This Ascomycete fungus affects citrus plants throughout subtropical climates, causing a reduction in both fruit quantity and quality.

[4] An isolate of P. citricarpa was found to produce the medically important compound, taxol under certain growth conditions.

[5] Citrus Black Spot was first found in Sydney, Australia, in 1895[6] [7] and then appeared in South Africa along the coast of Natal in 1929.

[8] The disease was first reported in North America during March 2010, in Collier and Hendry counties of southern Florida.

[citation needed] Moderately susceptible hosts are Hamlin sweet oranges, tangerine/ mandarin type fruit, and grapefruit.

They are similar in appearance to the freckle spot lesions, but under high humidity can cover the entire fruit.

[14] Leaf symptoms are generally observed on highly susceptible citrus varieties, such as lemons, as well in poorly-managed orchards.

Red-brown, pin-point dots may develop into larger, circular necrotic lesions with gray centers and red or brown margins.

Diagnosis is also complicated by the morphological similarities of the fungal structures to the non-pathogenic strain Phyllosticta capitalensis (formerly referred to as Guignarida mangiferae).

[26] Upon landing on susceptible tissue, the ascospores germinate and form appresoria after a 24-48 hour wetting period.

To control Guignardia citriparpa fungicides like copper and/or strobilurins should be applied monthly from early May to the middle of September (in the northern hemisphere).

Applications of the fungicides are recommended in early April (northern hemisphere) if that month has experienced more rainfall than usual resulting in the ideal conditions for citrus black spot to form.

Recommended Chemical Controls for Citrus Black Spot[34] 1)Lower rates can be used on smaller trees.

Accelerating this decomposition reduces the chance for ascospore inoculation which generally takes place in the middle of March.

Urea, lime, and calcium carbonate reduce the number of fungal structures and spore production.

[19] Along with these methods it is also important to get rid of debris such as fallen fruit or twigs in a manner that reduces the chances of infecting other plants.

To dispose of citrus debris it should either be heated to a minimum of 180 °F for two hours, incinerated, buried in a landfill, or fed to livestock.

This type of economic impact is felt most in Australia and South Africa where the disease has been present for a number of years.

[37] In Australia, South Africa, and China citrus is of particular importance due to the large role it plays in international trade.

When this happens the shipment usually has to be repackaged and resold to a less sensitive market which leads to large financial losses.

This ban was justified by a study by the European Food Safety Authority (EFSA) on the risk of transmission.

However, a specially convened panel of eminent scientists from Brazil, Argentina, the USA, Uruguay, Australia and South Africa concluded that there is no risk of transmission through fruit to European climates.