Citrus black spot (CBS) is a citrus disease caused by the fungus Phyllosticta citricarpa (previously known as Guignardia citricarpa). This fungus affects citrus plants throughout subtropical climates, reducing both fruit quantity and quality. All commercial cultivars are susceptible, but late-maturing cultivars and lemons are most vulnerable.
Both ascospores (sexual spores) and conidia (asexual spores) of Phyllosticta citricarpa can infect susceptible tissues. Ascospores are found in microscopic fungal structures embedded in the leaf litter. They are the most important source of inoculum, causing nearly all infections. Ascospores have not been found in fruit lesions or lesions on attached leaves. The ascospores are released when the leaf litter is wetted by moisture, such as heavy dew, rainfall, or irrigation.
On April 7, 2010, the Animal and Plant Health Inspection Service (APHIS) confirmed the first U.S. detection of citrus black spot on citrus fruit from a commercial Valencia orange grove in Collier County, Florida. In 2010, CBS was also detected in Hendry County, Florida. The disease is still limited to southern Florida.
Symptoms can be found on fruit and leaves, but are easiest to identify on mature fruit. Fruit are susceptible to infection for six months following fruit set. Leaves typically do not show symptoms, but foliar lesions can be observed on highly susceptible varieties, such as lemon, or on stressed trees. On lemon, fruit pedicels may also show symptoms. All citrus varieties are susceptible to citrus black spot, making strict regulation and management necessary to prevent spread of this disease.
Young foliar lesions are small, round, slightly raised, reddish-brown with light centers and a diffuse yellow halo.
Older lesions are sunken, with a gray center and dark brown margin.
Lesions on fruit are diverse and grouped by symptom-based names.
Hard spot is the most typical symptom of citrus black spot on fruits. Symptoms appear as the fruit matures, often around the time of color change, as circular depressions that are 3-10 mm (0.12 - 0.4 inch) in diameter. Lesions have tan to gray centers with a distinct or prominent brick-red to dark brown margin. Lesions develop on the side of the fruit most exposed to sunlight.
False melanose symptoms appear as numerous, small lesions that are dark brown, raised, and less than 1 mm (0.04 inch) in diameter. These lesions are much smaller than hard spot lesions. False melanose occurs on green fruit.
Freckle spot lesions are round, depressed lesions that are 1-3 mm (0.04 - 0.12 inch) in diameter, and reddish in color. This type of symptom is considered a sign of a heavy infection. Freckle spot lesions can remain as single lesions or coalesce to form the virulent spot type of lesion late in the season or during storage.
Cracked spots lesions are dark, smooth, and variable in size with irregular margins and a cracked surface. They form on green fruit and remain visible on mature fruit. This symptom has only been observed in the Americas and is often found associated with rust mite damage.
Virulent spot lesions occur on heavily-infected mature fruit toward the end of the growing season and are necrotic, sunken and irregular lesions that cover a large area of the fruit. This symptom is caused by the expansion and/or fusion of other lesions. Virulent spot may accompany premature fruit drop and serious post-harvest damage because the lesions may extend into the fleshy part of the fruit.
For details on requirements for moving a regulated article, please consult the regulated articles table below. The table is organized by regulated article so users can find the requirements for moving fruit or other regulated articles.
Huanglongbing (HLB) is spread by a tiny insect, the Asian citrus psyllid (ACP, Diaphorina citri). First detected in Florida in 1998, ACP spread to Texas in 2001, California in 2008, and Arizona in 2009. ACP is now present in all citrus growing regions of the United States.
ACP reproduce on newly developing leaves, and while the insect itself causes little direct feeding damage, the insect can carry the bacteria that causes huanglongbing (Candidatus Liberibacter asiaticus, CLas). ACP can transmit HLB to uninfected citrus trees as it feeds.
Citrus black spot (CBS), which is caused by the fungal pathogen Phyllostricta citricarpa (previously known as Guignardia citricarpa) was first found in south Florida, near Immokalee, in March 2010. CBS symptoms on fruit include hard spot, cracked spot, false melanose, freckle spot or early virulent spot, and virulent spot. Symptoms of CBS are easiest to observe during color break, when fruit turns from green to ripe coloration. When trees are severely infected, CBS can cause premature fruit drop before harvest, resulting in significant yield loss.
CBS is spread when wind-borne spores embed in the leaf litter under trees and are carried long distances by air currents. Rain splash may move spores short distances from infected fruit and/or leaf litter. Human-assisted movement of fruit and infected nursery stock is the main form of long distance movement.
Citrus canker is a disease caused by the bacterium, Xanthomonas citri subspecies citri. Infection causes lesions on the leaves, stems, and fruit of citrus trees. Typical lesions of the disease are raised, tan to brown in color, and have a water-soaked margin and yellow halos. The bacteria propagate in the lesions, which ooze bacterial cells that are dispersed by windblown rain, contaminated equipment, and movement of infected plants.
While not harmful to humans, uncontrolled canker infection can significantly affect tree health, causing leaves and fruit to drop prematurely. A fruit infected with canker is safe to eat, but its appearance can decrease its marketability.
Canker originated in southeast Asia. Citrus canker was first detected in the United States in 1910 and was eradicated in 1933. It was discovered again in 1995 in Miami-Dade County, Florida. Despite an aggressive tree removal program, USDA was not able to eliminate canker in Florida a second time and ended eradication efforts in 2006. Canker is present in Florida, Louisiana, and parts of Texas.
Huanglongbing (HLB, also known as citrus greening) is the most serious citrus disease in the world and is caused by the bacterium Candidatus Liberibacter asiaticus. There is no cure for this disease once a tree is infected. While the disease poses no threat to humans or animals, it has devastated millions of acres of citrus production around the world, including in the United States.
HLB has been known in Asia since 1900, and Africa since 1920. The first detection of HLB in the Americans was in Brazil in 2004. The first detection of HLB in the United States was in Florida in 2005. HLB has been detected in all the major citrus growing states in the United States, except Arizona.
Once a tree is infected with the bacteria, the tree can remain without detectable symptoms for months or years. During this symptomless phase, the tree can serve as a source of bacteria to infect other trees. Over time, an infected tree will start producing fewer fruit that are smaller, shaped irregulary, and taste bitter. Affected trees have leaves with blotchy mottling, stunted growth, root die-back, and are prone to dropping fruit before it is ripe. Trees infected with HLB will eventually succumb to the disease.
Sweet orange scab (SOS) is a disease caused by the fungus Elsinöe australis, which results in scab-like lesions primarily on fruit. The fruit are safe to eat, but the blemishes result in reduced marketability in the fresh fruit market. SOS can cause premature fruit drop and stunt young nursery trees and new field plantings.SOS was first detected in the United States in 2010 in Texas. SOS is now confirmed in Louisiana, Florida, Mississippi, Texas, Arizona, and parts of California.
Moving citrus trees is the fastest way that citrus diseases are spread. When you move citrus trees, you risk losing America’s citrus.
You Can Help Prevent Citrus Disease
If you think you have identified an infected plant, report it immediately. To avoid spreading the disease, do not move your plant. Complete the "Report It" form below or call your local USDA State Plant Health Director’s office.
Report It Form (English)
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If you are younger than 18 years of age, please ask a parent, guardian or trusted adult to help you complete the form.
Thank you for helping stop the spread of citrus disease!