Dr. Ozgur Batuman | Plant Pathology Department | University of Florida Institute for Food and Agricultural Sciences | Southwest Florida Research and Education Center, Immokalee FL
Common Florida Citrus Diseases
Below is a list of common pathogens that may affect citrus varieties around Florida.
Please consider submitting samples for diagnosis through the SWFREC Diagnostic Clinic if you suspect a problem.
Citrus Greening - HLB (Huanglongbing)
Causal Agent: bacteria, Candidatus liberibacter, unculturable
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms: asymetric blotchy bottling of leaves with multiple shades of green, mishapen green fruits that do not ripen before falling prematurely.
There is also "green islands" sumptom where dark green areas get reduced to small dark green dots. Mottled leaves may be thicker and more leathery and have corky raised veins. Some of these syptoms ressemble zinc patterned deficiency. The difference is diseased trees have symptoms occuring in random manner, whereas nutrient issues happen uniformly.
Citrus Canker
Causal Agent: bacteria, Xanthomonas axonopodis pv. citri
Symptoms: Leaf lesions range from 2-10mm and have raised concentric circles on underside of leaf. They often have water-soaked mragin and yellow halo. Yellow halo eventually changes to dark brown or black. Lesions always penetrate through both sides of leaf.
Fruit lesions are similar, 1-10mm in size, large lesions can penetrate a few milimeters into rind. Lesions may coalesce. Texture of lesion may include corky appearance and cracking as it ages.
Citrus Black Spot
Causal Agent: fungus, Phyllosticta citricarpa
Symptoms: three main spot symptoms: virulent spot, cracked spot, hard spot. Virulent spot is small red spots, cracked is a thicker blister/scab like appearance, hard spot is the most typical symptom, appears usually around color change. All of these lesions range from 3-10mm in diameter. Younger lesions are small and reddish, with yellow halos. Foliar lesions are not as common as fruit symptoms.
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Greasy Spot
Causal Agent: fungus, Mycosphaerella citri
Symptoms: foliar spots that appear yellow at first, with a slightly raised area on lower surface, and later these spots become brown or black, with a slightly "greasy" appearance
Citrus Leprosis
Causal Agent: virus, Citrus leprosis virus (CiLV)
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms: foliar and fruit lesions. Symptoms appear 1-2 months after mite vector inoculates. Typical lesions are circular with dark brown central mite feeding spot, 2-3mm in diameter. Feeding spot is surrounded by a chlorotic halo. Lesions may coalesce, and crack in high temperature conditions
Citrus Tristeza Virus
Causal Agent: virus, Citrus Tristeza Virus (CTV)
Symptoms: various symptoms and often asymptomatic. The most distinct ones are quick decline, stem pitting, and seedling yellows.
Brown Rot
Causal Agent: fungus, Phytophthora nicotianae or P. palmivora
Symptoms: rotting appears on mature or nearly mature fruit, starts with leathery lesions that may have water-soaked appearance. They are olive brown, have an odor, and may turn soft from secondary infections. Sometimes infection spreads to twigs, leaves, and blossoms.
Environment: when conditions are cool and wet, and to fruit closest to the ground because phytphthora spores are splashed from soil during rainstorms and infections develop under continued wet conditions.
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Viroids: Exocortis and Cachexia
Causal Agent: viroids (small infectious citrcular-RNA molecules)
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms: Exocortis causes dwarfing and bark scaling on rootstocks like trifoliate orange and many hybrids, including Rangpur lime, Carrizo citrange, etc. Stunting is more severe on some rootstocks like trifoliate orange.
Cachexia causes severe pitting and gumming in the bark and wood of trunks and branches.
Spread mechanically from tree to tree, through contaminated equipment
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Citrus Blight
Causal Agent: unknown
Symptoms
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Phytophthora spp.
Causal Agent: water mold, oomycete (fungus like)
Symptoms
Leaf: yellow foliage and shoot die-back. possible notching if citrus weevils are feeding
Fruit: reduced fruit size and yield
Trunk: dark water soaked areas in active infection. Lesions on bark or bud union. May be gummosis and necrosis under lesions. Dead bark may break way from trunk in vertical strips
Whole tree: poor tree health, thin canopy, little water ad nutrient uptake leading to wilting
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Pythium
Causal Agent: water mold, oomycete (fungus like)
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms
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Postbloom Fruit Drop (PFD)
Causal Agent: bacteria, Candidatus liberibacter, unculturable
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms
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Citrus Scab
Causal Agent: bacteria, Candidatus liberibacter, unculturable
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms
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Anthracnose
Causal Agent: bacteria, Candidatus liberibacter, unculturable
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms
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Diplodia
Causal Agent: bacteria, Candidatus liberibacter, unculturable
Vector: Asian citrus psyllid (Diaphorina citri)
Symptoms
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