[citation needed] It is thought that a toxin produced by the nymph stage of the psyllid causes these symptoms.
If pest control occurs at an early stage of the disease, the plants appear to be able to recover.
In severe cases, the yellowing progresses to plant death.
In addition to psyllid feeding, a new species of bacterium 'Candidatus Liberibacter solanacearum' [2] has been associated with this disease.
Capsicum crops show a similar fruit effect, but generally with no, or very little, foliar symptom.