Tissue-graft indexing is done by budding at least four buds from suspect trees onto indicator seedlings (2 buds/seedling) grown under warm conditions.
TRANSMISSION
Propagation with infected buds is the main way the disease is spread. In the orchard, the Asian citrus pyslla, Diapholina citri kuwayama ( Fig. 5 ) persistently transmits the pathogen. Transmission ability is affected by the biotype of the psyllid: the Taiwan biotype, for example, has a very low transmission rate of less than 1%. However, field transmission of the pathogen by the psyllid vector might be significant, since citrus trees are exposed to infection in the open for quite a long time.
The jasmine orange shrub (Muraya puniculata), the most suitable host for psyllid propagation, does not serve as an intermediate host for the pathogen. The pathogen moves slowly through citrus trees, and in the early stage of infection tends to remain confined to the localized branches into which it has been introduced by the psyllid vector.
CONTROL
Control of citrus greening can be achieved by such integrated measures as eradicating infected plant material, introducing clean nursery seedlings, and eliminating the insect vectors. Treating affected trees with injections of antibiotics alleviates the symptoms, but does not cure the diseased plants. Prompt elimination of diseased trees is strongly advised.
It is of primary importance to propagate and plant pathogen-free seedlings derived from foundation stock obtained by heat therapy, shoot-tip grafting, health indexing, or nucellar lines.
The vector psylla are controlled by spraying insecticide (e.g. dimethoate) on citrus trees and jasmine orange shrubs when their leaves are sprouting.
The introduction and application of ectoparasites, such as Tetrastichus dryi and T. radiatus, can be used for effective biological control of the psyllid vectors.
