Not known to transmit any human or animal pathogens.

Not known to vector any pathogens or other associated organisms.

'Ca. P. citri' is vectored by the leafhopper, Hishimonus phycitis, which is not known to occur in the United States. The pathogen can also be transmitted by vegetative propagation of infected plant tissues (grafting, cuttings, etc.). Asian citrus psyllid, Diaphorina citri, can also vector the phytoplasma. Asian citrus psyllid is present in the United States, but those areas are quarantined to prevent the spread of citrus greening, which is vectored by the psyllid.

Follow instructions in Phytoplasma Sample Screening and Confirmation. If you have completed phytoplasma specific training or proficiency testing for DNA extraction and real-time PCR from S&T Plant Pathogen Confirmatory Diagnostics Laboratory (PPCDL, formerly Beltsville lab), you can screen your own phytoplasma samples. Note: You will still have to follow the protocol in the linked document for confirmations.

In key lime (Citrus aurantifolia): symptoms of WBDL include witches' broom (excessive production of shoots with short internodes and small, light green leaves), abnormal flowers (phyllody), stunting, and reduced fruit production. Infected trees eventually decline and collapse over 3 to 8 years. In some cases, trees remain asymptomatic, or they may die back or weaken over time instead of showing typical WBDL symptoms. This slow or asymptomatic form of the disease is likely due to unfavorable environmental conditions (extremely hot and dry or too cool).

Other citrus: key lime is the primary host, but other citrus species (Bakraee, citron, grapefruit and limequat) may express similar symptoms to key lime when environmental conditions are favorable for disease development.

Generally, the best time to survey for phytoplasmas is summer when symptoms are most likely to be apparent. A study in Iran found that samples taken in August had higher concentrations of 'Ca. P. citri' than those taken in March or December.

Visually inspect host plants throughout the survey site for symptoms such as witches' broom, reduced flowering and fruiting, and the general decline of the tree. Collect symptomatic leaves for sample screening.

Survey for 'Ca. P. citri' in key lime (preferred) or other citrus (if showing witches' broom symptoms) in commercial or residential settings.

For most phytoplasma diseases, leaves with symptoms are optimal for diagnostic testing. It is important to sample tissue from different parts of the same tree, as phytoplasmas are often unevenly distributed. Do not sample dead leaves.

Follow instructions in Phytoplasma Sample Screening and Confirmation

As of June 2025, there are no known phytoplasmas associated with citrus in the continental United States. The most significant bacterial threat to the domestic industry is Citrus Greening (CG, also known as Huanglongbing, HLB), which is caused by another phloem-limited bacteria 'Candidatus Liberibacter asiaticus'. This disease is currently present in several areas of the United States, which are under quarantine to prevent further spread. While citrus greening can cause blotchy yellowing of leaves and overall tree decline, symptoms that may be confused with the lighter foliage found in WBDL, it does not produce the "witches' broom" shoot proliferation. In Puerto Rico, a phytoplasma within the pigeon pea group (16SrIX) has been associated with orange, tangerine, and lemon. Although found causing symptoms similar to citrus greening, it does not cause witches' broom.

In India, 'Ca. P. cynodontis'-related strains (16SrXIV-A) have been associated with witches' broom symptoms similar to those seen in WBDL. Multiple phytoplasmas have been associated with citrus in Asia, the Caribbean, Central America, and South America. These phytoplasmas can cause witches' broom or nonspecific symptoms such as reduced flowering, stunting, dieback, and decline. Because these pathogens present overlapping symptoms, molecular diagnostics are required to differentiate and confirm the specific pathogen when a disease associated with phytoplasma is suspected in citrus.