions usually occur on the bark or at the bud union. Lesions may exude copious amount of gum and a brown necrotic area will be found under the bark lesions. Dead bark tends to break away from the trunk in vertical strips. Lesions may spread around the circumference of the trunk slowly girdling the tree.

Whole tree - Phytophthora may result in poor tree health, thin canopy, failure to make new growth, and little water and nutrient uptake leading to wilting. When roots are infected the surface of the root becomes soft, discolored and appears water-soaked. Fibrous roots slough their cortex leaving only the white thread-like root cylinder.

It should be noted that: Phytophthora root rot symptoms progress much more rapidly in the presence of the citrus root weevil.

Host range 

Most scion cultivars are susceptible to bark infection, while most root stocks are moderately tolerant to bark infection. In ascending order, Cleopatra mandarin, Sour orange, rough lemon, Rangpur lime, Carrizo, Troyer are tolerant to root rot. Trifoliate, Swingle citrumelo, Yuman and alemow are considered highly resistant to bark infection and tolerant to root rot. Swingle citrumelo is the most tolerant rootstock. The presence of Diaprepesroot weevils, Phytophthora palmivora and poorly drained soil can render normally tolerant Swingle citrimelo and Carrizo suseptible to Phytophthora root rot infection.

Distribution 

Phytophthora spp. are found in citrus producing region around the world.

Easily confused with 

Phytophthora bark infection can be easily confused with psorosis.

Pseudocercospora fruit and leaf spot

Pseudocercospora angolensis is a fungus that requires moisture for infection and the production of wind-borne conidia. Other than by wind, conidia can be transported on infected fruit or propagative material. Local dispersal is primarily by rain-splash or raindrops. Humans mediate in the dissemination of the fungus through transport of infected plant material and/or fruits from infected areas. Because leaf lesions produce more conidia than similar lesions on fruit, it is more likely that they constitute the main source of infection during disease spread in infected areas.

The fungus probably survives in dormant lesions on infected material until the onset of conditions is conducive to sporulation.

The disease is favored by prolonged wet weather that stimulates the production of new susceptible flush. Lesions produced the previous season can begin to sporulate within two weeks of the beginning of the rainy season, at most temperatures in the tropics, and those spores infect the new tissue.

 

Symptoms 

Leaf - the fungus produces circular, mostly solitary spots up to 10 mm in diameter, which often coalesce. Lesions have light brown or grayish centers when dormant and are non-sporulating during the dry season, but becoming black with sporulation after the onset of the rainy season. The lesions are usually surrounded by a dark brown margin and a prominent yellow halo; occasionally the centre of the lesions falls out, creating a shot-holeeffect. At first glance the young lesions appear similar to those of canker (caused by Xanthomonas citri spp.-pv citri) but differ in being flat or shrunken. Leaf spots, especially on younger leaves, often coalesce and cause generalized chlorosis, followed by premature abscission and defoliation of the affected tree. Yound leaves and fruit appear to be more susceptible than older mature leaves, but whether the leaves or fruit are more affected varies with the hose species, variety, and location.

Fruit - the spots are circular to irregular, discrete or coalescent, and mostly up to 10 mm in diameter. On young fruits, infection often results in hyperplasia, producing raised tumor-like growths surrounded by a yellow halo; these develop central necrosis and collapse. Lesionson mature fruit are normally flat but sometimes have a slightly sunken brown centre. Diseased fruits ripen prematurely and drop (can be significant) or dry up and remain on the tree. Infection by the fungus seems to predispose the fruit to secondary infection by Colletotrichum gloeosporioides; it is common to find a dark-brown to black sunken margin of anthracnose around the fruit spots.

Stem - stem lesions are not frequent and mostly occur as an extension of lesions on the petiole. Occurrence of several such lesions at the stem tip results in dieback; those on other parts of the stem coalesce, become corky, and crack. At the base of the dead stem, there is usually a profuse growth of secondary shoots.

Host range 

Citrus spp. (Rutaceae); the disease has been observed on all citrus species, including grapefruit, lemon, lime, orange, pummelo, and mandarin. Grapefruit, orange, pummelo, and mandarin are very susceptible, lemon is less susceptible, and lime is the least susceptible.

Distribution 

Africa (in the humid tropics), Comoros Islands, and Asia (Yemen)

Easily confused with 

At an early stage, the lesions caused by Pseudocercospora angolensis on leaves appear similar to those of citrus canker caused by bacterium Xanthomonas citri spp. citri (Hasse) Dye. They differ in being flat or shrunken, rather than raised. Canker lesions on leaves also have a yellow halo, but are distinguished by a water-soaked margin around the spot, as are the flat lesions caused by other bacterial pathogens of citrus.

The fungus Guignardia citricarpa Kiely also causes spots on leaves and/or fruits of citrus in Africa, Asia, Australia, and South America, but leaf lesions are uncommon. The lesions of the disease called "black spot" may resemble those produced by P. angolensis, particularly on lemon leaves. Small, globose, black fungal pycnidia containing single-celled colorless spores often are produced in these spots.

Psorosis

Psorosis is transmitted by grafting. There is some evidence of natural spread, possibly by Olpidium brassicae which transmits other ophioviruses, or by an aerial vector. The incidence of psorosis has been reduced in many areas by using budwood certification programs.

Symptoms 

Leaf - foliar symptoms have a wide range and are best seen on young leaves nearing full expansion. Symptoms include chlorotic flecks that are irregularly distributed, leaf mottling, and round chlorotic spots. Symptoms may fade as leaves mature. 

Fruit - fruit may have ring shaped chlorotic patterns.

Whole tree- the most distinguishable symptom of psorosis is the scaling and flaking of the bark on the trunk and limbs. In the early stages this shows as small pimples or bubbles that later enlarge and break up into loose scales. Wood becomes impregnated with gum and is stained. Psorosis B caused bark lesions that are rampant and expand rapidly sloughing off large strips of bark.

Host range 

Psorosis affects most citrus species and their hybrids. Sweet orange, grapefruit and tangerines are severely affected.

Distribution 

Psorosis is found throughout the citrus producing world.

Easily confused with 

On the trunk citrus leprosis bark scaling symptoms can appear similar to citrus psorosis. However, the psorosis virus causes wood staining while citrus leprosis does not.


Septoria

Septoria has saprophytic capabilities and pycnidia often form on dead twigs and leaves. Conidia from these pycnidia are spread by splashing water and may infect leaves and fruit. However, symptoms may not result for up to six months after infection. 

 

Symptoms 

Leaf - foliar lesions are blister-like, raised, black and 1-4 mm in diameter. Over time the center of the lesions become necrotic and pale brown. Pycnidia develop in the lesionsespecially following leaf drop when the lesion turns dark brown with dark margins. When conditions are favorable, the disease may cause severe leaf drop in the lower portion of the tree.

Fruit - early fruit lesions are small light tan to reddish brown pits 1-2 mm in diameter that extend no deeper than the flavedo. Older lesions are darker sunken 20-30 mm in diameter. Dark fruiting bodies, pycnidia, may develop in these lesionsLesions may appear in the form of "tear stains" patterns. Spots are more evident on ripe fruit.

Host range 

All citrus cultivar are susceptible. However, Valencia oranges, Navel oranges, lemons and grapefruit are frequently damaged.

Distribution 

This disease has been reported from most citrus producing areas throughout the world.

Sweet orange scab

Sweet orange scab forms spores on the surface of the scab pustules. This species of scab attacks mainly fruits. The conidia (asexual spores) are similar to those of E. fawcettii,require moisture for sporeproductionand are primarily spread by splashing rain. Fruits are susceptible for 6 to 8 weeks after petal fall. The role of ascospores (sexual spores) is uncertain.

 

Symptoms 

Sweet orange scab does not usually form lesions on leaves or twigs in contrast to the more common Citrus scab.

Fruit- the rinds of young fruit display relatively large flat or warty outgrowths (windscar) which vary in color from a light pink to a grayish-brown with age. Sweet orange scablesions are flatter than those produced by E. fawcettii (Citrus scab).

Host range 

Grapefruit, sweet orange, lemon, and tangerine cultivars.

Distribution 

Rio Grande Valley-Texas, Arizona, Florida, Brazil, Argentina, Bolivia, and Uruguay.

Easily confused with 

Citrus scab (Elsinoe fawcettii)

 

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