Citrus Diseases

Alternaria Stem-End Rot (Black Rot)

Fungal pathogen

Alternaria citri

Area(s) affected

Fruit                                   

Signs/Symptoms

Cracks in the stylar end of the fruit, or the bellybutton of the fruit, allow the fungus to enter and infect the fruit. Infected fruit will change color prematurely and may drop early from the tree.  A light brown to black spot on the rind can be noticed near the stylar end of the fruit and when the it is sliced open one can observe the black rot inside the fruit.

For more information

http://www.ipm.ucdavis.edu/PMG/r107100811.html

http://www.plantprotection.hu/modulok/angol/citrus/alternariarot_cit.htm

 

Cachexia (Xyloporosis)

Causal agent

Viroid

Area(s) affected

Trunks and branches

Signs/Symptoms

When the bark is peeled back one can observe smooth depressions in the wood which correspond to projections extending from the inner bark.

For more information

https://edis.ifas.ufl.edu/cg037

 

 

Citrus Greening (Huanglongbing)

Bacterial pathogen

Candidatus Liberibacter spp.

Area(s) affected

Entire tree

Signs/Symptoms

Infected trees may decline and eventually die. Fruit maybe small and lopsided.  Irregular patterns of dark green, light green and yellow blotches (mottling) cross the veins of leaves and are asymmetrically displayed on the leaf blade. Infected leaves may be thicker and leathery compared to healthy leaves.

Photo credit: Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

Photo credit: Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, Bugwood.org

For more information

http://www.texascitrusgreening.org/

http://idtools.org/id/citrus/diseases/factsheet.php?name=Huanglongbing+%28HLB%29

 

Citrus Tatter Leaf

Causal agent

Citrus tatter leaf capillovirus, (syn. Citrange stunt virus)

Area(s) affected

Entire tree

Signs/Symptoms

Infected plants are usually symptomless. However, when symptoms are produced, one can observe leaf yellowing, leaf deformation, twig deformation, stunting, overblooming, and premature fruit drop. This virus also causes a bud-union crease, which can be seen when the bark is peeled back. One can observe a yellow to brown line where the scion and stock were grafted together.

For more information

http://www.eppo.int/QUARANTINE/virus/Citrus_tatter_leaf/CTLV00_ds.pdf

 

 

Cotton Root Rot

Fungal pathogen

Phymatotrichopsis omnivora, (syn. Phymatotrichum omnivorum)

Area(s) affected

Roots

Signs/Symptoms

Infected plants die suddenly. Root bark is decayed and brownish, and bronze colored wooly strands of the fungus are frequently apparent on the root surface. Leaves will turn brown and remain attached to the branches.

For more information

http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2321/EPP-7621web.pdf

 

 

Diplodia Stem-End Rot

Fungal pathogen

Diplodia natalensis, (syn. Physalospora rhodina)

Area(s) affected

Fruit

Signs/Symptoms

This disease remains dormant while the fruit is still attached to the tree. Once the fruit is removed and put into storage, symptoms will be produced. The rind will first turn brown near the stem end of the fruit and then will progress down the fruit forming brown, finger-like streaks. The whole fruit will eventually turn black and give off a sour, fermented odor.

For more information

http://edis.ifas.ufl.edu/ch107

 

 

Exocortis

Causal agent

Citrus exocortis viroid (CEVd)

Area(s) affected

Rootstock

Signs/Symptoms

Infected rootstocks will be stunted and the bark at the crown of the tree will peel off, this is known as bark shelling. A gummy substance may also exude from the base of the trunk.

For more information

https://edis.ifas.ufl.edu/cg037

 

Flyspeck

Fungal pathogen

Leptothyrium pomi

Area(s) affected

Fruit

Signs/Symptoms

Small black dots form on the rind near the oil glands. This causes the affected area to remain green when the fruit matures, or turns yellow. This does not affect the fruit or juice quality, only the fruit grade.

For more information

http://aggie-horticulture.tamu.edu/citrus/l2316a.htm

 

 

Green Mold

Fungal pathogen

Penicillium digitatum

Area(s) affected

Fruit

Signs/Symptoms

Fruit injured during harvesting and handling may be infected by this fungus. The fungus enters the fruit only through wounds in the rind and these wounds soon turn to water soaked lesions. A white substance eventually forms on the lesion and as the lesion gets larger, the center will turn olive green and be outlined in white.

Photo credit: Gerald Holmes, Valent USA Corporation, Bugwood.org

Photo credit: Gerald Holmes, Valent USA Corporation, Bugwood.org

For more information

http://edis.ifas.ufl.edu/ch106

 

 

Greasy Spot

Fungal pathogen

Mycosphaerella citri

Area(s) affected

Leaves and fruit

Signs/Symptoms

Yellow to dark brown to black spots form on the underside of the leaf. As these spots darken, corresponding yellow spots will form on the upper leaf surface. Leaves may drop prematurely. If the fruit is infected, small black spots will form on the rind and the surrounding area will remain green longer.

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

For more information

http://edis.ifas.ufl.edu/hs263

 

 

Heart Rot/Wood Rot

Fungal pathogen(s)

Ganoderma spp.

Area(s) affected

Trunk

Signs/Symptoms

At the base of infected trunks, brown to reddish-brown, fan-shaped structures can be observed.  This infection causes internal wood rot and the affected tree will eventually decline or die.

For more information

http://edis.ifas.ufl.edu/hs269

 

 

Citrus Leafminer

Pest

Phyllocnistis citrella

Area(s) affected

Leaves

Damage

Females lay larvae singly on the underside of the leaf. After the larvae hatch they begin to feed in shallow, serpent-like tunnels in the leaves. The tunnels are filled with frass, or excrement. Affected leaves will curl and be distorted.

Photo credit: Whitney Cranshaw, Bugwood.org

Photo credit: Whitney Cranshaw, Bugwood.org

For more information

http://edis.ifas.ufl.edu/in165

http://www.ipm.ucdavis.edu/PMG/r107303211.html

 

Melanose

Fungal pathogen

Diaporthe citri

Area(s) affected

Leaves and fruit

Signs/Symptoms

Small, brown spots surrounded by a yellow halo form on the leaf surface. As the disease progresses, a gummy substance exudes from the spot, dries, hardens, and gives the leaf a sandpaper texture.  Leaves may drop prematurely.

Small, brown to black raised spots form on the fruit surface. If these spots coalesce they form an irregular, cracked pattern known as “mudcake melanose.” Sometimes these spots develop in a tear-streaked pattern known as “tear-stain melanose.”

Photo credit: Cesar Calderon, USDA APHIS PPQ, Bugwood.org

Photo credit: Cesar Calderon, USDA APHIS PPQ, Bugwood.org

For more information

http://edis.ifas.ufl.edu/ch019

http://idtools.org/id/citrus/diseases/factsheet.php?name=Melanose

 

Physiological Disorders

Causal agent(s)

Wind, strong sunlight, nutrient deficiencies, herbicide toxicity

Area(s) affected

Leaves and fruit

 

Firing: wind desiccation

Leaf Yellowing: Magnesium, iron or zinc deficiencies and herbicide injury.

Oleocellosis: Peel oil is released when rind cells have been injured as a result of abrasion or rough handling. Sunken spots form on the rind.

Spray Burn: The fruit has a dry, brown sunken spot.

Sunscald: When the undersides of leaves are exposed to direct sunlight, irregular, brown, raised spots may be observed.

Wind Scar: This damage occurs as the result of twigs or leaves rubbing against young fruit

For more information

 

 

Phytophthora Diseases

Fungal pathogen(s)

Phytophthora citrophthora, P. parasitica, and other Pytophthora spp.

Area(s) affected

Fruit, roots, and trunk

Signs/Symptoms

Brown Rot: The low-hanging fruit become infected first and then water will disseminate the fungus to fruit higher in the tree. Light brown lesions will form on the rind. As the disease progresses, in humid conditions, a white velvety growth can be observed on the rind and the fruit will give off a pungent, rancid odor.

Feeder Root Rot: The fungus infects the cortex of feeder roots, giving the root system a stringy appearance. This can lead to yield loss and a general prolonged tree decline.

Foot Rot/Gummosis: Infection of the trunk results in a dark, water-soaked areas, often with profuse exudation of a dark resin from the lesion. The dead bark frequently sloughs off the wood in vertical strips. If the lesion encircles the trunk, girdling occurs, leading to the death of the tree.

For more information

http://edis.ifas.ufl.edu/ch109#IMAGE%20CH:CH109P

http://www.ipm.ucdavis.edu/PMG/r107100111.html

http://www.ipm.ucdavis.edu/PMG/r107100411.html

https://edis.ifas.ufl.edu/hs261

 

Rio Grande Gummosis

Fungal pathogen

Physalospora rhodina, (syn.  Diplodia natalensis) and several other factors

Area(s) affected

Trunk and branches

Signs/Symptoms

Blisters on the trunk exude a pale yellow, gummy substance. The wood beneath infected tissue is pink to orange in color. Gum pockets may form.

For more information

http://aggie-horticulture.tamu.edu/citrus/l2313.htm

http://www.ivia.es/iocv/enfermedades/Rio_Grande_Gummosis/Rio_Grande_Gummosis.htm

 

Citrus Rust Mite (Silver Mite)

Pest

Phyllocoptruta oleivora

Area(s) affected

Fruit

Signs/Symptoms

Mites feed on the fruit destroying the rind cells. When the fruit is green destroyed cells turn black (“bronzing”) and when the fruit is mature destroyed cells turn rust brown and are rough to the touch (“sharkskin”).

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

For more information

http://edis.ifas.ufl.edu/ch179

http://www.ipm.ucdavis.edu/PMG/r107400511.html

 

Psorosis (Scaly Bark)

Causal agent

Citrus psorosis virus

Area(s) affected

Entire tree

Signs/Symptoms

Leaves may exhibit yellow irregular flecks, blotches or round spots. Fruit may exhibit a yellow ring shaped pattern on the rind. Trunk and limbs will exhibit bark scaling or flaking, where the bark sloughs off. A gummy substance may form around the bark lesions, impregnating the wood, eventually leading to the rapid decline of the tree. The tree will become unproductive.

For more information

http://idtools.org/id/citrus/diseases/factsheet.php?name=Psorosis

http://www.ipm.ucdavis.edu/PMG/r107100100.html

 

Slow Decline

Causal agent

Tylenchulus semipenetrans

Area(s) affected

Entire tree

Signs/Symptoms

The nematode feeds on the roots causing aboveground symptoms: canopy thinning, lack of vigor, poor fruit production, small leaf and fruit size, and exposure of bare crown limbs.

For more information

http://edis.ifas.ufl.edu/in941

http://www.ipm.ucdavis.edu/PMG/r107200111.html

 

Sooty Mold

Fungal pathogen

Capnodium spp.

Area(s) affected

Leaves, fruit and branches

Signs/Symptoms

Leaves, fruit and sometimes branches have a black, moldy appearance. The fungi causing sooty mold do not actually infect the plant, instead they grow on the sugary exudates (honeydew) of insects such as aphids, brown soft scale, blackflies and whiteflies. This can cause premature leaf drop and stunting of the tree.

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

Photo credit: Don Ferrin, Louisiana State University Agricultural Center, Bugwood.org

For more information

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74108.html

 

Sweet Orange Scab (SOS)

Fungal pathogen

Elsinoe australis

Area(s) affected

Fruit

Signs/Symptoms

Tan to gray, corky, wart-like scabs will form on the fruit rind.

Photo credit: Corinne Rhodes, Texas A&M University

Photo credit: Corinne Rhodes, Texas A&M University

Photo credit: Corinne Rhodes, Texas A&M University

Photo credit: Corinne Rhodes, Texas A&M University

Photo credit: Corinne Rhodes, Texas A&M University

Photo credit: Corinne Rhodes, Texas A&M University

For more information

http://idtools.org/id/citrus/diseases/factsheet.php?name=Sweet+orange+scab

 

Tristeza (Quick Decline)

Causal agent

Citrus tristeza virus

Area(s) affected

Entire tree

Signs/Symptoms

The symptoms produced depend on the variety of plant, environmental conditions, and the virus strain. The virus can cause the tree to decline, leading to tree death. There are three distinct syndromes of the disease: quick decline, stem pitting, and seedling yellows. Leaves will exhibit yellow flecking, leaf cupping, and light green to yellow leaf veins. Fruit quality and size will be reduced. Branches and trunks will exhibit pitting, and if it is serious they will take on a ropey appearance.

Photo credit: L. Navarro, Instituto Valenciano de Investigaciones Agrarias, Bugwood.org

Photo credit: L. Navarro, Instituto Valenciano de Investigaciones Agrarias, Bugwood.org

For more information

http://idtools.org/id/citrus/diseases/factsheet.php?name=Tristeza#

http://edis.ifas.ufl.edu/cg039

 

Twig Dieback

Fungal pathogen

various fungi, as well as other factors

Area(s) affected

Branches

Signs/Symptoms

Fungal infection often occurs following a freeze or mechanical or chemical injury. Affected young branches die back from the tip, sometimes producing gum exudation. Wood discoloration under the bark maybe observed.

For more information

 

 

For additional support and current disease management information, contact your local AgriLife Extension Office: http://counties.agrilife.org/

Content editor: Corinne Rhodes, Undergraduate Extension Assistant, Texas Plant Disease Diagnostic Laboratory.  This project was performed to satisfy BESC485 requirement under the supervision of Dr. Kevin Ong,  kevo@tamu.edu, Director, Texas Plant Disease Diagnostic Laboratory, Texas A&M University, Texas AgriLife Extension Service (April 25, 2014)

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